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NSDL National Science Digital Library
WGBH Educational Foundation
In this interactive game adapted from the Bigelow Laboratory for Ocean Sciences, build a food web that illustrates the flow of energy in an Antarctic ecosystem and the relationships between predators and prey.
Food web of an Antarctic midwater ecosystem
T. L. Hopkins
The diets of 93 species of plankton and micronekton taken in the upper 1000 m of Croker Passage (Gerlache Strait) in the austral fall, 1983, were examined and the principal features of the food web were characterized. Most species were small particle feeders, with phytoplankton and debris (of phytoplankton and krill) being the principal diet components. Krill remains were found
Effects of sea-ice extent and krill or salp dominance on the Antarctic food web
V. Loeb; V. Siegel; O. Holm-Hansen; R. Hewitt; W. Fraser; W. Trivelpiece; S. Trivelpiece
Krill (Euphausia superba) provide a direct link between primary producers and higher trophic levels in the Antarctic marine food web. The pelagic tunicate Salpa thompsoni can also be important during spring and summer through the formation of extensive and dense blooms. Although salps are not a major dietary item for Antarctic vertebrate predators,, their blooms can affect adult krill reproduction
NSDL National Science Digital Library
This lesson plan introduces students to the animals of Antarctica and to the Antarctic food chain. Students will draw pictures of a variety of animals and attach the pictures to a wall collage. They will then listen to or read statements about the diet of each animal and draw arrows to show which animals eat which other animals. Students will end up with a food web that illustrates the importance of krill to the Antarctic ecosystem.
Food webs in subAntarctic lakes: a stable isotope approach
Lars-Anders Hansson; Lars J. Tranvik
In order to improve the understanding of food-web interactions in sub-Antarctic freshwater systems, we complemented earlier experimental studies with analyses of differences in stable isotopes ( 15N and 13C) among organisms in two lakes with contrasting productivity. The distribution of the stable isotopes showed that the small copepod Boeckella michaelseni feeds mainly on pelagic POM (particulate organic material), whereas the
Penguin eggshell membranes reflect homogeneity of mercury in the marine food web surrounding the Antarctic Peninsula.
Brasso, Rebecka L; Polito, Michael J; Lynch, Heather J; Naveen, R; Emslie, Steven D
Remote regions such as the Antarctic have become increasingly important for investigations into far-reaching anthropogenic impacts on the environment, most recently in regard to the global mercury cycle. Spatial patterns of mercury availability in four regions of the Antarctic Peninsula were investigated using three species of sympatrically breeding Pygoscelis penguins as biomonitors. Eggshells with intact membranes from Adķlie, Gentoo, and Chinstrap penguins were collected at 24 breeding colonies in the South Orkney Islands, South Shetland Islands, eastern Antarctic Peninsula, and western Antarctic Peninsula during the 2006/2007 austral summer. In addition, we compared eggshell membrane mercury concentrations with eggshell stable isotope values (?(15)N and ?(13)C) to determine if species-specific trophic or foraging habitat preferences influenced female mercury exposure prior to breeding. With few exceptions, mercury concentrations were found to be fairly homogeneous throughout the Antarctic Peninsula suggesting little spatial variation in the risk of exposure to dietary mercury in this food web. Mercury concentrations in Gentoo and Adķlie penguins were similar while Chinstrap penguins tended to have higher eggshell membrane mercury concentrations than their congeners. However, inter and intra-specific differences in eggshell membrane mercury concentration were not related to eggshell ?(15)N or ?(13)C values, a likely result of all three species foraging at similar trophic positions. The lack of regional-scale differences in mercury availability in this marine ecosystem may be a reflection of generally uniform atmospheric deposition and upwelling of regionally homogeneous deep water rather than from geographically distinct point sources. PMID:23069932
Productivity and linkages of the food web of the southern region of the western Antarctic Peninsula continental shelf
NASA Astrophysics Data System (ADS)
Ballerini, Tosca; Hofmann, Eileen E.; Ainley, David G.; Daly, Kendra; Marrari, Marina; Ribic, Christine A.; Smith, Walker O.; Steele, John H.
The productivity and linkages in the food web of the southern region of the west Antarctic Peninsula continental shelf were investigated using a multi-trophic level mass balance model. Data collected during the Southern Ocean Global Ocean Ecosystem Dynamics field program were combined with data from the literature on the abundance and diet composition of zooplankton, fish, seabirds and marine mammals to calculate energy flows in the food web and to infer the overall food web structure at the annual level. Sensitivity analyses investigated the effects of variability in growth and biomass of Antarctic krill (Euphausia superba) and in the biomass of Antarctic krill predators on the structure and energy fluxes in the food web. Scenario simulations provided insights into the potential responses of the food web to a reduced contribution of large phytoplankton (diatom) production to total primary production, and to reduced consumption of primary production by Antarctic krill and mesozooplankton coincident with increased consumption by microzooplankton and salps. Model-derived estimates of primary production were 187-207 g C m-2 y-1, which are consistent with observed values (47-351 g C m-2 y-1). Simulations showed that Antarctic krill provide the majority of energy needed to sustain seabird and marine mammal production, thereby exerting a bottom-up control on higher trophic level predators. Energy transfer to top predators via mesozooplanton was a less efficient pathway, and salps were a production loss pathway because little of the primary production they consumed was passed to higher trophic levels. Increased predominance of small phytoplankton (nanoflagellates and cryptophytes) reduced the production of Antarctic krill and of its predators, including seabirds and seals.
Winter and spring controls on the summer food web of the coastal West Antarctic Peninsula.
Saba, Grace K; Fraser, William R; Saba, Vincent S; Iannuzzi, Richard A; Coleman, Kaycee E; Doney, Scott C; Ducklow, Hugh W; Martinson, Douglas G; Miles, Travis N; Patterson-Fraser, Donna L; Stammerjohn, Sharon E; Steinberg, Deborah K; Schofield, Oscar M
Understanding the mechanisms by which climate variability affects multiple trophic levels in food webs is essential for determining ecosystem responses to climate change. Here we use over two decades of data collected by the Palmer Long Term Ecological Research program (PAL-LTER) to determine how large-scale climate and local physical forcing affect phytoplankton, zooplankton and an apex predator along the West Antarctic Peninsula (WAP). We show that positive anomalies in chlorophyll-a (chl-a) at Palmer Station, occurring every 4-6 years, are constrained by physical processes in the preceding winter/spring and a negative phase of the Southern Annular Mode (SAM). Favorable conditions for phytoplankton included increased winter ice extent and duration, reduced spring/summer winds, and increased water column stability via enhanced salinity-driven density gradients. Years of positive chl-a anomalies are associated with the initiation of a robust krill cohort the following summer, which is evident in Adķlie penguin diets, thus demonstrating tight trophic coupling. Projected climate change in this region may have a significant, negative impact on phytoplankton biomass, krill recruitment and upper trophic level predators in this coastal Antarctic ecosystem. PMID:25000452
14C as a tracer of labile organic matter in Antarctic benthic food webs
NASA Astrophysics Data System (ADS)
Purinton, Brett L.; DeMaster, David J.; Thomas, Carrie J.; Smith, Craig R.
14C measurements were made on surface plankton, particle-trap material, surface sediment, benthic invertebrate gut contents, and body tissue samples to assess the effectiveness of this radioisotope as a tracer of labile organic carbon in Antarctic benthic food webs. Samples were collected on five cruises to the West Antarctic Peninsula (WAP) shelf between November 1999 and March 2001 as part of the Food for Benthos on the ANtarctic Continental-Shelf (FOODBANCS) Project. The 14C contents of the body tissues from a variety of deposit feeders (-126▒13 per mil) were substantially enriched relative to the surface sediment (-234▒13 per mil) and statistically similar to the organic matter collected in plankton tows (-135▒10 per mil), indicating that recently produced marine plankton are the primary source of nutrition for these deposit feeders on the West Antarctic shelf. Selective ingestion was the primary feeding strategy used by echiuran worms and certain holothurians (i.e. Peniagone vignoni) for incorporating labile organic carbon into their tissues as demonstrated by the large differences (105▒13 per mil) between surface sediment and gut content 14C activities. In contrast, digestive and/or assimilatory selection was the predominant strategy used by an irregular urchin ( Amphipneustes lorioli) and several other holothurians ( Protelpidia murrayi, Bathyplotes fuscivinculum and the head-down conveyor belt feeder, Molpadia musculus), as demonstrated by large differences (42▒7 per mil) between the 14C activities of their foregut or whole-gut organic contents and their body tissues. Despite large fluctuations in carbon export from the euphotic zone, benthic feeding strategies remained essentially constant over the 15-month sampling period. No seasonal variation was evident in either the 14C abundance of the deposit-feeder body tissues, or in the 14C abundance of their gut contents. The mean 14C abundance in the body tissues of the two sub-surface deposit feeders ( A. lorioli and M. musculus; mean=-136.2▒8.5 per mil) was distinct ( p=0.0008) from the mean 14C abundance in the body tissues of the four surface deposit feeders (echiuran worm, P. vignoni, P. murrayi, and B. fusciviculum; -122.6▒12.3 per mil). The mean 14C abundance of the gut contents from the sub-surface deposit feeders (-178.0▒18.6 per mil) also was significantly depleted ( p=0.0009) relative to that of the surface deposit feeders (-149.5▒26.6 per mil). The 14C measurements proved to be a much more sensitive tracer for tracking labile organic carbon during ingestive and assimilatory processes than the stable isotopes of carbon or nitrogen.
NSDL National Science Digital Library
In this activity, students construct a food web of Antarctic organisms. Working from a trophic table that provides information about each organisms's role in the food web, they will attempt to place them in their correct positions on a blank food web chart. Links to a glossary are embedded in the text.
NSDL National Science Digital Library
Ms. B
What are the differences and similarities between food chain and food web? Print (2) Garden Gate Print (1) Venn Diagram Garden Gate Venn Diagram Let's learn about the food chain and food web.Read the notes.Food Chain 4 Also, view more notes on food chain and food web. Go to the 7th title Food Chain which is before the Habitats and food chain title of the webpage.Food Chain Power Point Presentation Record what you learn ...
NSDL National Science Digital Library
The representation depicts 4 different food webs: Antarctica, the African Grasslands, the Australia Grasslands and a Marine environment. A separate food web for scavengers and decomposers is present in the African Grasslands section. Viewers must first build the web by moving boxes with the organism's picture and name to the appropriate spot on a grid. Clues describing food requirements are given as the boxes are moved. When the boxes are correctly placed a complete food web (with arrows) is displayed.
NSDL National Science Digital Library
Mr. Wood
Food web reading. Build a food web and design a creature. Requires downloaded program. Download your assignment Food Web Assignment Sheet. Use the following sites and activities to answer the questions. Do not start the creature creator until Mr. Wood has seen your food web and completed assignment and allowed you to move on. Type your answers on the sheet and edit it to fit one page. When ...
Energy Content of Antarctic Mesopelagic Fishes: Implications for the Marine Food Web
Anton Van de Putte; Hauke Flores; Filip Volckaert; Jan Andries van Franeker
For a better understanding of the role of mesopelagic fish in the Southern Ocean food web, the energy and water content of Bathylagus antarcticus, Electrona antarctica and Gymnoscopelus braueri from the Lazarev Sea were investigated. Mean dry weight energy content of B. antarcticus (20.4ĀkJĀg?1) was significantly lower than in E. antarctica and G. braueri (both 29.4ĀkJĀg?1). In E. antarctica, an
Ecological Controls on Biogeochemical Fluxes in the Western Antarctic Peninsula: Long-Term Observations and Inverse Food Web Model Results
NASA Astrophysics Data System (ADS)
Ducklow, H. W.; Sailley, S. F.; Stammerjohn, S. E.; Saba, G. K.; Doney, S. C.
Sea ice in the Western Antarctic Peninsula (WAP) region is both highly variable and rapidly changing. In the Palmer Station region, the ice season duration has decreased by 92 days since 1978. The sea-ice changes affect ocean stratification and freshwater balance; and in turn impact every component of the polar marine ecosystem. Long-term observations from the WAP shelf region show a pattern of chlorophyll (Chl) variability with three to five years of negative Chl anomalies interrupted by one or two years of positive anomalies. Observations and results from an inverse food-web model show that these low and high Chl regimes differed significantly from each other, with high primary productivity and net community production (NCP) associated with the high Chl years and vice-versa. Gross primary production averaged 40 mmolC m-2 d-1 in the low Chl years and 100 mmolC m-2 d-1 in the high Chl years, with 30-40% going to NCP across regimes. Only the food web in the southern region in high Chl years was dominated by large phytoplankton and krill, whereas in in all other cases, foodwebs were dominated by small phytoplankton and microzooplankton. These contrasts were strongest between the northern, low Chl years and southern, high Chl years, consistent with earlier north to south observations of sea ice and ecosystem change along the WAP. The relative importance of major bulk carbon flows did not differ substantially between high and low Chl years. Both the northern/low Chl and southern/high Chl regimes had roughly equal proportions of NCP, although its composition reflected shifts in dominance by large versus small plankton. These results suggest that food webs dominated by smaller phytoplankton and grazers have pathways that funnel production into NCP, and likely, export.
NSDL National Science Digital Library
In this activity, learners construct possible food webs for six different ecosystems as they learn about the roles of different kinds of living organisms. Learners will also discuss and classify producers vs. consumers and different kinds of consumers (herbivores, carnivores, omnivores, decomposers and scavengers). This lesson guide includes background information, variations and bilingual (English/Spanish) cards.
NSDL National Science Digital Library
Katie Hale (CSUF; Biological Sciences)
Food webs are an interconnection of producers, consumers, and decomposers. It is important to understand that a change to any level of the food web directly and indirectly affects other organisms within the food web.
NSDL National Science Digital Library
This lesson explains how energy travels through an ecosystem. This flow can be diagrammed in food chains and food webs as shown in the lesson's illustrations. Key terms are hyperlinked so students can easily view definitions of new concepts.
NSDL National Science Digital Library
Ms. Thompson
Learn more about food chains, food webs, and how the organisms in them affect each other. In class, you have learned what food webs and food chains are. Today, you will explore how the organisms in these systems interact. Step One: Food Chains What happens when you take something out of a food chain? Go to the Chain Reaction website: Chain Reaction--Food Chains This internet site will help you ...
ERIC Educational Resources Information Center
Smith, Karl D.
Explains an upper elementary game of tag that illustrates energy flow in food webs using candy bars as food sources. A follow-up field trip to a river and five language arts projects are also suggested. (CS)
NSDL National Science Digital Library
In this activity, learners investigate feeding relationships. Learners complete a food web and then make a mobile to represent a food chain. Use this activity to talk about predator/prey relationships and ecosystems.
B. Drossel; A. J. McKane
We review theoretical approaches to the understanding of food webs. After an overview of the available food web data, we discuss three different classes of models. The first class comprise static models, which assign links between species according to some simple rule. The second class are dynamical models, which include the population dynamics of several interacting species. We focus on
D. Garlaschelli
Among recently studied real-world networks, food webs are particularly interesting since they provide an example of biological organization at the largest scale, namely that of ecological communities. Quite surprisingly, recent results reveal that food webs do not display those properties which are observed in almost all other networks, such as a scale-free degree distribution and a large clustering coefficient. However,
NSDL National Science Digital Library
Office of Biological and Environmental Research of the U.S. Department of Energy Office of Science
This visualization illustrates the carbon cycle throughout the oceanic zones, beginning at the surface and traveling to the deep. The concept map-like connections encourage students to link the abiotic and biotic interactions within the oceanic food web.
Notre Dame, University of
2005, Elsevier, Inc. All rights reserved. Except Chapter 4.1 Chapter 4.1 O 2005, Joel E. Cohen FOOD WEB: STATISTICAL QUESTIONS IN ESTIMATING THE RELATIONSHIP Joel E. Cohen and Stephen R. Carpenter.") Enquist et al. (1998, p. 1641, Cohen et al. (2003, p. 1784),and most plant ecologistsplotted log Mon
NSDL National Science Digital Library
Katie Hale (CSUF; Biological Sciences)
The lowest level of a food web includes producers, which are plants that make their own energy from the sun. Animals that eat these producers are called primary consumers, and consumers that eat other consumers are called secondary consumers. Decomposers break down dead plants and animals to release nutrients into the soil.
NSDL National Science Digital Library
This lesson plan is designed to help students understand the interrelatedness of food webs and to see how populations of organisms affect each other. Students assume the roles of the various organisms in the ecosystem; the ones that are dependent upon each other are symbolically connected by lengths of yarn. A materials list, instructions, assessment ideas, and educational standards are provided.
A. J. McKane
We describe the properties of a model which links the ecology of food web structure with the evolutionary dynamics of speciation and extinction events; the model describes the dynamics of ecological communities on an evolutionary timescale. Species are defined as sets of characteristic features, and these features are used to determine interaction scores between species. A realistic population dynamics, which
A. J. McKanea
We describe the properties of a model which links the ecology of food web structure with the evolutionary dynamics of speciation and extinction events; the model describes the dynamics of ecological communities on an evolutionary timescale. Species are defined as sets of characteristic features, and these features are used to determine interaction scores between species. A realistic population dynamics, which
NSDL National Science Digital Library
Mary Cahill
This lesson plan is part of the DiscoverySchool.com lesson plan library for grades 6-8. It focuses on the seasonal changes that affect life in a temperate forest ecosystem and how organisms in a temperate forest are dependent on one another for proper nutrition. Students describe the three major types of organisms that live in an ecosystem, three types of consumers, food webs, and food chains. They then create a food web diagram for display in their classrooms. Included are objectives, materials, procedures, discussion questions, evaluation ideas, suggested readings, and vocabulary. There are videos available to order which complement this lesson, and links to teaching tools for making custom quizzes, worksheets, puzzles and lesson plans.
NSDL National Science Digital Library
This lesson plan is part of the DiscoverySchool.com lesson plan library for grades 6-8. It focuses on the seasonal changes that affect life in a temperate forest ecosystem and how organisms in a temperate forest are dependent on one another for proper nutrition. Students describe the three major types of organisms that live in an ecosystem, three types of consumers, food webs, and food chains. They then create a food web diagram for display in their classrooms. Included are objectives, materials, procedures, discussion questions, evaluation ideas, suggested readings, and vocabulary. There are videos available to order which complement this lesson, and links to teaching tools for making custom quizzes, worksheets, puzzles and lesson plans.
ERIC Educational Resources Information Center
Baker, Marjane L.
Presents a play for students in grades four to nine that incorporates the scientific names, physical characteristics, feeding habits, interactions, and interdependence of the plants and animals that make up the Great Lakes food web to facilitate the learning of this complex system. Includes a Great Lakes food web chart. (AIM)
Dispersal dynamics in food webs.
Melißn, Carlos J; K?ivan, Vlastimil; Altermatt, Florian; Star², Petr; Pellissier, Lo'c; De Laender, Frederik
Studies of food webs suggest that limited nonrandom dispersal can play an important role in structuring food webs. It is not clear, however, whether density-dependent dispersal fits empirical patterns of food webs better than density-independent dispersal. Here, we study a spatially distributed food web, using a series of population-dispersal models that contrast density-independent and density-dependent dispersal in landscapes where sampled sites are either homogeneously or heterogeneously distributed. These models are fitted to empirical data, allowing us to infer mechanisms that are consistent with the data. Our results show that models with density-dependent dispersal fit the ?, ?, and ? tritrophic richness observed in empirical data best. Our results also show that density-dependent dispersal leads to a critical distance threshold beyond which site similarity (i.e., ? tritrophic richness) starts to decrease much faster. Such a threshold can also be detected in the empirical data. In contrast, models with density-independent dispersal do not predict such a threshold. Moreover, preferential dispersal from more centrally located sites to peripheral sites does not provide a better fit to empirical data when compared with symmetric dispersal between sites. Our results suggest that nonrandom dispersal in heterogeneous landscapes is an important driver that shapes local and regional richness (i.e., ? and ? tritrophic richness, respectively) as well as the distance-decay relationship (i.e., ? tritrophic richness) in food webs. PMID:25616136
NSDL National Science Digital Library
Janet R. Galle
This chapter discusses the concept of a food web and energy flow. Its activities will assist students in defining and constructing an energy pyramid. These activities can be incorporated into lessons which teach students how to create a food web and and identify the interdependencies within that habitat. Students will learn how to identify and illustrate parts of the water cycle, the carbon-oxygen cycle, and the nitrogen cycle. This section also offers students the tools to demonstrate active knowledge of conservation measures.
Food Chains and Food Webs - Balance within Natural Systems
NSDL National Science Digital Library
VU Bioengineering RET Program,
With a continued focus on the Sonoran Desert, students are introduced to the concepts of food chains and food webs through a PowerPoint« presentation. They learn the difference between producers and consumers and study how these organisms function within their communities as participants in various food chains. They further understand ecosystem differences by learning how multiple food chains link together to form intricate and balanced food webs. At lesson end, students construct food webs using endemic desert species.
NSDL National Science Digital Library
Science Netlinks
In this Science NetLinks lesson, students will research plants and animals that live in the submerged aquatic vegetation (SAV) of a bay area. After researching the organisms, students will do class presentations and create a food web using pictures of all of the organisms. At the end of the lesson, they will discuss ideas of organisms sharing food, space, water, air, and shelter.
Community assembly and food web stability
Post, W.M.; Pimm, S.L.
The ecological assembly of food webs is considered as a process of predator colonizations and extinctions. The results of computer simulations using predator-prey equations allow us to identify three types of food web stability and examine how they may change through development of food webs. Species turnover stability increases, stability to extensive species extinction remains constant, and local stability to population fluctuations decreases as food web assembly proceeds. 28 references, 7 figures, 3 tables.
Persistence of complex food webs in metacommunities
Persistence of complex food webs in metacommunities Gesa A. B©ohme 1 and Thilo Gross 2 1 Max of Engineering Mathematics, Bristol, UK Keywords: metacommunities, food webs, predator-prey interactions, geo diversity and food web complexity. Recently Pillai et al. proposed a simple modeling framework
INTRODUCTION Aquatic food-webs' ecology
INTRODUCTION Aquatic food-webs' ecology: old and new challenges Andrea Belgrano Looking up ``aquatic food web'' on Google provides a dizzying array of eclectic sites and information (and disinformation!) to choose from. However, even within this morass it is clear that aquatic food-web research has
Simple Rules Yield Complex Food Webs
Neo Martinez
Several of the most ambitious theories in ecology describe food webs that document the structure of strong and weak trophic links among diverse assemblages of species. Early mechanism-based theory asserted that food webs have little omnivory and several properties that are independent of species richness. This theory was overturned by empirical studies that found food webs to be much more
Community assembly and food web stability
W. M. Post; S. L. Pimm
The ecological assembly of food webs is considered as a process of predator colonizations and extinctions. The results of computer simulations using predator-prey equations allow us to identify three types of food web stability and examine how they may change through development of food webs. Species turnover stability increases, stability to extensive species extinction remains constant, and local stability to
Compartments revealed in food-web structure
Ann E. Krause; Kenneth A. Frank; Doran M. Mason; Robert E. Ulanowicz; William W. Taylor
Compartments in food webs are subgroups of taxa in which many strong interactions occur within the subgroups and few weak interactions occur between the subgroups. Theoretically, compartments increase the stability in networks, such as food webs. Compartments have been difficult to detect in empirical food webs because of incompatible approaches or insufficient methodological rigour. Here we show that a method
Got Energy? Spinning a Food Web
NSDL National Science Digital Library
Integrated Teaching and Learning Program,
Students learn about energy flow in food webs, including the roles of the sun, producers, consumers and decomposers in the energy cycle. They model a food web and create diagrams of food webs using their own drawings and/or images from nature or wildlife magazines. Students investigate the links between the sun, plants and animals, building their understanding of the web of nutrient dependency and energy transfer.
A Stochastic Theory of Community Food Webs: II. Individual Webs
J. E. Cohen; C. M. Newman; F. Briand
The species scaling law and the link scaling law of community food webs can be derived from a simple mathematical model, called the cascade model, which incorporates the link-species scaling law. In the previous test of this model against data on 62 community food webs, the ratio of links to species is estimated from aggregated data on all webs taken
NSDL National Science Digital Library
Pulse of the Planet
Teachers could incorporate this brief radio program into a variety of learning settings. For example, teachers living in the temperate deciduous forest biome can play the program for students when leaves begin to fall in autumn. The program could also be used whenever students anywhere are learning about food webs or soil. Teachers can choose to use either the audio or text version (or both) to give students listening or reading practice.
Food web dynamics in the Scotia Sea in summer: A stable isotope study
G. Stowasser; A. Atkinson; R. A. R. McGill; R. A. Phillips; M. A. Collins; D. W. Pond
The pelagic food web of the Scotia Sea was studied by analysing natural abundances of nitrogen and carbon stable isotopes of primary producers and pelagic consumers, sampled from the seasonal ice edge in the south to the Antarctic Polar Front in the north. The analysis covered, within a single mid-summer period, particulate organic matter (POM) and 38 taxa, ranging from
Live from Antarctica 2: The Food Web Game
NSDL National Science Digital Library
This activity will help students understand that increases in the ozone hole will result in damaging ultraviolet-B (UV-B) rays penetrating deep into the ocean, and harming young marine life, such as floating fish eggs, fish larvae, juvenile fish, and shrimp larvae, and affecting phytoplankton movement. Students will discover how others in the Antarctic food web will be affected if phytoplankton are harmed by depletion of the ozone layer. They will also find out what will survive UV-B radiation in Antarctica.
Simulation approach to understanding the processes that structure food webs
H. I. Jager; R. H. Gardner; D. L. DeAngelis; W. M. Post
A simulation model of food web dynamics, WEB, was constructed and used in Monte Carlo experiments to study the relationship between structure and function in food webs. Four main experiments were designed using WEB. The first tested the robustness of food web structures at equilibrium to variations in the functional response of predators in the food web to the densities
Phytoplankton food quality control of planktonic food web processes
Marta G. Danielsdottir; Michael T. Brett; George B. Arhonditsis
We developed a mechanistic model of nutrient, phytoplankton, zooplankton and fish interactions to test the effects of phytoplankton\\u000a food quality for herbivorous zooplankton on planktonic food web processes. When phytoplankton food quality is high strong\\u000a trophic cascades suppress phytoplankton biomass, the zooplankton can withstand intense zooplanktivory, and energy is efficiently\\u000a transferred through the food web sustaining higher trophic level production.
Simple rules yield complex food webs
Richard J. Williams; Neo D. Martinez
Several of the most ambitious theories in ecology describe food webs that document the structure of strong and weak trophic links that is responsible for ecological dynamics among diverse assemblages of species. Early mechanism-based theory asserted that food webs have little omnivory and several properties that are independent of species richness. This theory was overturned by empirical studies that found
Trophic links of community food webs
Joel E. Cohen
This report describes and explains regularities in the numbers and kinds of trophic links in community food webs. To a first approximation, the mean number of trophic links in a community food web is proportional to the total number of trophic species. The mean number of trophic links between any two categories of trophic species (basal, intermediate, and top) is
The dynamics of spatially coupled food webs
K. S. McCann; J. B. Rasmussen; J. Umbanhowar
The dynamics of ecological systems include a bewildering number of biotic interactions that unfold over a vast range of spatial scales. Here, employing simple and general empirical arguments concerning the nature of movement, trophic position and behaviour we outline a general theory concerning the role of space and food web structure on food web stability. We argue that consumers link
Quantitative Descriptors of Food-Web Matrices
Louis-Felix Bersier; Carolin Banas?ek-Richter; Marie-France Cattin
A food web customarily describes the qualitative feeding relationships in a community. Descriptors have been used to extract ecologically meaningful information from such data, e.g., the proportion of top species (the proportion of taxa without consumers) or vulnerability (the average number of consumers per taxon). Analyses of collections of food webs based on these properties have revealed regularities that fostered
KELP FOREST FOOD WEBS IN GWAII HAANAS: Ecosystem-Level Effects of Predator Depletion and Recovery Grazing Rates on Kelp Assimilation of Kelp-derived Organic Carbon in Kelp Forest Food Webs | 33 Intertidal . firstname.lastname@example.com Anne Salomon . firstname.lastname@example.com Report Design: Lynn Lee #12;4 ACKNOWLEDGEMENTS
Food web networks: Scaling relation revisited
Stefano Allesina; Antonio Bodini
Food webs seem to possess scale invariant attributes among which efficiency has been recently included. Considering food webs as transportation networks it has been shown that minimum spanning trees, topologies that minimize cost for delivering medium, satisfy a universal scaling relation. It is not clear, however, whether resource distribution follows the criterion of minimum cost, because longer, less efficient routes
Lafferty, Kevin D.
Most species interactions probably involve parasites. This review considers the extent to which marine ecologists should consider parasites to fully understand marine communities. Parasites are influential parts of food webs in estuaries, temperate reefs, and coral reefs, but their ecological importance is seldom recognized. Though difficult to observe, parasites can have substantial biomass, and they can be just as common as free-living consumers after controlling for body mass and trophic level. Parasites have direct impacts on the energetics of their hosts and some affect host behaviors, with ecosystem-level consequences. Although they cause disease, parasites are sensitive components of ecosystems. In particular, they suffer secondary extinctions due to biodiversity loss. Some parasites can also return to a system after habitat restoration. For these reasons, parasites can make good indicators of ecosystem integrity. Fishing can indirectly increase or decrease parasite populations and the effects of climate change on parasites are likely to be equally as complex.
Small World Patterns in Food Webs
The analysis of some species-rich, well-defined food webs shows that they display the so-called small world behavior shared by a number of disparate complex systems. The three systems analysed (Ythan estuary web, Silwood web and the Little Rock lake web) have different levels of taxonomic resolution, but all of them involve high clustering and short path lengths (near two degrees
envi- ronments. The concentration factor found in the known and describable food chain of the Salton in the simple linear food chain ex- isting in that isolated marine environment and that the cesium/potassium (CsUNSTRUCTURED MARINE FOOD WEBS AND "POLLUTANT ANALOGUES" JOHN D. ISAACS' ABSTRACT The several
A Stochastic Theory of Community Food Webs IV: Theory of Food Chain Lengths in Large Webs
C. M. Newman; J. E. Cohen
This paper develops a theory of the length of food chains in community food webs. The theory derives from a mathematical model of webs called the cascade model. Our analysis concerns the behaviour of chain lengths for webs in which the number, S, of species is large. From an exact formula for the expected number of chains of each length,
Antarctic data management at the National Snow and Ice Data Center: Web-based geospatial tools for Antarctic discovery and analysis
NASA Astrophysics Data System (ADS)
Bauer, R.; Husted, L.; Scambos, T.; Bohlander, J.; Haran, T.; Judy, C.; Scharfen, G.
Located at the National Snow and Ice Data Center (NSIDC), the Antarctic Glaciological Data Center (AGDC) and the U.S. Antarctic Data Coordination Center (USADCC), supported by the National Science Foundation's Office of Polar Programs, archive and distribute Antarctic glaciological and cryospheric system data collected by researchers affiliated with the U.S. Antarctic Program. The centers provide long-term access to Antarctic data sets and information so that past and present findings are available for comparison with future data in change detection studies. By facilitating broad data and information access, the centers promote interdisciplinary scientific research. The AGDC and the USADCC offer a geospatial presentation of data sets and information using maps or image data of the Antarctic. They are currently migrating image data such as the surface morphology and snow grain size derived from Moderate Resolution Imaging Spectroradiometer (MODIS) images into the Mosaic of Antarctica (MOA) data product. They are also contributing data set locations from the USADCC's metadata files, image time-series data from the AGDC's Images of Antarctic Ice Shelves, PI-field project point data from the AGDC's Web archive (http://nsidc.org/agdc), and velocity vector locations from Antarctic outlet glaciers to a Web-available search and discovery tool (such as, Google Earth and the Minnesota Map Server).
Mountains in the Sea: Food Web Mystery
NSDL National Science Digital Library
In this activity, students will focus on some unique aspects of food webs in the vicinity of seamounts. They will be able to describe typical marine food webs, and explain why food is generally scarce in the deep-ocean environment. They will then discuss reasons why seamounts may be able to support a higher density of biological organisms than would appear to be possible considering food available from primary production at the ocean's surface. In addition to being tied to the National Science Education Standards, the hands-on, inquiry-based activities includes focus questions, background information for teachers, links to interesting websites, and extensions.
Food Chain to Food Web: A Natural Progression?
ERIC Educational Resources Information Center
Webb, Paul; Boltt, Gill
Investigated is the ability of high school pupils and university students to answer questions based on relationships within food webs using sound ecological principles. Research methods used and the results of this study are discussed. (CW)
ThunderPelican: An Interactive Food Web Display
Zhangbo Liu
Visualizing food web is an interesting and challenging task because of the high complexity of the food web. Creating diagram in exist- ing ecosystem modeling applications such as Ecopath is extremely tedious and time-consuming. In this paper, we introduce the Thun- derPelican, an interactive food web display system by which we could easily and efficiently generate interactive food web diagram.
Local dynamical equivalence of certain food webs
Thilo Gross; Ulrike Feudel
An important challenge in theoretical ecology is to find good coarse-grained representations of complex food webs. Here, we\\u000a use the approach of generalized modeling to show that it may be possible to formulate a coarse-graining algorithm that conserves\\u000a the local dynamics of the model exactly. We show examples of food webs with a different number of species that have exactly
Trophic levels in community food webs
Joel E. Cohen; Tomasz ?uczak
SummaryĀĀFour concepts are considered for the trophic level of a species in a community food web. The long-way-up-level (or LU-level) of species A is the length of the longest simple food chain from a basal species (one with no prey in the web) to A. (A simple chain is a chain that does not pass through any given species more
Lesson Summary Students participate in a food web "string game"
Mojzsis, Stephen J.
the connection between Antarctic animals. Prior Knowledge & Skills -Basic knowledge about the food chain -Basic Food Chain" found at http://drake.marin.k12.ca.us/stuwork/ROCKwate r/PLANKTON/Food%20Chain.htm NASA element eats what. Pass the free end of the string along, up the food chain to the larger predators. 3
Compartments revealed in food-web structure
NASA Astrophysics Data System (ADS)
Krause, Ann E.; Frank, Kenneth A.; Mason, Doran M.; Ulanowicz, Robert E.; Taylor, William W.
Compartments in food webs are subgroups of taxa in which many strong interactions occur within the subgroups and few weak interactions occur between the subgroups. Theoretically, compartments increase the stability in networks, such as food webs. Compartments have been difficult to detect in empirical food webs because of incompatible approaches or insufficient methodological rigour. Here we show that a method for detecting compartments from the social networking science identified significant compartments in three of five complex, empirical food webs. Detection of compartments was influenced by food web resolution, such as interactions with weights. Because the method identifies compartmental boundaries in which interactions are concentrated, it is compatible with the definition of compartments. The method is rigorous because it maximizes an explicit function, identifies the number of non-overlapping compartments, assigns membership to compartments, and tests the statistical significance of the results. A graphical presentation reveals systemic relationships and taxa-specific positions as structured by compartments. From this graphic, we explore two scenarios of disturbance to develop a hypothesis for testing how compartmentalized interactions increase stability in food webs.
Scale and Structure in Natural Food Webs
Karl Havens
The degree to which widely accepted generalizations about food web structure apply to natural communities was determined through examination of 50 pelagic webs sampled consistently with even taxonomic resolution of all trophic levels. The fraction of species in various trophic categories showed no significant overall trends as the number of species varied from 10 to 74. In contrast, the number
Simple Rules Yield Complex Food Webs
NASA Astrophysics Data System (ADS)
Martinez, Neo
Several of the most ambitious theories in ecology describe food webs that document the structure of strong and weak trophic links among diverse assemblages of species. Early mechanism-based theory asserted that food webs have little omnivory and several properties that are independent of species richness. This theory was overturned by empirical studies that found food webs to be much more complex, but these studies did not provide mechanistic explanations for the complexity. Here we show that a remarkably simple model fills this scientific void by successfully predicting key structural properties of the most complex and comprehensive food webs in the primary literature. These properties include the fractions of species at top, intermediate and basal trophic levels, the means and variabilities of generality, vulnerability and food-chain length, and the degrees of cannibalism, omnivory, looping and trophic similarity. More recent tests using an expanded empirical base show that our model also successfully predicts the degrees of separation, degree distributions, and sensitivities to error and attack found in large complex food webs. Using only two empirical parameters, species number and connectance, our `niche model' extends the existing `cascade model' and improves its fit by constraining species to consume a contiguous sequence of prey in a one-dimensional trophic niche. The simplicity and success of the model has allowed new advances in the combined study of the structure and nonlinear dynamics of ecological networks.
Constructing Sonoran Desert Food Chains and Food Webs
NSDL National Science Digital Library
Is the food chain shown above accurate? Does the first link depict a producer, the second link a herbivore, and the third link an omnivore / carnivore? Students must correctly determine whether a species is a producer or consumer, and what type of consumer; herbivore, omnivore, or carnivore. Students are provided with a list of Sonoran Desert species and asked to construct, within their groups, several food chains. These food chains are then be used to construct a food web. In order to complete this activity, students must first research the individual species to understand their feeding habits.
Nutrient dynamics and food-web stability
DeAngelis, D.L.; Mulholland, P.J.; Palumbo, A.V.; Steinman, A.D.; Huston, M.A.; Elwood, J.W. (Environmental Sciences Div., Oak Ridge National Lab., Oak Ridge, TN (US))
The importance of nutrient limitation and recycling in ecosystems is widely recognized. Nutrients, defined in the broad sense as all material elements vital to biological functions, are in such small supply that they limit production in many ecosystems. Such limitation can affect ecosystem properties, including the structure and dynamics of the food webs that link species through their feeding relationships. What are the effects of limiting nutrients on the stability of ecosystem food webs Most of the literature on food web stability centers around the dynamics of population numbers and/or biomasses. Nevertheless, a growing body of theoretical and empirical research considers the role that both nutrient limitation and recycling can play in stability. In this paper, it is the authors objective to summarize the current understanding of several important types of stability. The theoretical and empirical evidence relating these types of stability and nutrient cycling is described. A central generalization is produced in each case.
The Antarctic Ecosystem: Where Would It Be Without Krill?
NSDL National Science Digital Library
This lesson plan asks students to investigate the importance of krill to the Antarctic ecosystem by researching the animals that depend on it. Students will read and answer questions about krill; research Antarctic animals and take note of the place of each animal in the food chain; and draw an Antarctic food web, using the animals they have researched. They will conclude by writing paragraphs explaining the potential consequences of a decline in krill populations.
Simple rules yield complex food webs
NASA Astrophysics Data System (ADS)
Williams, Richard J.; Martinez, Neo D.
Several of the most ambitious theories in ecology describe food webs that document the structure of strong and weak trophic links that is responsible for ecological dynamics among diverse assemblages of species. Early mechanism-based theory asserted that food webs have little omnivory and several properties that are independent of species richness. This theory was overturned by empirical studies that found food webs to be much more complex, but these studies did not provide mechanistic explanations for the complexity. Here we show that a remarkably simple model fills this scientific void by successfully predicting key structural properties of the most complex and comprehensive food webs in the primary literature. These properties include the fractions of species at top, intermediate and basal trophic levels, the means and variabilities of generality, vulnerability and food-chain length, and the degrees of cannibalism, omnivory, looping and trophic similarity. Using only two empirical parameters, species number and connectance, our `niche model' extends the existing `cascade model' and improves its fit ten-fold by constraining species to consume a contiguous sequence of prey in a one-dimensional trophic niche.
NSDL National Science Digital Library
The representation depicts the food-based interconnections of selected organisms in a pond. Through the interactive interface, users can read about changes to organism populations as one species increases or decreases in number.
Plankton, antarctic food chain base, respond to increased ultraviolet radiation
Dybas, C.
With the growth of the austral spring ozone hole phytoplankton in antarctic waters beneath the depleted ozone layer are now being exposed to twice the amount of ultraviolet radiation as organisms outside the hole. This briefly describes the results of a major study examining this issue. A significant observation was a decrease in phytoplankton production by a minimum of 6-12 percent. Implications for other life forms are discussed briefly along with the effects of increased UV light on the whole ecosystem.
Due to the difficulty associated with sampling deep aquatic systems, food web relationships among deepwater fauna are often poorly known. We are characterizing nearshore versus offshore habitats in the Great Lakes and investigating food web linkages among profundal, pelagic, and ...
Nutrient dynamics and food-web stability
D. L. DeAngelis; P. J. Mulholland; A. V. Palumbo; A. D. Steinman; M. A. Huston; J. W. Elwood
The importance of nutrient limitation and recycling in ecosystems is widely recognized. Nutrients, defined in the broad sense as all material elements vital to biological functions, are in such small supply that they limit production in many ecosystems. Such limitation can affect ecosystem properties, including the structure and dynamics of the food webs that link species through their feeding relationships.
Structural Degradation in Mediterranean Sea Food Webs
Myers, Ransom A.
Structural Degradation in Mediterranean Sea Food Webs: Testing Ecological Hypotheses Using-Central Adriatic and South Catalan Sea) and two time periods (mid-late 1970s and 1990s) in the Mediterranean Sea to species removal; Niche model; Ecopath model; Mediterranean Sea. INTRODUCTION Degradation of marine
Food web models: a plea for groups
Stefano Allesina; Mercedes Pascual
The concept of a group is ubiquitous in biology. It underlies classifications in evolution and ecology, including those used to describe phylogenetic levels, the habitat and functional roles of organisms in ecosystems. Surprisingly, this concept is not explicitly included in simple models for the structure of food webs, the ecological networks formed by consumer-resource interactions. We present here the simplest
Population Dynamics on Complex Food Webs
Gian Marco Palamara; Vinko Zlatic; Guido Caldarelli
In this work we analyze the topological and dynamical properties of a simple model of complex food webs, namely the niche model. We describe the system as an oriented weighted graph and we assign a Lotka-Volterra population dynamics on the structure created by the niche model. After this we introduce \\
In a recent paper, Isaacs has proposed a model for an unstructured food web in which the interconnecŁ tions are so diverse that all heterotrophs in the system can be treated as if they were at the same average trophic position. This paper recasts the original model in terms of a 3 x 3 matrix using three empirical constants. In
ERIC Educational Resources Information Center
Dunne, Barbara B.
The Maryland Marine Science Education Project has produced a series of mini-units in marine science education for the junior high/middle school classroom. This unit focuses on food chains in an estuary. Although the unit specifically treats the Chesapeake Bay, it may be adapted for use with similar estuarine systems. In addition, the unit may beģ
Kenichi Nakazato
We demonstrate that complex food webs may originate from mass extinctions. For this purpose, a minimal computa- tional model for the evolution of food webs is constructed. In the model, food web structure is represented by a kind of dynamic random graph with some biological constraints, and evolves under the condition without fitness, competition among species, nor population dynamics. It
An explanatory model for food-web structure and evolution
A. G. Rossberg; H. Matsuda; T. Amemiya; K. Itoh
Food webs are networks describing who is eating whom in an ecological community. By now it is clear that many aspects of food-web structure are reproducible across diverse habitats, yet little is known about the driving force behind this structure. Evolutionary and population dynamical mechanisms have been considered. We propose a model for the evolutionary dynamics of food-web topology and
Quantitative analysis of the local structure of food webs
J. Camachoa
We analyze the local structure of model and empirical food webs through the statistics of three-node subgraphs. We study analytically and numerically the number of appearances of each subgraph for a simple model of food web topology, the so-called generalized cascade model, and compare them with 17 empirical community food webs from a variety of environments, including aquatic, estuarine, and
Quantitative analysis of the local structure of food webs
J. Camacho; D. B. Stouffer; L. A. N. Amaral
We analyze the local structure of model and empirical food webs through the statistics of three-node subgraphs. We study analytically and numerically the number of appearances of each subgraph for a simple model of food web topology, the so-called generalized cascade model, and compare them with 17 empirical community food webs from a variety of environments, including aquatic, estuarine, and
Food webs: reconciling the structure and function of biodiversity
Hall Jr., Robert O.
in and between living organisms and between living organisms and their environment. Cascade model: a food-webFood webs: reconciling the structure and function of biodiversity Ross M. Thompson1 , Ulrich Brose2, whereas ecosystem ecology focuses on fluxes of energy and materials. Food webs provide a quantitative
Food web complexity and higher-level ecosystem services
Jose M. Montoya; Miguel A. Rodr§ ┤ guez; Bradford A. Hawkins
Studies mostly focused on communities of primary producers have shown that species richness provides and promotes fundamental ecosystem services. However, we know very little about the factors influencing ecosystem services provided by higher trophic levels in natural food webs. Here we present evidence that differences in food web structure and the richness of herbivores in 19 plant-herbivore-parasitoid food webs influence
Evolutionary emergence of size-structured food webs
Nicolas Loeuille; Michel Loreau
Explaining the structure of terrestrial and aquatic food webs remains one of the most important challenges of ecological theory. Most existing models use emergent properties of food webs, such as diversity and connectance as parameters, to determine other food-web descriptors. Lower-level processes, in particular adaptation (whether by behavioral, developmental, or evolutionary mechanisms), are usually not considered. Here, we show that
Development and Verification of a Benthic/Pelagic Food Web
Gobas, Frank
Development and Verification of a Benthic/Pelagic Food Web Bioaccumulation Model for PCB Congeners of this model to predict contaminant transfer in a complex food web and its potential applicability to other food webs indicate that it could be an important tool for managing contaminants on an ecosystem level
Food web structure and the evolution of ecological communities
McKane, Alan
Food web structure and the evolution of ecological communities Christopher Quince1 , Paul G. Higgs2 the population dynamics of the species for any structure of the food web. The equations account for competition of speciations and extinctions, and on the statistical properties of the food webs that are generated
However food webs have always been considered as a central issue of ecology, their value and usefulness are frequently questioned. In this paper, I overview some causes of this skepticism and discuss in which cases two or more food webs can be compared. I suggest that the comparability of different food webs is a key to possible applications. I show
Historical Food Web Structure and Restoration of Native Aquatic
Vander Zanden, Jake
Historical Food Web Structure and Restoration of Native Aquatic Communities in the Lake Tahoe as embedded within a broader food web context. In this study, we quantify food web changes in Lake Tahoe (CaliforniaŁNevada) over the last century based on stable isotope analysis of museum-ar- chived, preserved
Comparison of food webs constructed by evolution and by immigration
Craig R. Powell; Alan J. McKane
We present results contrasting food webs constructed using the same model where the source of species was either evolution or immigration from a previously evolved species pool. The overall structure of the webs are remarkably similar, although we find some important differences which mainly relate to the percentage of basal and top species. Food webs assembled from evolved webs also
NSDL National Science Digital Library
In this video, students learn that the Exxon Valdez oil spill in Alaska in 1989 was not the sole cause of the decline of species in the local ecosystem. Rather, an explanation is posited for why some animal populations were already in decline when the spill occurred. Many of these animals share a common food: the sand lance, a fish whose populations have shrunk with the steady rise in ocean temperature that began in the late 1970s.
Parasites in food webs: the ultimate missing links
Lafferty, Kevin D; Allesina, Stefano; Arim, Matias; Briggs, Cherie J; De Leo, Giulio; Dobson, Andrew P; Dunne, Jennifer A; Johnson, Pieter T J; Kuris, Armand M; Marcogliese, David J; Martinez, Neo D; Memmott, Jane; Marquet, Pablo A; McLaughlin, John P; Mordecai, Erin A; Pascual, Mercedes; Poulin, Robert; Thieltges, David W
Parasitism is the most common consumer strategy among organisms, yet only recently has there been a call for the inclusion of infectious disease agents in food webs. The value of this effort hinges on whether parasites affect food-web properties. Increasing evidence suggests that parasites have the potential to uniquely alter food-web topology in terms of chain length, connectance and robustness. In addition, parasites might affect food-web stability, interaction strength and energy flow. Food-web structure also affects infectious disease dynamics because parasites depend on the ecological networks in which they live. Empirically, incorporating parasites into food webs is straightforward. We may start with existing food webs and add parasites as nodes, or we may try to build food webs around systems for which we already have a good understanding of infectious processes. In the future, perhaps researchers will add parasites while they construct food webs. Less clear is how food-web theory can accommodate parasites. This is a deep and central problem in theoretical biology and applied mathematics. For instance, is representing parasites with complex life cycles as a single node equivalent to representing other species with ontogenetic niche shifts as a single node? Can parasitism fit into fundamental frameworks such as the niche model? Can we integrate infectious disease models into the emerging field of dynamic food-web modelling? Future progress will benefit from interdisciplinary collaborations between ecologists and infectious disease biologists. PMID:18462196
Evolutionary emergence of size-structured food webs.
Loeuille, Nicolas; Loreau, Michel
Explaining the structure of terrestrial and aquatic food webs remains one of the most important challenges of ecological theory. Most existing models use emergent properties of food webs, such as diversity and connectance as parameters, to determine other food-web descriptors. Lower-level processes, in particular adaptation (whether by behavioral, developmental, or evolutionary mechanisms), are usually not considered. Here, we show that complex, realistic food webs may emerge by evolution from a single ancestor based on very simple ecological and evolutionary rules. In our model, adaptation acts on body size, whose impact on the metabolism and interactions of organisms is well established. Based on parameters defined at the organism scale, the model predicts emergent properties at the food-web scale. Variations of two key parameters (width of consumption niche and competition intensity) allow very different food-web structures and functionings to emerge, which are similar to those observed in some of the best-documented food webs. PMID:15824324
Evolutionary emergence of size-structured food webs
Loeuille, Nicolas; Loreau, Michel
Explaining the structure of terrestrial and aquatic food webs remains one of the most important challenges of ecological theory. Most existing models use emergent properties of food webs, such as diversity and connectance as parameters, to determine other food-web descriptors. Lower-level processes, in particular adaptation (whether by behavioral, developmental, or evolutionary mechanisms), are usually not considered. Here, we show that complex, realistic food webs may emerge by evolution from a single ancestor based on very simple ecological and evolutionary rules. In our model, adaptation acts on body size, whose impact on the metabolism and interactions of organisms is well established. Based on parameters defined at the organism scale, the model predicts emergent properties at the food-web scale. Variations of two key parameters (width of consumption niche and competition intensity) allow very different food-web structures and functionings to emerge, which are similar to those observed in some of the best-documented food webs. PMID:15824324
FoodFit: A Web Application to Illustrate Healthier Food and Physical Activity Choices
Toronto, University of
FoodFit: A Web Application to Illustrate Healthier Food and Physical Activity Choices Meriyan Eren their lifestyles to include healthier food choices and more frequent physical activities. Lack of motivation is a major obstacle to achievement of healthier lifestyle. FoodFit is a web application to illustrate food
PRIMARY RESEARCH PAPER Phytoplankton food quality control of planktonic food web
Arhonditsis, George B.
PRIMARY RESEARCH PAPER Phytoplankton food quality control of planktonic food web processes Marta G to test the effects of phytoplankton food quality for herbivorous zooplankton on planktonic food web processes. When phyto- plankton food quality is high strong trophic cascades suppress phytoplankton biomass
Understanding food-web persistence from local to global scales
Daniel B. Stouffer; Jordi Bascompte
Understanding food-web persistence is an important long-term objective of ecology because of its relevance in maintaining biodiversity. To date, many dynamic studies of food-web behaviourŚboth empirical and theoreticalŚhave focused on smaller sub- webs, called trophic modules, because these modules are more tractable experimentally and analytically than whole food webs. The question remains to what degree studies of trophic modules are
Allometric Scaling of Weighted Food Webs
NASA Astrophysics Data System (ADS)
Zhang, Jiang
Allometric scaling is an important universal property of metabolic living systems. It also describes the self-similar branching tree-liked structures in transportation networks. This paper presented a new approach to calculate the allometric scaling power law relations for arbitrary flow networks. This method can not only avoid the shortcoming of losing lots of information in the process of generating spanning trees in the conventional approaches but also can be applied to arbitrary weighted networks. The allometric scaling properties of 20 empirical weighted food webs (weights are energy fluxes) are computed according to the new approach, the power law relationships are derived with the universal exponent ?= 1.0298 which reflects the transportation efficiency of the food webs.
Trophic coherence determines food-web stability
Johnson, Samuel; DomĒnguez-GarcĒa, Virginia; Donetti, Luca; Mu±oz, Miguel A.
Why are large, complex ecosystems stable? Both theory and simulations of current models predict the onset of instability with growing size and complexity, so for decades it has been conjectured that ecosystems must have some unidentified structural property exempting them from this outcome. We show that trophic coherenceŚa hitherto ignored feature of food webs that current structural models fail to reproduceŚis a better statistical predictor of linear stability than size or complexity. Furthermore, we prove that a maximally coherent network with constant interaction strengths will always be linearly stable. We also propose a simple model that, by correctly capturing the trophic coherence of food webs, accurately reproduces their stability and other basic structural features. Most remarkably, our model shows that stability can increase with size and complexity. This suggests a key to MayÆs paradox, and a range of opportunities and concerns for biodiversity conservation. PMID:25468963
Testing the cascade model for food webs
John M. Roberts
The cascade model is a standard model for food web data. This article describes a method for testing the cascade model that\\u000a complements existing tests. Like existing tests, the new test is conditional on the number of links observed in the predation\\u000a matrix. One important feature of the cascade model is that an ordering of species is required, but in
Effects of taxonomic and trophic aggregation on food web properties
George Sugihara; L.-F. Bersier; Kenneth Schoenly
Historically, ecologists have been more interested in organisms feeding at the tops of food chains than in organisms feeding\\u000a at or near the bottom. The problem of taxonomic and trophic inconsistency within and among described food webs is central\\u000a to criticisms of contemporary food web research. To study the effects of taxonomic and trophic aggregation on food web properties,\\u000a 38
IsoWeb: A Bayesian Isotope Mixing Model for Diet Analysis of the Whole Food Web
Taku Kadoya; Yutaka Osada; Gaku Takimoto
Quantitative description of food webs provides fundamental information for the understanding of population, community, and ecosystem dynamics. Recently, stable isotope mixing models have been widely used to quantify dietary proportions of different food resources to a focal consumer. Here we propose a novel mixing model (IsoWeb) that estimates diet proportions of all consumers in a food web based on stable
Current trends in food web theory report on a food web workshop. Environmental Sciences Division Publication No. 2224
DeAngelis, D.L.; Post, W.M.; Sugihara, G. (eds.)
This report summarizes the Food Web Workshop, held at Fontana Village Inn, October 25-27, 1982. The objective of the workshop was to review and assess recent progress in the understanding of ecological food webs. The workshop focused on three main areas: (1) what has been observed of food web patterns (food chain length, intervality, predator-prey ratios, etc.), (2) processes involved in food chains (energy flow and nutrient cycles), and (3) the dynamic behavior of food webs (Lyapunov stability, resilience, etc.). The introduction reviews some of the important contributions to food web theory during the past decade. The synopses of the presentations by invited speakers address many of the specific themes in current thought on food webs.
A study of equal node models for food webs
Thomas Wilhelm
It is argued to study better non-binary (weighted) food webs where links are measured quantitatively, instead of binary (unweighted) food webs where links are just present or absent. Binary webs can simply be deduced from the more general non-binary ones: if a flux is larger than a critical flux value (below denoted by ōcutö) a link is drawn, otherwise it
Competition in di- and tri-trophic food web modules.
K?ivan, Vlastimil
Competition in di- and tri-trophic food web modules with many competing species is studied. The food web modules considered are apparent competition between n species sharing a single predator and a diamond-like food web with a single resource, a single top predator and many competing middle species. The predators have either fixed preferences for their prey, or they switch between available prey in a way that maximizes their fitness. Dependence of these food web dynamics on environmental carrying capacity and food web connectance is studied. The results predict that optimal flexible foraging strongly weakens apparent competition and promotes species coexistence. Food web robustness (defined here as the proportion of surviving species) does not decrease with increased connectance in these food-webs. Moreover, it is shown that flexible prey switching leads to the same population equilibria as in corresponding food webs with highly specialized predators. The results show that flexible foraging behavior by predators can have very strong impact on species richness, as well as the response of communities to changes in resource enrichment and food-web connectance when compared to the same food-web topology with inflexible top predators. Several results on global stability using Lyapunov functions are provided. PMID:24316384
Increased Feeding and Nutrient Excretion of Adult Antarctic Krill, Euphausia superba, Exposed to Enhanced
@marine.rutgers.edu Introduction The Antarctic krill, Euphausia superba, is a key species in Antarctic food webs [1], [2]. E. The funders had no role in study design, data collection and analysis, decision to publish, or preparation. superba is a major consumer of phytoplankton [3Ł5] and a primary food source for many of the top predators
Invertebrate food webs along a stream resource gradient
SUMMARY 1. The flow of energy through food webs with similar species can vary with both space and time. The river continuum concept (RCC) provides a useful framework for predicting variability in the biota and food availability along streams. We estimated the flow of organic matter (g m)2 year)1) through food webs, arrayed along a stream, that had different resource
Warming and resource availability shift food web structure and metabolism.
O'Connor, Mary I; Piehler, Michael F; Leech, Dina M; Anton, Andrea; Bruno, John F
Climate change disrupts ecological systems in many ways. Many documented responses depend on species' life histories, contributing to the view that climate change effects are important but difficult to characterize generally. However, systematic variation in metabolic effects of temperature across trophic levels suggests that warming may lead to predictable shifts in food web structure and productivity. We experimentally tested the effects of warming on food web structure and productivity under two resource supply scenarios. Consistent with predictions based on universal metabolic responses to temperature, we found that warming strengthened consumer control of primary production when resources were augmented. Warming shifted food web structure and reduced total biomass despite increases in primary productivity in a marine food web. In contrast, at lower resource levels, food web production was constrained at all temperatures. These results demonstrate that small temperature changes could dramatically shift food web dynamics and provide a general, species-independent mechanism for ecological response to environmental temperature change. PMID:19707271
Geo-Spatial Browse and Distribution of NSF-OPP's Antarctic Ice and Climate Data via the Web: Antarctic Cryosphere Access Portal (A-CAP)
NASA Astrophysics Data System (ADS)
Bauer, R.; Scambos, T.; Haran, T.; Maurer, J.; Bohlander, J.
A prototype of the Antarctic Cryosphere Access Portal (A-CAP) has been released for public use. Developed at the National Snow and Ice Data Center (NSIDC) Antarctic Glaciological Data Center (AGDC), A-CAP aims to be a geo-visualization and data download tool for AGDC data and other Antarctic-wide parameters, including glaciology, ice core data, snow accumulation, satellite imagery, digital elevation models (DEMs), sea ice concentration, and many other cryosphere-related scientific measurements. The user can zoom in to a specific region as well as overlay coastlines, placenames, latitude/longitude, and other geographic information. In addition to providing an interactive Web interface, customizable A-CAP map images and source data are also accessible via specific Uniform Resource Locator strings (URLs) to a standard suite of Open Geospatial Consortium (OGC) services: Web Map Service (WMS), Web Feature Service (WFS), and Web Coverage Service (WCS). The international specifications of these services provide an interoperable framework for sharing maps and geospatial data over the Internet, allowing A-CAP products to be easily exchanged with other data centers worldwide and enabling remote access for users through OGC-compliant software applications such as ArcGIS, Google Earth, ENVI, and many others. A-CAP is built on MapServer, an Open Source development environment for building spatially-enabled Internet applications. MapServer uses data sets that have been formatted as GeoTIFF or Shapefile to allow rapid sub-setting and over-the-Web presentation of large geospatial data files, and has no requirement for a user-installed client software package (besides a Web browser).
Simulation approach to understanding the processes that structure food webs
Jager, H.I.; Gardner, R.H.; DeAngelis, D.L.; Post, W.M.
A simulation model of food web dynamics, WEB, was constructed and used in Monte Carlo experiments to study the relationship between structure and function in food webs. Four main experiments were designed using WEB. The first tested the robustness of food web structures at equilibrium to variations in the functional response of predators in the food web to the densities of their prey. The second experiment clarified the roles of predation and resource limitation in the process of structuring food webs. A third experiment studied the influence of productivity on food web structure and function using simulated food webs. The final experiment was designed to study the differential successes of generalists and specialists. The main advantage gained by using a simulation approach in each of these experiments was the ability to assess the roles played by processes of predation and competition in structuring model food webs. This was accomplished by interpreting the order of extinction events that occurred in the simulations and relating these to the species configurations at equilibrium. 61 references, 23 figures.
Metacommunity theory explains the emergence of food web complexity
Pillai, Pradeep; Gonzalez, Andrew; Loreau, Michel
Food webs are highly complex ecological networks, dynamic in both space and time. Metacommunity models are now at the core of unified theories of biodiversity, but to date they have not addressed food web complexity. Here we show that metacommunity theory can explain the emergence of species-rich food webs with complex network topologies. Our analysis shows that network branching in the food web is maximized at intermediate colonization rates and limited dispersal scales, which also leads to concomitant peaks in species diversity. Increased food web complexity and species diversity are made possible by the structural role played by network branches that are supported by omnivore and generalist feeding links. Thus, in contrast to traditional food web theory, which emphasizes the destabilizing effect of omnivory feeding in closed systems, metacommunity theory predicts that these feeding links, which are commonly observed in empirical food webs, play a critical structural role as food webs assemble in space. As this mechanism functions at the metacommunity level, evidence for its operation in nature will be obtained through multiscale surveys of food web structure. Finally, we apply our theory to reveal the effects of habitat destruction on network complexity and metacommunity diversity. PMID:22084089
Metacommunity theory explains the emergence of food web complexity.
Pillai, Pradeep; Gonzalez, Andrew; Loreau, Michel
Food webs are highly complex ecological networks, dynamic in both space and time. Metacommunity models are now at the core of unified theories of biodiversity, but to date they have not addressed food web complexity. Here we show that metacommunity theory can explain the emergence of species-rich food webs with complex network topologies. Our analysis shows that network branching in the food web is maximized at intermediate colonization rates and limited dispersal scales, which also leads to concomitant peaks in species diversity. Increased food web complexity and species diversity are made possible by the structural role played by network branches that are supported by omnivore and generalist feeding links. Thus, in contrast to traditional food web theory, which emphasizes the destabilizing effect of omnivory feeding in closed systems, metacommunity theory predicts that these feeding links, which are commonly observed in empirical food webs, play a critical structural role as food webs assemble in space. As this mechanism functions at the metacommunity level, evidence for its operation in nature will be obtained through multiscale surveys of food web structure. Finally, we apply our theory to reveal the effects of habitat destruction on network complexity and metacommunity diversity. PMID:22084089
The Disruption of Coastal Food Webs
NSDL National Science Digital Library
Payne, Laura X.
This week's In The News addresses recent findings (published in the October 16, 1998 issue of Science) that killer whale predation on sea otters in the North Pacific has "created an ecological chain reaction in nearshore ecosystems." Such ecological chain reactions refer to the disruption of the complex balance between predator and prey species. Killer whales, which traditionally fed on the (now scarce) Steller sea lions and harbor seals, have recently shifted their diet to sea otters. The resulting decline in sea otters has, in turn, led to an increase in sea urchins (sea otter prey), which in turn have deforested many kelp (seaweed) beds in the nearshore marine community. Although killer whales are playing a critical role in the current disruption, this chain of interactions "was probably initiated by anthropogenic changes in the offshore oceanic ecosystem" -- namely, the region's burgeoning fisheries, higher ocean temperatures, and the depletion of baleen whales. Similar "trophic cascades" have been well documented for lakes and in other systems (e.g. Snow Geese in the Arctic), but this research provides a new example of a disrupted food web that may reach a wider audience -- as it involves several highly charismatic vertebrates. The nine resources discussed describe the recent scientific findings, provide background information on food webs, and offer several resources for understanding ecological (trophic) chain reactions.
Food web persistence is enhanced by non-trophic interactions.
Hammill, Edd; Kratina, Pavel; Vos, Matthijs; Petchey, Owen L; Anholt, Bradley R
The strength of interspecific interactions is often proposed to affect food web stability, with weaker interactions increasing the persistence of species, and food webs as a whole. However, the mechanisms that modify interaction strengths, and their effects on food web persistence are not fully understood. Using food webs containing different combinations of predator, prey, and nonprey species, we investigated how predation risk of susceptible prey is affected by the presence of species not directly trophically linked to either predators or prey. We predicted that indirect alterations to the strength of trophic interactions translate to changes in persistence time of extinction-prone species. We assembled interaction webs of protist consumers and turbellarian predators with eight different combinations of prey, predators and nonprey species, and recorded abundances for over 130 prey generations. Persistence of predation-susceptible species was increased by the presence of nonprey. Furthermore, multiple nonprey species acted synergistically to increase prey persistence, such that persistence was greater than would be predicted from the dynamics of simpler food webs. We also found evidence suggesting increased food web complexity may weaken interspecific competition, increasing persistence of poorer competitors. Our results demonstrate that persistence times in complex food webs cannot be predicted from the dynamics of simplified systems, and that species not directly involved in consumptive interactions likely play key roles in maintaining persistence. Global species diversity is currently declining at an unprecedented rate and our findings reveal that concurrent loss of species that modify trophic interactions may have unpredictable consequences for food web stability. PMID:25656586
Adaptive foraging and flexible food web topology Vlastimil Krivan
Krivan, Vlastimil
modelling shows that single systems of predators, adaptive herbivores and resources can display food chain, adaptive omnivory causes the exploitative competition, linear food chain and multi-trophic level omnivory be confounded by topological shifts in the system itself. Keywords: adaptive foraging, food chain, food web
A Stochastic Theory of Community Food Webs III. Predicted and Observed Lengths of Food Chains
J. E. Cohen; F. Briand; C. M. Newman
This paper offers a quantitative theory of the length of food chains. The theory derives from a mathematical model of community food webs called the cascade model. The paper tests the predictions against data from real webs. An exact formula for the expected number of chains of each length in a model web with any given finite number, S, of
Amphipod-supported food web: Themisto gaudichaudii, a key food resource for fishes in the southern Patagonian Shelf
NASA Astrophysics Data System (ADS)
Padovani, Luciano N.; Vi±as, MarĒa Delia; Sßnchez, Felisa; Mianzan, Hermes
The trophic role of the hyperiid amphipod Themisto gaudichaudii in the southern Patagonian shelf food web was assessed from the analysis of stomach contents of the local fish assemblage. A total of 461 trawl samples were collected during seven seasonal cruises. A total of 17 out of 38 fish species were found to ingest T. gaudichaudii. This amphipod was a main prey item in five of these species, showing high values of alimentary index: Seriolella porosa (99.9%), Macruronus magellanicus (68.8%), Micromesistius australis (59.1%), Patagonotothen ramsayi (48.6%), and Merluccius hubbsi (10.9%). The contribution of T. gaudichaudii, in weight, to their summer diet was 60%, on average. This contribution was minimal in winter and maximal in summer. Fisheries studies have indicated that these five species, mainly M. magellanicus, account for almost 85% of the fish biomass in the area. Although the remaining 15% did not feed heavily on T. gaudichaudii, they are known to prey on the main hyperiid predators. Our study shows that T. gaudichaudii contributes greatly, both directly and indirectly, to supporting the fish community. We thus proposed that T. gaudichaudii plays a key role as a "wasp-waist" species in the sub-Antarctic region, similar to that of krill in Antarctic waters, channeling the energy flow and enabling a short and efficient food chain.
Experimental Ecology of Food Webs: Complex Systems in Temporary Ponds
Henry M. Wilbur
A food web graphically represents the paths of nutrients and energy through the living components of an ecosystem and the context in which individuals exploit their prey and avoid their enemies. Temporary ponds are excellent arenas for the study of food webs because they are discrete communities that can be mimicked in containers that approach the realism of natural habitats.
Investigation a food web: producers, consumers, and decomposers
NSDL National Science Digital Library
This activity is a field investigation where students list plants and animals they observe. Students will organize their data as producers, consumers, or decomposers and create a food web showing how they affect each other. They will predict what will happen if the food web becomes imbalanced by extinction or over population.
Building trophic modules into a persistent food web
Michio Kondoh
Understanding what maintains species and perpetuates their coexistence in a network of feeding relationships (the food web) is of great importance for biodiversity conservation. A food web can be viewed as consisting of a number of simple subunits called trophic modules. Intraguild predation (IGP), in which a prey and its predator compete for the same resource, is one of the
Food Web Stability: The Influence of Trophic Flows across Habitats
Kevin McCann
In nature, fluxes across habitats often bring both nu- ory, which plays a central role in consumer-resource in- trient and energetic resources into areas of low productivity from areas of higher productivity. These inputs can alter consumption teractions and food web dynamics. They further rates of consumer and predator species in the recipient food webs, suggested that multichannel omnivory can
Dynamics of PCBs in the Food Web of Lake Winnipeg
Sarah B. Gewurtz; Nilima Gandhi; Gary A. Stern; William G. Franzin; Bruno Rosenberg; Miriam L. Diamond
The bioaccumulation of polychlorinated biphenyls (PCBs) is examined in the food web of Lake Winnipeg using measured contaminant concentrations, stable isotopes of nitrogen, and a food web model. Measured concentrations of the sum of 103 PCB congeners are higher in south basin water, sediment, and biota compared with the north. The trophic positions of the top predators as well as
Bioaccumulation of Phthalate Esters in Aquatic Food-Webs
Frank A. P. C. Gobas; Cheryl E. Mackintosh; Glenys Webster; Michael Ikonomou; Thomas F. Parkerton; Kenneth Robillard
This chapter explores the bioaccumulation behavior of several phthalate esters in aquatic food-webs. It includes: (i) a compilation of bioconcentration data from reported laboratory studies in the literature, (ii) an overview and discussion of the results from a recently completed food-web bioaccumulation field study, and (iii) an analysis of the results of a bioaccumulation modeling study. The study concludes that
Scaling behaviors of weighted food webs as energy transportation networks
Jiang Zhang; Liangpeng Guo
Food webs can be regarded as energy transporting networks in which the weight of each edge denotes the energy flux between two species. By investigating 21 empirical weighted food webs as energy flow networks, we found several ubiquitous scaling behaviors. Two random variables Ai and Ci defined for each vertex i, representing the total flux (also called vertex intensity) and
A "Bottom-Up" Approach to Food Web Construction
ERIC Educational Resources Information Center
Demetriou, Dorita; Korfiatis, Konstantinos; Constantinou, Constantinos
The ability to comprehend trophic (nutritional) relationships and food web dynamics is an essential part of environmental literacy. However, students face severe difficulties in grasping the variety of causal patterns in food webs. We propose a curriculum for comprehending trophic relations in elementary school. The curriculum allows students toģ
Ecological food web analysis for chemical risk assessment
Damian V. Preziosi; Robert A. Pastorok
Food web analysis can be a critical component of ecological risk assessment, yet it has received relatively little attention among risk assessors. Food web data are currently used in modeling bioaccumulation of toxic chemicals and, to a limited extent, in the determination of the ecological significance of risks. Achieving more realism in ecological risk assessments requires new analysis tools and
Compilation and Network Analyses of Cambrian Food Webs
Jennifer A Dunne; Richard J Williams; Neo D Martinez; Rachel A Wood; Douglas H Erwin
A rich body of empirically grounded theory has developed about food websŚthe networks of feeding relationships among species within habitats. However, detailed food-web data and analyses are lacking for ancient ecosystems, largely because of the low resolution of taxa coupled with uncertain and incomplete information about feeding interactions. These impediments appear insurmountable for most fossil assemblages; however, a few assemblages
Food webs and the dimensionality of trophic niche space
Cohen, Joel E.
If the trophic niche of a kind of organism is a connected region in niche space, then it is possible for trophic niche overlaps to be described in a one-dimensional niche space if and only if the trophic niche overlap graph is an interval graph. An analysis of 30 food webs, using the combinatorial theory of interval graphs, suggests that a niche space of dimension 1 suffices, with unexpectedly high frequency and perhaps always, to describe the trophic niche overlaps implied by real food webs in single habitats. Consequently, real food webs fall in a small subset of the set of mathematically possible food webs. That real food webs are compatible with one-dimensional trophic niche spaces, more often than can be explained by chance alone, has not been noticed previously. PMID:16592451
Food webs and the dimensionality of trophic niche space.
Cohen, J E
If the trophic niche of a kind of organism is a connected region in niche space, then it is possible for trophic niche overlaps to be described in a one-dimensional niche space if and only if the trophic niche overlap graph is an interval graph. An analysis of 30 food webs, using the combinatorial theory of interval graphs, suggests that a niche space of dimension 1 suffices, with unexpectedly high frequency and perhaps always, to describe the trophic niche overlaps implied by real food webs in single habitats. Consequently, real food webs fall in a small subset of the set of mathematically possible food webs. That real food webs are compatible with one-dimensional trophic niche spaces, more often than can be explained by chance alone, has not been noticed previously. PMID:16592451
Characteristics of Food Industry Web Sites and "Advergames" Targeting Children
ERIC Educational Resources Information Center
Culp, Jennifer; Bell, Robert A.; Cassady, Diana
Objective: To assess the content of food industry Web sites targeting children by describing strategies used to prolong their visits and foster brand loyalty; and to document health-promoting messages on these Web sites. Design: A content analysis was conducted of Web sites advertised on 2 children's networks, Cartoon Network and Nickelodeon. Aģ
Persistence and flow reliability in simple food webs
Ferenc Jordßn; Istvßn Scheuring; Istvßn Molnßr
Twenty-five model food webs can be designed from five points (species) and five links (trophic interactions), if they contain a single top-predator (i.e. sink webs). According to a simple topological approach, we presented elsewhere a reliability theoretical analysis of this set of food web graphs. The question addressed here is how network flow reliability is related to the dynamical behavior
TOWARD AN INTEGRATION OF LANDSCAPE AND FOOD WEB ECOLOGY:The Dynamics of Spatially Subsidized Food Webs
Gary A. Polis; Wendy B. Anderson; Robert D. Holt
We focus on the implications of movement, landscape variables, and spatial het- erogeneity for food web dynamics. Movements of nutrients, detritus, prey, and consumers among habitats are ubiquitous in diverse biomes and can strongly influence population, consumer-resource, food web, and community dynamics. Nutrient and detrital subsidies usually increase primary and secondary produc- tivity, both directly and indirectly. Prey subsidies, by
Food-web dynamics in a large river discontinuum
Cross, Wyatt F.; Baxter, Colden V.; Rosi-Marshall, Emma J.; Hall, Robert O., Jr.; Kennedy, Theodore A.; Donner, Kevin C.; Kelly, Holly A. Wellard; Seegert, Sarah E.Z.; Behn, Kathrine E.; Yard, Michael D.
Nearly all ecosystems have been altered by human activities, and most communities are now composed of interacting species that have not co-evolved. These changes may modify species interactions, energy and material flows, and food-web stability. Although structural changes to ecosystems have been widely reported, few studies have linked such changes to dynamic food-web attributes and patterns of energy flow. Moreover, there have been few tests of food-web stability theory in highly disturbed and intensely managed freshwater ecosystems. Such synthetic approaches are needed for predicting the future trajectory of ecosystems, including how they may respond to natural or anthropogenic perturbations. We constructed flow food webs at six locations along a 386-km segment of the Colorado River in Grand Canyon (Arizona, USA) for three years. We characterized food-web structure and production, trophic basis of production, energy efficiencies, and interaction-strength distributions across a spatial gradient of perturbation (i.e., distance from Glen Canyon Dam), as well as before and after an experimental flood. We found strong longitudinal patterns in food-web characteristics that strongly correlated with the spatial position of large tributaries. Above tributaries, food webs were dominated by nonnative New Zealand mudsnails (62% of production) and nonnative rainbow trout (100% of fish production). The simple structure of these food webs led to few dominant energy pathways (diatoms to few invertebrate taxa to rainbow trout), large energy inefficiencies (i.e., Below large tributaries, invertebrate production declined ?18-fold, while fish production remained similar to upstream sites and comprised predominately native taxa (80¢100% of production). Sites below large tributaries had increasingly reticulate and detritus-based food webs with a higher prevalence of omnivory, as well as interaction strength distributions more typical of theoretically stable food webs (i.e., nearly twofold higher proportion of weak interactions). Consistent with theory, downstream food webs were less responsive to the experimental flood than sites closest to the dam. We show how human-induced shifts to food-web structure can affect energy flow and interaction strengths, and we show that these changes have consequences for food-web function and response to perturbations.
Food Web Structure in a Harsh Glacier-Fed River
Clitherow, Leonie R.; Carrivick, Jonathan L.; Brown, Lee E.
Glacier retreat is occurring across the world, and associated river ecosystems are expected to respond more rapidly than those in flowing waters in other regions. The river environment directly downstream of a glacier snout is characterised by extreme low water temperature and unstable channel sediments but these habitats may become rarer with widespread glacier retreat. In these extreme environments food web dynamics have been little studied, yet they could offer opportunities to test food web theories using highly resolved food webs owing to their low taxonomic richness. This study examined the interactions of macroinvertebrate and diatom taxa in the ųdenwinkelkees river, Austrian central Alps between 2006 and 2011. The webs were characterised by low taxon richness (13¢22), highly connected individuals (directed connectance up to 0.19) and short mean food chain length (2.00¢2.36). The dominant macroinvertebrates were members of the Chironomidae genus Diamesa and had an omnivorous diet rich in detritus and diatoms as well as other Chironomidae. Simuliidae (typically detritivorous filterers) had a diet rich in diatoms but also showed evidence of predation on Chironomidae larvae. Food webs showed strong species-averaged and individual size structuring but mass-abundance scaling coefficients were larger than those predicted by metabolic theory, perhaps due to a combination of spatial averaging effects of patchily distributed consumers and resources, and/or consumers deriving unquantified resources from microorganisms attached to the large amounts of ingested rock fragments. Comparison of food web structural metrics with those from 62 published river webs suggest these glacier-fed river food web properties were extreme but in line with general food web scaling predictions, a finding which could prove useful to forecast the effects of anticipated future glacier retreat on the structure of aquatic food webs. PMID:23613751
Food web stability: the influence of trophic flows across habitats.
Huxel, G R; McCann, K
In nature, fluxes across habitats often bring both nutrient and energetic resources into areas of low productivity from areas of higher productivity. These inputs can alter consumption rates of consumer and predator species in the recipient food webs, thereby influencing food web stability. Starting from a well-studied tritrophic food chain model, we investigated the impact of allochthonous inputs on the stability of a simple food web model. We considered the effects of allochthonous inputs on stability of the model using four sets of biologically plausible parameters that represent different dynamical outcomes. We found that low levels of allochthonous inputs stabilize food web dynamics when species preferentially feed on the autochthonous sources, while either increasing the input level or changing the feeding preference to favor allochthonous inputs, or both, led to a decoupling of the food chain that could result in the loss of one or all species. We argue that allochthonous inputs are important sources of productivity in many food webs and their influence needs to be studied further. This is especially important in the various systems, such as caves, headwater streams, and some small marine islands, in which more energy enters the food web from allochthonous inputs than from autochthonous inputs. PMID:18811452
Hydrogeomorphology and river impoundment affect food-chain length of diverse Neotropical food webs
Hoeinghaus, David J.
Hydrogeomorphology and river impoundment affect food-chain length of diverse Neotropical food webs-900 Parana┤, Brasil. Food-chain length is a central characteristic of ecological communities that affects community structure and ecosystem function. What determines the length of food chains is not well resolved
Adaptations in a hierarchical food web of southeastern Lake Michigan
Krause, Ann E.; Frank, Ken A.; Jones, Michael L.; Nalepa, Thomas F.; Barbiero, Richard P.; Madenjian, Charles P.; Agy, Megan; Evans, Marlene S.; Taylor, William W.; Mason, Doran M.; Leonard, Nancy J.
Two issues in ecological network theory are: (1) how to construct an ecological network model and (2) how do entire networks (as opposed to individual species) adapt to changing conditions? We present a novel method for constructing an ecological network model for the food web of southeastern Lake Michigan (USA) and we identify changes in key system properties that are large relative to their uncertainty as this ecological network adapts from one time point to a second time point in response to multiple perturbations. To construct our food web for southeastern Lake Michigan, we followed the list of seven recommendations outlined in Cohen et al. [Cohen, J.E., et al., 1993. Improving food webs. Ecology 74, 252¢258] for improving food webs. We explored two inter-related extensions of hierarchical system theory with our food web; the first one was that subsystems react to perturbations independently in the short-term and the second one was that a system's properties change at a slower rate than its subsystemsÆ properties. We used Shannon's equations to provide quantitative versions of the basic food web properties: number of prey, number of predators, number of feeding links, and connectance (or density). We then compared these properties between the two time-periods by developing distributions of each property for each time period that took uncertainty about the property into account. We compared these distributions, and concluded that non-overlapping distributions indicated changes in these properties that were large relative to their uncertainty. Two subsystems were identified within our food web system structure (p < 0.001). One subsystem had more non-overlapping distributions in food web properties between Time 1 and Time 2 than the other subsystem. The overall system had all overlapping distributions in food web properties between Time 1 and Time 2. These results supported both extensions of hierarchical systems theory. Interestingly, the subsystem with more non-overlapping distributions in food web properties was the subsystem that contained primarily benthic taxa, contrary to expectations that the identified major perturbations (lower phosphorous inputs and invasive species) would more greatly affect the subsystem containing primarily pelagic taxa. Future food-web research should employ rigorous statistical analysis and incorporate uncertainty in food web properties for a better understanding of how ecological networks adapt.
Consumers indirectly increase infection risk in grassland food webs
Crews, Stephen
Consumers indirectly increase infection risk in grassland food webs Elizabeth T. Borera,1 , Charles by increasing the relative abundance of highly-competent hosts in the grassland community. This large
RAPID COMMUNICATION / COMMUNICATION RAPIDE Simplified food webs lead to energetic
Hontela, Alice
diet and community analysis indicated that the food web leading to yellow perch (Perca flavescens nourriture disponible aux perchaudes (Perca flavescens) provenant de lacs polluķs par les mķtaux lourds a ķtķ
Compilation and Network Analyses of Cambrian Food Webs
Dunne, Jennifer A; Williams, Richard J; Martinez, Neo D; Wood, Rachel A; Erwin, Douglas H
A rich body of empirically grounded theory has developed about food websŚthe networks of feeding relationships among species within habitats. However, detailed food-web data and analyses are lacking for ancient ecosystems, largely because of the low resolution of taxa coupled with uncertain and incomplete information about feeding interactions. These impediments appear insurmountable for most fossil assemblages; however, a few assemblages with excellent soft-body preservation across trophic levels are candidates for food-web data compilation and topological analysis. Here we present plausible, detailed food webs for the Chengjiang and Burgess Shale assemblages from the Cambrian Period. Analyses of degree distributions and other structural network properties, including sensitivity analyses of the effects of uncertainty associated with Cambrian diet designations, suggest that these early Paleozoic communities share remarkably similar topology with modern food webs. Observed regularities reflect a systematic dependence of structure on the numbers of taxa and links in a web. Most aspects of Cambrian food-web structure are well-characterized by a simple ōniche model,ö which was developed for modern food webs and takes into account this scale dependence. However, a few aspects of topology differ between the ancient and recent webs: longer path lengths between species and more species in feeding loops in the earlier Chengjiang web, and higher variability in the number of links per species for both Cambrian webs. Our results are relatively insensitive to the exclusion of low-certainty or random links. The many similarities between Cambrian and recent food webs point toward surprisingly strong and enduring constraints on the organization of complex feeding interactions among metazoan species. The few differences could reflect a transition to more strongly integrated and constrained trophic organization within ecosystems following the rapid diversification of species, body plans, and trophic roles during the Cambrian radiation. More research is needed to explore the generality of food-web structure through deep time and across habitats, especially to investigate potential mechanisms that could give rise to similar structure, as well as any differences. PMID:18447582
Re-Evaluating the Omnivory-Stability Relationship in Food Webs
Kevin McCann; Alan Hastings
Under equilibrium conditions, previous theory has shown that the presence of omnivory destabilizes food webs. Correspondingly, omnivory ought to be rare in real food webs. Although early food-web data appeared to verify this, recently many ecologists have found omnivory to be ubiquitous in food-web data gathered at a high taxonomic resolution. In this paper, we reinvestigate the role of omnivory
A robust measure of food web intervality Daniel B. Stouffer*, Juan Camacho*
Stouffer, Daniel B.
A robust measure of food web intervality Daniel B. Stouffer*, Juan Camacho* , and Lui┤s A. Nunes, 2006 (received for review May 10, 2006) Intervality of a food web is related to the number of trophic for food web intervality. It has previously been noted that empirical food webs are not strictly interval
Journal of Theoretical Biology 245 (2007) 705714 Biodiversity maintenance in food webs with regulatory
Dunham, Amy E.
Journal of Theoretical Biology 245 (2007) 705Ł714 Biodiversity maintenance in food webs the food web is one of the most fundamental and oldest concepts in ecology, elucidating the strategies within complex and realistic food-web models enhance biodiversity. The food webs are generated through
Barcoding a Quantified Food Web: Crypsis, Concepts, Ecology and Hypotheses
Smith, M. Alex; Eveleigh, Eldon S.; McCann, Kevin S.; Merilo, Mark T.; McCarthy, Peter C.; Van Rooyen, Kathleen I.
The efficient and effective monitoring of individuals and populations is critically dependent on correct species identification. While this point may seem obvious, identifying the majority of the more than 100 natural enemies involved in the spruce budworm (Choristoneura fumiferana ¢ SBW) food web remains a non-trivial endeavor. Insect parasitoids play a major role in the processes governing the population dynamics of SBW throughout eastern North America. However, these species are at the leading edge of the taxonomic impediment and integrating standardized identification capacity into existing field programs would provide clear benefits. We asked to what extent DNA barcoding the SBW food web would alter our understanding of the diversity and connectence of the food web and the frequency of generalists vs. specialists in different forest habitats. We DNA barcoded over 10% of the insects collected from the SBW food web in three New Brunswick forest plots from 1983 to 1993. For 30% of these specimens, we amplified at least one additional nuclear region. When the nodes of the food web were estimated based on barcode divergences (using molecular operational taxonomic units (MOTU) or phylogenetic diversity (PD) ¢ the food web became much more diverse and connectence was reduced. We tested one measure of food web structure (the ōbird feeder effectö) and found no difference compared to the morphologically based predictions. Many, but not all, of the presumably polyphagous parasitoids now appear to be morphologically-cryptic host-specialists. To our knowledge, this project is the first to barcode a food web in which interactions have already been well-documented and described in space, time and abundance. It is poised to be a system in which field-based methods permit the identification capacity required by forestry scientists. Food web barcoding provided an effective tool for the accurate identification of all species involved in the cascading effects of future budworm outbreaks. Integrating standardized barcodes within food webs may ultimately change the face of community ecology. This will be most poignantly felt in food webs that have not yet been quantified. Here, more accurate and precise connections will be within the grasp of any researcher for the first time. PMID:21754977
Stream food web fueled by methane-derived carbon
Ayato Kohzu; Chika Kato; Tomoya Iwata; Daisuke Kishi; Masashi Murakami; Shigeru Nakano; Eitaro Wada
Food webs driven by energy from the oxidation of methane are now recognized to be omnipresent in terrestrial and freshwater ecosystems (e.g. lakes, soils and peat bogs), as well as in deep-sea hydrothermal vents and cold seeps. However, the incorporation of methane-derived carbon into stream food webs has never been reported. Here we present the first circumstantial evidence from stable
Cascading extinctions and community collapse in model food webs
Jennifer A. Dunne; Richard J. Williams
Species loss in ecosystems can lead to secondary extinctions as a result of consumer-resource relationships and other species interactions. We compare levels of secondary extinctions in communities generated by four structural food-web models and a fifth null model in response to sequential primary species removals. We focus on various aspects of food-web structural integrity including robustness, community collapse and threshold
The inverse niche model for food webs with parasites
Christopher P. Warren; Mercedes Pascual; Kevin D. Lafferty; Armand M. Kuris
Although parasites represent an important component of ecosystems, few field and theoretical studies have addressed the structure\\u000a of parasites in food webs. We evaluate the structure of parasitic links in an extensive salt marsh food web, with a new model\\u000a distinguishing parasitic links from non-parasitic links among free-living species. The proposed model is an extension of the\\u000a niche model for
Phylogeny versus body size as determinants of food web structure
Naisbit, Russell E.; Rohr, Rudolf P.; Rossberg, Axel G.; Kehrli, Patrik; Bersier, Louis-Fķlix
Food webs are the complex networks of trophic interactions that stoke the metabolic fires of life. To understand what structures these interactions in natural communities, ecologists have developed simple models to capture their main architectural features. However, apparently realistic food webs can be generated by models invoking either predator¢prey body-size hierarchies or evolutionary constraints as structuring mechanisms. As a result, this approach has not conclusively revealed which factors are the most important. Here we cut to the heart of this debate by directly comparing the influence of phylogeny and body size on food web architecture. Using data from 13 food webs compiled by direct observation, we confirm the importance of both factors. Nevertheless, phylogeny dominates in most networks. Moreover, path analysis reveals that the size-independent direct effect of phylogeny on trophic structure typically outweighs the indirect effect that could be captured by considering body size alone. Furthermore, the phylogenetic signal is asymmetric: closely related species overlap in their set of consumers far more than in their set of resources. This is at odds with several food web models, which take only the view-point of consumers when assigning interactions. The echo of evolutionary history clearly resonates through current food webs, with implications for our theoretical models and conservation priorities. PMID:22628467
Genetic variation, predator¢prey interactions and food web structure
Moya-Lara±o, Jordi
Food webs are networks of species that feed on each other. The role that within-population phenotypic and genetic variation plays in food web structure is largely unknown. Here, I show via simulation how variation in two key traits, growth rates and phenology, by influencing the variability of body sizes present through time, can potentially affect several structural parameters in the direction of enhancing food web persistence: increased connectance, decreased interaction strengths, increased variation among interaction strengths and increased degree of omnivory. I discuss other relevant traits whose variation could affect the structure of food webs, such as morphological and additional life-history traits, as well as animal personalities. Furthermore, trait variation could also contribute to the stability of food web modules through metacommunity dynamics. I propose future research to help establish a link between within-population variation and food web structure. If appropriately established, such a link could have important consequences for biological conservation, as it would imply that preserving (functional) genetic variation within populations could ensure the preservation of entire communities. PMID:21444316
The inverse niche model for food webs with parasites
Warren, Christopher P.; Pascual, Mercedes; Lafferty, Kevin D.; Kuris, Armand M.
Although parasites represent an important component of ecosystems, few field and theoretical studies have addressed the structure of parasites in food webs. We evaluate the structure of parasitic links in an extensive salt marsh food web, with a new model distinguishing parasitic links from non-parasitic links among free-living species. The proposed model is an extension of the niche model for food web structure, motivated by the potential role of size (and related metabolic rates) in structuring food webs. The proposed extension captures several properties observed in the data, including patterns of clustering and nestedness, better than does a random model. By relaxing specific assumptions, we demonstrate that two essential elements of the proposed model are the similarity of a parasite's hosts and the increasing degree of parasite specialization, along a one-dimensional niche axis. Thus, inverting one of the basic rules of the original model, the one determining consumers' generality appears critical. Our results support the role of size as one of the organizing principles underlying niche space and food web topology. They also strengthen the evidence for the non-random structure of parasitic links in food webs and open the door to addressing questions concerning the consequences and origins of this structure.
Food Web Structure and the Evolution of Complex Networks
Guido Caldarelli; Diego Garlaschelli; Luciano Pietronero
In addition to traditional properties such as the degree distribution P( k), in this work we propose two other useful quantities that can help in characterizing the topology of food webs quantitatively, namely the allometric scaling relations C( A) and the branch size distribution P(A) A which are defined on the spanning tree of the webs. These quantities, whose use
OIKOS 94: 118129. Copenhagen 2001 Field biology, food web models, and management: challenges of
Power, Mary Eleanor
trajectories of specific populations or ecosystem variables. Food chain and simple food web models, used either of dynamic food chain or food web models can organize our thinking about a range of applied problems properties. In other applications, a food chain or web may be incorporated as one element in models
Invertebrate food webs along a stream resource gradient
Emma J. Rosi-Marshall; J. Bruce Wallace
SUMMARY 1. The flow of energy through food webs with similar species can vary with both space and time. The river continuum concept (RCC) provides a useful framework for predicting variability in the biota and food availability along streams. We estimated the flow of organic matter (g m~2 year\\
Kumi Tanabe; Toshiyuki Namba
Omnivory, defined as feeding on more than one trophic level, was considered rare in nature because of its destabilizing effect. However, recent elaborate studies of natural food webs have shown that omnivory is ubiquitous. It is well known that a simple food chain model of three trophic levels can exhibit chaos if the functional responses are non- linear. We investigate
Reconciling complexity with stability in naturally assembling food webs.
Neutel, Anje-Margriet; Heesterbeek, Johan A P; van de Koppel, Johan; Hoenderboom, Guido; Vos, An; Kaldeway, Coen; Berendse, Frank; de Ruiter, Peter C
Understanding how complex food webs assemble through time is fundamental both for ecological theory and for the development of sustainable strategies of ecosystem conservation and restoration. The build-up of complexity in communities is theoretically difficult, because in random-pattern models complexity leads to instability. There is growing evidence, however, that nonrandom patterns in the strengths of the interactions between predators and prey strongly enhance system stability. Here we show how such patterns explain stability in naturally assembling communities. We present two series of below-ground food webs along natural productivity gradients in vegetation successions. The complexity of the food webs increased along the gradients. The stability of the food webs was captured by measuring the weight of feedback loops of three interacting 'species' locked in omnivory. Low predator-prey biomass ratios in these omnivorous loops were shown to have a crucial role in preserving stability as productivity and complexity increased during succession. Our results show the build-up of food-web complexity in natural productivity gradients and pin down the feedback loops that govern the stability of whole webs. They show that it is the heaviest three-link feedback loop in a network of predator-prey effects that limits its stability. Because the weight of these feedback loops is kept relatively low by the biomass build-up in the successional process, complexity does not lead to instability. PMID:17914396
Cascading extinctions and community collapse in model food webs
Dunne, Jennifer A.; Williams, Richard J.
Species loss in ecosystems can lead to secondary extinctions as a result of consumer¢resource relationships and other species interactions. We compare levels of secondary extinctions in communities generated by four structural food-web models and a fifth null model in response to sequential primary species removals. We focus on various aspects of food-web structural integrity including robustness, community collapse and threshold periods, and how these features relate to assumptions underlying different models, different species loss sequences and simple measures of diversity and complexity. Hierarchical feeding, a fundamental characteristic of food-web structure, appears to impose a cost in terms of robustness and other aspects of structural integrity. However, exponential-type link distributions, also characteristic of more realistic models, generally confer greater structural robustness than the less skewed link distributions of less realistic models. In most cases for the more realistic models, increased robustness and decreased levels of web collapse are associated with increased diversity, measured as species richness S, and increased complexity, measured as connectance C. These and other results, including a surprising sensitivity of more realistic model food webs to loss of species with few links to other species, are compared with prior work based on empirical food-web data. PMID:19451122
Effects of whaling on the structure of the Southern Ocean food web: insights on the "krill surplus" from ecosystem modelling.
Surma, Szymon; Pakhomov, Evgeny A; Pitcher, Tony J
The aim of this study was to examine the ecological plausibility of the "krill surplus" hypothesis and the effects of whaling on the Southern Ocean food web using mass-balance ecosystem modelling. The depletion trajectory and unexploited biomass of each rorqual population in the Antarctic was reconstructed using yearly catch records and a set of species-specific surplus production models. The resulting estimates of the unexploited biomass of Antarctic rorquals were used to construct an Ecopath model of the Southern Ocean food web existing in 1900. The rorqual depletion trajectory was then used in an Ecosim scenario to drive rorqual biomasses and examine the "krill surplus" phenomenon and whaling effects on the food web in the years 1900-2008. An additional suite of Ecosim scenarios reflecting several hypothetical trends in Southern Ocean primary productivity were employed to examine the effect of bottom-up forcing on the documented krill biomass trend. The output of the Ecosim scenarios indicated that while the "krill surplus" hypothesis is a plausible explanation of the biomass trends observed in some penguin and pinniped species in the mid-20th century, the excess krill biomass was most likely eliminated by a rapid decline in primary productivity in the years 1975-1995. Our findings suggest that changes in physical conditions in the Southern Ocean during this time period could have eliminated the ecological effects of rorqual depletion, although the mechanism responsible is currently unknown. Furthermore, a decline in iron bioavailability due to rorqual depletion may have contributed to the rapid decline in overall Southern Ocean productivity during the last quarter of the 20th century. The results of this study underscore the need for further research on historical changes in the roles of top-down and bottom-up forcing in structuring the Southern Ocean food web. PMID:25517505
Notre Dame, University of
TOP-DOWN AND BOTTOM-UP EFFECTS IN A DETRITAL FOOD WEB: THE PITCHER PLANT INQUILINE COMMUNITY AS A MODEL FOOD WEB A Dissertation Submitted to the Graduate School of the University of Notre Dame;TOP-DOWN AND BOTTOM-UP EFFECTS IN A DETRITAL FOOD WEB: THE PITCHER PLANT INQUILINE COMMUNITY
Development of a Food Web Model (DOVE-Digital Organisms in a Virtual Ecosystem) to Examine Indirect Interactions in Food Webs and
are developing a computational model to examine food webs. The computational model is designed to addressDevelopment of a Food Web Model (DOVE- Digital Organisms in a Virtual Ecosystem) to Examine Indirect Interactions in Food Webs and Invasive Species Primary Investigator: Scott Peacor - Michigan State
Tracing Food Webs with Stable Hydrogen Isotopes
Marilyn F. Estep; Halina Dabrowski
The hydrogen isotopic content of an animal's food, not water, determines that animal's hydrogen isotopic content. Liver and muscle tissue from mice reared on a diet such that the ratio of deuterium to hydrogen (D\\/H) of their food and water was kept constant, have the same average D\\/H ratio as the food source. In a simple, natural population of snails
Quantitative analysis of the local structure of food webs.
Camacho, J; Stouffer, D B; Amaral, L A N
We analyze the local structure of model and empirical food webs through the statistics of three-node subgraphs. We study analytically and numerically the number of appearances of each subgraph for a simple model of food web topology, the so-called generalized cascade model, and compare them with 17 empirical community food webs from a variety of environments, including aquatic, estuarine, and terrestrial ecosystems. We obtain analytical expressions for the probability of appearances of each subgraph in the model, and also for randomizations of the model that preserve species' numbers of prey and number of predators; their difference allows us to quantify which subgraphs are over- or under-represented in both the model and the empirical food webs. We find agreement between the model predictions and the empirical results. These results indicate that simple models such as the generalized cascade can provide a good description not only of the global topology of food webs, as recently shown, but also of its local structure. PMID:17292921
When do evolutionary food web models generate complex networks?
Allhoff, Korinna T; Drossel, Barbara
Evolutionary foodweb models are used to build food webs by the repeated addition of new species. Population dynamics leads to the extinction or establishment of a newly added species, and possibly to the extinction of other species. The food web structure that emerges after some time is a highly nontrivial result of the evolutionary and dynamical rules. We investigate the evolutionary food web model introduced by Loeuille and Loreau (2005), which characterizes species by their body mass as the only evolving trait. Our goal is to find the reasons behind the model's remarkable robustness and its capability to generate various and stable networks. In contrast to other evolutionary food web models, this model requires neither adaptive foraging nor allometric scaling of metabolic rates with body mass in order to produce complex networks that do not eventually collapse to trivial structures. Our study shows that this is essentially due to the fact that the difference in niche value between predator and prey as well as the feeding range are constrained so that they remain within narrow limits under evolution. Furthermore, competition between similar species is sufficiently strong, so that a trophic level can accommodate several species. We discuss the implications of these findings and argue that the conditions that stabilize other evolutionary food web models have similar effects because they also prevent the occurrence of extreme specialists or extreme generalists that have in general a higher fitness than species with a moderate niche width. PMID:23778160
Relevance of evolutionary history for food web structure
Ekl÷f, Anna; Helmus, Matthew R.; Moore, M.; Allesina, Stefano
Explaining the structure of ecosystems is one of the great challenges of ecology. Simple models for food web structure aim at disentangling the complexity of ecological interaction networks and detect the main forces that are responsible for their shape. Trophic interactions are influenced by species traits, which in turn are largely determined by evolutionary history. Closely related species are more likely to share similar traits, such as body size, feeding mode and habitat preference than distant ones. Here, we present a theoretical framework for analysing whether evolutionary historyŚrepresented by taxonomic classificationŚprovides valuable information on food web structure. In doing so, we measure which taxonomic ranks better explain species interactions. Our analysis is based on partitioning of the species into taxonomic units. For each partition, we compute the likelihood that a probabilistic model for food web structure reproduces the data using this information. We find that taxonomic partitions produce significantly higher likelihoods than expected at random. Marginal likelihoods (Bayes factors) are used to perform model selection among taxonomic ranks. We show that food webs are best explained by the coarser taxonomic ranks (kingdom to class). Our methods provide a way to explicitly include evolutionary history in models for food web structure. PMID:22090387
Key Features of Intertidal Food Webs That Support Migratory Shorebirds
Saint-Bķat, Blanche; Dupuy, Christine; Bocher, Pierrick; Chalumeau, Julien; De Crignis, Margot; Fontaine, Camille; Guizien, Katell; Lavaud, Johann; Lefebvre, Sķbastien; Montaniķ, HķlĶne; Mouget, Jean-Luc; Orvain, Francis; Pascal, Pierre-Yves; Quaintenne, Gwenaļl; Radenac, Gilles; Richard, Pierre; Robin, Frķdķric; Vķzina, Alain F.; Niquil, Nathalie
The migratory shorebirds of the East Atlantic flyway land in huge numbers during a migratory stopover or wintering on the French Atlantic coast. The Brouage bare mudflat (Marennes-Olķron Bay, NE Atlantic) is one of the major stopover sites in France. The particular structure and function of a food web affects the efficiency of carbon transfer. The structure and functioning of the Brouage food web is crucial for the conservation of species landing within this area because it provides sufficient food, which allows shorebirds to reach the north of Europe where they nest. The aim of this study was to describe and understand which food web characteristics support nutritional needs of birds. Two food-web models were constructed, based on in situ measurements that were made in February 2008 (the presence of birds) and July 2008 (absence of birds). To complete the models, allometric relationships and additional data from the literature were used. The missing flow values of the food web models were estimated by Monte Carlo Markov Chain ¢ Linear Inverse Modelling. The flow solutions obtained were used to calculate the ecological network analysis indices, which estimate the emergent properties of the functioning of a food-web. The total activities of the Brouage ecosystem in February and July are significantly different. The specialisation of the trophic links within the ecosystem does not appear to differ between the two models. In spite of a large export of carbon from the primary producer and detritus in winter, the higher recycling leads to a similar retention of carbon for the two seasons. It can be concluded that in February, the higher activity of the ecosystem coupled with a higher cycling and a mean internal organization, ensure the sufficient feeding of the migratory shorebirds. PMID:24204666
Freshness Matters: In Flowers, Food, and Web Authority Na Dai and Brian D. Davison
Davison, Brian D.
Freshness Matters: In Flowers, Food, and Web Authority Na Dai and Brian D. Davison Department-link activity, and design a web surfer model that incorporates web freshness, based on a temporal web graph, such as flowers and food. The same is also true for web page au- thority estimation. Pages being fresh tend
8 Food Webs in the Ocean: Who Eats Whom and How Much?
Andrew W. Trites
Over 100 food webs have been published for marine ecosystems to describe the transfer of food energy from its source in plants, through herbivores, to carnivores and higher order predators. The webs suggest that the lengths of the chains that form food webs are typically short (3-4 links), and that ecosystems with long food chains may be less stable than
Functional group diversity increases with modularity in complex food webs.
Montoya, D; Yallop, M L; Memmott, J
Biodiversity increases the ability of ecosystems to provide multiple functions. Most studies report a positive relationship between species richness and the number of ecosystem functions. However, it is not known whether the number of functional groups is related to the structure of the underlying species interaction network. Here we present food web data from 115 salt marsh islands and show that network structure is associated with the number of functional groups present. Functional group diversity is heterogeneously distributed across spatial scales, with some islands hosting more functional groups than others. Functional groups form modules within the community so that food webs with more modular architectures have more functional group diversity. Further, in communities with different interaction types, modularity can be seen as the multifunctional equivalent of trophic complementarity. Collectively, these findings reveal spatial heterogeneity in the number of functional groups that emerges from patterns in the structure of the food web. PMID:26059871
Food web dynamics in a seasonally varying wetland
DeAngelis, D.L.; Trexler, J.C.; Donalson, D.D.
A spatially explicit model is developed to simulate the small fish community and its underlying food web, in the freshwater marshes of the Everglades. The community is simplified to a few small fish species feeding on periphyton and invertebrates. Other compartments are detritus, crayfish, and a piscivorous fish species. This unit food web model is applied to each of the 10,000 spatial cells on a 100 x 100 pixel landscape. Seasonal variation in water level is assumed and rules are assigned for fish movement in response to rising and falling water levels, which can cause many spatial cells to alternate between flooded and dry conditions. It is shown that temporal variations of water level on a spatially heterogeneous landscape can maintain at least three competing fish species. In addition, these environmental factors can strongly affect the temporal variation of the food web caused by top-down control from the piscivorous fish.
Functional group diversity increases with modularity in complex food webs
Montoya, D.; Yallop, M.L.; Memmott, J.
Biodiversity increases the ability of ecosystems to provide multiple functions. Most studies report a positive relationship between species richness and the number of ecosystem functions. However, it is not known whether the number of functional groups is related to the structure of the underlying species interaction network. Here we present food web data from 115 salt marsh islands and show that network structure is associated with the number of functional groups present. Functional group diversity is heterogeneously distributed across spatial scales, with some islands hosting more functional groups than others. Functional groups form modules within the community so that food webs with more modular architectures have more functional group diversity. Further, in communities with different interaction types, modularity can be seen as the multifunctional equivalent of trophic complementarity. Collectively, these findings reveal spatial heterogeneity in the number of functional groups that emerges from patterns in the structure of the food web. PMID:26059871
Changes in host-parasitoid food web structure with elevation.
Maunsell, Sarah C; Kitching, Roger L; Burwell, Chris J; Morris, Rebecca J
Gradients in elevation are increasingly used to investigate how species respond to changes in local climatic conditions. Whilst many studies have shown elevational patterns in species richness and turnover, little is known about how food web structure is affected by elevation. Contrasting responses of predator and prey species to elevation may lead to changes in food web structure. We investigated how the quantitative structure of a herbivore-parasitoid food web changes with elevation in an Australian subtropical rain forest. On four occasions, spread over 1Āyear, we hand-collected leaf miners at twelve sites, along three elevational gradients (between 493Ām and 1159Ām a.s.l). A total of 5030 insects, including 603 parasitoids, were reared, and summary food webs were created for each site. We also carried out a replicated manipulative experiment by translocating an abundant leaf-mining weevil Platynotocis sp., which largely escaped parasitism at high elevations (?900Ām a.s.l.), to lower, warmer elevations, to test if it would experience higher parasitism pressure. We found strong evidence that the environmental change that occurs with increasing elevation affects food web structure. Quantitative measures of generality, vulnerability and interaction evenness decreased significantly with increasing elevation (and decreasing temperature), whilst elevation did not have a significant effect on connectance. Mined plant composition also had a significant effect on generality and vulnerability, but not on interaction evenness. Several relatively abundant species of leaf miner appeared to escape parasitism at higher elevations, but contrary to our prediction, Platynotocis sp. did not experience greater levels of parasitism when translocated to lower elevations. Our study indicates that leaf-mining herbivores and their parasitoids respond differently to environmental conditions imposed by elevation, thus producing structural changes in their food webs. Increasing temperatures and changes in vegetation communities that are likely to result from climate change may have a restructuring effect on host-parasitoid food webs. Our translocation experiment, however, indicated that leaf miners currently escaping parasitism at high elevations may not automatically experience higher parasitism under warmer conditions and future changes in food web structure may depend on the ability of parasitoids to adapt to novel hosts. PMID:25244661
Tracing food webs with stable hydrogen isotopes.
Estep, M F; Dabrowski, H
The hydrogen isotopic content of an animal's food, not water, determines that animal's hydrogen isotopic content. Liver and muscle tissue from mice reared on a diet such that the ratio of deuterium to hydrogen (DIH) of their food and water was kept constant, have the same average D/H ratio as the food source. In a simple, natural population of snails and their possible algal diets, Littorina obtusata (northern Atlantic intertidal snails that feed almost exclusively on the brown alga Fucus vesiculosus) has the same D/H ratio as Fucus vesiculosis and not that of the other algae available to the snails. PMID:17745967
Molecular evidence for genetic subdivision of Antarctic krill (Euphausia superba Dana) populations.
Zane, L; Ostellari, L; Maccatrozzo, L; Bargelloni, L; Battaglia, B; Patarnello, T
Antarctic krill (Euphausia superba Dana) is a key species in the Antarctic food web and occurs on a circumcontinental scale. Population genetic structure of this species was investigated by sequence analysis of the ND1 mitochondrial gene in four population samples collected at different geographical localities around the Antarctic continent. Results indicate the existence of significant genetic differences between samples, and we suggest that oceanographic barriers could be sufficiently strong and temporally stable to restrict gene flow between distinct areas. Moreover, our data indicate that Antarctic krill is not at mutation-drift equilibrium and that the species possibly has a low effective population size as compared to the census size. PMID:9921678
8 Food Webs in the Ocean: Who Eats Whom and How Much?
that form food webs are typically short (3Ł4 links), and that ecosystems with long food chains may be less stable than those with shorter food chains. Stomach contents have been the primary means for determining any level of the food chain and any size of prey. Food web analysis and estimates of consumption
Traditional stream food web studies provide static models of trophic structures. These models provide information about interspecific relationships, but not about material flows through food webs. Traditional ecosystem models developed from budgets or tracers provide quantitative...
Designing an Illustrated Food Web to Teach Ecological Concepts: Challenges and Solutions.
ERIC Educational Resources Information Center
Godkin, Celia M.
Argues that food webs are an efficient method through which to communicate the core idea of ecology--that all living things are interconnected. Assesses the challenges and solutions to using illustrated food webs. (Author/CCM)
ORIGINAL PAPER Food web overlap among native axolotl (Ambystoma
Vander Zanden, Jake
ORIGINAL PAPER Food web overlap among native axolotl (Ambystoma mexicanum) and two exotic fishes period, wild populations of the microendemic axolotl salamander (Ambystoma mexicanum) have been dra two exotic fishes: carp and tilapia, and the native axolotl. Axolotl had more diverse diets
Stability and feedback levels in food web models.
Smith, Matthew J; Sander, Elizabeth; Barabßs, Gy÷rgy; Allesina, Stefano
Neutel & Thorne (Ecology Letters, 17:651-661, June 2014) provide an approximation for the leading eigenvalue of a food web community matrix involving coefficients of its characteristic polynomial. Though valuably incorporating three-way species interactions, two critical problems emerge when one considers the dimensions of the system, calling the approach's accuracy and precision into question. PMID:25847355
Integrating Bacteria into Food Webs: Studies with Sarracenia purpurea Inquilines
D. Liane Cochran-Stafira; Carl N. von Ende
Predation can have both direct and indirect effects on the population dy- namics and community structure of freshwater plankton communities, but its effects on the bacterial component of aquatic systems are less well known. We used a series of laboratory reconstructions of the detritus-based food web in the leaves of the northern pitcher plant Sarracenia purpurea to test the hypothesis
9 Food Web Structure and the Evolution of Complex Networks
Caldarelli, Guido
against species removal. We present the analysis of the data for both real food webs and numerical is one of the major issues of mo- dern ecology [1, 2, 3]. Understanding how communities are assembled change with the scale of the system (the num- ber of species). A variety of ecological quantities
Nutritional constraints in terrestrial and freshwater food webs
James J. Elser; William F. Fagan; Robert F. Denno; Dean R. Dobberfuhl; Ayoola Folarin; Andrea Huberty; Sebastian Interlandi; Susan S. Kilham; Edward McCauley; Kimberly L. Schulz; Evan H. Siemann; Robert W. Sterner
Biological and environmental contrasts between aquatic and terrestrial systems have hindered analyses of community and ecosystem structure across Earth's diverse habitats. Ecological stoichiometry provides an integrative approach for such analyses, as all organisms are composed of the same major elements (C, N, P) whose balance affects production, nutrient cycling, and food-web dynamics. Here we show both similarities and differences in
Aquatic Food Web Interactions: Microcosms as Lake Models
NSDL National Science Digital Library
John C. Holz (University of Nebraska; )
As a laboratory exercise for increasing knowledge of trophic cascades in aquatic ecosystems has led to a better understanding of several basic ecological tenets, including competition, predation, and a variety of other community-level food web interactions using microcosms from whole water plankton collections. This lab exercise incorporates student use of rigorous quantitative skills in enumeration, data collection, and statistical inference.
Adaptations in a hierarchical food web of southeastern Lake Michigan
Ann E. Krause; Ken A. Frank; Michael L. Jones; Thomas F. Nalepa; Richard P. Barbiero; Charles P. Madenjian; Megan Agy; Marlene S. Evans; William W. Taylor; Doran M. Mason; Nancy J. Leonard
Two issues in ecological network theory are: (1) how to construct an ecological network model and (2) how do entire networks (as opposed to individual species) adapt to changing conditions? We present a novel method for constructing an ecological network model for the food web of southeastern Lake Michigan (USA) and we identify changes in key system properties that are
Food Webs, Body Size, and Species Abundance in Ecological
Cohen, Joel E.
RESEARCH VOL. 36 ▀ 2005 by Tomas Jonsson, Joel E. Cohen, 0065-2504/05 $35.00 and Stephen R. Carpenter AllFood Webs, Body Size, and Species Abundance in Ecological Community Description TOMAS JONSSON, JOEL E. COHEN, AND STEPHEN R. CARPENTER I. Summary
Interaction strengths in food webs: issues and opportunities
Eric L. Berlow; Anje-Margiet Neutel; Joel E. Cohen; Peter C. de Ruiter; Bo Ebenman; Mark Emmerson; Jeremy W. Fox; Vincent A. A. Jansen; J. Iwan Jones; Giorgos D. Kokkoris; Dmitrii O. Logofet; Alan J. McKane; Jose M. Montoya; Owen Petchey
Summary 1. Recent efforts to understand how the patterning of interaction strength affects both structure and dynamics in food webs have highlighted several obstacles to productive synthesis. Issues arise with respect to goals and driving questions, methods and approaches, and placing results in the context of broader ecological theory. 2. Much confusion stems from lack of clarity about whether the
Community food webs have scale-invariant structure
Frķdķric Briand; Joel E. Cohen
We have analysed 62 community food webs drawn from published studies and have found a remarkable regularity in ecosystem structure: in biological communities, the proportions of top, intermediate and basal species are, on average, independent of the total number of species. Hence, there is a direct proportionality between the numbers of prey and predators.
Predator foraging behaviour drives food-web topological structure
Xavier Lazzaro; Gķrard Lacroix; BenoŅt Gauzens; Jacques Gignoux; Stķphane Legendre
Summary 1. The structure and dynamics of prey populations are shaped by the foraging behaviours of their predators. Yet, there is still little documentation on how distinct predator foraging types control biodiversity, food-web architecture and ecosystem functioning. 2. We experimentally compared the effects of model fish species of two major foraging types of lake planktivores: a size-selective visual feeder (bluegill),
Emergence of complexity in evolving niche-model food webs
Christian Guill; Barbara Drossel
We have analysed mechanisms that promote the emergence of complex structures in evolving model food webs. The niche model is used to determine predator¢prey relationships. Complexity is measured by species richness as well as trophic level structure and link density. Adaptive dynamics that allow predators to concentrate on the prey species they are best adapted to lead to a strong
Food web complexity and higher-level ecosystem services
RodrĒguez, Miguel ┴ngel
and decomposition rates (Daly 1997; Chapin et al. 2000; Loreau et al. 2001; Kinzig et al. 2002; Loreau et al. 2002 is well developed (e.g. Tilman et al. 1997; Loreau 1998; Yachi & Loreau 1999), the theoretical background (Loreau 1996; Zheng et al. 1997). Indeed, one challenge is establishing a link between food web theory
Using a Simulation To Teach Food Web Dynamics.
ERIC Educational Resources Information Center
Rueter, John G.; Perrin, Nancy A.
Reports on research that tested the effect of using a computer simulation to teach the concept of a food web to nonbiology majors in a large introductory course. Concludes that the use of the simulation resulted in significantly better performance on an open-ended essay question for those students who used the software, particularly for averageģ
Toxic marine phytoplankton, zooplankton grazers, and pelagic food webs
JefSerson T. Turner; Patricia A. Tester
Interactions between toxic phytoplankton and their zooplankton grazers are complex. Some zooplanktcrs ingest some toxic phytoplankters with no apparent harm, whereas others are deleteriously affected. Phycotoxins vary in their modes of action, levels of toxicity and solubility, and affect grazers in different ways. Beyond effects on direct grazers, toxins may accumulate in and be transfcrrcd through marine food webs, affecting
Unravelling the Food Web: Dietary Analysis in Modern Ecology.
ERIC Educational Resources Information Center
Calver, M. C.; Porter, B. D.
Presents information that gives a methodological background to the concept of food webs. Stresses the importance of calibrated techniques in ecological research and explains direct methods for studying animal diets. Exercises for gathering first-hand data on bird diets and analyzing secondary data on mammal diets are suggested. (ML)
Food Webs and Environmental Disturbance: What's the Connection?
ERIC Educational Resources Information Center
Ford, Bob; Smith, Bruce M.
Two professors assert that it is not enough to simply tell students that all living organisms are mutually dependent. Describes an activity that allows students to become members of a food web and results in a greater understanding of and appreciation for the interdependencies of living things. Ideas for extension are provided. (ZWH)
Biodiversity, productivity and stability in real food webs
Duffy, J. Emmett
Biodiversity, productivity and stability in real food webs Boris Worm1 and J. Emmett Duffy2 1, The College of William and Mary, Gloucester Point, VA 23062Ł1346, USA The global biodiversity crisis has motivated new theory and experiments that explore relationships between biodiversity (species richness
While trophic levels have found broad application throughout ecology, they are also in much contention on analytical and empirical grounds. Here, we use a new generation of data and theory to examine long-standing questions about trophic-level limits and degrees of omnivory. The data include food webs of the Chesapeake Bay, USA, the island of St. Martin, a UK grassland, and
Abiotic controls on the functional structure of soil food webs
Walter G. Whitford
The hypothesis that the trophic structure of soil food webs changes as a result of the abiotic environment was examined by reviewing studies of soil biota. In dry soils with a water potential below -1.5 MPa, most bacteria, protozoans, and many species of nematodes are not active. These taxa persist in the soil in a state of anhydrobiosis. Because soil
Reconciling complexity with stability in naturally assembling food webs
Anje-Margriet Neutel; Johan A. P. Heesterbeek; Johan van de Koppel; Guido Hoenderboom; An Vos; Coen Kaldeway; Frank Berendse; Peter C. de Ruiter
Understanding how complex food webs assemble through time is fundamental both for ecological theory and for the development of sustainable strategies of ecosystem conservation and restoration. The build-up of complexity in communities is theoretically difficult, because in random-pattern models complexity leads to instability. There is growing evidence, however, that nonrandom patterns in the strengths of the interactions between predators and
Simplified food webs lead to energetic bottlenecks in polluted lakes
Graham D. Sherwood; Jennifer Kovecses; Alice Hontela; Joseph B. Rasmussen
Very little is known about the consequence of human activities on the flow of energy through natural ecosystems. Here, we present a trophic-based approach to describing energy relationships in pollutant-disturbed lakes, emphasizing the importance of prey diversity in maintaining energy transfer to growing fish. Both diet and community analysis indicated that the food web leading to yellow perch (Perca flavescens)
The robustness of keystone indices in food webs
Anna Fedor; Vera Vasas
Species that have outstanding importance in the functioning of a community are called keystone species. Network indices are increasingly used to identify them, e.g. for conservation biological purposes. The problem is that the calculation of these indices is based on the particular network model of the studied food web, which can include network construction errors. For example, additional, unnecessary trophic
Food Webs and the Dimensionality of Trophic Niche Space
Joel E. Cohen
If the trophic niche of a kind of organism is a connected region in niche space, then it is possible for trophic niche overlaps to be described in a one-dimensional niche space if and only if the trophic niche overlap graph is an interval graph. An analysis of 30 food webs, using the combinatorial theory of interval graphs, suggests that
A mathematical model of carbon fluxes through the heterotrophic microbial food web is developed from a synthesis of laboratory and field research,The basis of the model is the segregation of organic carbon into lability classes that are defined by bioassay experiments. acteria, p...
A mathematical model of carbon fluxes through the heterotrophic microbial food web is developed from a synthesis of laboratory and field research. he basis of the model is the segregation of organic carbon into lability classes that are defined by bioassay experiments. acteria, p...
Are there real differences among aquatic and terrestrial food webs?
Jonathan M Chase
Recently, aquatic and terrestrial ecologists have put forward several hypotheses regarding similarities and differences in food-web structure and function among these ecosystem types. Although many of these hypotheses explore why strong top-down effects and trophic cascades might be less common in terrestrial than in aquatic ecosystems, there is little theoretical or empirical evidence available to support or refute these hypotheses.
Food-web complexity emerging from ecological dynamics on adaptive networks
Josep L. Garcia-Domingo; Joan Salda±a
Food webs are complex networks describing trophic interactions in ecological communities. Since Robert May's seminal work on random structured food webs, the complexity¢stability debate is a central issue in ecology: does network complexity increase or decrease food-web persistence? A multi-species predator¢prey model incorporating adaptive predation shows that the action of ecological dynamics on the topology of a food web (whose
Food caching in orb-web spiders (Araneae: Araneoidea)
NASA Astrophysics Data System (ADS)
Champion de Crespigny, Fleur E.; Herberstein, Marie E.; Elgar, Mark A.
Caching or storing surplus prey may reduce the risk of starvation during periods of food deprivation. While this behaviour occurs in a variety of birds and mammals, it is infrequent among invertebrates. However, golden orb-web spiders, Nephila edulis, incorporate a prey cache in their relatively permanent web, which they feed on during periods of food shortage. Heavier spiders significantly reduced weight loss if they were able to access a cache, but lost weight if the cache was removed. The presence or absence of stored prey had no effect on the weight loss of lighter spiders. Furthermore, N. edulis always attacked new prey, irrespective of the number of unprocessed prey in the web. In contrast, females of Argiope keyserlingi, who build a new web every day and do not cache prey, attacked fewer new prey items if some had already been caught. Thus, a necessary pre-adaptation to the evolution of prey caching in orb-web spiders may be a durable or permanent web, such as that constructed by Nephila.
Assimilation of diazotrophic nitrogen into pelagic food webs.
Woodland, Ryan J; Holland, Daryl P; Beardall, John; Smith, Jonathan; Scicluna, Todd; Cook, Perran L M
The fate of diazotrophic nitrogen (N(D)) fixed by planktonic cyanobacteria in pelagic food webs remains unresolved, particularly for toxic cyanophytes that are selectively avoided by most herbivorous zooplankton. Current theory suggests that N(D) fixed during cyanobacterial blooms can enter planktonic food webs contemporaneously with peak bloom biomass via direct grazing of zooplankton on cyanobacteria or via the uptake of bioavailable N(D) (exuded from viable cyanobacterial cells) by palatable phytoplankton or microbial consortia. Alternatively, N(D) can enter planktonic food webs post-bloom following the remineralization of bloom detritus. Although the relative contribution of these processes to planktonic nutrient cycles is unknown, we hypothesized that assimilation of bioavailable N(D) (e.g., nitrate, ammonium) by palatable phytoplankton and subsequent grazing by zooplankton (either during or after the cyanobacterial bloom) would be the primary pathway by which N(D) was incorporated into the planktonic food web. Instead, in situ stable isotope measurements and grazing experiments clearly documented that the assimilation of N(D) by zooplankton outpaced assimilation by palatable phytoplankton during a bloom of toxic Nodularia spumigena Mertens. We identified two distinct temporal phases in the trophic transfer of N(D) from N. spumigena to the plankton community. The first phase was a highly dynamic transfer of N(D) to zooplankton with rates that covaried with bloom biomass while bypassing other phytoplankton taxa; a trophic transfer that we infer was routed through bloom-associated bacteria. The second phase was a slowly accelerating assimilation of the dissolved-N(D) pool by phytoplankton that was decoupled from contemporaneous variability in N. spumigena concentrations. These findings provide empirical evidence that N(D) can be assimilated and transferred rapidly throughout natural plankton communities and yield insights into the specific processes underlying the propagation of N(D) through pelagic food webs. PMID:23840744
Salmon Life Histories, Habitats, and Food Webs in the Columbia River Estuary
Salmon Life Histories, Habitats, and Food Webs in the Columbia River Estuary Daniel J. Bottom NOAA of tidal wetlands could further limit the capacity of estuarine food webs to support juvenile salmon during the last century, contemporary salmon food webs still rely disproportionately on wetland
DEVELOPMENT, EVALUATION, AND APPLICATION OF A FOOD WEB BIOACCUMULATION MODEL FOR PCBS IN THE STRAIT Management Title of Research Project: Development, Evaluation, and Application of a Food Web Bioaccumulation of Georgia; food web; sediment quality guidelines iii #12;ACKNOWLEDGEMENTS I sincerely thank Frank Gobas, my
E.2. Electronic Appendix -Food Web Elements of the Fraser River Upper River (above rkm 210)
1 E.2. Electronic Appendix - Food Web Elements of the Fraser River Basin Upper River (above rkm 210) Food webs: Microbenthic algae (periphyton), detritus from riparian vegetation and littoral insects). Stressors: Water quality and habitat conditions have changed food webs in specific locations in the upper
Tracing algal support of marine food webs with fatty acids FHL Tide Bites #3 Nov. 2013
Carrington, Emily
, and seaweeds (algae). These photosynthetic organisms create `biomass' that all members of the food web need "biomarkers" consisting of fatty acids and isotopes of elements from the algae up through the food web and into marine animals. Why do we care? Understanding which energy sources "fuel" the food web will ultimately
Journal of Theoretical Biology 246 (2007) 260268 Quantitative analysis of the local structure of food webs
Stouffer, Daniel B.
model of food web topology, the so-called generalized cascade model, and compare them with 17 empirical analyze the local structure of model and empirical food webs through the statistics of three and the empirical food webs. We find agreement between the model predictions and the empirical results
Body-size determinants of niche overlap and intraguild predation within a complex food web
Guy Woodward; Alan G. Hildrew
Summary 1. Body-size may be an important feature of the structure of food webs. Detailed food web data are however scarce, particularly those including ontogenetic dietary shifts within species. We examined the predator guild in a well characterized food web, that of Broadstone Stream (UK), to assess the importance of body-size within and among species in relation to intraguild predation
Complex shifts between food web states in response to whole-ecosystem manipulations
Roos, Andrķ M. de
417 Complex shifts between food web states in response to whole-ecosystem manipulations Arne. Food webs can respond in surprising and complex ways to temporary alterations in their species composition. When such a perturbation is reversed, food webs have been shown to either return to the pre
Spatial Price Equilibrium and Food Webs: The Economics of Predator-Prey Networks
Nagurney, Anna
Spatial Price Equilibrium and Food Webs: The Economics of Predator-Prey Networks Anna Nagurney1 to present this research Anna and Ladimer S. Nagurney Spatial Price Equilibrium and Food Webs #12;Outline and Suggestions for Future Research Anna and Ladimer S. Nagurney Spatial Price Equilibrium and Food Webs #12
Jackson, George
BULLETIN OF MARINE SCIENCE, 73(3): 569Ł591, 2003 569 PLANKTONIC FOOD WEB DYNAMICS IN TWO plank- tonic food web for Florida Bay that can be coupled to results of seagrass modeling and studies of inter-basin exchange. Estimated rates of carbon flow through the planktonic food webs differed greatly
Evidence for the existence of a robust pattern of prey selection in food webs
Stouffer, Daniel B.
Evidence for the existence of a robust pattern of prey selection in food webs Daniel B. Stouffer1, Spain Food webs aim to provide a thorough representation of the trophic interactions found in an ecosystem. The complexity of empirical food webs, however, is leading many ecologists to focus dynamic
Food-Web Models Predict Species Abundances in Response to Habitat Change
Gotelli, Nicholas J.
Food-Web Models Predict Species Abundances in Response to Habitat Change Nicholas J. Gotelli1 trophic levels of the food web of invertebrates that inhabit rain-filled leaves of the carnivorous pitcher plant Sarracenia purpurea. Path models that incorporated food-web structure better predicted population
Spatial Price Equilibrium and Food Webs: The Economics of Predator-Prey Networks
Nagurney, Anna
Spatial Price Equilibrium and Food Webs: The Economics of Predator-Prey Networks Proceedings and analysis of complex food webs, which are nature's supply chains, through the formalism of network are consumed by predators. Index Terms--spatial price equilibrium, supply chains, food webs, predator prey
Automated Discovery of Food Webs from Ecological Data Using Logic-Based Machine Learning
Muggleton, Stephen H.
Automated Discovery of Food Webs from Ecological Data Using Logic-Based Machine Learning David A, Bracknell, Berks, United Kingdom Abstract Networks of trophic links (food webs) are used to describe low proportion of ecosystems have been studied using food web approaches due to difficulties in making
Structure and function Many scientists use food webs to portray ecolo-
Hessen, Dag Olav
PART I Structure and function Many scientists use food webs to portray ecolo- gical communities mechanisms regulate food-web function and can give rise to observed structure and dynamics. These mechanisms observe. This section of the book presents and discusses responses of food webs to trophic interactions
Rheagogies: Modelling non-trophic effects in food webs Roger Arditi a,*, Jerzy Michalski b,1
Alvarez, Nadir
Rheagogies: Modelling non-trophic effects in food webs Roger Arditi a,*, Jerzy Michalski b,1; accepted 11 April 2005 Available online 4 June 2005 Abstract In a food web, nutrients flow via trophic conservation. To further comply with this principle, we consider a food web model that includes nutrient
Successful Invasion of a Food Web in a Chemostat* GAIL S. K. WOLKOWICZ
Wolkowicz, Gail S. K.
Successful Invasion of a Food Web in a Chemostat* GAIL S. K. WOLKOWICZ Depurtment of Mathematics 1988 ABSTRACT A food web in a chemostat is considered in which an arbitrary number of competitor a food web in a chemostat in which an arbitrary number of competitor populations compete for a single
Examining food webs and trophic dynamics across a stream restoration intensity gradient
Vallino, Joseph J.
Examining food webs and trophic dynamics across a stream restoration intensity gradient Lena Weiss restoration, food webs, trophic dynamics Abstract: Stream ecosystems provide a plethora of important services systems, there is little examination of restoration on a system- level scale. By examining food webs
Identification of key players for the impact of perturbations in food webs
Identification of key players for the impact of perturbations in food webs By Helge Aufderheide1, complex system to a perturba- tion. Recent attempts to predict the behavior of food webs has revealed to efficiently arrive at this solution. Then, in our assessment of model food webs, we find that it is most
Modelling Size Structured Food Webs Using a Modified Niche Model with Two Predator Traits
Modelling Size Structured Food Webs Using a Modified Niche Model with Two Predator Traits Jan┤ Budejovice, Czech Republic Abstract The structure of food webs is frequently described using phenomenological stochastic models. A prominent example, the niche model, was found to produce artificial food webs resembling
Food web structure and habitat loss Carlos J. Melian* and Jordi
REPORT Food web structure and habitat loss Carlos J. Melia┬n* and Jordi Bascompte Estacio┬ n firstname.lastname@example.com Abstract In this paper we explore simple food web models to study how metacommunity structure affects to the kind of food web. Second, for intermediate species, a slight decrease in the exploration cost
Food-Web Structure of Seagrass Communities across Different Spatial Scales and Human Impacts
Myers, Ransom A.
Food-Web Structure of Seagrass Communities across Different Spatial Scales and Human Impacts Marta, a quantification of their food-web structure and functioning, and how these change across space and human impacts the structural features of food webs associated with Zostera marina across 16 study sites in 3 provinces
Visualizing the Food-Web Effects of Fishing for Tunas in the Pacific Ocean
Jefferson T. Hinke; Isaac C. Kaplan; Kerim Aydin; George M. Watters; Robert J. Olson; James F. Kitchell
We use food-web models to develop visualizations to compare and evaluate the interactions of tuna fisheries with their supporting food webs in the eastern tropical Pacific (ETP) and the central north Pacific (CNP) Oceans. In the ETP and CNP models, individual fisheries use slightly different food webs that are defined by the assemblage of targeted tuna species. Distinct energy pathways
Comparing energetic and dynamic descriptions of a single food web linkage
Vander Zanden, Jake
of food web connectance properties are increasingly relying on energetic data as a way to weight194 Comparing energetic and dynamic descriptions of a single food web linkage Christopher T. Hrabik, Dept of Biology, Univ. of Minnesota-Duluth, Duluth, MN 55812, USA. Food webs are a unifying
Automated Discovery of Food Webs from Ecological Data Using Logic-Based Machine Learning
David A. Bohan; Geoffrey Caron-Lormier; Stephen Muggleton; Alan Raybould; Alireza Tamaddoni-Nezhad
Networks of trophic links (food webs) are used to describe and understand mechanistic routes for translocation of energy (biomass) between species. However, a relatively low proportion of ecosystems have been studied using food web approaches due to difficulties in making observations on large numbers of species. In this paper we demonstrate that Machine Learning of food webs, using a logic-based
Learning from visualizing and Interacting with the Semantic Web Dog Food
Paris-Sud XI, Universitķ de
Learning from visualizing and Interacting with the Semantic Web Dog Food Christophe Gravier://portail.univ-st-etienne.fr Abstract. Semantic Web conferences such as WWW and ISWC fos- tered a collaborative effort to the Semantic Web Conference Corpus, a.k.a. the Semantic Web Dog Food Corpus. Many other conferences
Food web topology and parasites in the pelagic zone of a subarctic lake
Per-Arne Amundsen; Kevin D. Lafferty; Rune Knudsen; Raul Primicerio; Anders Klemetsen; Armand M. Kuris
Summary 1. Parasites permeate trophic webs with their often complex life cycles, but few studies have included parasitism in food web analyses. Here we provide a highly resolved food web from the pelagic zone of a subarctic lake and explore how the incorporation of parasites alters the topology of the web. 2. Parasites used hosts at all trophic levels and
Computer simulations of sympatric speciation in a simple food web.
Luz-Burgoa, K; Dell, Tony; de Oliveira, S Moss
Galapagos finches, have motivated much theoretical research aimed at understanding the processes associated with the formation of the species. Inspired by them, in this paper we investigate the process of sympatric speciation in a simple food web model. For that we modify the individual-based Penna model that has been widely used to study aging as well as other evolutionary processes. Initially, our web consists of a primary food source and a single herbivore species that feeds on this resource. Subsequently we introduce a predator that feeds on the herbivore. In both instances we manipulate directly a basal resource distribution and monitor the changes in the populations. Sympatric speciation is obtained for the top species in both cases, and our results suggest that the speciation velocity depends on how far up, in the food chain, the focus population is feeding. Simulations are done with three different sexual imprinting-like mechanisms, in order to discuss adaptation by natural selection. PMID:16090008
Invertebrate predator-prey body size relationships: an explanation for upper triangular food webs and patterns in food web structure?
P. H. Warren; J. H. Lawton
It has been suggested by Cohen and Newman (1985) that many of the patterns in published food webs can be derived from a stochastic model in which the species are arranged in a trophic hierarchy (the æcascade modelÆ). We suggest that, if predators are larger than their prey, a trophic hierarchy can be generated on the basis of body size
Assessment of some linear food web methods
NASA Astrophysics Data System (ADS)
Steele, John H.
We review some recent methods for the calculation of energy fluxes through marine ecosystems in terms of linear steady-state webs. We consider some problems in using such methods as input to non-linear dynamic simulations. The problems arise from the great range in space and time scales and from the heterogeneity in data used to determine energy fluxes. These problems compromise the apparent generality of the methods and their ability to assess uncertainties in flux estimates. We consider alternative approaches and illustrate these problems and methods with a budget for the Georges Bank (north-west Atlantic) ecosystem.
Understanding food webs in the Chesapeake Bay
Keough, J.R.; Haramis, G.M.; Perry, M.C.
Approaches to predictive modeling and to management of the Chesapeake Bay ecosystem are 'bottom up' (i.e., approaches involve the control of nutrient inputs in attempts to manage plankton productivity) and 'top down' (i.e., approaches involve controls on harvest of fisheries and wildlife in attempts to manage vertebrate populations). Both approaches are limited by a lack of understanding of trophic connections between nutrient inputs, primary producers, and higher trophic level consumers. This project is aimed at identifying trophic structure for the submersed aquatic vegetation habitat of the Chesapeake Bay. We are employing analysis of stable isotope ratios of plant and animal tissues to identify trophic levels and traditional food habits analysis to identify the foods of a number of species of waterfowl.
Geo-Spatial Browse and Distribution of NSF-OPP's Antarctic Ice and Climate Data via the Web: Antarctic Cryosphere Access Portal (A-CAP)
R. Bauer; T. Scambos; T. Haran; J. Maurer; J. Bohlander
A prototype of the Antarctic Cryosphere Access Portal (A-CAP) has been released for public use. Developed at the National Snow and Ice Data Center (NSIDC) Antarctic Glaciological Data Center (AGDC), A-CAP aims to be a geo-visualization and data download tool for AGDC data and other Antarctic-wide parameters, including glaciology, ice core data, snow accumulation, satellite imagery, digital elevation models (DEMs),
A synthesis of bentho-pelagic coupling on the Antarctic shelf: Food banks, ecosystem inertia and global climate change
NASA Astrophysics Data System (ADS)
Smith, Craig R.; Mincks, Sarah; DeMaster, David J.
The Antarctic continental shelf is large, deep (500-1000 m), and characterized by extreme seasonality in sea-ice cover and primary production. Intense seasonality and short pelagic foodwebs on the Antarctic shelf may favor strong bentho-pelagic coupling, whereas unusual water depth combined with complex topography and circulation could cause such coupling to be weak. Here, we address six questions regarding the nature and strength of coupling between benthic and water-column processes on the continental shelf surrounding Antarctica. We find that water-column production is transmitted to the shelf floor in intense pulses of particulate organic matter, although these pulses are often difficult to correlate with local phytoplankton blooms or sea-ice conditions. On regional scales, benthic habitat variability resulting from substrate type, current regime, and iceberg scour often may obscure the imprint of water-column productivity on the seafloor. However, within a single habitat type, i.e. the muddy sediments that characterize much of the deep Antarctic shelf, macrobenthic biomass appears to be correlated with regional primary production and sea-ice duration. Over annual time-scales, many benthic ecological processes were initially expected to vary in phase with the extraordinary boom/bust cycle of production in the water column. However, numerous processes, including sediment respiration, deposit feeding, larval development, and recruitment, often are poorly coupled to the summer bloom season. Several integrative, time-series studies on the Antarctic shelf suggest that this lack of phasing may result in part from the accumulation of a persistent sediment food bank that buffers the benthic ecosystem from the seasonal variability of the water column. As a consequence, a variety of benthic parameters (e.g., sediment respiration, inventories of labile organic matter, macrobenthic biomass) may act as "low-pass" filters, responding to longer-term (e.g., inter-annual) trends in water-column production. Bentho-pelagic coupling clearly will be altered by Antarctic climate change as patterns of sea-ice cover and water-column recycling vary. However, the nature of such climate-driven changes will be very difficult to predict without further studies of Antarctic benthic ecosystem response to (1) inter-annual variability in export flux, and (2) latitudinal gradients in duration of sea-ice cover and benthic ecosystem function.
Benchmarking successional progress in a quantitative food web.
Boit, Alice; Gaedke, Ursula
Central to ecology and ecosystem management, succession theory aims to mechanistically explain and predict the assembly and development of ecological communities. Yet processes at lower hierarchical levels, e.g. at the species and functional group level, are rarely mechanistically linked to the under-investigated system-level processes which drive changes in ecosystem properties and functioning and are comparable across ecosystems. As a model system for secondary succession, seasonal plankton succession during the growing season is readily observable and largely driven autogenically. We used a long-term dataset from large, deep Lake Constance comprising biomasses, auto- and heterotrophic production, food quality, functional diversity, and mass-balanced food webs of the energy and nutrient flows between functional guilds of plankton and partly fish. Extracting population- and system-level indices from this dataset, we tested current hypotheses about the directionality of successional progress which are rooted in ecosystem theory, the metabolic theory of ecology, quantitative food web theory, thermodynamics, and information theory. Our results indicate that successional progress in Lake Constance is quantifiable, passing through predictable stages. Mean body mass, functional diversity, predator-prey weight ratios, trophic positions, system residence times of carbon and nutrients, and the complexity of the energy flow patterns increased during succession. In contrast, both the mass-specific metabolic activity and the system export decreased, while the succession rate exhibited a bimodal pattern. The weighted connectance introduced here represents a suitable index for assessing the evenness and interconnectedness of energy flows during succession. Diverging from earlier predictions, ascendency and eco-exergy did not increase during succession. Linking aspects of functional diversity to metabolic theory and food web complexity, we reconcile previously disjoint bodies of ecological theory to form a complete picture of successional progress within a pelagic food web. This comprehensive synthesis may be used as a benchmark for quantifying successional progress in other ecosystems. PMID:24587353
Moving Up the Information Food Chain: Deploying Softbots on the World Wide Web
Oren Etzioni
I view the World Wide Web as an information food chain (figure 1). The maze of pages and hyperlinks that comprise the Web are at the very bottom of the chain. The WebCrawlers and Alta Vistas of the world are information herbivores; they graze on Web pages and regurgitate them as searchable indices. Today, most Web users feed near the
This paper was published in Soft Matter as part of the Food Science web theme issue
Weeks, Eric R.
Food This paper was published in Soft Matter as part of the Food Science web theme issue This Soft Matter theme issue explores fundamental interdisciplinary research into food science covering a variety of themes including food biophysics, food colloids and emulsions, and complex food structure. Please take
Nitrogen fixation by cyanobacteria stimulates production in Baltic food webs.
Karlson, Agnes M L; Duberg, Jon; Motwani, Nisha H; Hogfors, Hedvig; Klawonn, Isabell; Ploug, Helle; Barthel Svedķn, Jennie; Garbaras, Andrius; Sundelin, Brita; Hajdu, Susanna; Larsson, Ulf; Elmgren, Ragnar; Gorokhova, Elena
Filamentous, nitrogen-fixing cyanobacteria form extensive summer blooms in the Baltic Sea. Their ability to fix dissolved N2 allows cyanobacteria to circumvent the general summer nitrogen limitation, while also generating a supply of novel bioavailable nitrogen for the food web. However, the fate of the nitrogen fixed by cyanobacteria remains unresolved, as does its importance for secondary production in the Baltic Sea. Here, we synthesize recent experimental and field studies providing strong empirical evidence that cyanobacterial nitrogen is efficiently assimilated and transferred in Baltic food webs via two major pathways: directly by grazing on fresh or decaying cyanobacteria and indirectly through the uptake by other phytoplankton and microbes of bioavailable nitrogen exuded from cyanobacterial cells. This information is an essential step toward guiding nutrient management to minimize noxious blooms without overly reducing secondary production, and ultimately most probably fish production in the Baltic Sea. PMID:26022324
Ingestion and transfer of microplastics in the planktonic food web.
Setõlõ, Outi; Fleming-Lehtinen, Vivi; Lehtiniemi, Maiju
Experiments were carried out with different Baltic Sea zooplankton taxa to scan their potential to ingest plastics. Mysid shrimps, copepods, cladocerans, rotifers, polychaete larvae and ciliates were exposed to 10Ā?m fluorescent polystyrene microspheres. These experiments showed ingestion of microspheres in all taxa studied. The highest percentage of individuals with ingested spheres was found in pelagic polychaete larvae, Marenzelleria spp. Experiments with the copepod Eurytemora affinis and the mysid shrimp Neomysis integer showed egestion of microspheres within 12Āh. Food web transfer experiments were done by offering zooplankton labelled with ingested microspheres to mysid shrimps. Microscopy observations of mysid intestine showed the presence of zooplankton prey and microspheres after 3Āh incubation. This study shows for the first time the potential of plastic microparticle transfer via planktonic organisms from one trophic level (mesozooplankton) to a higher level (macrozooplankton). The impacts of plastic transfer and possible accumulation in the food web need further investigations. PMID:24220023
Evolution of Food-web Networks in Fluctuating Environments
Samraat Pawar; Oskar Burger; Brian Hallmark; Ganesh Bagler; Frank Wang; Xue Fu
ABSTRACT We use a network-theoretic approach to address questions about the evolution of food-web characteristics under fluctuating environments. Our model is a weighted, directed graph with nodes representing populations and edges the interactions between them. The dynamics,of the network are driven by stochastic generalized Lotka-Volterra equations. Networks evolve by extinction due to inter- and intra-specific density effects, followed by probabilistic
Why allometric scaling enhances stability in food web models
Boris Kartascheff; Lotta Heckmann; Barbara Drossel; Christian Guill
It has recently been shown that the incorporation of allometric scaling into the dynamic equations of food web models enhances\\u000a network stability if predators are assigned a higher body mass than their prey. We investigate the underlying mechanisms leading\\u000a to this stability increase. The dynamic equations can be written such that allometric scaling influences these equations at\\u000a three places: the
Food web structure and the evolution of ecological communities
Christopher Quince; Paul G. Higgs; Alan J. McKane
Simulations of the coevolution of many interacting species are performed using the Webworld model. The model has a realistic\\u000a set of predatorŚ prey equations that describe the population dynamics of the species for any structure of the food web. The\\u000a equations account for competition between species for the same resources, and for the diet choice of predators between alternative\\u000a prey
Trait and density mediated indirect interactions in simple food webs
Vlastimil K?ivan; Oswald J. Schmitz
This article compares indirect trait-mediated interactions in simple resource\\/ consumer\\/predator food webs with those that are density-mediated. It focuses on two well documented responses of consumers to predation risk: decrease in consumer activity and habitat switch. These behavioral effects are transmitted to resources and they cause similar indirect effects as those which are mediated by density changes in consumers. Two
Does invasion of hybrid cordgrass change estuarine food webs?
Elizabeth D. Brusati; Edwin D. Grosholz
Studies examining the impacts of introduced species on food webs often focus on the top-down effects of introduced predators.\\u000a However, marine and estuarine systems have been invaded by plants that have the potential to alter carbon and nitrogen sources\\u000a available to consumers. In San Francisco Bay, California, USA, hybridized cordgrass Spartina alternifloraĀūĀfoliosa is adding C4 carbon biomass to this system.
Road Salt Stress Induces Novel Food Web Structure and Interactions
Robin J. Van Meter; Christopher M. Swan; Jeff Leips; Joel W. Snodgrass
Freshwater salinization is an emerging global concern, and in northern latitudes can be largely attributed to road deicer\\u000a applications during winter and spring. To investigate the effects of road salt contamination on pond food webs, we manipulated\\u000a trophic structure and salt in experimental pond communities. In May 2008, we inoculated forty 600-L pond mesocosms with algae\\u000a and zooplankton. Using a
Enclosing decomposer food web: implications for community structure and function
J. K. Nieminen; H. Setõlõ
We designed a field experiment to evaluate how restriction of soil faunal movements affects decomposer community structure,\\u000a food web architecture, and decomposition of organic matter. Intact soil cores (3cm thick, diameter 16cm) were placed either\\u000a in ōopenö (mesh size 1mm, allowing all meso- and microfauna to move through) or ōclosedö (27?m, animal movement prevented\\u000a except for the smallest microfauna) mesh
Functional Effects of Parasites on Food Web Properties during the Spring Diatom Bloom in Lake Pavin: A Linear
Paris-Sud XI, Universitķ de
Functional Effects of Parasites on Food Web Properties during the Spring Diatom Bloom in Lake Pavin on a planktonic food web. We used a carbon-based food web model of Lake Pavin (Massif Central, France-derived fluxes. Model results support recent theories on the probable impact of parasites on food web function
Consumers indirectly increase infection risk in grassland food webs
Borer, Elizabeth T.; Mitchell, Charles E.; Power, Alison G.; Seabloom, Eric W.
Most pathogens exist within complicated food webs of interacting hosts, vectors, competitors, and predators. Although theory has demonstrated a variety of mechanisms by which predation and competition in food webs can indirectly control infection risk in hosts, there have until now been no experimental tests of this theory. We sampled the effect of long-term exclusion of large vertebrate herbivores on the prevalence of infection by a group of aphid-vectored viruses that infect grasses (barley and cereal yellow dwarf viruses) in an oak savannah in central California. We found that pathogen prevalence was ?4-fold higher in the presence of consumers than in areas where they were excluded. Vertebrate consumers did not directly alter infection rates by this aphid-vectored pathogen group, but rather increased infection risk by increasing the relative abundance of highly-competent hosts in the grassland community. This large-scale experiment, measuring changes in host abundance and infection risk in response to altered consumption rates, confirms theoretical predictions that consumers can indirectly increase infection risk by altering the composition of whole communities. Most importantly, these results demonstrate that, even in complex natural communities, alterations to food web composition such as consumer invasion or extinction can lead to significant impacts that cascade throughout entire communities, including changes in infection risk. PMID:19126681
Multiple anthropogenic stressors and the structural properties of food webs.
O'Gorman, Eoin J; Fitch, Jayne E; Crowe, Tasman P
Coastal environments are among the most productive on the planet, providing a wide range of ecosystem services. Development and exploitation mean that they are faced with stresses from a number of anthropogenic sources. Such stresses are typically studied in isolation, but multiple stressors can combine in unexpected ways to alter the structure of ecological systems. Here, we experimentally explore the impacts of inorganic nutrients and organic matter on a range of food web properties. We find that these two stressors combine additively to produce significant increases in connectance and mean food chain length. Such increases are typically associated with enhanced robustness to secondary extinctions and productivity, respectively. Despite these apparent beneficial effects, we find a simplification of web structure in terms of taxon richness and diversity, and altered proportions of basal and top species. These effects are driven by a reduction in community assembly and lower consistency in a range of system properties as a result of the multiple stressors. Consequently, impacted food webs are likely to be more vulnerable to human- or climate-induced perturbations in the long-term. PMID:22624198
Successional dynamics in the seasonally forced diamond food web.
Klausmeier, Christopher A; Litchman, Elena
Plankton seasonal succession is a classic example of nonequilibrium community dynamics. Despite the fact that it has been well studied empirically, it lacks a general quantitative theory. Here we investigate a food web model that includes a resource, two phytoplankton, and a shared grazer-the diamond food web-in a seasonal environment. The model produces a number of successional trajectories that have been widely discussed in the context of the verbal Plankton Ecology Group model of succession, such as a spring bloom of a good competitor followed by a grazer-induced clear-water phase, setting the stage for the late-season dominance of a grazer-resistant species. It also predicts a novel, counterintuitive trajectory where the grazer-resistant species has both early- and late-season blooms. The model often generates regular annual cycles but sometimes produces multiyear cycles or chaos, even with identical forcing each year. Parameterizing the model, we show how the successional trajectory depends on nutrient supply and the length of the growing season, two key parameters that vary among water bodies. This model extends nonequilibrium theory to food webs and is a first step toward a quantitative theory of plankton seasonal succession. PMID:22673647
Tracking the autochthonous carbon transfer in stream biofilm food webs.
Risse-Buhl, Ute; Trefzger, Nicolai; Seifert, Anne-Gret; Sch÷nborn, Wilfried; Gleixner, Gerd; K³sel, Kirsten
Food webs in the rhithral zone rely mainly on allochthonous carbon from the riparian vegetation. However, autochthonous carbon might be more important in open canopy streams. In streams, most of the microbial activity occurs in biofilms, associated with the streambed. We followed the autochthonous carbon transfer toward bacteria and grazing protozoa within a stream biofilm food web. Biofilms that developed in a second-order stream (Thuringia, Germany) were incubated in flow channels under climate-controlled conditions. Six-week-old biofilms received either ╣│C- or ╣▓C-labeled CO?, and uptake into phospholipid fatty acids was followed. The dissolved inorganic carbon of the flow channel water became immediately labeled. In biofilms grown under 8-h light/16-h dark conditions, more than 50% of the labeled carbon was incorporated in biofilm algae, mainly filamentous cyanobacteria, pennate diatoms, and nonfilamentous green algae. A mean of 29% of the labeled carbon reached protozoan grazer. The testate amoeba Pseudodifflugia horrida was highly abundant in biofilms and seemed to be the most important grazer on biofilm bacteria and algae. Hence, stream biofilms dominated by cyanobacteria and algae seem to play an important role in the uptake of CO? and transfer of autochthonous carbon through the microbial food web. PMID:22067054
Scaling behaviors of weighted food webs as energy transportation networks.
Zhang, Jiang; Guo, Liangpeng
Food webs can be regarded as energy transporting networks in which the weight of each edge denotes the energy flux between two species. By investigating 21 empirical weighted food webs as energy flow networks, we found several ubiquitous scaling behaviors. Two random variables A(i) and C(i) defined for each vertex i, representing the total flux (also called vertex intensity) and total indirect effect or energy store of i, were found to follow power law distributions with the exponents alpha approximately 1.32 and beta approximately 1.33, respectively. Another scaling behavior is the power law relationship, C(i) approximately A(i)(eta), where eta approximately 1.02. This is known as the allometric scaling power law relationship because A(i) can be treated as metabolism and C(i) as the body mass of the sub-network rooted from the vertex i, according to the algorithm presented in this paper. Finally, a simple relationship among these power law exponents, eta=(alpha-1)/(beta-1), was mathematically derived and tested by the empirical food webs. PMID:20303987
UpdateMarch / April 2011 At least for Aleuts, switching foods helps stabilize food web
a greater variety of plants and animals throughout the food web than other consumer species. In Mom vs. dad Ł that predicts when animals will fight. ReseaRch News > more on page 4 > more on page 2 > more on page 2 IN thIs IssUe > creating a liv
Food web dynamics in the Scotia Sea in summer: A stable isotope study
NASA Astrophysics Data System (ADS)
Stowasser, G.; Atkinson, A.; McGill, R. A. R.; Phillips, R. A.; Collins, M. A.; Pond, D. W.
The pelagic food web of the Scotia Sea was studied by analysing natural abundances of nitrogen and carbon stable isotopes of primary producers and pelagic consumers, sampled from the seasonal ice edge in the south to the Antarctic Polar Front in the north. The analysis covered, within a single mid-summer period, particulate organic matter (POM) and 38 taxa, ranging from suspension feeding copepods and salps to omnivorous euphausiids, pelagic fish and higher, land-based predators including fur seals, penguins and flying birds. Spatial variation in ? 15N of POM correlated well with nutrient availability and primary productivity. Latitudinal differences in ? 13C of POM were closely linked to variations in temperature, nutrients and productivity depending on the frontal region sampled. This translated to equivalent (although smaller) regional ? 13C differences among higher trophic levels. The trophic positions of species based on isotope values broadly agreed with previously published dietary data with three important exceptions. First, the carnivorous amphipod Themisto gaudichaudii had anomalously low ? 15N values. Second, Euphausia superba had ? 15N values that were also surprisingly low, considering the abundant literature suggesting its omnivory. Third, the copepod Rhincalanus gigas, considered a suspension feeder, had unexpectedly high ? 15N values rather more in keeping with omnivorous feeding. The consumer ? 15N values ranged from 1.2ē (min.) measured in Salpa thompsoni (designated here as trophic level (TL) 2 across all regions) to 15.2ē (max.) measured in white-chinned petrels ( Procellaria aequinoctialis, calculated as TL5 relative to the TL2 of salps). Excluding seabirds, the resulting food chain length of 3.7 TL (above POM at TL1) was lower than in most other Southern Ocean and temperate marine pelagic ecosystems. The majority (60%) of vertebrate predators occupied only 1-1.5 trophic levels above the herbivorous suspension feeders such as krill. This indicates the existence of the classic short food chain of POM-suspension feeder-vertebrate predator. However the presence of trophic levels 4 and above indicates the existence of alternative trophic pathways, for example involving myctophid fish or carrion, and that some wide-ranging predators which breed at South Georgia also feed outside the region. This conclusion is supported first by the continuum of ? 15N values between krill, suspension feeding copepods and myctophid fish, and secondly by higher trophic levels in several of the myctophid species in the low-krill region of the northern Scotia Sea, suggesting latitudinal differences in food web structure and food chain length.
Food-web stability signals critical transitions in temperate shallow lakes.
Kuiper, Jan J; van Altena, Cassandra; de Ruiter, Peter C; van Gerven, Luuk P A; Janse, Jan H; Mooij, Wolf M
A principal aim of ecologists is to identify critical levels of environmental change beyond which ecosystems undergo radical shifts in their functioning. Both food-web theory and alternative stable states theory provide fundamental clues to mechanisms conferring stability to natural systems. Yet, it is unclear how the concept of food-web stability is associated with the resilience of ecosystems susceptible to regime change. Here, we use a combination of food web and ecosystem modelling to show that impending catastrophic shifts in shallow lakes are preceded by a destabilizing reorganization of interaction strengths in the aquatic food web. Analysis of the intricate web of trophic interactions reveals that only few key interactions, involving zooplankton, diatoms and detritus, dictate the deterioration of food-web stability. Our study exposes a tight link between food-web dynamics and the dynamics of the whole ecosystem, implying that trophic organization may serve as an empirical indicator of ecosystem resilience. PMID:26173798
Complementary molecular information changes our perception of food web structure.
Wirta, Helena K; Hebert, Paul D N; Kaartinen, Riikka; Prosser, Sean W; Vßrkonyi, Gergely; Roslin, Tomas
How networks of ecological interactions are structured has a major impact on their functioning. However, accurately resolving both the nodes of the webs and the links between them is fraught with difficulties. We ask whether the new resolution conferred by molecular information changes perceptions of network structure. To probe a network of antagonistic interactions in the High Arctic, we use two complementary sources of molecular data: parasitoid DNA sequenced from the tissues of their hosts and host DNA sequenced from the gut of adult parasitoids. The information added by molecular analysis radically changes the properties of interaction structure. Overall, three times as many interaction types were revealed by combining molecular information from parasitoids and hosts with rearing data, versus rearing data alone. At the species level, our results alter the perceived host specificity of parasitoids, the parasitoid load of host species, and the web-wide role of predators with a cryptic lifestyle. As the northernmost network of host-parasitoid interactions quantified, our data point exerts high leverage on global comparisons of food web structure. However, how we view its structure will depend on what information we use: compared with variation among networks quantified at other sites, the properties of our web vary as much or much more depending on the techniques used to reconstruct it. We thus urge ecologists to combine multiple pieces of evidence in assessing the structure of interaction webs, and suggest that current perceptions of interaction structure may be strongly affected by the methods used to construct them. PMID:24449902
Complementary molecular information changes our perception of food web structure
Wirta, Helena K.; Hebert, Paul D. N.; Kaartinen, Riikka; Prosser, Sean W.; Vßrkonyi, Gergely; Roslin, Tomas
How networks of ecological interactions are structured has a major impact on their functioning. However, accurately resolving both the nodes of the webs and the links between them is fraught with difficulties. We ask whether the new resolution conferred by molecular information changes perceptions of network structure. To probe a network of antagonistic interactions in the High Arctic, we use two complementary sources of molecular data: parasitoid DNA sequenced from the tissues of their hosts and host DNA sequenced from the gut of adult parasitoids. The information added by molecular analysis radically changes the properties of interaction structure. Overall, three times as many interaction types were revealed by combining molecular information from parasitoids and hosts with rearing data, versus rearing data alone. At the species level, our results alter the perceived host specificity of parasitoids, the parasitoid load of host species, and the web-wide role of predators with a cryptic lifestyle. As the northernmost network of host¢parasitoid interactions quantified, our data point exerts high leverage on global comparisons of food web structure. However, how we view its structure will depend on what information we use: compared with variation among networks quantified at other sites, the properties of our web vary as much or much more depending on the techniques used to reconstruct it. We thus urge ecologists to combine multiple pieces of evidence in assessing the structure of interaction webs, and suggest that current perceptions of interaction structure may be strongly affected by the methods used to construct them. PMID:24449902
Food-Web Structure of Seagrass Communities across Different Spatial Scales and Human Impacts
Coll, Marta; Schmidt, Allison; Romanuk, Tamara; Lotze, Heike K.
Seagrass beds provide important habitat for a wide range of marine species but are threatened by multiple human impacts in coastal waters. Although seagrass communities have been well-studied in the field, a quantification of their food-web structure and functioning, and how these change across space and human impacts has been lacking. Motivated by extensive field surveys and literature information, we analyzed the structural features of food webs associated with Zostera marina across 16 study sites in 3 provinces in Atlantic Canada. Our goals were to (i) quantify differences in food-web structure across local and regional scales and human impacts, (ii) assess the robustness of seagrass webs to simulated species loss, and (iii) compare food-web structure in temperate Atlantic seagrass beds with those of other aquatic ecosystems. We constructed individual food webs for each study site and cumulative webs for each province and the entire region based on presence/absence of species, and calculated 16 structural properties for each web. Our results indicate that food-web structure was similar among low impact sites across regions. With increasing human impacts associated with eutrophication, however, food-web structure show evidence of degradation as indicated by fewer trophic groups, lower maximum trophic level of the highest top predator, fewer trophic links connecting top to basal species, higher fractions of herbivores and intermediate consumers, and higher number of prey per species. These structural changes translate into functional changes with impacted sites being less robust to simulated species loss. Temperate Atlantic seagrass webs are similar to a tropical seagrass web, yet differed from other aquatic webs, suggesting consistent food-web characteristics across seagrass ecosystems in different regions. Our study illustrates that food-web structure and functioning of seagrass habitats change with human impacts and that the spatial scale of food-web analysis is critical for determining results. PMID:21811637
Revisiting the use of 15 N in meso-scale studies of marine food webs by
Paris-Sud XI, Universitķ de
Revisiting the use of 15 N in meso-scale studies of marine food webs by considering spatio using 13 C and especially 15 N values in open ecosystems with complex food webs, using the Bay of Biscay of a consumer directly reflects that of its food. Nevertheless, few studies have attempted to define the limits
IMA Journal of Mathematics Applied in Medicine & Biology (1993) 10, 281-291 Selectivestrategiesin food webs
Krivan, Vlastimil
food webs RINALDO M. COLOMBO Mathematical Department, University of Milan, Via Saldini 50, 20133 Milano 'switching' are given for a one-predator-two-prey system. Keywords: population dynamics; food web; control 1993] Food websare describedascontrol systemswherethe controls are chosenaccording to given myopic
Ecological Stoichiometry, Biogeochemical Cycling, Invasive Species, and Aquatic Food Webs: San Francisco Estuary and Comparative Systems
Patricia M. Glibert; David Fullerton; Joann M. Burkholder; Jeffrey C. Cornwell; Todd M. Kana
Eutrophication has altered food webs across aquatic systems, but effects of nutrient stoichiometry (varying nutrient ratios) on ecosystem structure and function have received less attention. A prevailing assumption has been that nutrients are not ecologically relevant unless concentrations are limiting to phytoplankton. However, changes in nutrient stoichiometry fundamentally affect food quality at all levels of the food web. Here, 30-year
Fluctuations in density of an outbreak species drive diversity cascades in food webs
Eveleigh, Eldon S.; McCann, Kevin S.; McCarthy, Peter C.; Pollock, Steven J.; Lucarotti, Christopher J.; Morin, Benoit; McDougall, George A.; Strongman, Douglas B.; Huber, John T.; Umbanhowar, James; Faria, Lucas D. B.
Patterns in food-web structure have frequently been examined in static food webs, but few studies have attempted to delineate patterns that materialize in food webs under nonequilibrium conditions. Here, using one of nature's classical nonequilibrium systems as the food-web database, we test the major assumptions of recent advances in food-web theory. We show that a complex web of interactions between insect herbivores and their natural enemies displays significant architectural flexibility over a large fluctuation in the natural abundance of the major herbivore, the spruce budworm (Choristoneura fumiferana). Importantly, this flexibility operates precisely in the manner predicted by recent foraging-based food-web theories: higher-order mobile generalists respond rapidly in time and space by converging on areas of increasing prey abundance. This ōbirdfeeder effectö operates such that increasing budworm densities correspond to a cascade of increasing diversity and food-web complexity. Thus, by integrating foraging theory with food-web ecology and analyzing a long-term, natural data set coupled with manipulative field experiments, we are able to show that food-web structure varies in a predictable manner. Furthermore, both recent food-web theory and longstanding foraging theory suggest that this very same food-web flexibility ought to be a potent stabilizing mechanism. Interestingly, we find that this food-web flexibility tends to be greater in heterogeneous than in homogeneous forest plots. Because our results provide a plausible mechanism for boreal forest effects on populations of forest insect pests, they have implications for forest and pest management practices. PMID:17940003
Bioaccumulation of toxaphene congeners in the lake superior food web
Muir, D.C.G.; Whittle, D.M.; De Vault, D. S.; Bronte, C.R.; Karlsson, H.; Backus, S.; Teixeira, C.
The bioaccumulation and biotransformation of toxaphene was examined in the food webs of Lake Superior and Siskiwit Lake (Isle Royale) using congener specific analysis as well as stable isotope ratios of carbon and nitrogen to characterize food webs. Toxaphene concentrations (calculated using technical toxaphene) in lake trout (Salvelinus namaycush) from the western basin of Lake Superior (N = 95) averaged (▒SD) 889 ▒ 896 ng/g wet wt and 60 ▒ 34 ng/g wet wt in Siskiwit Lake. Major congeners in lake trout were B8-789 (P38), B8-2226 (P44), B9-1679 (P50), and B9-1025 (P62). Toxaphene concentrations were found to vary seasonally, especially in lower food web organisms in Lake Superior and to a lesser extent in Siskiwit Lake. Toxaphene concentrations declined significantly in lake herring (Coregonus artedii), rainbow smelt (Omerus mordax), and slimy sculpin (Cottus cognatus) as well as in zooplankton (> 102 &mn;m) and Mysis (Mysis relicta) between May and October. The seasonal variation may reflect seasonal shifts in the species abundance within the zooplankton community. Trophic magnification factors (TMF) derived from regressions of toxaphene congener concentrations versus ?15N were > 1 for most octa- and nonachlorobornanes in Lake Superior except B8-1413 (P26) and B9-715. Log bioaccumulation factors (BAFs) for toxaphene congeners in lake trout (ng/g lipid/ng/L dissolved) ranged from 4.54 to 9.7 and were significantly correlated with log octanol-water partition coefficients. TMFs observed for total toxaphene and congener B9-1679 in Lake Superior were similar to those in Arctic lakes, as well as to previous studies in the Great Lakes, which suggests that the bioaccumulation behavior of toxaphene is similar in pelagic food webs of large, cold water systems. However, toxaphene concentrations were lower in lake trout from Siskiwit Lake and lakes in northwestern Ontario than in Lake Superior possibly because of shorter food chains and greater reliance on zooplankton or other pelagic invertebrates.
Weaving marine food webs from end to end under global change
NASA Astrophysics Data System (ADS)
Moloney, Coleen L.; St John, Michael A.; Denman, Kenneth L.; Karl, David M.; K÷ster, Friedrich W.; Sundby, Svein; Wilson, Rory P.
Marine food web dynamics are determined by interactions within and between species and between species and their environment. Global change directly affects abiotic conditions and living organisms, impinging on all trophic levels in food webs. Different groups of marine researchers traditionally study different aspects of these changes. However, over medium to long time scales perturbations affecting food webs need to be considered across the full range from nutrients to top predators. Studies of end-to-end marine food webs not only span organism sizes and trophic levels, but should also help align multidisciplinary research to common goals and perspectives. Topics are described that bridge disciplinary gaps and are needed to develop new understanding of the reciprocal impacts of global change on marine food webs and ocean biogeochemistry. These include (1) the effects of nutrients on biomass and production, (2) the effects of varying element ratios on food web structure and food quality, (3) bulk flows of energy and material in food webs and their efficiencies of transfer, (4) the ecological effects of species richness and the roles of microbial organisms, (5) the role of feeding behaviour in food web dynamics and trophic controls, (6) the spatial dynamics of communities and links between different food webs, (7) the combined effects of body size and behaviour in determining dynamics of food webs, and (8) the extent to which the ability of marine organisms (and communities) to adapt will influence food web dynamics. An overriding issue that influences all topics concerns the time and space scales of ecosystem variability. Threads link different nodes of information among various topics, emphasizing the importance of tackling food web studies with a variety of modelling approaches and through a combination of field and experimental studies with a strong comparative approach.
Gene amplification and cold adaptation of pepsin in Antarctic fish. A possible strategy for food digestion at low temperature.
Carginale, Vincenzo; Trinchella, Francesca; Capasso, Clemente; Scudiero, Rosaria; Parisi, Elio
Cold-adapted organisms have developed a number of adjustments at the molecular level to maintain metabolic functions at low temperatures. Among other features, they can produce enzymes characterized by a high turnover number or a high catalytic efficiency. The present work is aimed at investigating the process of food digestion at low temperature through the study of pepsins in Antarctic notothenioids. For such a purpose, we have cloned and sequenced three forms of pepsin A and a single form of gastricsin from the gastric mucosa of Trematomus bernacchii (rock cod). Phylogenetic analysis has suggested that the three pepsin A isotypes arose from two gene duplication events leading to the most ancestral pepsin A3 and to the most recent forms represented by pepsin A1 and pepsin A2. Molecular modeling has unraveled significant structural differences in these enzymes with respect to their mesophilic counterparts. Hydropathy and flexibility determined on the substrate-binding subsites of Antarctic and mesophilic pepsins have shown for pepsin A2 reduced hydropathy and increased flexibility at the level of the substrate cleft, features typical of cold-adapted enzymes. Northern blot analysis of RNA from rock cod gastric mucosa hybridized with molecular probes designed on specific regions of different pepsin forms has shown that rock cod pepsin genes are expressed at comparable levels. The present results suggest that the Antarctic rock cod adopted two different strategies to accomplish efficient protein digestion at low temperature. One mechanism is the gene duplication that increases enzyme production to compensate for the reduced kinetic efficiency, the other is the expression of a new enzyme provided with features typical of cold-adapted enzymes. PMID:15246531
Land use alters the resistance and resilience of soil food webs to drought
NASA Astrophysics Data System (ADS)
de Vries, Franciska T.; Liiri, Mira E.; Bj°rnlund, Lisa; Bowker, Matthew A.; Christensen, S°ren; Setõlõ, Heikki M.; Bardgett, Richard D.
Soils deliver several ecosystem services including carbon sequestration and nutrient cycling, which are of central importance to climate mitigation and sustainable food production. Soil biota play an important role in carbon and nitrogen cycling, and, although the effects of land use on soil food webs are well documented, the consequences for their resistance and resilience to climate change are not known. We compared the resistance and resilience to drought--which is predicted to increase under climate change--of soil food webs of two common land-use systems: intensively managed wheat with a bacterial-based soil food web and extensively managed grassland with a fungal-based soil food web. We found that the fungal-based food web, and the processes of C and N loss it governs, of grassland soil was more resistant, although not resilient, and better able to adapt to drought than the bacterial-based food web of wheat soil. Structural equation modelling revealed that fungal-based soil food webs and greater microbial evenness mitigated C and N loss. Our findings show that land use strongly affects the resistance and resilience of soil food webs to climate change, and that extensively managed grassland promotes more resistant, and adaptable, fungal-based soil food webs.
Land use alters the resistance and resilience of soil food webs to drought
de Vries, Franciska T.; Liiri, Mira E.; Bj°rnlund, Lisa; Bowker, Matthew A.; Christensen, S°ren; Setõlõ, Heikki; Bardgett, Richard D.
Soils deliver several ecosystem services including carbon sequestration and nutrient cycling, which are of central importance to climate mitigation and sustainable food production. Soil biota play an important role in carbon and nitrogen cycling, and, although the effects of land use on soil food webs are well documented the consequences for their resistance and resilience to climate change are not known. We compared the resistance and resilience to drought--which is predicted to increase under climate change of soil food webs of two common land-use systems: intensively managed wheat with a bacterial-based soil food web and extensively managed grassland with a fungal-based soil food web. We found that the fungal-based food web, and the processes of C and N loss it governs, of grassland soil was more resistant, although not resilient, and better able to adapt to drought than the bacterial-based food web of wheat soil. Structural equation modelling revealed that fungal-based soil food webs and greater microbial evenness mitigated C and N loss. Our findings show that land use strongly affects the resistance and resilience of soil food webs to climate change, and that extensively managed grassland promotes more resistant, and adaptable, fungal-based soil food webs.
Food-web complexity emerging from ecological dynamics on adaptive networks.
Garcia-Domingo, Josep L; Salda±a, Joan
Food webs are complex networks describing trophic interactions in ecological communities. Since Robert May's seminal work on random structured food webs, the complexity-stability debate is a central issue in ecology: does network complexity increase or decrease food-web persistence? A multi-species predator-prey model incorporating adaptive predation shows that the action of ecological dynamics on the topology of a food web (whose initial configuration is generated either by the cascade model or by the niche model) render, when a significant fraction of adaptive predators is present, similar hyperbolic complexity-persistence relationships as those observed in empirical food webs. It is also shown that the apparent positive relation between complexity and persistence in food webs generated under the cascade model, which has been pointed out in previous papers, disappears when the final connection is used instead of the initial one to explain species persistence. PMID:17512552
Native and nonnative fish populations of the Colorado River are food limited--evidence from new food web analyses
Kennedy, Theodore A.; Cross, Wyatt F.; Hall, Robert O., Jr.; Baxter, Colden V.; Rosi-Marshall, Emma J.
Fish populations in the Colorado River downstream from Glen Canyon Dam appear to be limited by the availability of high-quality invertebrate prey. Midge and blackfly production is low and nonnative rainbow trout in Glen Canyon and native fishes in Grand Canyon consume virtually all of the midge and blackfly biomass that is produced annually. In Glen Canyon, the invertebrate assemblage is dominated by nonnative New Zealand mudsnails, the food web has a simple structure, and transfers of energy from the base of the web (algae) to the top of the web (rainbow trout) are inefficient. The food webs in Grand Canyon are more complex relative to Glen Canyon, because, on average, each species in the web is involved in more interactions and feeding connections. Based on theory and on studies from other ecosystems, the structure and organization of Grand Canyon food webs should make them more stable and less susceptible to large changes following perturbations of the flow regime relative to food webs in Glen Canyon. In support of this hypothesis, Grand Canyon food webs were much less affected by a 2008 controlled flood relative to the food web in Glen Canyon.
Mesoscale symmetries explain dynamical equivalence of food webs
Aufderheide, Helge; Gross, Thilo
A present challenge in complex systems is to identify mesoscale structures that have distinct dynamical implications. In this paper we present a detailed investigation of a previously observed dynamical equivalence of certian ecological food webs. We show that this equivalence is rooted in mesoscale symmetries that exist in these webs. Certain eigenvectors of the Jacobian describing dynamical modes of the system, such as specific instabilities or responses to perturbations, localize on these symmetric motifs. On the one hand this means that by removing a symmetry from the network one obtains a system which has identical dynamics except for the removal of the localized mode. This explains the previously observed equivalence. On the other hand it means that we can identify dynamical modes that only depend on the symmetric motif. Symmetric structures thus provide an example for mesoscale network motifs having distinct and exact implications for the dynamics.
Rigorous conditions for food-web intervality in high-dimensional trophic niche spaces
┼ke Brõnnstr÷m; Linus Carlsson; Axel G. Rossberg
Food webs represent trophic (feeding) interactions in ecosystems. Since the late 1970s, it has been recognized that food-webs\\u000a have a surprisingly close relationship to interval graphs. One interpretation of food-web intervality is that trophic niche\\u000a space is low-dimensional, meaning that the trophic character of a species can be expressed by a single or at most a few quantitative\\u000a traits. In
Food-Web Models Predict Species Abundances in Response to Habitat Change
Nicholas J Gotelli; Aaron M Ellison
Plant and animal population sizes inevitably change following habitat loss, but the mechanisms underlying these changes are poorly understood. We experimentally altered habitat volume and eliminated top trophic levels of the food web of invertebrates that inhabit rain-filled leaves of the carnivorous pitcher plant Sarracenia purpurea. Path models that incorporated food-web structure better predicted population sizes of food-web constituents than
Parasites alter the topology of a stream food web across seasons
Alexander D. Hernandez; Michael V. K. Sukhdeo
Relatively few published food webs have included parasites, and in this study we examined the animal community in a stream\\u000a across eight contiguous seasons to test how inclusion of helminth parasites alters the topology or structure of the food web.\\u000a Food webs constructed for each season and analyzed using common binary matrix measures show that species richness, linkage\\u000a density, and
Reducing Methylmercury Accumulation in the Food Webs of San Francisco Bay and Its Local Watershed
Ł Food web shifts Knobs #12;Reservoir Ę Elective strategies Ł Slow knobs Ę THg inputs Ł Fast knobs#12;#12;Reducing Methylmercury Accumulation in the Food Webs of San Francisco Bay and Its Local food web Hg Gehrke et al. 2011. ES&T 45 (4), pp 1264Ł1270 #12;0 0.1 0.2 0.3 0.4 0.5 Louisiana
Trophic structure, stability, and parasite persistence threshold in food webs.
McQuaid, C Finn; Britton, Nicholas F
Food web structure of free-living species is an important determinant of parasite species richness. Downwardly asymmetric predator-prey interactions (where there are more prey than predator species) have been shown, both theoretically and empirically, to harbour more trophically transmitted parasite species than expected due to chance. Here, we demonstrate that this could be due to the increase in the basic reproductive ratio that the addition of non-host prey species to a system creates. However, we note that the basic reproductive ratio is only increased by those prey that stabilise oscillations in a predator-prey system, and is decreased by those that do not. PMID:23943365
Modelling Size Structured Food Webs Using a Modified Niche Model with Two Predator Traits
Klecka, Jan
The structure of food webs is frequently described using phenomenological stochastic models. A prominent example, the niche model, was found to produce artificial food webs resembling real food webs according to a range of summary statistics. However, the size structure of food webs generated by the niche model and real food webs has not yet been rigorously compared. To fill this void, I use a body mass based version of the niche model and compare prey-predator body mass allometry and predator-prey body mass ratios predicted by the model to empirical data. The results show that the model predicts weaker size structure than observed in many real food webs. I introduce a modified version of the niche model which allows to control the strength of size-dependence of predator-prey links. In this model, optimal prey body mass depends allometrically on predator body mass and on a second trait, such as foraging mode. These empirically motivated extensions of the model allow to represent size structure of real food webs realistically and can be used to generate artificial food webs varying in several aspects of size structure in a controlled way. Hence, by explicitly including the role of species traits, this model provides new opportunities for simulating the consequences of size structure for food web dynamics and stability. PMID:25119999
Food and Beverage Brands that Market to Children and Adolescents on the Internet: A Content Analysis of Branded Web Sites
ERIC Educational Resources Information Center
Henry, Anna E.; Story, Mary
Objective: To identify food and beverage brand Web sites featuring designated children's areas, assess marketing techniques present on those industry Web sites, and determine nutritional quality of branded food items marketed to children. Design: Systematic content analysis of food and beverage brand Web sites and nutrient analysis of food andģ
The paradox of pelagic food webs in the northern Bering SeaŚI. Seabird food habits
NASA Astrophysics Data System (ADS)
Springer, Alan M.; Murphy, Edward C.; Roseneau, David G.; McRoy, C. Peter; Cooper, Brian A.
Two distinct environmental settings in the Bering Strait region of the northern Bering Sea lead to characteristic pathways of energy flow through primarily pelagic food webs to avian consumers. In Norton Sound, a large, shallow embayment on the northeastern coast, the physical environment is dominated by the discharge of the Yukon River and by a large seasonal temperature signal. Seabirds breeding at Bluff, the largest colony in Norton Sound, number in the order of 5 ū 10 4 and require 1.2 ū 10 6 g C d -1. Two piscivorous species constitute the bulk of all seabirds there and are supported by a pelagic food web typical of the coastal zone of the Bering and Chukchi seas. This food web also is present around St. Lawrence Island, on the northwestern shelf, and is important to at least one species of seabird there. In addition, and generally more important, St. Lawrence Island is in a biologically rich environment resulting from the northward flow of water that originates along the continental shelf break of the Bering Sea. This flow apparently accounts for the unexpected presence of oceanic zooplankton and a diversity of forage fishes on the shallow northern shelf that support an abundant and taxonomically rich avifauna. In comparison to Norton Sound, breeding seabirds on St. Lawrence Island number in the order of 2 ū 10 6, with planktivores consuming about 8 ū 10 6 g C d -1 and piscivores consuming about 16 ū 10 6 g C d -1.
Model of carbon cycling in planktonic food webs
Connolly, J.P. [HydroQual, Inc., Mahwah, NJ (United States); Coffin, R.B. [Environmental Protection Agency, Gulf Breeze, FL (United States). Environmental Research Lab.
A mathematical model of carbon fluxes through the heterotrophic microbial food web is developed from a synthesis of laboratory and field research. The basis of the model is the segregation of organic carbon into lability classes that are defined by bioassay experiments. Bacteria, phytoplankton, three trophic levels of zooplankton, and dissolved organic carbon (DOC) and particulate organic carbon (POC) are modeled. The descriptions of bacterial growth and utilization of the various classes of substrate were treated as universal constants in the application of the model to three distinct ecosystems, ranging from oligotrophic to highly eutrophic. The successful application of the model to these diverse ecosystems supports the basic validity of the description of the microbial food web and the dynamics of carbon flux. The model indicates that the dynamics of bacteria and protozoan zooplankton production govern the rates of oxidation of carbon entering the water column. Explicit consideration of these groups would improve the capability of eutrophication models to predict dissolved oxygen dynamics, particularly when projecting responses to loading changes.
Dynamics of the Lake Michigan food web, 1970-2000
Madenjian, Charles P.; Fahnenstiel, Gary L.; Johengen, Thomas H.; Nalepa, Thomas F.; Vanderploeg, Henry A.; Fleischer, Guy W.; Schneeberger, Philip J.; Benjamin, Darren M.; Smith, Emily B.; Bence, James R.; Rutherford, Edward S.; Lavis, Dennis S.; Robertson, Dale M.; Jude, David J.; Ebener, Mark P.
Herein, we document changes in the Lake Michigan food web between 1970 and 2000 and identify the factors responsible for these changes. Control of sea lamprey (Petromyzon marinus) and alewife (Alosa pseudoharengus) populations in Lake Michigan, beginning in the 1950s and 1960s, had profound effects on the food web. Recoveries of lake whitefish (Coregonus clupeaformis) and burbot (Lota lota) populations, as well as the buildup of salmonine populations, were attributable, at least in part, to sea lamprey control. Based on our analyses, predation by salmonines was primarily responsible for the reduction in alewife abundance during the 1970s and early 1980s. In turn, the decrease in alewife abundance likely contributed to recoveries of deepwater sculpin (Myoxocephalus thompsoni), yellow perch (Perca flavescens), and burbot populations during the 1970s and 1980s. Decrease in the abundance of all three dominant benthic macroinvertebrate groups, including Diporeia, oligochaetes, and sphaeriids, during the 1980s in nearshore waters (50 m deep) of Lake Michigan, was attributable to a decrease in primary production linked to a decline in phosphorus loadings. Continued decrease in Diporeia abundance during the 1990s was associated with the zebra mussel (Dreissena polymorpha) invasion, but specific mechanisms for zebra mussels affecting Diporeia abundance remain unidentified.
Application of information theory methods to food web reconstruction
Moniz, L.J.; Cooch, E.G.; Ellner, S.P.; Nichols, J.D.; Nichols, J.M.
In this paper we use information theory techniques on time series of abundances to determine the topology of a food web. At the outset, the food web participants (two consumers, two resources) are known; in addition we know that each consumer prefers one of the resources over the other. However, we do not know which consumer prefers which resource, and if this preference is absolute (i.e., whether or not the consumer will consume the non-preferred resource). Although the consumers and resources are identified at the beginning of the experiment, we also provide evidence that the consumers are not resources for each other, and the resources do not consume each other. We do show that there is significant mutual information between resources; the model is seasonally forced and some shared information between resources is expected. Similarly, because the model is seasonally forced, we expect shared information between consumers as they respond to the forcing of the resources. The model that we consider does include noise, and in an effort to demonstrate that these methods may be of some use in other than model data, we show the efficacy of our methods with decreasing time series size; in this particular case we obtain reasonably clear results with a time series length of 400 points. This approaches ecological time series lengths from real systems.
Scaling Behaviors of Weighted Food Webs as Energy Transportation Networks
Zhang, Jiang; 10.1016/j.jtbi.2010.03.024
Food webs can be regarded as energy transporting networks in which the weight of each edge denotes the energy flux between two species. By investigating 21 empirical weighted food webs as energy flow networks, we found several ubiquitous scaling behaviors. Two random variables $A_i$ and $C_i$ defined for each vertex $i$, representing the total flux (also called vertex intensity) and total indirect effect or energy store of $i$, were found to follow power law distributions with the exponents $\\alpha\\approx 1.32$ and $\\beta\\approx 1.33$, respectively. Another scaling behavior is the power law relationship, $C_i\\sim A_i^\\eta$, where $\\eta\\approx 1.02$. This is known as the allometric scaling power law relationship because $A_i$ can be treated as metabolism and $C_i$ as the body mass of the sub-network rooted from the vertex $i$, according to the algorithm presented in this paper. Finally, a simple relationship among these power law exponents, $\\eta=(\\alpha-1)/(\\beta-1)$, was mathematically derived and tested by ...
Significance of predation by protists in aquatic microbial food webs.
Sherr, Evelyn B; Sherr, Barry F
Predation in aquatic microbial food webs is dominated by phagotrophic protists, yet these microorganisms are still understudied compared to bacteria and phytoplankton. In pelagic ecosystems, predaceous protists are ubiquitous, range in size from 2 gm flagellates to > 100 microm ciliates and dinoflagellates, and exhibit a wide array of feeding strategies. Their trophic states run the gamut from strictly phagotrophic, to mixotrophic: partly autotrophic and partly phagotrophic, to primarily autotrophic but capable of phagotrophy. Protists are a major source of mortality for both heterotrophic and autotrophic bacteria. They compete with herbivorous meso- and macro-zooplankton for all size classes of phytoplankton. Protist grazing may affect the rate of organic sinking flux from the euphotic zone. Protist excretions are an important source of remineralized nutrients, and of colloidal and dissolved trace metals such as iron, in aquatic systems. Work on predation by protists is being facilitated by methodological advances, e.g., molecular genetic analysis of protistan diversity and application of flow cytometry to study population growth and feeding rates. Examples of new research areas are studies of impact of protistan predation on the community structure of prey assemblages and of chemical communication between predator and prey in microbial food webs. PMID:12448728
Defining and Measuring Trophic Role Similarity in Food Webs Using Regular Equivalence
We present a graph theoretic model of analysing food web structure called regular equivalence. Regular equivalence is a method for partitioning the species in a food web into ōisotrophic classesö that play the same structural roles, even if they are not directly consuming the same prey or if they do not share the same predators. We contrast regular equivalence models,
Influence of food web structure on the growth and bioenergetics of lake trout (Salvelinus namaycush)
Rasmussen, Joseph
Influence of food web structure on the growth and bioenergetics of lake trout (Salvelinus namaycush energy budgets of lake trout (Salvelinus namaycush) populations in contrasting food webs. Nonpiscivorous des populations de touladis (Salvelinus namaycush) dans divers rķseaux trophiques. Les populations de
Comparative food web structure of larval macrolepidoptera and their parasitoids on two riparian tree species
Pedro Barbosa; Astrid Caldas; H. Charles J. Godfray
Single species or groups of species can be subjected to differing levels of parasitism on different plants. Previous studies\\u000a have reported that parasitism of larval macrolepidoptera in an assemblage on box elder (Acer negundo L.) was significantly greater than on black willow [Salix nigra (Marsh)]. In this study, quantitative food webs, parasitoid overlap diagrams and other food web attributes were
Stable isotope analyses of the pelagic food web in Lake Baikal
Koichi Yoshii; Natalia G. Melnik; Oleg A. Timoshkin; Nina A. Bondarenko; Pavel N. Anoshko; Takahito Yoshioka; Eitaro Wada
Stable isotope ratios of various organisms were analyzed to elucidate food web structure in the pelagic zone of Lake Baikal. The pelagic food web of Lake Baikal is simple and consists of five major ecological groups: phyto- plankton (Aulacoseira baicalensis), mesozooplankton (Epischura baicalensis), macrozooplankton amphipod (Ma- crohectopus branickii), fish (Coregonus autumnalis migratoriusand four species of cottoid fishes), and seal (Phoca
Review Behaviour and indirect interactions in food webs of plant-inhabiting arthropods
Arne Janssen; Angelo Pallini; Madelaine Venzon; Maurice W. Sabelis
With the increased use of biological control agents, artificial food webs are created in agricultural crops and the interactions between plants, herbivores and natural enemies change from simple tritrophic interactions to more complex food web interactions. Therefore, herbivore densities will not only be determined by direct predator¢prey interactions and direct and indirect defence of plants against herbivores, but also by
Influence of decomposer food web structure and nitrogen availability on plant growth t(u
Jouni Laaksol; Heikki Setala; Ansa Palojarvi
We studied the sensitivity of soil microbial communities and ecosystem processes to variation in the vertical and horizontal structure of decomposer food web under nitrogen poor and N-enriched conditions. Microcosms with humus and litter layer of boreal forest floor, birch seedlings infected with mycorrhizal fungi, and decomposer food webs with differing trophic group and species composition of soil fauna were
Network position of hosts in food webs and their parasite diversity
Hsuan-Wien Chen; Wei-Chung Liu; Andrew J. Davis; Ferenc Jordßn; Ming-Jing Hwang; Kwan-Tsao Shao
Parasites are ubiquitous in ecological communities but it is only recently that they have been routinely included in food web studies. Using recently published data and the tool of network analysis, we elucidate features associated with the pattern of parasitism in ecological communities. First we show here that parasitism is non-random in food webs. Second we demonstrate that parasite diversity,
Spatial prey subsidies and understanding the trophic population dynamics of a food web
Edward Shaw
What factors affect the dynamics of populations in food webs is a question which is fundamental to ecology. It is generally agreed that the integration of landscape ecology and food web theory is needed for progress to be made. Spatial prey subsidies are a concept which has arisen from this drive for integration. Here I assess the general theory of
Body Size and Food Web Structure: Testing the Cascade Model's Equiprobability Assumption
Michael G. Neubert; Steven C. Blumenshine; Daniel E. Duplisea
Abstract The cascade model successfuly predicts many patterns in reported food webs. A key assumption of this model is the existence of a predetermined trophic hierarchy; prey are always lower in the hierarchy than their predators. At least three studies have suggested that, in animal food webs, this hierarchy can be explained to a large extent by body size relationships.
The modified niche model: Including detritus in simple structural food web models
Geir Halnes; Brian D. Fath; Hans Liljenstr÷m
Food webs are constructed as structural directed graphs that describe ōwho eats whom,ö but it is common to interpret them as energy flow diagrams where predation represents an energy transfer from the prey to the predator. It is the aim of this work to demonstrate that food webs are incomplete as energy flow diagrams if they ignore passive flows to
Robustness to secondary extinctions: Comparing trait-based sequential deletions in static and dynamic food webs
Alva Curtsdotter; Amrei Binzer; Ulrich Brose; Francisco de Castro; Bo Ebenman; Anna Ekl÷f; Jens O. Riede; Aaron Thierry; Bj÷rn C. Rall
The loss of species from ecological communities can unleash a cascade of secondary extinctions, the risk and extent of which are likely to depend on the traits of the species that are lost from the community. To identify species traits that have the greatest impact on food web robustness to species loss we here subject allometrically scaled, dynamical food web
Success and its limits among structural models of complex food webs
Richard J. Williams; Neo D. Martinez
Summary 1. Following the development of the relatively successful niche model, several other simple structural food web models have been proposed. These models predict the detailed structure of complex food webs given only two input parameters, the numbers of species and the number of feeding links among them. 2. The models claim different degrees of success but have not been
Compartments in a marine food web associated with phylogeny, body mass, and habitat structure
Enrico L. Rezende; Eva M. Albert; Miguel A. Fortuna; Jordi Bascompte
A long-standing question in community ecology is whether food webs are organized in compartments, where species within the same compartment interact frequently among themselves, but show fewer interactions with species from other compartments. Finding evidence for this community organization is important since compartmentalization may strongly affect food web robustness to perturbation. However, few studies have found unequivocal evidence of compartments,
Developing a broader scientific foundation for river restoration: Columbia River food webs
Naiman, Robert J.; Alldredge, J. Richard; Beauchamp, David A.; Bisson, Peter A.; Congleton, James; Henny, Charles J.; Huntly, Nancy; Lamberson, Roland; Levings, Colin; Merrill, Erik N.; Pearcy, William G.; Rieman, Bruce E.; Ruggerone, Gregory T.; Scarnecchia, Dennis; Smouse, Peter E.; Wood, Chris C.
Well-functioning food webs are fundamental for sustaining rivers as ecosystems and maintaining associated aquatic and terrestrial communities. The current emphasis on restoring habitat structureŚwithout explicitly considering food websŚhas been less successful than hoped in terms of enhancing the status of targeted species and often overlooks important constraints on ecologically effective restoration. We identify three priority food web-related issues that potentially impede successful river restoration: uncertainty about habitat carrying capacity, proliferation of chemicals and contaminants, and emergence of hybrid food webs containing a mixture of native and invasive species. Additionally, there is the need to place these food web considerations in a broad temporal and spatial framework by understanding the consequences of altered nutrient, organic matter (energy), water, and thermal sources and flows, reconnecting critical habitats and their food webs, and restoring for changing environments. As an illustration, we discuss how the Columbia River Basin, site of one of the largest aquatic/riparian restoration programs in the United States, would benefit from implementing a food web perspective. A food web perspective for the Columbia River would complement ongoing approaches and enhance the ability to meet the vision and legal obligations of the US Endangered Species Act, the Northwest Power Act (Fish and Wildlife Program), and federal treaties with Northwest Indian Tribes while meeting fundamental needs for improved river management. PMID:23197837
Developing a broader scientific foundation for river restoration: Columbia River food webs
Naiman, Robert J.; Alldredge, Richard; Beauchamp, David A.; Bisson, Peter A.; Congleton, James; Henny, Charles J.; Huntly, Nancy; Lamberson, Roland; Levings, Colin; Merrill, Erik N.; Pearcy, William G.; Rieman, Bruce E.; Ruggerone, Gregory T.; Scarnecchia, Dennis; Smouse, Peter E.; Wood, Chris C.
Well-functioning food webs are fundamental for sustaining rivers as ecosystems and maintaining associated aquatic and terrestrial communities. The current emphasis on restoring habitat structureŚwithout explicitly considering food websŚhas been less successful than hoped in terms of enhancing the status of targeted species and often overlooks important constraints on ecologically effective restoration. We identify three priority food web-related issues that potentially impede successful river restoration: uncertainty about habitat carrying capacity, proliferation of chemicals and contaminants, and emergence of hybrid food webs containing a mixture of native and invasive species. Additionally, there is the need to place these food web considerations in a broad temporal and spatial framework by understanding the consequences of altered nutrient, organic matter (energy), water, and thermal sources and flows, reconnecting critical habitats and their food webs, and restoring for changing environments. As an illustration, we discuss how the Columbia River Basin, site of one of the largest aquatic/riparian restoration programs in the United States, would benefit from implementing a food web perspective. A food web perspective for the Columbia River would complement ongoing approaches and enhance the ability to meet the vision and legal obligations of the US Endangered Species Act, the Northwest Power Act (Fish and Wildlife Program), and federal treaties with Northwest Indian Tribes while meeting fundamental needs for improved river management.
Can You Build It? Using Manipulatives to Assess Student Understanding of Food-Web Concepts
ERIC Educational Resources Information Center
Grumbine, Richard
This article outlines an exercise that assesses student knowledge of food-web and energy-flow concepts. Students work in teams and use manipulatives to build food-web models based on criteria assigned by the instructor. The models are then peer reviewed according to guidelines supplied by the instructor.
Trophic transfer of metals along freshwater food webs: Evidence of cadmium biomagnification in nature
Marie-Noļle Croteau; Samuel N. Luoma; A. Robin Stewart
We conducted a study with cadmium (Cd) and copper (Cu) in the delta of San Francisco Bay, using nitrogen and carbon stable isotopes to identify trophic position and food web structure. Cadmium is progressively enriched among trophic levels in discrete epiphyte-based food webs composed of macrophyte-dwelling invertebrates (the first link being epiphytic algae) and fishes (the first link being gobies).
Disruption of the lower food web in Lake Ontario: Did it affect alewife growth or condition?
R. OGorman; S. E. Prindle; J. R. Lantry; B. F. Lantry
From the early 1980s to the late 1990s, a succession of non-native invertebrates colonized Lake Ontario and the suite of consequences caused by their colonization became known as ōfood web disruptionö. For example, the native burrowing amphipod Diporeia spp., a key link in the profundal food web, declined to near absence, exotic predaceous cladocerans with long spines proliferated, altering the
Potential Effects of Elevated SeaWater Temperature on Pelagic Food Webs
U. M³ren; J. Berglund; K. Samuelsson; A. Andersson
The effect of temperature changes on the marine pelagic food web was studied in three successive mesocosm experiments, performed during the spring bloom 2001 in the northern Baltic Sea. The temperature was varied from 5 to 20Ā░C in each experiment, running over a 3-week period. The experiments included food webs of at least four trophic levels: (1) phytoplankton-bacteria, (2) flagellates,
GULF OF MEXICO SHRIMP PRODUCTION: A FOOD WEB HYPOTHESISl R. WARREN FLINT AND NANCY N. RABALAIS'
GULF OF MEXICO SHRIMP PRODUCTION: A FOOD WEB HYPOTHESISl R. WARREN FLINT AND NANCY N. RABALAIS populations. These results stimulated us to develop a theoretical food web for the shrimp populations the largest fishery in terms of weight harvested and effort expended along the gulfcoast. For example, from
Predicting the carrying capacity of bivalve shellfish culture using a steady, linear food web model
Weimin Jiang; Mark T. Gibbs
An investigation into the potential carrying capacity of suspended bivalve culture was undertaken using a linear food web model. The investigation involved configuring the model for the present state using all available information, and then perturbing the food web by introducing the bivalve culture until pre-determined carrying capacity limits were achieved. These carrying capacity trigger levels were defined by the
Recent Progress and Problems in Food Web Theory Joel E. Cohen
Cohen, Joel E.
showed that, in community food webs in a single habitat, the data on trophic niche overlap were in the niche overlap graph, was shown (Cohen, 1978, p. 69) to be very well described by the model (P to set lower bounds on the dimensionality of trophic niche space by using data on food webs. In 19'78 I
Estuarine Microbial Food Web Patterns in a Lake Erie Coastal P.J. Lavrentyev1
Jochem, Frank J.
Estuarine Microbial Food Web Patterns in a Lake Erie Coastal Wetland P.J. Lavrentyev1 , M.J. Mc protists were examined relative to microbial food web dynamics (growth, grazing, and nitrogen cycling rates pattern. Large light/dark NH4 + uptake differences were observed in the hypereutrophic OWC interior
Coalescence in the Lake Washington story: Interaction strengths in a planktonic food web
Stephanie E. Hampton; Mark D. Scheuerell; Daniel E. Schindler
Lake Washington is arguably the most famous case study of lake pollution and subsequent recovery, and the widely cited story implicates just a few major players in the lake's food web transformations. ''The Lake Washington story'' historically highlights key players that negatively affect other taxaŚfilamentous cyanobacteria, the influential grazer Daphnia, and its predator Neomysis. This food web model has been
Comparison of the structure of lower and upper estuary food webs for Yaquina Bay (OR)
Food web models can be used to estimate effects of water quality, habitat distribution or species loss on productivity, carbon flow and ecosystem service production in Pacific NW estuaries. Here we present a comparison of floral and faunal data used to parameterize food web mode...
Benthic versus Planktonic Foundations of Three Lake Superior Coastal Food Webs
The structure of aquatic food webs can provide information on system function, trophic dynamics and, potentially, responses to anthropogenic stressors. Stable isotope analyses in a Lake Superior coastal wetland (Allouez Bay, WI, USA) revealed that the food web was based upon carb...
Simplification of seagrass food webs across a gradient of nutrient enrichment
Alexander Tewfik; Joseph B. Rasmussen; Kevin S. McCann
Anthropogenic nutrient enrichment has resulted in significant changes in food web structure. Although such changes have been associated with the loss of diversity and ecosystem services, little empirical work has been done to study food webs of similar systems across a nutrient enrichment gradient. We examined 11 seagrass beds along a gra- dient of increasing ?15N of primary consumers, where
A BACI (before-after-control-impact) sampling design was applied to determine the possible effects of ramping rate (RR) regulation on food webs structure and function in a regulated boreal river. We used carbon and nitrogen stable isotope signatures of primary producers, macroinvertebrates and fish to determine variations in the source of carbon fuelling the food web as well as changes in the
Suppressive service of the soil food web: Effects of environmental management
Sara Sßnchez-Moreno; Howard Ferris
Soil food webs perform the important ecosystem services necessary to maintain both agricultural productivity and ecosystem health. Higher trophic levels in soil food webs can play a role suppressing plant parasites and affecting nutrient dynamics by modifying abundance of intermediate consumers. Natural and agricultural landscapes were sampled to compare soil faunal structure. Top-down soil suppressiveness of a parasitic nematode, Meloidogyne
Sonja B. Otto; Eric L. Berlow; Nathan E. Rank; John Smiley; Ulrich Brose
Declining predator diversity may drastically affect the biomass and productivity of herbivores and plants. Understanding how changes in predator diversity can propagate through food webs to alter ecosystem function is one of the most challenging ecological research topics today. We studied the effects of predator removal in a simple natural food web in the Sierra Nevada mountains of California (USA).
Spatial scales of carbon flow in a river food web
Finlay, J.C.; Khandwala, S.; Power, M.E.
Spatial extents of food webs that support stream and river consumers are largely unknown, but such information is essential for basic understanding and management of lotic ecosystems. We used predictable variation in algal ??13C with water velocity, and measurements of consumer ??13C and ??15N to examine carbon flow and trophic structure in food webs of the South Fork Eel River in Northern California. Analyses of ??13C showed that the most abundant macroinvertebrate groups (collector-gatherers and scrapers) relied on algae from local sources within their riffle or shallow pool habitats. In contrast, filter-feeding invertebrates in riffles relied in part on algal production derived from upstream shallow pools. Riffle invertebrate predators also relied in part on consumers of pool-derived algal carbon. One abundant taxon drifting from shallow pools and riffles (baetid mayflies) relied on algal production derived from the habitats from which they dispersed. The trophic linkage from pool algae to riffle invertebrate predators was thus mediated through either predation on pool herbivores dispersing into riffles, or on filter feeders. Algal production in shallow pool habitats dominated the resource base of vertebrate predators in all habitats at the end of the summer. We could not distinguish between the trophic roles of riffle algae and terrestrial detritus, but both carbon sources appeared to play minor roles for vertebrate consumers. In shallow pools, small vertebrates, including three-spined stickleback (Gasterosteus aculeatus), roach (Hesperoleucas symmetricus), and rough-skinned newts (Taricha granulosa), relied on invertebrate prey derived from local pool habitats. During the most productive summer period, growth of all size classes of steelhead and resident rainbow trout (Oncorhynchus mykiss) in all habitats (shallow pools, riffles, and deep unproductive pools) was largely derived from algal production in shallow pools. Preliminary data suggest that the strong role of shallow pool algae in riffle steelhead growth during summer periods was due to drift of pool invertebrates to riffles, rather than movement of riffle trout. Data for ??15N showed that resident rainbow trout (25-33 cm standard length) in deep pools preyed upon small size classes of juvenile steelhead that were most often found in riffles or shallow pools. While many invertebrate consumers relied primarily on algal production derived from local habitats, our study shows that growth of top predators in the river is strongly linked to food webs in adjacent habitats. These results suggest a key role for emigration of aquatic prey in determining carbon flow to top predators.
Untangling the roles of parasites in food webs with generative network models
Jacobs, Abigail Z; Moore, Cristopher; Clauset, Aaron
Food webs represent the set of consumer-resource interactions among a set of species that co-occur in a habitat, but most food web studies have omitted parasites and their interactions. Recent studies have provided conflicting evidence on whether including parasites changes food web structure, with some suggesting that parasitic interactions are structurally distinct from those among free-living species while others claim the opposite. Here, we describe a principled method for understanding food web structure that combines an efficient optimization algorithm from statistical physics called parallel tempering with a probabilistic generalization of the empirically well-supported food web niche model. This generative model approach allows us to rigorously estimate the degree to which interactions that involve parasites are statistically distinguishable from interactions among free-living species, whether parasite niches behave similarly to free-living niches, and the degree to which existing hypotheses about foo...
Cranberry Bogs: The effect of cultivation and restoration on habitat distribution, benthic invertebrate communities, and food webs in stream ecosystems
Vallino, Joseph J.
invertebrate communities, and food webs in stream ecosystems Kimberly Morrell Department of Biology, Carleton habitat distribution, benthic invertebrate communities, and food webs in stream ecosystems. To understand transects and analyzed benthic invertebrate samples. Stable isotope analyses clarified the relationships
Theoretical Population Biology 67 (2005) 8599 Adaptive omnivory and species coexistence in tri-trophic food webs
Krivan, Vlastimil
-trophic food webs Vlastimil Kr ivana,├, Sebastian Diehlb a Department of Theoretical Biology, Institute; Diet rule; Optimal foraging; Population dynamics; Food webs 1. Introduction Omnivory, the consumption
Sampling effects and the robustness of quantitative and qualitative food-web descriptors
Carolin Ban; Marie-France Cattina
Food-web descriptors serve as a means for among-web comparisons that are necessary for the discovery of regularities in respect to food-web structure. Qualitative descriptors were however found to be highly sensitive to varying levels of sampling effort. To circumvent these shortcomings, quantitative counterparts were proposed which take the magnitude of trophic interaction between species into consideration. For 14 properties we
Sampling effects and the robustness of quantitative and qualitative food-web descriptors
Carolin BanaÜek-Richter; Marie-France Cattin; Louis-Fķlix Bersier
Food-web descriptors serve as a means for among-web comparisons that are necessary for the discovery of regularities in respect to food-web structure. Qualitative descriptors were however found to be highly sensitive to varying levels of sampling effort. To circumvent these shortcomings, quantitative counterparts were proposed which take the magnitude of trophic interaction between species into consideration. For 14 properties we
Stability and Resilience as Organizing Constructs for Aquatic Food Webs
NASA Astrophysics Data System (ADS)
Laws, E. A.
The idea that physical, chemical, and biological systems tend to persist in stable configurations underlies much theoretical understanding of systems behavior. Systems analysis indicates that locally (as opposed to globally) stable configurations of systems may persist indefinitely. The existence of such locally stable configurations may to some extent explain the phenomenon of regime shifts and the irreversibility of some anthropogenic impacts on ecosystems. In a stochastic environment merely being stable is not good enough. Resilience becomes important. Given a multitude of stable system configurations, a stochastic environment will tend to select for those configurations that are most resilient. The greater the variance associated with environmental noise, the greater the selection pressure. Application of the concept of maximum resilience to pelagic and mesopelagic food webs leads to predictions about system behavior that are in remarkable agreement with observations. The predictions underscore the role of temperature as a regulator of community behavior.
Trophic transfer of nanoparticles in a simplified invertebrate food web.
Holbrook, R David; Murphy, Karen E; Morrow, Jayne B; Cole, Ken D
The unique chemical and physical properties of engineered nanomaterials that make them attractive for numerous applications also contribute to their unexpected behaviour in the environment and biological systems. The potential environmental risks, including their impact on aquatic organisms, have been a central argument for regulating the growth of the nanotechnology sector. Here we show in a simplified food web that carboxylated and biotinylated quantum dots can be transferred to higher trophic organisms (rotifers) through dietary uptake of ciliated protozoans. Quantum dot accumulation from the surrounding environment (bioconcentration) was limited in the ciliates and no quantum dot enrichment (biomagnification) was observed in the rotifers. Our findings indicate that dietary uptake of nanomaterials should be considered for higher trophic aquatic organisms. However, limited bioconcentration and lack of biomagnification may impede the detection of nanomaterials in invertebrate species. PMID:18654546
Food-web constraints on biodiversity-ecosystem functioning relationships.
Thķbault, Elisa; Loreau, Michel
The consequences of biodiversity loss for ecosystem functioning and ecosystem services have aroused considerable interest during the past decade. Recent work has focused mainly on the impact of species diversity within single trophic levels, both experimentally and theoretically. Experiments have usually showed increased plant biomass and productivity with increasing plant diversity. Changes in biodiversity, however, may affect ecosystem processes through trophic interactions among species as well. An important current challenge is to understand how these trophic interactions affect the relationship between biodiversity and ecosystem functioning. Here we present a mechanistic model of an ecosystem with multiple trophic levels in which plants compete for a limiting soil nutrient. In contrast to previous studies that focused on single trophic levels, we show that plant biomass does not always increase with plant diversity and that changes in biodiversity can lead to complex if predictable changes in ecosystem processes. Our analysis demonstrates that food-web structure can profoundly influence ecosystem properties. PMID:14638942
Food-web constraints on biodiversity¢ecosystem functioning relationships
Thķbault, Elisa; Loreau, Michel
The consequences of biodiversity loss for ecosystem functioning and ecosystem services have aroused considerable interest during the past decade. Recent work has focused mainly on the impact of species diversity within single trophic levels, both experimentally and theoretically. Experiments have usually showed increased plant biomass and productivity with increasing plant diversity. Changes in biodiversity, however, may affect ecosystem processes through trophic interactions among species as well. An important current challenge is to understand how these trophic interactions affect the relationship between biodiversity and ecosystem functioning. Here we present a mechanistic model of an ecosystem with multiple trophic levels in which plants compete for a limiting soil nutrient. In contrast to previous studies that focused on single trophic levels, we show that plant biomass does not always increase with plant diversity and that changes in biodiversity can lead to complex if predictable changes in ecosystem processes. Our analysis demonstrates that food-web structure can profoundly influence ecosystem properties. PMID:14638942
Parasites as prey in aquatic food webs: implications for predator infection and parasite transmission
Thieltges, David W.; Amundsen, Per-Arne; Hechinger, Ryan F.; Johnson, Pieter T.J.; Lafferty, Levin D.; Mouritsen, Kim N.; Preston, Daniel L.; Reise, Karsten; Zander, C. Dieter; Poulin, Robert
While the recent inclusion of parasites into food-web studies has highlighted the role of parasites as consumers, there is accumulating evidence that parasites can also serve as prey for predators. Here we investigated empirical patterns of predation on parasites and their relationships with parasite transmission in eight topological food webs representing marine and freshwater ecosystems. Within each food web, we examined links in the typical predator¢prey sub web as well as the predator¢parasite sub web, i.e. the quadrant of the food web indicating which predators eat parasites. Most predator¢ parasite links represented æconcomitant predationÆ (consumption and death of a parasite along with the prey/host; 58¢72%), followed by ætrophic transmissionÆ (predator feeds on infected prey and becomes infected; 8¢32%) and predation on free-living parasite life-cycle stages (4¢30%). Parasite life-cycle stages had, on average, between 4.2 and 14.2 predators. Among the food webs, as predator richness increased, the number of links exploited by trophically transmitted parasites increased at about the same rate as did the number of links where these stages serve as prey. On the whole, our analyses suggest that predation on parasites has important consequences for both predators and parasites, and food web structure. Because our analysis is solely based on topological webs, determining the strength of these interactions is a promising avenue for future research.
Bioaccumulation of organochlorines in the Arctic marine food web
Hargrave, B.; Phillips, G.; Vass, W.; Harding, G. [Department of Fisheries and Oceans, Dartmouth, Nova Scotia (Canada). Bedford Inst. of Oceanography; Welch, H. [Department of Fisheries and Oceans, Winnipeg, Manitoba (Canada). Freshwater Inst.
Five classes of organochlorine (OC) compounds (hexachlorocyclohexane (HCB and HCHs), cyclodienes, isomers of DDT and its metabolites and congeners of polychlorinated biphenyls (PCBs) and toxaphene (CHBs)) have been detected in under-ice epontic particulate matter and tissue samples of marine biota from lower trophic levels of the Arctic Ocean at sites in Barrow Strait within the Canadian archipelago (75{degree}N), coastal (79{degree}N) and central Arctic basin (85{degree}N) locations. HCBs, PCBs, isomers of DDT and DDE, chlordane, dieldrin, alpha-endosulphan, HCB and {alpha}-HCH were present in quantifiable amounts in all samples. {beta}- and {gamma}-HCH and the cyclodienes aldrin, endrin, heptachlor, heptachlor epoxide, methoxychlor and mirex were detected but could not be quantified. All OCs measured in biota were also present in the Arctic atmosphere, particulate and dissolved fractions of snow, ice melt water and seawater, Small bodied marine organisms such as zooplankton and amphipods which are short-lived have a lower lipid content for storage of OCs than larger animals such as fish and mammals. Biomagnification factors calculated from presumed predator-prey links in the marine food web varied over two orders of magnitude for different OCs. Ratios for epontic particulates and plankton (< 10) were generally lower than values for trophic links between amphipods and published values for arctic marine fish and mammals (10--100). PCBs, DDT and chlordanes are biomagnified in the Arctic marine food web to a far greater degree than more abundant OC compounds such as HCHs and HCB that have a higher water solubility.
Shifts in the trophic base of intermittent stream food webs
Dekar, Matthew; Magoulick, Daniel D.; Huxel, G.R.
Understanding spatial and temporal variation in the trophic base of stream food webs is critical for predicting population and community stability, and ecosystem function. We used stable isotope ratios (13C/12C, and 15N/14N) to characterize the trophic base of two streams in the Ozark Mountains of northwest Arkansas, U.S.A. We predicted that autochthonous resources would be more important during the spring and summer and allochthonous resources would be more important in the winter due to increased detritus inputs from the riparian zone during autumn leaf drop. We predicted that stream communities would demonstrate increased reliance on autochthonous resources at sites with larger watersheds and greater canopy openness. The study was conducted at three low-order sites in the Mulberry River Drainage (watershed area range: 81-232 km2) seasonally in 2006 and 2007. We used circular statistics to examine community-wide shifts in isotope space among fish and invertebrate consumers in relation to basal resources, including detritus and periphyton. Mixing models were used to quantify the relative contribution of autochthonous and allochthonous energy sources to individual invertebrate consumers. Significant isotopic shifts occurred but results varied by season and site indicating substantial variation in the trophic base of stream food webs. In terms of temporal variation, consumers shifted toward periphyton in the summer during periods of low discharge, but results varied during the interval between summer and winter. Our results did not demonstrate increased reliance on periphyton with increasing watershed area or canopy openness, and detritus was important at all the sites. In our study, riffle-pool geomorphology likely disrupted the expected spatial pattern and stream drying likely impacted the availability and distribution of basal resources.
Deep-Sea Research I 51 (2004) 12451274 Carbon fluxes through food webs of the eastern equatorial
Jackson, George
Deep-Sea Research I 51 (2004) 1245Ł1274 Carbon fluxes through food webs of the eastern equatorial inverse and network analyses to examine food web interactions at 0 , 140 W during EqPac time approach allowed us to trace the pathway of fixed carbon through a representative food web
Vander Zanden, Jake
THE EFFECTS OF IMPOUNDMENT AND NON-NATIVE SPECIES ON A RIVER FOOD WEB IN MEXICO'S CENTRAL PLATEAU understanding of food web changes resulting from the introduction of non-native species, flow alteration the effects of non-native species, and reservoirs on food webs of the Laja river ecosystem (Guanajuato
Deleting species from model food webs Christopher Quince, Paul G. Higgs and Alan J. McKane
McKane, Alan
Deleting species from model food webs Christopher Quince, Paul G. Higgs and Alan J. McKane Quince, C., Higgs, P. G. and McKane, A. J. 2005. Deleting species from model food webs. ┴/ Oikos 110: 283┴ causing extinction of further species from the food web. To investigate these effects we used
Journal of Theoretical Biology 252 (2008) 649661 The characteristics of species in an evolutionary food web model
McKane, Alan
food web model Carlos A. Lugo, Alan J. McKane├ Theoretical Physics Group, School of Physics the consequences of modifying the way in which species are defined in an evolutionary food web model explicit features and find that we are still able to grow model food webs. We assess the quality
Preliminary Report: the Tidal Marsh Food Web Report to the San Francisco Bay Fund for the grant
Preliminary Report: the Tidal Marsh Food Web Report to the San Francisco Bay Fund for the grant: Food web pathways of bird contamination in Bay Area tidal marshes. J. Letitia Grenier1 , Joshua N, Oakland, CA 94621-1424. Spring 2002 12 pages #12;PRELIMINARY REPORT: THE TIDAL MARSH FOOD WEB Introduction
Food Web Response to Invasive Species and Hypoxia in Lake Erie, Saginaw Bay Lake Huron, and Southeast Lake Michigan
Food Web Response to Invasive Species and Hypoxia in Lake Erie, Saginaw Bay Lake Huron mussel invasions and hypoxia. We propose to incorporate these data into a food web simulation analysisPath/EcoSim (EwE) (http://www.EcoPath.org) to forecast responses of the food web in each area to different hypoxia
Long-term food web change in Lake Superior Stephanie N. Schmidt, M. Jake Vander Zanden, and James F. Kitchell
Vander Zanden, Jake
and museum-preserved specimens to describe and quantify 100 years of food web changes in the Lake SuperiorLong-term food web change in Lake Superior Stephanie N. Schmidt, M. Jake Vander Zanden, and James F a perspective that considers species within a broader food web context. We used stable isotope analysis
A newly designed web application to illustrate food and physical activity choices
Toronto, University of
A newly designed web application to illustrate food and physical activity choices Alyssa Rosenzweig;ECDRE REU 2007 #12;USDA National Nutrient Database Running, 6mph X -1 hr- Breakfast X + #12;Ę Saved food and activity planners Ę Tab organization #12;Ę Analyze Ł Macro- and micronutrients Ł Food group distribution
From Ontology Selection and Semantic Web to an Integrated Information System for Food-
Peng, Yun
From Ontology Selection and Semantic Web to an Integrated Information System for Food- borne of ontology libraries on food-borne patho- gens and design automatic algorithms with formal inference Diseases and Food Safety Xianghe Yan1,* , Yun Peng2 , Jianghong Meng3 , Juliana Ruzante3 , Pina M
Accumulation of atmospheric and sedimentary PCBs and toxaphene in a Lake Michigan food web.
Stapleton, H M; Masterson, C; Skubinna, J; Ostrom, P; Ostrom, N E; Baker, J E
Seston, sediment, settling organic matter, and food web members were collected from Grand Traverse Bay, Lake Michigan, between April 1997 and September 1998 to examine PCB and toxaphene biomagnification. Stable isotopes of nitrogen and carbon were analyzed in samples and used to establish trophic structure of the food web and to determine the importance of atmospheric versus sedimentary sources in delivering PCBs to the food web. Nitrogen isotopes were confounded by multiple variables in this system, particularly seasonal variation, and did not display a simple pattern of enrichment among trophic levels. However, delta13C displayed little seasonal variation and was positively correlated with PCB concentrations among food web members (r2 = 0.69). Plots of delta13C vs PCBs separate food web members into three distinct groupings comprised of invertebrates, primary forage fish, and predatory fish. Stable isotope values of the primary organic sources indicate that the atmosphere, and not the sediment, is the most likely source of PCBs to the food web of Lake Michigan. Additionally, we suggest that seston may be important in delivering PCBs to pelagic food web members and species that receive a majority of their nutrition through pelagic sources. In contrast, settling particles are implicated in delivering PCBs to benthic organisms and Mysis relicta. PMID:11529566
Designing an illustrated food web to teach ecological concepts: challenges and solutions.
Godkin, C M
The core idea in ecology is that all living things are interconnected. Food webs are an efficient way to communicate this message, and though they can be depicted non-pictorially, illustrated food webs are far more appealing to the general audience. Because of their inherent complexity, however, they present a considerable organizational and design challenge for the illustrator. Based on seven years of teaching illustrated food webs to students in Biomedical Communications at the University of Toronto, this paper outlines those challenges and presents solutions. PMID:10216827
Topics include Southern Ocean food web & trophic interactions
Brierley, Andrew
Expedition vessel from Ushuaia to Antarctica Extras: Payment of expedition fee (international travel, land & marine mammal & sea bird distribution in Antarctica Anthropogenic effects on Antarctic ecosystem Tutorials during & post-expedition Assessment (100% CA) Podcast on selected field course topic Practical
A synthesis of bentho-pelagic coupling on the Antarctic shelf: Food banks, ecosystem inertia and global climate change
Craig R. Smith; Sarah Mincks; David J. Demaster
The Antarctic continental shelf is large, deep (500 1000 m), and characterized by extreme seasonality in sea-ice cover and primary production. Intense seasonality and short pelagic foodwebs on the Antarctic shelf may favor strong bentho-pelagic coupling, whereas unusual water depth combined with complex topography and circulation could cause such coupling to be weak. Here, we address six questions regarding the
Fluorinated organic compounds in an eastern Arctic marine food web.
Tomy, Gregg T; Budakowski, Wes; Halldorson, Thor; Helm, Paul A; Stern, Gary A; Friesen, Ken; Pepper, Karen; Tittlemier, Sheryl A; Fisk, Aaron T
An eastern Arctic marine food web was analyzed for perfluorooctanesulfonate (PFOS, C8F17SO3-), perfluorooctanoate (PFOA, C7F15COO-), perfluorooctane sulfonamide (PFOSA, C8F17SO2NH2), and N-ethylperfluorooctane sulfonamide (N-EtPFOSA, C8F17SO2NHCH2CH3) to examine the extent of bioaccumulation. PFOS was detected in all species analyzed, and mean concentrations ranged from 0.28 +/- 0.09 ng/g (arithmetic mean +/- 1 standard error, wet wt, whole body) in clams (Mya truncata) to 20.2 +/- 3.9 ng/g (wet wt, liver) in glaucous gulls (Larus hyperboreus). PFOA was detected in approximately 40% of the samples analyzed at concentrations generally smaller than those found for PFOS; the greatest concentrations were observed in zooplankton (2.6 +/- 0.3 ng/g, wet wt). N-EtPFOSA was detected in all species except redfish with mean concentrations ranging from 0.39 +/- 0.07 ng/g (wet wt) in mixed zooplankton to 92.8 +/- 41.9 ng/g (wet wt) in Arctic cod (Boreogadus saida). This is the first report of N-EtPFOSA in Arctic biota. PFOSA was only detected in livers of beluga (Delphinapterus leucas) (20.9 +/- 7.9 ng/g, wet wt) and narwhal (Monodon monoceros) (6.2 +/- 2.3 ng/g, wet wt), suggesting that N-EtPFOSA and other PFOSA-type precursors are likely present but are being biotransformed to PFOSA. A positive linear relationship was found between PFOS concentrations (wet wt) and trophic level (TL), based on delta15N values, (r2 = 0.51, p < 0.0001) resulting in a trophic magnification factor of 3.1. TL-corrected biomagnification factor estimates for PFOS ranged from 0.4 to 9. Both results indicate that PFOS biomagnifies in the Arctic marine food web when liver concentrations of PFOS are used for seabirds and marine mammals. However, transformation of N-EtPFOSA and PFOSA and potential other perfluorinated compounds to PFOS may contribute to PFOS levels in marine mammals and may inflate estimated biomagnification values. None of the other fluorinated compounds (N-EtPFOSA, PFOSA, and PFOA) were found to have a significant relationship with TL, but BMF(TL) values of these compounds were often >1, suggesting potential for these compounds to biomagnify. The presence of perfluorinated compounds in seabirds and mammals provides evidence that trophic transfer is an important exposure route of these chemicals to Arctic biota. PMID:15669302
Analysis of governmental Web sites on food safety issues: a global perspective.
Namkung, Young; Almanza, Barbara A
Despite a growing concern over food safety issues, as well as a growing dependence on the Internet as a source of information, little research has been done to examine the presence and relevance of food safety-related information on Web sites. The study reported here conducted Web site analysis in order to examine the current operational status of governmental Web sites on food safety issues. The study also evaluated Web site usability, especially information dimensionalities such as utility, currency, and relevance of content, from the perspective of the English-speaking consumer. Results showed that out of 192 World Health Organization members, 111 countries operated governmental Web sites that provide information about food safety issues. Among 171 searchable Web sites from the 111 countries, 123 Web sites (71.9 percent) were accessible, and 81 of those 123 (65.9 percent) were available in English. The majority of Web sites offered search engine tools and related links for more information, but their availability and utility was limited. In terms of content, 69.9 percent of Web sites offered information on foodborne-disease outbreaks, compared with 31.5 percent that had travel- and health-related information. PMID:17066944
Dispersed oil disrupts microbial pathways in pelagic food webs.
Ortmann, Alice C; Anders, Jennifer; Shelton, Naomi; Gong, Limin; Moss, Anthony G; Condon, Robert H
Most of the studies of microbial processes in response to the Deepwater Horizon oil spill focused on the deep water plume, and not on the surface communities. The effects of the crude oil and the application of dispersants on the coastal microbial food web in the northern Gulf of Mexico have not been well characterized even though these regions support much of the fisheries production in the Gulf. A mesocosm experiment was carried out to determine how the microbial community off the coast of Alabama may have responded to the influx of surface oil and dispersants. While the addition of glucose or oil alone resulted in an increase in the biomass of ciliates, suggesting transfer of carbon to higher trophic levels was likely; a different effect was seen in the presence of dispersant. The addition of dispersant or dispersed oil resulted in an increase in the biomass of heterotrophic prokaryotes, but a significant inhibition of ciliates, suggesting a reduction in grazing and decrease in transfer of carbon to higher trophic levels. Similar patterns were observed in two separate experiments with different starting nutrient regimes and microbial communities suggesting that the addition of dispersant and dispersed oil to the northern Gulf of Mexico waters in 2010 may have reduced the flow of carbon to higher trophic levels, leading to a decrease in the production of zooplankton and fish on the Alabama shelf. PMID:22860136
Mercury in the Pelagic Food Web of Lake Champlain
Chen, Celia; Kamman, Neil; Shanley, James; Chalmers, Ann; Jackson, Brian; Taylor, Vivien; Smeltzer, Eric; Stangel, Pete; Shambaugh, Angela
Lake Champlain continues to experience mercury contamination resulting in public advisories to limit human consumption of top trophic level fish such as walleye. Prior research suggested that mercury levels in biota could be modified by differences in ecosystem productivity as well as mercury loadings. We investigated relationships between mercury in different trophic levels in Lake Champlain. We measured inorganic and methyl mercury in water, seston, and two size fractions of zooplankton from 13 sites representing a range of nutrient loading conditions and productivity. Biomass varied significantly across lake segments in all measured ecosystem compartments in response to significant differences in nutrient levels. Local environmental factors such as alkalinity influenced the partitioning of mercury between water and seston. Mercury incorporation into biota was influenced by the biomass and mercury content of different ecosystem strata. Pelagic fish tissue mercury was a function of fish length and the size of the mercury pool associated with large zooplankton. We used these observations to parameterize a model of mercury transfers in the Lake Champlain food web that accounts for ecosystem productivity effects. Simulations using the mercury trophic transfer model suggest that reductions of 25 to 75% in summertime dissolved eplimnetic total mercury will likely allow fish tissue mercury concentrations to drop to the target level of 0.3 Ąg g?1 in a 40-cm fish in all lake segments. Changes in nutrient loading and ecosystem productivity in eutrophic segments may delay any response to reduced dissolved mercury and may result in increases in fish tissue mercury. PMID:22193540
Experimental demonstration of chaos in a microbial food web.
Becks, Lutz; Hilker, Frank M; Malchow, Horst; J³rgens, Klaus; Arndt, Hartmut
Discovering why natural population densities change over time and vary with location is a central goal of ecological and evolutional disciplines. The recognition that even simple ecological systems can undergo chaotic behaviour has made chaos a topic of considerable interest among theoretical ecologists. However, there is still a lack of experimental evidence that chaotic behaviour occurs in the real world of coexisting populations in multi-species systems. Here we study the dynamics of a defined predator-prey system consisting of a bacterivorous ciliate and two bacterial prey species. The bacterial species preferred by the ciliate was the superior competitor. Experimental conditions were kept constant with continuous cultivation in a one-stage chemostat. We show that the dynamic behaviour of such a two-prey, one-predator system includes chaotic behaviour, as well as stable limit cycles and coexistence at equilibrium. Changes in the population dynamics were triggered by changes in the dilution rates of the chemostat. The observed dynamics were verified by estimating the corresponding Lyapunov exponents. Such a defined microbial food web offers a new possibility for the experimental study of deterministic chaos in real biological systems. PMID:15988524
Dispersed Oil Disrupts Microbial Pathways in Pelagic Food Webs
Ortmann, Alice C.; Anders, Jennifer; Shelton, Naomi; Gong, Limin; Moss, Anthony G.; Condon, Robert H.
Most of the studies of microbial processes in response to the Deepwater Horizon oil spill focused on the deep water plume, and not on the surface communities. The effects of the crude oil and the application of dispersants on the coastal microbial food web in the northern Gulf of Mexico have not been well characterized even though these regions support much of the fisheries production in the Gulf. A mesocosm experiment was carried out to determine how the microbial community off the coast of Alabama may have responded to the influx of surface oil and dispersants. While the addition of glucose or oil alone resulted in an increase in the biomass of ciliates, suggesting transfer of carbon to higher trophic levels was likely; a different effect was seen in the presence of dispersant. The addition of dispersant or dispersed oil resulted in an increase in the biomass of heterotrophic prokaryotes, but a significant inhibition of ciliates, suggesting a reduction in grazing and decrease in transfer of carbon to higher trophic levels. Similar patterns were observed in two separate experiments with different starting nutrient regimes and microbial communities suggesting that the addition of dispersant and dispersed oil to the northern Gulf of Mexico waters in 2010 may have reduced the flow of carbon to higher trophic levels, leading to a decrease in the production of zooplankton and fish on the Alabama shelf. PMID:22860136
Spatial Differences in East Scotia Ridge Hydrothermal Vent Food Webs: Influences of Chemistry, Microbiology and Predation on Trophodynamics
Reid, William D. K.; Sweeting, Christopher J.; Wigham, Ben D.; Zwirglmaier, Katrin; Hawkes, Jeffrey A.; McGill, Rona A. R.; Linse, Katrin; Polunin, Nicholas V. C.
The hydrothermal vents on the East Scotia Ridge are the first to be explored in the Antarctic and are dominated by large peltospiroid gastropods, stalked barnacles (Vulcanolepas sp.) and anomuran crabs (Kiwa sp.) but their food webs are unknown. Vent fluid and macroconsumer samples were collected at three vent sites (E2, E9N and E9S) at distances of tens of metres to hundreds of kilometres apart with contrasting vent fluid chemistries to describe trophic interactions and identify potential carbon fixation pathways using stable isotopes. ?13C of dissolved inorganic carbon from vent fluids ranged from ?4.6ē to 0.8ē at E2 and from ?4.4ē to 1.5ē at E9. The lowest macroconsumer ?13C was observed in peltospiroid gastropods (?30.0ē to ?31.1ē) and indicated carbon fixation via the Calvin-Benson-Bassham (CBB) cycle by endosymbiotic gamma-Proteobacteria. Highest ?13C occurred in Kiwa sp. (?19.0ē to ?10.5ē), similar to that of the epibionts sampled from their ventral setae. Kiwa sp. ?13C differed among sites, which were attributed to spatial differences in the epibiont community and the relative contribution of carbon fixed via the reductive tricarboxylic acid (rTCA) and CBB cycles assimilated by Kiwa sp. Site differences in carbon fixation pathways were traced into higher trophic levels e.g. a stichasterid asteroid that predates on Kiwa sp. Sponges and anemones at the periphery of E2 assimilated a proportion of epipelagic photosynthetic primary production but this was not observed at E9N. Differences in the ?13C and ?34S values of vent macroconsumers between E2 and E9 sites suggest the relative contributions of photosynthetic and chemoautotrophic carbon fixation (rTCA v CBB) entering the hydrothermal vent food webs vary between the sites. PMID:23762393
Spatial differences in East scotia ridge hydrothermal vent food webs: influences of chemistry, microbiology and predation on trophodynamics.
Reid, William D K; Sweeting, Christopher J; Wigham, Ben D; Zwirglmaier, Katrin; Hawkes, Jeffrey A; McGill, Rona A R; Linse, Katrin; Polunin, Nicholas V C
The hydrothermal vents on the East Scotia Ridge are the first to be explored in the Antarctic and are dominated by large peltospiroid gastropods, stalked barnacles (Vulcanolepas sp.) and anomuran crabs (Kiwa sp.) but their food webs are unknown. Vent fluid and macroconsumer samples were collected at three vent sites (E2, E9N and E9S) at distances of tens of metres to hundreds of kilometres apart with contrasting vent fluid chemistries to describe trophic interactions and identify potential carbon fixation pathways using stable isotopes. ?(13)C of dissolved inorganic carbon from vent fluids ranged from -4.6ē to 0.8ē at E2 and from -4.4ē to 1.5ē at E9. The lowest macroconsumer ?(13)C was observed in peltospiroid gastropods (-30.0ē to -31.1ē) and indicated carbon fixation via the Calvin-Benson-Bassham (CBB) cycle by endosymbiotic gamma-Proteobacteria. Highest ?(13)C occurred in Kiwa sp. (-19.0ē to -10.5ē), similar to that of the epibionts sampled from their ventral setae. Kiwa sp. ?(13)C differed among sites, which were attributed to spatial differences in the epibiont community and the relative contribution of carbon fixed via the reductive tricarboxylic acid (rTCA) and CBB cycles assimilated by Kiwa sp. Site differences in carbon fixation pathways were traced into higher trophic levels e.g. a stichasterid asteroid that predates on Kiwa sp. Sponges and anemones at the periphery of E2 assimilated a proportion of epipelagic photosynthetic primary production but this was not observed at E9N. Differences in the ?(13)C and ?(34)S values of vent macroconsumers between E2 and E9 sites suggest the relative contributions of photosynthetic and chemoautotrophic carbon fixation (rTCA v CBB) entering the hydrothermal vent food webs vary between the sites. PMID:23762393
Rapid food web recovery in response to removal of an introduced apex predator
Kraft, Clifford E.
a native apex predator (lake trout (Salvelinus namaycush)) were used to measure food web changes following d'un prķdateur du sommet du rķseau alimentaire (le touladi, Salvelinus namaycush) nous servent Ó
Quantification and Resolution of a Complex, Size-Structured Food Web
Mottram, Nigel
trophic status) bias in less exhaustively sampled webs. Trivariate relationships between body size. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 B. Estimation of Abundance and Biomass of Trophic Elements . . . . 94 C. Construction of the Food
javaFoodWeb: Bridging the gap between Excel and Niches
NSDL National Science Digital Library
Vince Steif (University of Wisconsin-- Madison; )
javaFoodWeb is a portable application that will take data from an Excel spreadsheet showing Predators (consumers) and the Prey (resources) which they depend upon and allow students to visualize the competition spaces (niches) that they define.
Large River Food Webs: Influence of Nutrients, Turbidity, and Flow, and Implications for ManagementĀ
Roach, Katherine
factor influencing river ecology. In Chapter II, I reviewed the scientific literature to test conceptual models of river food webs and predictions of environmental factors that might produce variation in basal production sources supporting consumer...
Food web interactions between larval bluegill (Lepomis macrochirus) and exotic zebra mussels
Food web interactions between larval bluegill (Lepomis macrochirus) and exotic zebra mussels (Lepomis macrochirus), exotic invasive zebra mussels (Dreissena polymorpha), and zooplankton were examined a servi Ó ķtudier les relations trophiques entre les larves de crapets arlequins (Lepomis macrochirus
Reducing Methylmercury Accumulation in the Food Webs of San Francisco Bay and Its Local Watershed
it into the food web Ę Sediment from historic mining regions is clearly a concern Ę Elemental Hg from gold mining.5 Louisiana Narragansett Bay Chesapeake Bay South Carolina New Jersey San Francisco Bay Mercury (ppm wet
Food Web Structure and Habitat Connectivity in Fish Estuarine NurseriesŚImpact of River Flow
Catarina Vinagre; JoŃo Salgado; Henrique N. Cabral; Maria J. Costa
River flow variability is known to influence estuarine production, yet knowledge on its effect upon estuarine food webs dynamics\\u000a is still scarce. Stable carbon and nitrogen isotopes were used to assess the effect of river flow in the connectivity and\\u000a food web interactions between the two main fish nursery areas of the Tagus estuary. The aims of the present work
Influence of decomposer food web structure and nitrogen availability on plant growth
Jouni Laakso; Heikki Setõlõ; Ansa Palojõrvi
We studied the sensitivity of soil microbial communities and ecosystem processes to variation in the vertical and horizontal\\u000a structure of decomposer food web under nitrogen poor and N-enriched conditions. Microcosms with humus and litter layer of\\u000a boreal forest floor, birch seedlings infected with mycorrhizal fungi, and decomposer food webs with differing trophic group\\u000a and species composition of soil fauna were
Initial impacts of Microcystis aeruginosa blooms on the aquatic food web in the San Francisco Estuary
P. W. LehmanS; S. J. Teh; G. L. Boyer; M. L. Nobriga; E. Bass; C. Hogle
The impact of the toxic cyanobacterium Microcystis\\u000a aeruginosa on estuarine food web production in San Francisco Estuary is unknown. It is hypothesized that Microcystis contributed to a recent decline in pelagic organisms directly through its toxicity or indirectly through its impact on the\\u000a food web after 1999. In order to evaluate this hypothesis, phytoplankton, cyanobacteria, zooplankton, and fish were collected
Ontogenetic niche shift, food-web coupling, and alternative stable states
Takefumi Nakazawa
Several recent studies have shown that food web coupling by ontogenetic niche shifts can generate alternative stable states\\u000a (ASS). However, these studies mainly considered cases where juvenile and adult stages are the top level consumers. The conditions\\u000a under which ASS occur in more structurally diverse food web configurations have not been explored. In this study, I examine\\u000a the influence of
Interplay of omnivory, energy channels and C availability in a microbial-based soil food web
J. Mikola; H. Setõlõ
To study the effects of omnivory on the structure and function of soil food webs and on the control of trophic-level biomasses\\u000a in soil, two food webs were established in microcosms. The first one contained fungi, bacteria, a fungivorous nematode (Aphelenchoides saprophilus) and a bacterivorous nematode (Caenorhabditis elegans), and the second one fungi, bacteria, the fungivore and an omnivorous nematode
Food web manipulation without nutrient control: A useful strategy in lake restoration?
Jiirgen Benndorf; Sektion Wasserwesen
The results of long-term, full-scale experiments in biomanipulation (in the closer sense of top-down control of the food web)\\u000a in water bodies having extremely different phosphorus loads reveal that there is a close connection between the efficiency\\u000a of food web manipulation and the nutrient situation in the particular water body. Top-down control provides a high probability\\u000a of improving water quality
Food web structure in exotic and native mangroves: a Hawaii¢Puerto Rico comparison
Amanda W. J. Demopoulos; Brian Fry; Craig R. Smith
Plant invasions can fundamentally alter detrital inputs and the structure of detritus-based food webs. We examined the detrital\\u000a pathways in mangrove food webs in native (Puerto Rican) and introduced (Hawaiian) Rhizophora mangle forests using a dual isotope approach and a mixing model. Based on trophic-level fractionation of 0¢1ē for ?\\u000a 13C and 2¢3ē for ?\\u000a 15N, among the invertebrates, only
Body size and food web structure: testing the equiprobability assumption of the cascade model
Michael G. Neubert; Steven C. Blumenshine; Daniel E. Duplisea; Tomas Jonsson; Brenda Rashleigh
The cascade model successfuly predicts many patterns in reported food webs. A key assumption of this model is the existence\\u000a of a predetermined trophic hierarchy; prey are always lower in the hierarchy than their predators. At least three studies\\u000a have suggested that, in animal food webs, this hierarchy can be explained to a large extent by body size relationships. A
Effects of habitat configuration on host¢parasitoid food web structure
Masashi Murakami; Toshihide Hirao; Akiko Kasei
The dispersal of organisms among patches affects community structure in spatially heterogeneous habitats. The enhancement\\u000a of dispersal frequency among patches can be expected to increase potential interaction between organisms in food webs. However,\\u000a it has been difficult to fairly evaluate the effects of dispersal on the food web structure because the quantification of\\u000a actual dispersal is difficult. In this study,
Contributions of stable-isotope data to elucidating food webs of Mediterranean rocky littoral fishes
John K. Pinnegar; N. V. C. Polunin
The food webs of rocky infra-littoral ecosystems in the Mediterranean have been little studied. In this investigation stable\\u000a isotopes and dietary data were compared in an attempt to describe features of the food webs concerned. ?13C and ?15N were determined for plants, invertebrates and fishes from the Bay of Calvi, Corsica. Dietary data were derived from the\\u000a literature. ?13C of
Food web of macroinvertebrate community in a Yangtze shallow lake: trophic basis and pathways
Xue-Qin Liu; Hong-Zhu Wang; Xiao-Min Liang
No detailed food web research on macroinvertebrate community of lacustrine ecosystem was reported in China. The present study\\u000a is the first attempt on the subject in Lake Biandantang, a macrophytic lake in Hubei Province. Food webs of the macroinvertebrate\\u000a community were compiled bimonthly from March, 2002 to March, 2003. Dietary information was obtained from gut analysis. Linkage\\u000a strength was quantified
Indirect Effects of Fishery Exploitation and Pest Control in a Riverine Food Web
Michael J. Roell; Donald J. Orth
We used an energy-based food web model to evaluate indirect effects of fishery exploitation and aquatic insect pest control on food web structure and recreational fisheries in the New River, West Virginia. Key groups represented in the model were aquatic insects, age-1 and age-2 crayfish (Cambaridae), age-1 and age-2 larvae of the dobsonfly Corydalus cornutus (hellgrammites), prey fishes, and age-0
The Bioenergetic Consequences of Invasive-Induced Food Web Disruption to Lake Ontario Alewives
Thomas J. Stewart; Robert OGorman; W. Gary Sprules; B. F. Lantry
Alewives Alosa pseudoharengus are the dominant prey fish in Lake Ontario, and their response to ecological change can alter the structure and function of the Lake Ontario food web. Using stochastic population-based bioenergetic models of Lake Ontario alewives for 1987¢1991 and 2001¢2005, we evaluated changes to alewife production, consumption, and associated bioenergetic ratios after invasive-induced food web disruption. After the
Simple predator¢prey interactions control dynamics in a plankton food web model
Roger Cropp; John Norbury
A plankton food web model is analysed using interaction parameter values appropriate to the upper mixed layer of the high latitude oceans. The dynamics of this four-variable system are analysed in terms of the dynamics of much simpler two-variable predator¢prey subsystems. Thus, the food web's robust, periodic, four-dimensional dynamics are explained by means of two-dimensional spirals and limit cycles. These
13 C label identifies eelgrass ( Zostera marina ) Carbon in an Alaskan estuarine food web
T. McConnaughey; C. P. McRoy
The food web of Izembek Lagoon, Alaska draws most of its carbon from eelgrass (Zostera marina) and phytoplankton. The13C:12C ratios of these primary producers are sufficiently different to enable their contributions to consumers to be estimated from consumer13C:12C ratios. Although the technique is conceptually simple, carbon inputs from other sources and isotope fractionations occurring in the food web limit its
Drifting plankton from a reservoir subsidize downstream food webs and alter community structure
Hideyuki Doi; Kwang-Hyeon Chang; Takamitsu Ando; Hiroyuki Imai; Shin-ichi Nakano; Akio Kajimoto; Izumi Katano
Subsidy between ecosystems has been considered in many natural ecosystems, and should alter food webs and communities in human-impacted\\u000a ones. We estimated how drifting plankton from a reservoir contribute to downstream food webs and showed that they alter community\\u000a structures over a 10-km reach below the dam. To estimate the contribution of the drifting plankton to macroinvertebrates,\\u000a we used C
Nutrient Enrichment and Food Web Composition Affect Ecosystem Metabolism in an Experimental Seagrass Habitat
Amanda C. Spivak; Elizabeth A. Canuel; J. Emmett Duffy; J. Paul Richardson; John F. Bruno
BackgroundFood web composition and resource levels can influence ecosystem properties such as productivity and elemental cycles. In particular, herbivores occupy a central place in food webs as the species richness and composition of this trophic level may simultaneously influence the transmission of resource and predator effects to higher and lower trophic levels, respectively. Yet, these interactions are poorly understood.Methodology\\/Principal FindingsUsing
Use of an Integrated Mercury Food Web Model for Ecological Risk Assessment
John G. Hunter; Joanna Burger; Keith R. Cooper
We developed an integrated food web model for mercury, using the CATS (Contaminants in Aquatic and Terrestrial ecoSytems) model developed by Traas and co-workers (Traas, T.P.; Stõb, J.A.; Kramer, P.R.G.; Cofino, W.P.; Aldenberg, T. Modeling and risk assessment of tributyltin accumulation in the food web of a shallow freshwater lake. Environ. Sci. Technol. 1996, 30 (4), 1227¢1237). It was translated
Does Microorganism Stoichiometry Predict Microbial Food Web Interactions After a Phosphorus Pulse?
Presentaci¾n Carrillo; Manuel Villar-Argaiz; Juan M. Medina-Sßnchez
Knowledge of variations in microbial food web interactions resulting from atmospheric nutrient loads is crucial to improve\\u000a our understanding of aquatic food web structure in pristine ecosystems. Three experiments mimicking atmospheric inputs at\\u000a different nitrogen\\/phosphorus (N\\/P) ratios were performed in situ covering the seasonal biological succession of the pelagic zone in a high-mountain Spanish lake. In all experiments, abundance,\\u000a biomass,
Examining the potential effects of species aggregation on the network structure of food webs
Ken Arii; Raphaļlle Derome; Lael Parrott
One of the key measures that have been used to describe the topological properties of complex networks is the ōdegree distributionö\\u000a which is a measure that describes the frequency distribution of number of links per node. Food webs are complex ecological\\u000a networks that describe the trophic relationships among species in a community, and the topological properties of empirical\\u000a food webs,
A trophic cascade in a macrophyte-based food web at the land¢water ecotone
Thomas A. Schlacher; Greg Cronin
Trophic cascades may purportedly be more common in aquatic than terrestrial food webs, but herbivory on freshwater vascular\\u000a plants has historically been considered low. Water lilies are an exception, suffering severe grazing damage by leaf beetles.\\u000a To test whether a central prediction of cascade modelsŚthat predator effects propagate downwards to plantsŚoperates in a macrophyte-based\\u000a food web, we experimentally manipulated predation
Freshness matters: in flowers, food, and web authority
Na Dai; Brian D. Davison
The collective contributions of billions of users across the globe each day result in an ever-changing web. In verticals like news and real-time search, recency is an obvious significant factor for ranking. However, traditional link-based web ranking algorithms typically run on a single web snapshot without concern for user activities associated with the dynamics of web pages and links. Therefore,
Food web topology and parasites in the pelagic zone of a subarctic lake.
Amundsen, Per-Arne; Lafferty, Kevin D; Knudsen, Rune; Primicerio, Raul; Klemetsen, Anders; Kuris, Armand M
1. Parasites permeate trophic webs with their often complex life cycles, but few studies have included parasitism in food web analyses. Here we provide a highly resolved food web from the pelagic zone of a subarctic lake and explore how the incorporation of parasites alters the topology of the web. 2. Parasites used hosts at all trophic levels and increased both food-chain lengths and the total number of trophic levels. Their inclusion in the network analyses more than doubled the number of links and resulted in an increase in important food-web characteristics such as linkage density and connectance. 3. More than half of the parasite taxa were trophically transmitted, exploiting hosts at multiple trophic levels and thus increasing the degree of omnivory in the trophic web. 4. For trophically transmitted parasites, the number of parasite-host links exhibited a positive correlation with the linkage density of the host species, whereas no such relationship was seen for nontrophically transmitted parasites. Our findings suggest that the linkage density of free-living species affects their exposure to trophically transmitted parasites, which may be more likely to adopt highly connected species as hosts during the evolution of complex life cycles. 5. The study supports a prominent role for parasites in ecological networks and demonstrates that their incorporation may substantially alter considerations of food-web structure and functioning. PMID:19175443
Food web topology and parasites in the pelagic zone of a subarctic lake
Amundsen, P.-A.; Lafferty, K.D.; Knudsen, R.; Primicerio, R.; Klemetsen, A.; Kuris, A.M.
Parasites permeate trophic webs with their often complex life cycles, but few studies have included parasitism in food web analyses. Here we provide a highly resolved food web from the pelagic zone of a subarctic lake and explore how the incorporation of parasites alters the topology of the web. 2. Parasites used hosts at all trophic levels and increased both food-chain lengths and the total number of trophic levels. Their inclusion in the network analyses more than doubled the number of links and resulted in an increase in important food-web characteristics such as linkage density and connectance. 3. More than half of the parasite taxa were trophically transmitted, exploiting hosts at multiple trophic levels and thus increasing the degree of omnivory in the trophic web. 4. For trophically transmitted parasites, the number of parasite-host links exhibited a positive correlation with the linkage density of the host species, whereas no such relationship was seen for nontrophically transmitted parasites. Our findings suggest that the linkage density of free-living species affects their exposure to trophically transmitted parasites, which may be more likely to adopt highly connected species as hosts during the evolution of complex life cycles. 5. The study supports a prominent role for parasites in ecological networks and demonstrates that their incorporation may substantially alter considerations of food-web structure and functioning. ?? 2009 British Ecological Society.
Intraguild predation, invertebrate predators, and trophic cascades in lake food webs.
Hart, Deborah
The top-down and bottom-up properties of model food webs that include intraguild predation and self-limiting factors such as cannibalism are investigated. Intraguild predation can dampen or even reverse the top-down effects predicted by food chain theory. The degree of self-limitation among the intraguild prey is a key factor in determining the direction and strength of the top-down response. Intraguild predation and self-limiting factors can also substantially alter the bottom-up effects of enrichment. These results can help explain the disparate results of trophic cascade experiments in lakes, where cascades are usually seen when large Daphnia are the primary herbivores, but not when smaller-bodied herbivores are dominant. Top-down manipulations should cascade at least modestly to phytoplankton in those lakes whose food web can be reasonably approximated by a chain (typically, those where Daphnia is the dominant herbivore), as predicted by food chain theory. On the other hand, smaller-bodied zooplankton are often preyed upon heavily by invertebrate predators as well as by planktivorous fish, thereby introducing elements of intraguild predation into these food webs. In this case, conventional food chain theory is likely to give incorrect predictions. Very large cascade effects may be due primarily to regime shifts between intraguild predation-dominated food webs and those that more resemble food chains, rather than due to the simple food chain cascade usually considered. PMID:12297074
Towards a framework for assessment and management of cumulative human impacts on marine food webs.
Giakoumi, Sylvaine; Halpern, Benjamin S; Michel, Lo'c N; Gobert, Sylvie; Sini, Maria; Boudouresque, Charles-Franńois; Gambi, Maria-Cristina; Katsanevakis, Stelios; Lejeune, Pierre; Montefalcone, Monica; Pergent, Gerard; Pergent-Martini, Christine; Sanchez-Jerez, Pablo; Velimirov, Branko; Vizzini, Salvatrice; Abadie, Arnaud; Coll, Marta; Guidetti, Paolo; Micheli, Fiorenza; Possingham, Hugh P
Effective ecosystem-based management requires understanding ecosystem responses to multiple human threats, rather than focusing on single threats. To understand ecosystem responses to anthropogenic threats holistically, it is necessary to know how threats affect different components within ecosystems and ultimately alter ecosystem functioning. We used a case study of a Mediterranean seagrass (Posidonia oceanica) food web and expert knowledge elicitation in an application of the initial steps of a framework for assessment of cumulative human impacts on food webs. We produced a conceptual seagrass food web model, determined the main trophic relationships, identified the main threats to the food web components, and assessed the components' vulnerability to those threats. Some threats had high (e.g., coastal infrastructure) or low impacts (e.g., agricultural runoff) on all food web components, whereas others (e.g., introduced carnivores) had very different impacts on each component. Partitioning the ecosystem into its components enabled us to identify threats previously overlooked and to reevaluate the importance of threats commonly perceived as major. By incorporating this understanding of system vulnerability with data on changes in the state of each threat (e.g., decreasing domestic pollution and increasing fishing) into a food web model, managers may be better able to estimate and predict cumulative human impacts on ecosystems and to prioritize conservation actions. PMID:25704365
Predators, parasitoids and pathogens: species richness, trophic generality and body sizes in a natural food web
J. Memmott; N. D. Martinez; J. E. Cohen
Summary 1. A food web is presented which describes trophic interactions among the herbi- vores, parasitoids, predators and pathogens associated with broom, Cytisus scopar- ius (L.) Link. The data come from published work on the community at a single site. The web comprises a total of 154 taxa: one plant, 19 herbivores, 66 parasi- toids, 60 predators, five omnivores and
Predicting abundance¢body size relationships in functional and taxonomic subsets of food webs
T. A. D. Maxwell; S. Jennings
Abundance¢body size relationships are widely observed macroecological patterns in complete food webs and in taxonomically or functionally defined subsets of those webs. Observed abundance¢body size relationships have frequently been compared with predictions based on the energetic equivalence hypothesis and, more recently, with predictions based on energy availability to different body size classes. Here, we consider the ways in which working
Trophic transfer of metals along freshwater food webs: Evidence of cadmium biomagnification in nature
Croteau, M.-N.; Luoma, S.N.; Stewart, A.R.
We conducted a study with cadmium (Cd) and copper (Cu) in the delta of San Francisco Bay, using nitrogen and carbon stable isotopes to identify trophic position and food web structure. Cadmium is progressively enriched among trophic levels in discrete epiphyte-based food webs composed of macrophyte-dwelling invertebrates (the first link being epiphytic algae) and fishes (the first link being gobies). Cadmium concentrations were biomagnified 15 times within the scope of two trophic links in both food webs. Trophic enrichment in invertebrates was twice that of fishes. No tendency toward trophic-level enrichment was observed for Cu, regardless of whether organisms were sorted by food web or treated on a taxonomic basis within discrete food webs. The greatest toxic effects of Cd are likely to occur with increasing trophic positions, where animals are ingesting Cd-rich prey (or food). In Franks Tract this occurs within discrete food chains composed of macrophyte-dwelling invertebrates or fishes inhabiting submerged aquatic vegetation. Unraveling ecosystem complexity is necessary before species most exposed and at risk can be identified. ?? 2005, by the American Society of Limnology and Oceanography, Inc.
Stable nitrogen isotopic composition of amino acids reveals food web structure in stream ecosystems.
Ishikawa, Naoto F; Kato, Yoshikazu; Togashi, Hiroyuki; Yoshimura, Mayumi; Yoshimizu, Chikage; Okuda, Noboru; Tayasu, Ichiro
The stable N isotopic composition of individual amino acids (SIAA) has recently been used to estimate trophic positions (TPs) of animals in several simple food chain systems. However, it is unknown whether the SIAA is applicable to more complex food web analysis. In this study we measured the SIAA of stream macroinvertebrates, fishes, and their potential food sources (periphyton and leaf litter of terrestrial C3 plants) collected from upper and lower sites in two streams having contrasting riparian landscapes. The stable N isotope ratios of glutamic acid and phenylalanine confirmed that for primary producers (periphyton and C3 litter) the TP was 1, and for primary consumers (e.g., mayfly and caddisfly larvae) it was 2. We built a two-source mixing model to estimate the relative contributions of aquatic and terrestrial sources to secondary and higher consumers (e.g., stonefly larva and fishes) prior to the TP calculation. The estimated TPs (2.3-3.5) roughly corresponded to their omnivorous and carnivorous feeding habits, respectively. We found that the SIAA method offers substantial advantages over traditional bulk method for food web analysis because it defines the food web structure based on the metabolic pathway of amino groups, and can be used to estimate food web structure under conditions where the bulk method cannot be used. Our result provides evidence that the SIAA method is applicable to the analysis of complex food webs, where heterogeneous resources are mixed. PMID:24719209
Food-web structure in two shallow salt lakes in Los Monegros (NE Spain): energetic vs dynamic constraints
Paloma Alcorlo; Angel Baltanßs; Carlos Montes
Energetic and dynamic constraints have been proposed as rival factors in determining food-web structure. Food-web length might be controlled either by the amount of energy entering the web (energetic constraints) or by time span between consecutive disturbances relative to time needed to build up a population (dynamic constraints). Dynamic constraints are identified with processes functioning at a regional scale such
A synthesis of bentho-pelagic coupling on the Antarctic shelf: Food banks, ecosystem inertia and global climate change
Craig R. Smith; Sarah Mincks; David J. DeMaster
The Antarctic continental shelf is large, deep (500¢1000m), and characterized by extreme seasonality in sea-ice cover and primary production. Intense seasonality and short pelagic foodwebs on the Antarctic shelf may favor strong bentho-pelagic coupling, whereas unusual water depth combined with complex topography and circulation could cause such coupling to be weak. Here, we address six questions regarding the nature and
Biogeochemistry and the structure of tropical brown food webs.
Kaspari, Michael; Yanoviak, Stephen P
Litter invertebrates are notoriously patchy at small scales. Here we show that the abundance of 10 litter taxa also varies 100-fold at landscape and regional scales across 26 forest stands in Peru and Panama. We contrast three hypotheses that link gradients of abundance to ecosystem biogeochemistry. Of 14 factors considered (12 chemical elements, plus fiber and litter depth), four best predicted the abundance of litter invertebrates. In the Secondary Productivity Hypothesis, phosphorus limits abundance via the conversion of detritus to microbial biomass. Two of four microbivore taxa, collembola and isopods, increased with the percentage of P (%P) of decomposing litter. However, percentage of S (correlated with %P) best predicted the abundance of collembola, oribatids, and diplopods (r2 = 0.38, 0.33, 0.21, respectively). In the Structural Elements Hypotheses, N and Ca limit the abundance of silk-spinning and calcareous taxa, respectively. Mesostigmatids, pseudoscorpions, and spiders, all known to make silk, each increased with percentage of N of litter (r2 = 0.22, 0.31, 0.26, respectively). Calcareous isopods, but not diplopods, increased with percentage of Ca of litter (r2 = 0.59). In the Ecosystem Size Hypothesis, top predators are limited by available space. The abundance of the three remaining predators, chilopods, staphylinids, and ants, increased with litter depth (r2 = 0.31, 0.74, 0.69, respectively), and food webs from forests with deeper litter supported a higher ratio of predators to microbivores. These results suggest that biogeochemical gradients can provide a mechanism, through stoichiometry and trophic theory, shaping the geography of community structure. PMID:20120804
Road salts as environmental constraints in urban pond food webs.
Van Meter, Robin J; Swan, Christopher M
Freshwater salinization is an emerging environmental filter in urban aquatic ecosystems that receive chloride road salt runoff from vast expanses of impervious surface cover. Our study was designed to evaluate the effects of chloride contamination on urban stormwater pond food webs through changes in zooplankton community composition as well as density and biomass of primary producers and consumers. From May - July 2009, we employed a 2ū2ū2 full-factorial design to manipulate chloride concentration (low?=?177 mg L(-1) Cl(-/)high?=?1067 mg L(-1) Cl(-)), gray treefrog (Hyla versicolor) tadpoles (presence/absence) and source of stormwater pond algae and zooplankton inoculum (low conductance/high conductance urban ponds) in 40, 600-L mesocosms. Road salt did serve as a constraint on zooplankton community structure, driving community divergence between the low and high chloride treatments. Phytoplankton biomass (chlorophyll [a] Ąg L(-1)) in the mesocosms was significantly greater for the high conductance inoculum (P<0.001) and in the high chloride treatment (P?=?0.046), whereas periphyton biomass was significantly lower in the high chloride treatment (P?=?0.049). Gray treefrog tadpole time to metamorphosis did not vary significantly between treatments. However, mass at metamorphosis was greater among tadpoles that experienced a faster than average time to metamorphosis and exposure to high chloride concentrations (P?=?0.039). Our results indicate differential susceptibility to chloride salts among algal resources and zooplankton taxa, and further suggest that road salts can act as a significant environmental constraint on urban stormwater pond communities. PMID:24587259
Methane carbon supports aquatic food webs to the fish level.
Sanseverino, Angela M; Bastviken, David; Sundh, Ingvar; Pickova, Jana; Enrich-Prast, Alex
Large amounts of the greenhouse gas methane (CH(4)) are produced by anaerobic mineralization of organic matter in lakes. In spite of extensive freshwater CH(4) emissions, most of the CH(4) is typically oxidized by methane oxidizing bacteria (MOB) before it can reach the lake surface and be emitted to the atmosphere. In turn, it has been shown that the CH(4)-derived biomass of MOB can provide the energy and carbon for zooplankton and macroinvertebrates. In this study, we demonstrate the presence of specific fatty acids synthesized by MOB in fish tissues having low carbon stable isotope ratios. Fish species, zooplankton, macroinvertebrates and the water hyacinth Eichhornia crassipes were collected from a shallow lake in Brazil and analyzed for fatty acids (FA) and carbon stable isotope ratios (?(13)C). The fatty acids 16:1?8c, 16:1?8t, 16:1?6c, 16:1?5t, 18:1?8c and 18:1?8t were used as signature for MOB. The ?(13)C ratios varied from -27.7ē to -42.0ē and the contribution of MOB FA ranged from 0.05% to 0.84% of total FA. Organisms with higher total content of MOB FAs presented lower ?(13)C values (i.e. they were more depleted in (13)C), while organisms with lower content of MOB signature FAs showed higher ?(13)C values. An UPGMA cluster analysis was carried out to distinguish grouping of organisms in relation to their MOB FA contents. This combination of stable isotope and fatty acid tracers provides new evidence that assimilation of methane-derived carbon can be an important carbon source for the whole aquatic food web, up to the fish level. PMID:22880091
Towards methodological approaches to implement the zooplankton component in ``end to end" food-web models
Poggiale, Jean-Christophe
Towards methodological approaches to implement the zooplankton component in ``end to end" food history: Available online xxxx a b s t r a c t The modelling of marine zooplankton has made great progress to functional groups. A new challenge is to dynamically represent zooplankton within marine food webs coupling
A framework for soil food web diagnostics: extension of the nematode faunal analysis concept
H. Ferris; T. Bongers; R. G. M. de Goede
Nematodes, the earthÆs most abundant metazoa, are ubiquitous in the soil environment. They are sufficiently large to be identifiable by light microscopy and sufficiently small to inhabit water films surrounding soil particles. They aggregate around and in food sources. They include component taxa of the soil food web at several trophic levels. They can be categorized into functional guilds whose
Food Chains & Webs. A Multimedia CD-ROM. [CD-ROM].
ERIC Educational Resources Information Center
This CD-ROM is designed for classroom and individual use to teach and learn about food chains and food webs. Integrated animations, custom graphics, three-dimensional representations, photographs, and sound are featured for use in user-controlled activities. Interactive lessons are available to reinforce the subject material. Pre- and post-testingģ
Sampling effects and the robustness of quantitative and qualitative food-web descriptors.
Banasek-Richter, Carolin; Cattin, Marie-France; Bersier, Louis-Fķlix
Food-web descriptors serve as a means for among-web comparisons that are necessary for the discovery of regularities in respect to food-web structure. Qualitative descriptors were however found to be highly sensitive to varying levels of sampling effort. To circumvent these shortcomings, quantitative counterparts were proposed which take the magnitude of trophic interaction between species into consideration. For 14 properties we examined the performance with increasing sampling effort of a qualitative, an unweighted quantitative (giving the same weight to each taxon), and a weighted quantitative version (weighing each taxon by the amount of incoming and outgoing flows). The evaluation of 10 extensively documented quantitative webs formed the basis for this analysis. The quantitative versions were found to be much more robust against variable sampling effort. This increase in accuracy is accomplished at the cost of a slight decrease in precision as compared to the qualitative properties. Conversely, the quantitative descriptors also proved less sensitive to differences in evenness in the distribution of link magnitude. By more adequately incorporating the information inherent to quantitative food-web compilations, quantitative descriptors are able to better represent the web, and are thus more suitable for the elucidation of general trends in food-web structure. PMID:14637051
Nutrition Content of Food and Beverage Products on Web Sites Popular With Children
Lingas, Elena O.; Bukofzer, Eliana
We assessed the nutritional quality of branded food and beverage products advertised on 28 Web sites popular with children. Of the 77 advertised products for which nutritional information was available, 49 met Institute of Medicine criteria for foods to avoid, 23 met criteria for foods to neither avoid nor encourage, and 5 met criteria for foods to encourage. There is a need for further research on the nature and extent of food and beverage advertising online to aid policymakers as they assess the impact of this marketing on children. PMID:19443816
Parameter uncertainty, sensitivity, and sediment coupling in bioenergetics-based food web models
Barron, M.G.; Cacela, D.; Beltman, D. [Hagler Bailly, Boulder, CO (United States)
A bioenergetics-based food web model was developed and calibrated using measured PCB water and sediment concentrations in two Great Lakes food webs: Green Bay, Michigan and Lake Ontario. The model incorporated functional based trophic levels and sediment, water, and food chain exposures of PCBs to aquatic biota. Sensitivity analysis indicated the parameters with the greatest influence on PCBs in top predators were lipid content of plankton and benthos, planktivore assimilation efficiency, Kow, prey selection, and ambient temperature. Sediment-associated PCBs were estimated to contribute over 90% of PCBs in benthivores and less than 50% in piscivores. Ranges of PCB concentrations in top predators estimated by Monte Carlo simulation incorporating parameter uncertainty were within one order of magnitude of modal values. Model applications include estimation of exceedences of human and ecological thresholds. The results indicate that point estimates from bioenergetics-based food web models have substantial uncertainty that should be considered in regulatory and scientific applications.
Vertical flux of biogenic carbon in the ocean: Is there food web control?
Rivkin, R.B.; Legendre, L.; Deibel, D. [and others
Models of biogenic carbon (BC) flux assume that short herbivorous food chains lead to high export, whereas complex microbial or omnivorous food webs lead to recycling and low export, and that export of BC from the euphotic zone equals new production (NP). In the Gulf of St. Lawrence, particulate organic carbon fluxes were similar during the spring phytoplankton bloom, when herbivory dominated, and during nonbloom conditions, when microbial and omnivorous food webs dominated. In contrast, NP was 1.2 to 161 times greater during the bloom than after it. Thus, neither food web structure nor NP can predict the magnitude or patterns of BC export, particularly on time scales over which the ocean is in nonequilibrium conditions. 29 refs., 3 figs., 1 tab.
Cycling Through the Food Web: Let's Go on a Research Cruise
NSDL National Science Digital Library
This site presents an account of a research cruise to investigate how the food webs in different oceanic habitats vary. The scientists wanted to see ocean life in its natural environment and conduct experiments that would not be possible in the laboratory. They looked specifically at three types of ocean habitat: the open ocean, the continental shelf, and an upwelling area. The researchers were hoping to learn the answers to two questions: 'How well do the actual marine food webs match our food chain models for the three habitats?' and 'How does the microbial community in each food web change with depth?'. Students can follow their research and fill out an activity and question checklist as they go along. There is also a page of information for teachers.
Defining ecospace of Arctic marine food webs using a novel quantitative approach
NASA Astrophysics Data System (ADS)
Gale, M.; Loseto, L. L.
The Arctic is currently facing unprecedented change with developmental, physical and climatological changes. Food webs within the marine Arctic environment are highly susceptible to anthropogenic stressors and have thus far been understudied. Stable isotopes, in conjunction with a novel set of metrics, may provide a framework that allows us to understand which areas of the Arctic are most vulnerable to change. The objective of this study was to use linear distance metrics applied to stable isotopes to a) define and quantify four Arctic marine food webs in ecospace; b) enable quantifiable comparisons among the four food webs and with other ecosystems; and, c) evaluate vulnerability of the four food webs to anthropogenic stressors such as climate change. The areas studied were Hudson Bay, Beaufort Sea, Lancaster Sound and North Water Polynya. Each region was selected based on the abundance of previous research and published and available stable isotope data in peer-review literature. We selected species to cover trophic levels ranging from particulate matter to polar bears with consideration of pelagic, benthic and ice-associated energy pathways. We interpret higher diversity in baseline carbon energy as signifying higher stability in food web structure. Based on this, the Beaufort Sea food web had the highest stability; the Beaufort Sea food web occupied the largest isotopic niche space and was supported by multiple carbon sources. Areas with top-down control system, such as Lancaster Sound and North Water Polynya, would be the first to experience an increase in trophic redundancy and possible hardships from external stressors, as they have fewer basal carbon sources and greater numbers of mid-high level consumers. We conclude that a diverse carbon energy based ecosystem such as the Beaufort Sea and Hudson Bay regions are more resilient to change than a top down control system.
Sources and transfers of methylmercury in adjacent river and forest food webs.
Tsui, Martin Tsz Ki; Blum, Joel D; Kwon, Sae Yun; Finlay, Jacques C; Balogh, Steven J; Nollet, Yabing H
Nearly all ecosystems are contaminated with highly toxic methylmercury (MeHg), but the specific sources and pathways leading to the uptake of MeHg within and among food webs are not well understood. In this study, we report stable mercury (Hg) isotope compositions in food webs in a river and an adjacent forest in northern California and demonstrate the utility of Hg isotopes for studying MeHg sources and cross-habitat transfers. We observed large differences in both ?(202)Hg (mass-dependent fractionation) and ?(199)Hg (mass-independent fractionation) within both food webs. The majority of isotopic variation within each food web could be accounted for by differing proportions of inorganic Hg [Hg(II)] and MeHg along food chains. We estimated mean isotope values of Hg(II) and MeHg in each habitat and found a large difference in ?(202)Hg between Hg(II) and MeHg (?2.7ē) in the forest but not in the river (?0.25ē). This is consistent with in situ Hg(II) methylation in the study river but suggests Hg(II) methylation may not be important in the forest. In fact, the similarity in ?(202)Hg between MeHg in forest food webs and Hg(II) in precipitation suggests that MeHg in forest food webs may be derived from atmospheric sources (e.g., rainfall, fog). Utilizing contrasting ?(202)Hg values between MeHg in river food webs (-1.0ē) and MeHg in forest food webs (+0.7ē), we estimate with a two-source mixing model that ?55% of MeHg in two riparian spiders is derived from riverine sources while ?45% of MeHg originates from terrestrial sources. Thus, stable Hg isotopes can provide new information on subtle differences in sources of MeHg and trace MeHg transfers within and among food webs in natural ecosystems. PMID:23033864
Lateral cascade of indirect effects in food webs with different types of adaptive behavior.
Kamran-Disfani, Ahmad R; Golubski, Antonio J
It is widely recognized that indirect effects due to adaptive behaviors can have important effects on food webs. One consequence may be to change how readily perturbations propagate through the web, because species' behaviors as well as densities may respond to perturbations. It is not well understood which types of behavior are more likely to facilitate versus inhibit propagation of disturbances through a food web, or how this might be affected by the shape of a food web or the patterns of interaction strengths within it. We model two simple, laterally expanded food webs (one with three trophic levels and one with four), and compare how various adaptive behaviors affect the potential for a newly introduced predator to change the equilibrium densities of distant species. Patterns of changes in response to the introduction were qualitatively similar across most models, as were the ways in which patterns of direct interaction strengths affected those responses. Depending on both the web structure and the specific adaptive behavior, the potential for density changes to propagate through the web could be either increased or diminished relative to the no-behavior model. Two behaviors allowed density changes to propagate through a four-level web that precluded such propagation in the no-behavior model, and each of these two behaviors led to qualitatively different patterns of density changes. In the one model (diet choice) in which density changes were able to propagate in both web structures, patterns of density changes differed qualitatively between webs. Some of our results flowed from the fact that behaviors did not interact directly in the systems we considered, so that indirect effects on distant species had to be at least partly density-mediated. Our models highlight this as an inherent limitation of considering in isolation behaviors that are strictly foraging-related or strictly defense-related, making a case for the value of simultaneously considering multiple interacting types of behavior in the same model. PMID:23810934
Planktonic food webs revisited: Reanalysis of results from the linear inverse approach
NASA Astrophysics Data System (ADS)
Hlaili, Asma Sakka; Niquil, Nathalie; Legendre, Louis
Identification of the trophic pathway that dominates a given planktonic assemblage is generally based on the distribution of biomasses among food-web compartments, or better, the flows of materials or energy among compartments. These flows are obtained by field observations and a posteriori analyses, including the linear inverse approach. In the present study, we re-analysed carbon flows obtained by inverse analysis at 32 stations in the global ocean and one large lake. Our results do not support two "classical" views of plankton ecology, i.e. that the herbivorous food web is dominated by mesozooplankton grazing on large phytoplankton, and the microbial food web is based on microzooplankton significantly consuming bacteria; our results suggest instead that phytoplankton are generally grazed by microzooplankton, of which they are the main food source. Furthermore, we identified the "phyto-microbial food web", where microzooplankton largely feed on phytoplankton, in addition to the already known "poly-microbial food web", where microzooplankton consume more or less equally various types of food. These unexpected results led to a (re)definition of the conceptual models corresponding to the four trophic pathways we found to exist in plankton, i.e. the herbivorous, multivorous, and two types of microbial food web. We illustrated the conceptual trophic pathways using carbon flows that were actually observed at representative stations. The latter can be calibrated to correspond to any field situation. Our study also provides researchers and managers with operational criteria for identifying the dominant trophic pathway in a planktonic assemblage, these criteria being based on the values of two carbon ratios that could be calculated from flow values that are relatively easy to estimate in the field.
FOOD WEBS IN URBAN FISH `COMMUNITIES' FROM THE SALT RIVER PROJECT CANALS Lara A. Ferry, Bonnie Ahr
Hall, Sharon J.
al. (2009)*who quantified food webs flathead catfish Pylodictis olivaris channel catfish Ictalurus punctatus sonora sucker Catostomus insignis desert sucker Pantosteus clarki largemouth bass Micropterus
A new modeling approach to define marine ecosystems food-web status with uncertainty assessment
NASA Astrophysics Data System (ADS)
Chaalali, Aurķlie; Saint-Bķat, Blanche; Lassalle, Gķraldine; Le Loc'h, Franńois; Tecchio, Samuele; Safi, Georges; Savenkoff, Claude; Lobry, Jķrķmy; Niquil, Nathalie
Ecosystem models are currently one of the most powerful approaches used to project and analyse the consequences of anthropogenic and climate-driven changes in food web structure and function. The modeling community is however still finding the effective representation of microbial processes as challenging and lacks of techniques for assessing flow uncertainty explicitly. A linear inverse model of the Bay of Biscay continental shelf was built using a Monte Carlo method coupled with a Markov Chain (LIM-MCMC) to characterize the system's trophic food-web status and its associated structural and functional properties. By taking into account the natural variability of ecosystems (and their associated flows) and the lack of data on these environments, this innovative approach enabled the quantification of uncertainties for both estimated flows and derived food-web indices. This uncertainty assessment constituted a real improvement on the existing Ecopath model for the same area and both models results were compared. Our results suggested a food web characterized by main flows at the basis of the food web and a high contribution of primary producers and detritus to the entire system input flows. The developmental stage of the ecosystem was characterized using estimated Ecological Network Analysis (ENA) indices; the LIM-MCMC produced a higher estimate of flow specialization (than the estimate from Ecopath) owing to better consideration of bacterial processes. The results also pointed to a detritus-based food-web with a web-like structure and an intermediate level of internal flow complexity, confirming the results of previous studies. Other current research on ecosystem model comparability is also presented.
Warming and nitrogen affect size structuring and density dependence in a host-parasitoid food web.
de Sassi, Claudio; Staniczenko, Phillip P A; Tylianakis, Jason M
Body size is a major factor constraining the trophic structure and functioning of ecological communities. Food webs are known to respond to changes in basal resource abundance, and climate change can initiate compounding bottom-up effects on food-web structure through altered resource availability and quality. However, the effects of climate and co-occurring global changes, such as nitrogen deposition, on the density and size relationships between resources and consumers are unknown, particularly in host-parasitoid food webs, where size structuring is less apparent. We use a Bayesian modelling approach to explore the role of consumer and resource density and body size on host-parasitoid food webs assembled from a field experiment with factorial warming and nitrogen treatments. We show that the treatments increased resource (host) availability and quality (size), leading to measureable changes in parasitoid feeding behaviour. Parasitoids interacted less evenly within their host range and increasingly focused on abundant and high-quality (i.e. larger) hosts. In summary, we present evidence that climate-mediated bottom-up effects can significantly alter food-web structure through both density- and trait-mediated effects. PMID:23007092
Linking Water Quality and Quantity in Environmental Flow Assessment in Deteriorated Ecosystems: A Food Web View
Chen, He; Ma, Lekuan; Guo, Wei; Yang, Ying; Guo, Tong; Feng, Cheng
Most rivers worldwide are highly regulated by anthropogenic activities through flow regulation and water pollution. Environmental flow regulation is used to reduce the effects of anthropogenic activities on aquatic ecosystems. Formulating flow alteration¢ecological response relationships is a key factor in environmental flow assessment. Traditional environmental flow models are characterized by natural relationships between flow regimes and ecosystem factors. However, food webs are often altered from natural states, which disturb environmental flow assessment in such ecosystems. In ecosystems deteriorated by heavy anthropogenic activities, the effects of environmental flow regulation on species are difficult to assess with current modeling approaches. Environmental flow management compels the development of tools that link flow regimes and food webs in an ecosystem. Food web approaches are more suitable for the task because they are more adaptive for disordered multiple species in a food web deteriorated by anthropogenic activities. This paper presents a global method of environmental flow assessment in deteriorated aquatic ecosystems. Linkages between flow regimes and food web dynamics are modeled by incorporating multiple species into an ecosystem to explore ecosystem-based environmental flow management. The approach allows scientists and water resources managers to analyze environmental flows in deteriorated ecosystems in an ecosystem-based way. PMID:23894669
Soil food web properties explain ecosystem services across European land use systems.
de Vries, Franciska T; Thķbault, Elisa; Liiri, Mira; Birkhofer, Klaus; Tsiafouli, Maria A; Bj°rnlund, Lisa; Bracht J°rgensen, Helene; Brady, Mark Vincent; Christensen, S°ren; de Ruiter, Peter C; d'Hertefeldt, Tina; Frouz, Jan; Hedlund, Katarina; Hemerik, Lia; Hol, W H Gera; Hotes, Stefan; Mortimer, Simon R; Setõlõ, Heikki; Sgardelis, Stefanos P; Uteseny, Karoline; van der Putten, Wim H; Wolters, Volkmar; Bardgett, Richard D
Intensive land use reduces the diversity and abundance of many soil biota, with consequences for the processes that they govern and the ecosystem services that these processes underpin. Relationships between soil biota and ecosystem processes have mostly been found in laboratory experiments and rarely are found in the field. Here, we quantified, across four countries of contrasting climatic and soil conditions in Europe, how differences in soil food web composition resulting from land use systems (intensive wheat rotation, extensive rotation, and permanent grassland) influence the functioning of soils and the ecosystem services that they deliver. Intensive wheat rotation consistently reduced the biomass of all components of the soil food web across all countries. Soil food web properties strongly and consistently predicted processes of C and N cycling across land use systems and geographic locations, and they were a better predictor of these processes than land use. Processes of carbon loss increased with soil food web properties that correlated with soil C content, such as earthworm biomass and fungal/bacterial energy channel ratio, and were greatest in permanent grassland. In contrast, processes of N cycling were explained by soil food web properties independent of land use, such as arbuscular mycorrhizal fungi and bacterial channel biomass. Our quantification of the contribution of soil organisms to processes of C and N cycling across land use systems and geographic locations shows that soil biota need to be included in C and N cycling models and highlights the need to map and conserve soil biodiversity across the world. PMID:23940339
The cesium:potassium index of food web structure -- A complementary approach to stable isotope indicators
Young, D. [Environmental Protection Agency, Newport, OR (United States)
Stable isotope shifts with trophic or average feeding level are an important tool in characterizing sampled food webs for biomagnification and other studies. However, spatial and temporal variations in isotope ratios in the environment can introduce uncertainties in interpreting such data. An elemental index, the Cs/K ratio, has proved to be a useful tool in assessing the reliability of the trophic level approach to characterizing marine and estuarine food webs. A major advantage is the constant value of this elemental ratio in seawater. Studies conducted over the last three decades in a variety of aquatic ecosystems generally have yielded consistent results using the Cs/K Index. The mean Trophic Transfer Factor obtained from twelve food web surveys was 2.0 +/- 0.1 (SE), indicating substantial structure for most of the food webs sampled. An empirical technique, termed the Exponential Biomagnification Model, was developed to simplify the observed variation of Cs/K with Trophic Level Assignment. This approach has proved useful in assessing sampled food webs with non-integer Trophic Level Assignments, and obtaining average Trophic Transfer Factors for the Cs/K ratio and corresponding tissue concentrations of environmental contaminants.
The role of body mass in diet contiguity and food-web structure
Stouffer, Daniel B.; Rezende, Enrico L.; Amaral, LuĒs A. Nunes
Summary The idea that species occupy distinct niches is a fundamental concept in ecology. Classically, the niche was described as an n-dimensional hypervolume where each dimension represents a biotic or abiotic characteristic. More recently, it has been hypothesised that a single dimension may be sufficient to explain the system-level organization of trophic interactions observed between species in a community.Here, we test the hypothesis that species body mass is that single dimension. Specifically, we determine how the intervality of food webs ordered by body size compares to that of randomly ordered food webs. We also extend this analysis beyond the community level to the effect of body mass in explaining the diets of individual species.We conclude that body mass significantly explains the ordering of species and the contiguity of diets in empirical communities.At the species-specific level, we find that the degree to which body mass is a significant explanatory variable depends strongly on the phylogenetic history, suggesting that other evolutionarily conserved traits partly account for speciesÆ roles in the food web.Our investigation of the role of body mass in food webs thus helps us to better understand the important features of community food-web structure and the evolutionary forces that have led us to the communities we observe. PMID:21401590
Hydrological and Biogeochemical Controls on Seasonal and Spatial Differences in Food Webs in the Everglades
NASA Astrophysics Data System (ADS)
Kendall, C.; Wankel, S. D.; Bemis, B. E.; Rawlik, P. S.; Krabbenhoft, D. P.; Lange, T.
Stable isotopes can be used to determine the relative trophic positions of biota within a food web, and to improve our understanding of the biomagnification of contaminants. Plants at the base of the food web uptake dissolved organic carbon (DIC) and nitrogen (DIN) for growth, and their tissue reflects the isotopic composition of these sources. Animals then mirror the isotopic composition of the primary producers, as modified by consumer-diet fractionations at successive trophic steps. During 1995-99, we collected algae, macrophyte, invertebrate, and fish samples from 15 USGS sites in the Everglades and analyzed them for d13C and d15N with the goal of characterizing seasonal and spatial differences in food web relations. Carbon isotopes effectively distinguish between two main types of food webs: ones where algae is the dominant base of the food web, which are characteristic of relatively pristine marsh sites with long hydroperiods, and ones where macrophyte debris appears to be a significant source of nutrients, which are apparently characteristic of shorter hydroperiod sites, and nutrient-impacted marshes and canals. There usually is an inverse relation between d13C and d15N of organisms over time, especially in more pristine environments, reflecting seasonal changes in the d13C of DIC and the d15N of DIN. The d13C and d15N of algae also show strong positive correlations with seasonal changes in water levels. This variability is substantially damped up the food chain, probably because of the longer integration times of animals vs. plants. We speculate that these seasonal shifts in water level result in changes in biogeochemical reactions and nutrient levels, with corresponding variations in the d15N and d13C of biota. For example, small changes in water level may change the balance of photosynthesis, bacterial respiration, and atmospheric exchange reactions that control the d13C of DIC. Such changes will probably also affect the d15N of dissolved inorganic N (DIN) because of corresponding changes in N uptake and redox conditions. During the dry season, the marshes probably become more anoxic because of shallower water levels, less photosynthesis, and increased quantities of decaying vegetation. During this season, macrophyte debris appears to be a significant source of nutrients to local food webs. Our isotope data are consistent with seasonal differences in food webs, related to seasonal differences in water levels. Hence, biota isotopes provide a powerful tool for monitoring how future ecosystem changes, in particular changes in hydroperiod, will affect food webs across the Everglades.
Do edge responses cascade up or down a multi-trophic food web?
Wimp, Gina M; Murphy, Shannon M; Lewis, Danny; Ries, Leslie
Despite nearly 100?years of edge studies, there has been little effort to document how edge responses 'cascade' to impact multi-trophic food webs. We examined changes within two, four-tiered food webs located on opposite sides of a habitat edge. Based on a 'bottom-up' resource-based model, we predicted plant resources would decline near edges, causing similar declines in specialist herbivores and their associated predators, while a generalist predator was predicted to increase due to complementary resource use. As predicted, we found declines in both specialist herbivores and predators near edges, but, contrary to expectations, this was not driven by gradients in plant resources. Instead, the increase in generalist predators near edges offers one alternative explanation for the observed declines. Furthermore, our results suggest how recent advances in food web theory could improve resource-based edge models, and vice versa. PMID:21790930
Seasonal variation in mercury and food web biomagnification in Lake Ontario, Canada.
Zhang, Liang; Campbell, Linda M; Johnson, Timothy B
Seasonal variation in mercury (Hg) concentrations and food web structure was assessed for eastern Lake Ontario. Hg concentrations, measured in 6 species of invertebrates and 8 species of fishes, tended to be highest in the spring and lowest in the summer for most biota. Yellow perch (Perca flavescens) exhibited significant ontogenetic shifts in diet and Hg, although such patterns were not evident for other species. Food web structure, as indicated by stable isotope values (?(15)N, ?(13)C) was not static. Log-transformed Hg data were strongly and consistently correlated with ?(15)N values for the whole food web in each of the three seasons (slopes, 0.17-0.24) and across the entire year (slope, 0.2). While significantly different between seasons, the regression slope values are still consistent with published global Hg biomagnification rates. Our results indicate that the assessment of Hg trends in Great Lakes must take into account seasonal patterns and time of sampling. PMID:22230083
More than a meal: integrating non-feeding interactions into food webs
Kķfi, Sonia; Berlow, Eric L.; Wieters, Evie A.; Navarrete, Sergio A.; Petchey, Owen L.; Wood, Spencer A.; Boit, Alice; Joppa, Lucas N.; Lafferty, Kevin D.; Williams, Richard J.; Martinez, Neo D.; Menge, Bruce A.; Blanchette, Carol A.; Iles, Alison C.; Brose, Ulrich
Organisms eating each other are only one of many types of well documented and important interactions among species. Other such types include habitat modification, predator interference and facilitation. However, ecological network research has been typically limited to either pure food webs or to networks of only a few (<3) interaction types. The great diversity of non-trophic interactions observed in nature has been poorly addressed by ecologists and largely excluded from network theory. Herein, we propose a conceptual framework that organises this diversity into three main functional classes defined by how they modify specific parameters in a dynamic food web model. This approach provides a path forward for incorporating non-trophic interactions in traditional food web models and offers a new perspective on tackling ecological complexity that should stimulate both theoretical and empirical approaches to understanding the patterns and dynamics of diverse species interactions in nature.
Bioaccumulation of mercury in pelagic freshwater food webs
C. J. Watras; R. C. Back; S. Halvorsen; R. J. M. Hudson; K. A. Morrison; S. P. Wente
Current paradigms regarding the bioaccumulation of mercury are rooted in observations that monomethyl mercury (meHg) biomagnifies along pelagic food chains. However, mechanisms regulating the formation of meHg, its initial incorporation at the base of pelagic food chains, and its subsequent trophic transfer remain controversial. Here we use field data from 15 northern Wisconsin lakes, equilibrium aqueous speciation modeling, and statistical
Parasites affect food web structure primarily through increased diversity and complexity
Dunne, Jennifer A.; Lafferty, Kevin D.; Dobson, Andrew P.; Hechinger, Ryan F.; Kuris, Armand M.; Martinez, Neo D.; McLaughlin, John P.; Mouritsen, Kim N.; Poulin, Robert; Reise, Karsten; Stouffer, Daniel B.; Thieltges, David W.; Williams, Richard J.; Zander, Claus Dieter
Comparative research on food web structure has revealed generalities in trophic organization, produced simple models, and allowed assessment of robustness to species loss. These studies have mostly focused on free-living species. Recent research has suggested that inclusion of parasites alters structure. We assess whether such changes in network structure result from unique roles and traits of parasites or from changes to diversity and complexity. We analyzed seven highly resolved food webs that include metazoan parasite data. Our analyses show that adding parasites usually increases link density and connectance (simple measures of complexity), particularly when including concomitant links (links from predators to parasites of their prey). However, we clarify prior claims that parasites æædominateÆÆ food web links. Although parasites can be involved in a majority of links, in most cases classic predation links outnumber classic parasitism links. Regarding network structure, observed changes in degree distributions, 14 commonly studied metrics, and link probabilities are consistent with scale-dependent changes in structure associated with changes in diversity and complexity. Parasite and free-living species thus have similar effects on these aspects of structure. However, two changes point to unique roles of parasites. First, adding parasites and concomitant links strongly alters the frequency of most motifs of interactions among three taxa, reflecting parasitesÆ roles as resources for predators of their hosts, driven by trophic intimacy with their hosts. Second, compared to free-living consumers, many parasitesÆ feeding niches appear broader and less contiguous, which may reflect complex life cycles and small body sizes. This study provides new insights about generic versus unique impacts of parasites on food web structure, extends the generality of food web theory, gives a more rigorous framework for assessing the impact of any species on trophic organization, identifies limitations of current food web models, and provides direction for future structural and dynamical models.
Impacts of food web structure and feeding behavior on mercury exposure in Greenland Sharks (Somniosus microcephalus).
McMeans, Bailey C; Arts, Michael T; Fisk, Aaron T
Benthic and pelagic food web components in Cumberland Sound, Canada were explored as sources of total mercury (THg) to Greenland Sharks (Somniosus microcephalus) via both bottom-up food web transfer and top-down shark feeding behavior. Log10THg increased significantly with ?(15)N and trophic position from invertebrates (0.01 ▒ 0.01 ?g Ę g(-1) [113 ▒ 1 ng Ę g(-1)] dw in copepods) to Greenland Sharks (3.54 ▒ 1.02 ?g Ę g(-1)). The slope of the log10THg vs. ?(15)N linear regression was higher for pelagic compared to benthic food web components (excluding Greenland Sharks, which could not be assigned to either food web), which resulted from THg concentrations being higher at the base of the benthic food web (i.e., in benthic than pelagic primary consumers). However, feeding habitat is unlikely to consistently influence shark THg exposure in Cumberland Sound because THg concentrations did not consistently differ between benthic and pelagic shark prey. Further, size, gender and feeding behavior (inferred from stable isotopes and fatty acids) were unable to significantly explain THg variability among individual Greenland Sharks. Possible reasons for this result include: 1) individual sharks feeding as generalists, 2) high overlap in THg among shark prey, and 3) differences in turnover time between ecological tracers and THg. This first assessment of Greenland Shark THg within an Arctic food web revealed high concentrations consistent with biomagnification, but low ability to explain intra-specific THg variability. Our findings of high THg levels and consumption of multiple prey types, however, suggest that Greenland Sharks acquire THg through a variety of trophic pathways and are a significant contributor to the total biotic THg pool in northern seas. PMID:24630590
Effects of lake acidification and recovery on the stability of zooplankton food webs
Locke, A. (Gulf Fisheries Centre, Moncton, News Brunswick (Canada)); Sprules, W.G. (Univ. of Toronto, Ontario (Canada))
The effect of food web structure on community stability and resilience has rarely been examined using empirical data. Yet there is a practical application for such studies insofar as resistance stability determines the ability of a system to adsorb' anthropogenic stress and adjustment stability determines the reversibility of resulting damage. The stability of zooplankton food webs in 46 Precambrian Shield lakes was examined using data collected in the 1970s, when pH ranged from 3.8 to 7.0, and in 1990, when pH had increased by up to two units in some lakes. Acidification overcame resistance stability at pH <5.0, as evidenced by decreases in species richness, numbers of predatory and competitive links, directed connectance, predator generalization, and linkage density, identified by analysis of variance. Adjustment stability was demonstrated by changes in food web attributes in lakes with higher pH in 1990 than in the 1970s. Species richness, numbers of predatory and competitive links, linkage density, and predator generalization all increased relative to the 1970s values. Food web attributes of recovering' lakes were statistically indistinguishable from those of lakes of similar pH that had not been more acidic in the 1970s. Similar trajectors of food web change were followed during environmental degradation and recovery. Planktonic food webs of anthropogenically acidified lakes may eventually recover to resemble their pre-acidification condition, given sufficient time without acidic inputs. Whether adjustment stability is a general feature of anthropogenically stressed systems remains to be determined. 42 refs., 2 figs., 4 tabs.
Sardine cycles, krill declines, and locust plagues: revisiting 'wasp-waist' food webs.
Atkinson, Angus; Hill, Simeon L; Barange, Manuel; Pakhomov, Evgeny A; Raubenheimer, David; Schmidt, Katrin; Simpson, Stephen J; Reiss, Christian
'Wasp-waist' systems are dominated by a mid trophic-level species that is thought to exert top-down control on its food and bottom-up control on its predators. Sardines, anchovy, and Antarctic krill are suggested examples, and here we use locusts to explore whether the wasp-waist concept also applies on land. These examples also display the traits of mobile aggregations and dietary diversity, which help to reduce the foraging footprint from their large, localised biomasses. This suggests that top-down control on their food operates at local aggregation scales and not at wider scales suggested by the original definition of wasp-waist. With this modification, the wasp-waist framework can cross-fertilise marine and terrestrial approaches, revealing how seemingly disparate but economically important systems operate. PMID:24755099
High-resolution food webs based on nitrogen isotopic composition of amino acids
Chikaraishi, Yoshito; Steffan, Shawn A; Ogawa, Nanako O; Ishikawa, Naoto F; Sasaki, Yoko; Tsuchiya, Masashi; Ohkouchi, Naohiko
Food webs are known to have myriad trophic links between resource and consumer species. While herbivores have well-understood trophic tendencies, the difficulties associated with characterizing the trophic positions of higher-order consumers have remained a major problem in food web ecology. To better understand trophic linkages in food webs, analysis of the stable nitrogen isotopic composition of amino acids has been introduced as a potential means of providing accurate trophic position estimates. In the present study, we employ this method to estimate the trophic positions of 200 free-roaming organisms, representing 39 species in coastal marine (a stony shore) and 38 species in terrestrial (a fruit farm) environments. Based on the trophic positions from the isotopic composition of amino acids, we are able to resolve the trophic structure of these complex food webs. Our approach reveals a high degree of trophic omnivory (i.e., noninteger trophic positions) among carnivorous species such as marine fish and terrestrial hornets.This information not only clarifies the trophic tendencies of species within their respective communities, but also suggests that trophic omnivory may be common in these webs. PMID:25360278
A non-equilibrium model for predicting bioaccumulation of organic contaminants in aquatic food-webs
Morrison, H.; Lazar, R.; Haffner, G.D. [Univ. of Windsor, Ontario (Canada). Dept. of Biological Sciences; Whittle, D.M. [Dept. of Fisheries and Oceans, Burlington, Ontario (Canada). Ecotoxicology Div.; Gobas, F.A.P.C. [Simon Fraser Univ., Burnaby, British Columbia (Canada)
A sub-model describing bioaccumulation and biomagnification in benthic invertebrates was incorporated into a steady-state food-web model (Gobas, 1993) was modified, to estimate concentrations of organic contaminants in aquatic organisms based on chemical concentrations in water and sediments. Model predictions were in good agreement with field data when applied to western Lake Erie. The improved ability of the model to simulate bioaccumulation by benthic invertebrates, makes this model particularly useful for quantifying contaminant transfer in the benthic food-web.
Stoichiometric Constraints on Food-Web Dynamics: A Whole-Lake Experiment on the Canadian Shield
James J. Elser; Thomas H. Chrzanowski; Robert W. Sterner; Kenneth H. Mills
A whole-lake manipulation of food-web structure (introduction of a top predator, northern pike, to a minnow-dominated lake)\\u000a was performed in a Canadian Shield lake (L110) to examine the stoichiometric consequences of changes in planktonic community\\u000a structure generated by altered food-web structure. Minnow abundance, zooplankton biomass and community composition, microconsumer\\u000a abundance, and concentration and carbon¢phosphorus (C:P) ratio of suspended particulate matter
The National Food Safety Database Web Site: Irradiation
NSDL National Science Digital Library
The National Food Safety Database, a cooperative project of the United States Department of Agriculture and several universities, provides a section on food irradiation that discusses the process, the history of irradiation, and its relationship to food safety, among other features. It is highlighted by a 39-part, annotated slide show that supports the process. Previously approved for use on poultry and fruits and vegetables in the US, irradiation can kill disease-causing bacteria like Salmonella and Escherichia coli 0157:H7 (discussed in the Scout Report for Science and Engineering's In the News section, September 17, 1997), and molds and funguses that cause rot. With recent US Food and Drug Administration (FDA) approval, irradiation can now be used to process red meat (e.g., beef, pork, lamb, and byproducts). The process involves exposing food to a source of radiation such as gamma rays from radioactive cobalt 60, cesium 137, or x-rays. No radioactive material is added to the product, and the technique is routinely used on grains and spices, as well as for sterilizing disposable medical devices. In spite of a number of tests conducted over the last 30 years substantiating its safety, irradiation has not gained widespread public acceptance in the US. This is largely due to the public's general fear of processes utilizing radiation. Supporters of the technology claim that it will virtually eliminate food-borne illness in the US, while skeptics feel that technology such as steam treatment can accomplish adequate sterilization without the purported risks and public concern associated with irradiation. (8) The National Food Safety Database, a cooperative project of the United States Department of Agriculture and several universities, provides a section on food irradiation that discusses the process, history of irradiation, and its relationship to food safety, among other features. It features a 39-part, annotated slide show that strongly supports the process.
Food web pathway determines how selenium affects aquatic ecosystems: A San francisco Bay case study
Stewart, A.R.; Luoma, S.N.; Schlekat, C.E.; Doblin, M.A.; Hieb, K.A.
Chemical contaminants disrupt ecosystems, but specific effects may be under-appreciated when poorly known processes such as uptake mechanisms, uptake via diet, food preferences, and food web dynamics are influential. Here we show that a combination of food web structure and the physiology of trace element accumulation explain why some species in San Francisco Bay are threatened by a relatively low level of selenium contamination and some are not. Bivalves and crustacean Zooplankton form the base of two dominant food webs in estuaries. The dominant bivalve Potamocorbula amurensis has a 10-fold slower rate constant of loss for selenium than do common crustaceans such as copepods and the mysid Neomysis mercedis (rate constant of loss, ke = 0.025, 0.155, and 0.25 d-1, respectively). The result is much higher selenium concentrations in the bivalve than in the crustaceans. Stable isotope analyses show that this difference is propagated up the respective food webs in San Francisco Bay. Several predators of bivalves have tissue concentrations of selenium that exceed thresholds thought to be associated with teratogenesis or reproductive failure (liver Se > 15 ??g g-1 dry weight). Deformities typical of selenium-induced teratogenesis were observed in one of these species. Concentrations of selenium in tissues of predators of Zooplankton are less than the thresholds. Basic physiological and ecological processes can drive wide differences in exposure and effects among species, but such processes are rarely considered in traditional evaluations of contaminant impacts.
Limits to trophic levels and omnivory in complex food webs: theory and data.
Williams, Richard J; Martinez, Neo D
While trophic levels have found broad application throughout ecology, they are also in much contention on analytical and empirical grounds. Here, we use a new generation of data and theory to examine long-standing questions about trophic-level limits and degrees of omnivory. The data include food webs of the Chesapeake Bay, U.S.A., the island of Saint Martin, a U.K. grassland, and a Florida seagrass community, which appear to be the most trophically complete food webs available in the primary literature due to their inclusion of autotrophs and empirically derived estimates of the relative energetic contributions of each trophic link. We show that most (54%) of the 212 species in the four food webs can be unambiguously assigned to a discrete trophic level. Omnivory among the remaining species appears to be quite limited, as judged by the standard deviation of omnivores' energy-weighted food-chain lengths. This allows simple algorithms based on binary food webs without energetic details to yield surprisingly accurate estimates of species' trophic and omnivory levels. While maximum trophic levels may plausibly exceed historically asserted limits, our analyses contradict both recent empirical claims that these limits are exceeded and recent theoretical claims that rampant omnivory eliminates the scientific utility of the trophic-level concept. PMID:15026980
Food web structure of two Mediterranean lagoons under varying degree of eutrophication
NASA Astrophysics Data System (ADS)
Carlier, Antoine; Riera, Pascal; Amouroux, Jean-Michel; Bodiou, Jean-Yves; Desmalades, Martin; Grķmare, Antoine
The food web structure and functioning of two north-western Mediterranean lagoons exhibiting contrasting degrees of eutrophication and marine influences were compared through ?13C and ?15N analysis of major potential food sources and consumers. The Lapalme Lagoon is well preserved and has kept a natural and temporary connection with the open sea. Conversely, the Canet Lagoon is heavily eutrophicated and its water exchange with the open sea has been artificially reduced. In Lapalme, all potential food sources and consumers exhibited ?15N values indicative of pristine coastal areas. Suspended particulate organic matter (POM) and sediment organic matter (SOM) pools seemed to constitute the main food sources of most primary consumers. Both primary producers and all consumers were much more 15N-enriched (by ś 10ē) and more 13C-depleted in Canet than in Lapalme. This reflected: (1) the assimilation of important amounts of anthropogenic nitrogen in the food web, and (2) a marked and uniform influence of 13C-depleted allochtonous sources of carbon. Based on the mean ?15N of primary consumers, we found rather similar food web lengths in both lagoons with top consumers at trophic levels 3.6 and 4.0 in Canet and Lapalme, respectively. However, the eutrophication of the Canet Lagoon resulted in a simplification of the food web structure (i.e., a single trophic pathway from a 15N-enriched fraction of the SOM pool to top predators) compared to what was observed in Lapalme Lagoon where additional 13C-enriched food sources played a significant trophic role. Moreover, some consumers of Canet tended to exploit primary producers to a larger extent (and thus to exhibit lower trophic levels) than in Lapalme.
Energy flow to two abundant consumers in a subtropical oyster reef food web
Lauren A. Yeager; Craig A. Layman
Oyster reefs are among the most threatened coastal habitat types, but still provide critical habitat and food resources for\\u000a many estuarine species. The structure of oyster reef food webs is an important framework from which to examine the role of\\u000a these reefs in supporting high densities of associated fishes. We identified major trophic pathways to two abundant consumers,\\u000a gray snapper
Intraguild Predation, Invertebrate Predators, and Trophic Cascades in Lake Food Webs
The top-down and bottom-up properties of model food webs that include intraguild predation and self-limiting factors such as cannibalism are investigated. Intraguild predation can dampen or even reverse the top-down effects predicted by food chain theory. The degree of self-limitation among the intraguild prey is a key factor in determining the direction and strength of the top-down response. Intraguild predation
Trophic relationships in an Arctic food web and implications for trace metal transfer
Larissa-A. Dehn; Erich H. Follmann; Dana L. Thomas; Gay G. Sheffield; Cheryl Rosa; Lawrence K. Duffy; Todd M. O'Hara
Tissues of subsistence-harvested Arctic mammals were analyzed for silver (Ag), cadmium (Cd), and total mercury (THg). Muscle (or total body homogenates of potential fish and invertebrate prey) was analyzed for stable carbon (?13C) and nitrogen (?15N) isotopes to establish trophic interactions within the Arctic food chain. Food web magnification factors (FWMFs) and biomagnification factors for selected predator¢prey scenarios (BMFs) were
Abundance-body mass relationships in size-structured food webs
Simon Jennings
In communities sharing a common energy source, the energetic equivalence hypothesis predicts that numerical abundance (N) scales with body mass (M )a sM )0.75. However, in size-structured food webs all individuals do not share a common energy source, and the energy available (E ) to larger individuals is constrained by inefficient energy transfer through the food chains that support them.
Some Properties of the Speciation Model for Food-Web Structure - Mechanisms for Degree Distributions and Intervality
A. G. Rossberg; H. Matsuda; T. Amemiya; K. Itoh
We present a mathematical analysis of the speciation model for food-web structure, which had in previous work been shown to yield a good description of empirical data of food-web topology. The degree distributions of the network are derived. Properties of the speciation model are compared to those of other models that successfully describe empirical data. It is argued that the
Nutrient-limited food webs with up to three trophic levels: Feasibility, stability, assembly rules, and effects of nutrient enrichment
Florence D. Hulot; Michel Loreau
Community structure is controlled, among multiple factors, by competition and predation. Using the R* rule and graphical analysis, we analyse here the feasibility, stability and assembly rules of resource-based food webs with up to three trophic levels. In particular, we show that (1) the stability of a food web with two plants and two generalist herbivores does not require that
Seasonal changes of trophic transfer efficiencies in a plankton food web derived from biomass size distributions and network analysis
Ursula Gaedke; Dietmar Straile
The trophic transfer efficiencies in the planktonic food web of large, deep, and mesoŁ eutrophic Lake Constance were derived independently from biomass size distributions and from mass-balanced carbon flow diagrams based on comprehensive data for biomass, production, and food web structure. The main emphasis was on the transfer of primary production to herbivores since this process dominates the flow of
Biomagnification and bioaccumulation of mercury in an arctic marine food web: insights from stable nitrogen isotope analysis
Lisa Atwell; Keith A. Hobson; Harold E. Welch
Several recent studies have shown that the use of ?15N analysis to characterize trophic relationships can be useful for tracing biocontaminants in food webs. In this study, concentration of total mercury was measured in tissues from 112 individuals representing 27 species from the arctic marine food web of Lancaster Sound, Northwest Territories. Samples ranged from particulate organic matter through polar
Age and trophic position dominate bioaccumulation of mercury and organochlorines in the food web of Lake Washington
Jenifer K. McIntyre; David A. Beauchamp
Understanding the mechanisms of bioaccumulation in food webs is critical to predicting which food webs are at risk for higher rates of bioaccumulation that endanger the health of upper-trophic predators, including humans. Mercury and organochlorines were measured concurrently with stable isotopes of nitrogen and carbon in key fishes and invertebrates of Lake Washington to explore important pathways of bioaccumulation in
Manipulations of a microbial based soil food web at two arctic sites Ś evidence of species redundancy among the nematode fauna?
Liliane Ruess; Inger K. Schmidt; Anders Michelsen; Sven Jonasson
Nutrient limitation is a major factor influencing ecosystem processes in arctic soils, but knowledge on the decomposer food web interactions and their effects on nutrient cycling is scarce. Manipulations of the soil food web were carried out at two contrasting subarctic sites, a low altitude heath and a high altitude fellfield. The amount of nutrients and energy in the soil
Carbon fluxes in soil food webs of increasing complexity revealed by 14C labelling and 13C natural abundance
Andrea Ruf; Yakov Kuzyakov; Olga Lopatovskaya
Soil food webs are mainly based on three primary carbon (C) sources: root exudates, litter, and recalcitrant soil organic matter (SOM). These C sources vary in their availability and accessibility to soil organisms, which could lead to different pathways in soil food webs. The presence of three C isotopes (12C, 13C and 14C) offers an unique opportunity to investigate all
A standard protocol for stable isotope analysis of zooplankton in aquatic food web research using mass balance correction models
Peter M. Smyntek; Mark A. Teece; Kimberly L. Schulz; Stephen J. Thackeray
Stable isotope analysis has become a crucial tool for aquatic food web ecologists, but a lack of methodological standardization hinders comparisons between studies. One methodological inconsistency in stable isotope food web research is the decision whether to extract lipids before stable isotope analysis. The depletion in zooplankton stable carbon isotope values (d13C) due to fatty acid content and the accuracy
Distribution of Phthalate Esters in a Marine Aquatic Food Web
Gobas, Frank
equivalent concentrations of the high-molecular-weight DPEs (i.e., C8-C10 DPEs: di(2-ethylhexyl), di samples produced a direct comparison of the bioaccumulation behavior of PCBs and DPEs. Lipid equivalent-Web Magnification Factor (FWMF) of the PCB congeners ranged from 1.8 to 9.5. Lipid equivalent concentrations of low
Food-web models that generate constant predator-prey ratios
S. J. Mithen; J. H. Lawton
An approximately constant ratio of number of predator species\\/number of prey species is observed in several natural communities, although the exact value of the ratio may vary with habitat and the types of organisms in the food web. We test the hypothesis that a constant predator\\/prey ratio can be generated by what Holt (1977) terms æapparent competitionÆ and what Jeffries
The Importance of Allochthonous Subsidies to an Estuarine Food Web along a Salinity Gradient
Estuarine food webs function within a heterogeneous mosaic and are supported by a mix of primary producers from both local and distant sources. Processes governing the exchange and consumption of organic matter (OM), however, are poorly understood. To study the contribution of ...
Are Algae Relevant to the Detritus-Based Food Web in Tank-Bromeliads?
Boyer, Edmond
assemblages were greatly altered by the predation of mosquito larvae. Grazing losses indicated of mosquito larvae. We conclude that algae are a relevant functional community of the aquatic food web in C, we evaluated the impact of mosquito foraging on algae, other microorganisms and rotifers. The prey
Effects of Diporeia Declines on Fish Diet, Growth and Food Web Dynamics in Southeast Lake Michigan
of Diporeia might be impacting Great Lakes fishes. Results Diet Composition, Relative Abundance, and EnergyEffects of Diporeia Declines on Fish Diet, Growth and Food Web Dynamics in Southeast Lake Michigan were: Ę Evaluate diets, condition, and relative abundance of planktivorous fish (alewife, bloater
Effects of light reduction on food webs and associated ecosystem services of Yaquina Bay
Reduced water clarity can affect estuarine primary production but little is known of its subsequent effects to consumer guilds or ecosystem services. We investigated those effects using inverse analysis of modeled food webs of the lower (polyhaline) and upper (mesohaline) reache...
From the Top of the World...to the Bottom of the Food Web
NSDL National Science Digital Library
Bigelow Laboratory for Ocean Sciences
This resource, by the Bigelow Laboratory, is designed to help teachers and students discover linkages among marine ecology, phytoplankton, the behavior of light at the ocean surface, and satellite-derived ocean color data. On-line standards, based educational activities, explore the topics of phytoplankton, food webs, and algal blooms using microscopy and remote sensing data.
Insect-Damaged Fossil Leaves Record Food Web Response to Ancient Climate Change and Extinction
P. Wilf
Plants and herbivorous insects have dominated terrestrial ecosystems for over 300 million years. Uniquely in the fossil record, foliage with well-preserved insect damage offers abundant and diverse information both about producers and about ecological and sometimes taxonomic groups of consumers. These data are ideally suited to investigate food web response to environmental perturbations, and they represent an invaluable deep-time complement
Increasing isolation reduces predator:prey species richness ratios in aquatic food webs
Rachel S. Shulman; Jonathan M. Chase
The number of species that live in a habitat typically declines as that habitat becomes more isolated. However, the influence of habitat isolation on patterns of food web structure, in particular the ratio of predator to prey species richness, is less well understood. We placed aquatic mesocosms at varying distances from ponds that acted as sources of potential colonists; then
Marine carbon and nitrogen in southeastern Alaska stream food webs: evidence from artificial and natural streams
Dominic T. Chaloner; Kristine M. Martin; Mark S. Wipfli; Peggy H. Ostrom; Gary A. Lamberti
Incorporation of marine-derived nutrients (MDN) into freshwater food webs of southeastern Alaska was studied by measuring the natural abundance of nitrogen and carbon stable isotopes in biota from artificial and natural streams. Biofilm, aquatic macroinvertebrates (detritivores, shredders, and predators), and fish (coho salmon, Oncorhynchus kisutch, and cutthroat trout, Oncorhynchus clarki) were sampled from streams in which Pacific salmon (Oncorhynchus spp.)
A Screening Level Probabilistic Risk Assessment of Mercury in Florida Everglades Food Webs
Stephanie E. Duvall; Mace G. Barron
A screening level probabilistic assessment of risks was performed on three species of piscivorous wildlife at the top of Everglades aquatic food webs: the American alligator (Alligator mississippiensis), the great egret (Egretta alba), and the raccoon (Procyon lotor varius). Ranges of dietary exposure concentrations (and probability distribution functions) were derived for two general areas of the Everglades: Shark Slough and
Influence of streamside vegetation on inputs of terrestrial invertebrates to salmonid food webs
Wagner, Diane
Influence of streamside vegetation on inputs of terrestrial invertebrates to salmonid food webs J, and spawning migrations. We examined the contribution of terrestrially derived invertebrates (TI) to juvenile of invertebrate mass averaged across all sites; no significant differences associated with location (plant
Stoichiometric Constraints on Food-Web Dynamics: A Whole-Lake
Sterner, Robert W.
of Minnesota, St. Paul, Minnesota 55108, USA; and 4Freshwater Institute, Department of Fisheries and Oceans generated by altered food-web structure. Minnow abundance, zooplankton bio- mass and community composition and Daphnia collapsed in 1995, the year of lowest minnow abundance. Total zooplankton biomass in both lakes
Evolutionary food web model based on body masses gives realistic networks with permanent species turnover.
Allhoff, K T; Ritterskamp, D; Rall, B C; Drossel, B; Guill, C
The networks of predator-prey interactions in ecological systems are remarkably complex, but nevertheless surprisingly stable in terms of long term persistence of the system as a whole. In order to understand the mechanism driving the complexity and stability of such food webs, we developed an eco-evolutionary model in which new species emerge as modifications of existing ones and dynamic ecological interactions determine which species are viable. The food-web structure thereby emerges from the dynamical interplay between speciation and trophic interactions. The proposed model is less abstract than earlier evolutionary food web models in the sense that all three evolving traits have a clear biological meaning, namely the average body mass of the individuals, the preferred prey body mass, and the width of their potential prey body mass spectrum. We observed networks with a wide range of sizes and structures and high similarity to natural food webs. The model networks exhibit a continuous species turnover, but massive extinction waves that affect more than 50% of the network are not observed. PMID:26042870
Evolutionary ecology in silico: evolving food webs, migrating population and speciation
Dietrich Stauffer; Ambarish Kunwar; Debashish Chowdhury
After a brief review of our recent works on ōunifiedö models of evolutionary ecology, we have generalized our ōunifiedö model by taking into account spatial variations from one ōpatchö to another. We model the spatial extension of the ecosystem (i.e., the geography) by a square lattice where each site corresponds to a distinct ōpatchö. A distinct self-organizing hierarchical food web
Experimental evidence for alternative stable equilibria in a benthic pond food web
Jonathan M. Chase
Both local and initial conditions have been implicated in causing variation in the strengths of predator effects among natural communities. In this study, I performed a controlled mesocosm experiment using two common snails, Physella gyrina and Helisoma trivolvis, and their insect predator, Belostoma flumineum, to explicitly quantify and understand the causes of previously observed variation in food web interactions in
Abstract The cascade model successfuly predicts many patterns in reported food webs. A key assumption of
Notre Dame, University of
Abstract The cascade model successfuly predicts many patterns in reported food webs. A key of the standard cascade model is that trophic links not prohibited by the hierarchy occur with equal probability the cascade mod- el. These results suggest that models with heterogene- ous predation probabilities will fit
Reciprocal diversification in a complex plant-herbivore-parasitoid food web
Tommi Nyman; Folmer Bokma; Jens-Peter Kopelke
BACKGROUND: Plants, plant-feeding insects, and insect parasitoids form some of the most complex and species-rich food webs. According to the classic escape-and-radiate (EAR) hypothesis, these hyperdiverse communities result from coevolutionary arms races consisting of successive cycles of enemy escape, radiation, and colonization by new enemy lineages. It has also been suggested that \\
Resource Edibility and Trophic Exploitation in an Old-Field Food Web
Oswald J. Schmitz
I tested a food web model that predicts how environmental productivity (nutrient supply) and top carnivores should mediate interactions among herbivores, edible plants, and plants that are resistant to herbivory because they possess anti-herbivore defenses. Feeding trials with the dominant grasshopper herbivore at the study site confirmed that certain plant species were resistant to herbivory because of protection by pubescent
EVects of seasonality and fish movement on tropical river food webs
K. O. Winemiller; D. B. Jepsen
Tropical rivers and their associated floodplain habitats are dynamic habitat mosaics to which fishes are challenged to respond in an adaptive manner. Migratory fishes create linkages among food webs that are partitioned along a nested hierarchy of spatial scales. Such linkages are examined across a hierarchy of spatio-temporal scales, ranging from small streams to entire drainage basins, for rivers in
Productivity and food web structure: association between productivity and link richness among top predators
Summary 1. A prime goal in ecology is to understand the consequences of different productivity levels on system structure and stability. The number of trophic connections per species is a main parameter of food web structure often associated with total number of species and disturbance but not with productivity. We analyse the association between number of trophic connections and productivity
Food-web connectance and predator interference dampen the paradox of enrichment
Bj÷rn C. Rall; Christian Guill; Ulrich Brose
Classic consumer-resource models with hyperbolic functional responses predict that enrichment increases the average biomasses of the species, but eventually leads to species' extinction due to accelerated oscillations (''paradox of enrichment''). However, empirical studies have stressed the complexity of natural food webs and the dominance of sigmoid or predator-interference functional responses, which may dampen population oscillations due to enrichment. Using analytical
Food-Web Structure of Seagrass Communities across Different Spatial Scales and Human Impacts
Marta Coll; Allison Schmidt; Tamara Romanuk; Heike K. Lotze
Seagrass beds provide important habitat for a wide range of marine species but are threatened by multiple human impacts in coastal waters. Although seagrass communities have been well-studied in the field, a quantification of their food-web structure and functioning, and how these change across space and human impacts has been lacking. Motivated by extensive field surveys and literature information, we
Using food web dominator trees to catch secondary extinctions in action
Antonio Bodini; Michele Bellingeri; Stefano Allesina; Cristina Bondavalli
In ecosystems, a single extinction event can give rise to multiple 'secondary' extinctions. Conservation effort would benefit from tools that help forecast the consequences of species removal. One such tool is the dominator tree, a graph-theoretic algorithm that when applied to food webs unfolds their complex architecture, yielding a simpler topology made of linear pathways that are essential for energy
Random Sequential Generation of Intervals for the Cascade Model of Food Webs
Yoshiaki Itoh
The cascade model generates a food web at random. In it the species are labeled from 0 to $m$, and arcs are given at random between pairs of the species. For an arc with endpoints $i$ and $j$ ($i
Evolution of body size in food webs: does the energetic equivalence rule hold?
Nicolas Loeuille; Michel Loreau
The energetic equivalence rule (EER), which is derived from empirical observations linking population density and body size and from the allometric law linking metabolism and body size, predicts that the amount of energy used by the various species should be independent of body size. Here, we examine this hypothesis using a model that allows entire food webs to emerge from
Bacterial traits, organism mass, and numerical abundance in the detrital soil food web of Dutch
Cohen, Joel E.
, collembolans, detritus, food web, microbial quotient, mites, nematodes, qCO2, soil basal respiration. Ecology). As the microbial biomass comprises the majority of the total biomass in soil, the role of top-down regulation). A useful quantitative approach to an ecological community, and to the soil community in particular
Food-web structure and network theory: The role of connectance and size
Jennifer A. Dunne; Richard J. Williams; Neo D. Martinez
Networks from a wide range of physical, biological, and social systems have been recently described as ''small-world'' and ''scale- free.'' However, studies disagree whether ecological networks called food webs possess the characteristic path lengths, clustering coefficients, and degree distributions required for membership in these classes of networks. Our analysis suggests that the disagree- ments are based on selective use of
The manuscript examines the effects of hydrology and nutrient enrichment on food-web structure. We find that the hydraulic residence time is a paramount constraint upon the relative contributions of planktonic versus benthic production to the fish community. Nutrient enrichment...
Indirect effects of metal contamination on energetics of yellow perch (Perca flavescens) resulting from food web
Rasmussen, Joseph
Indirect effects of metal contamination on energetics of yellow perch (Perca flavescens) resulting (Perca flavescens) diet, growth and activity levels from lakes along a metal-contamination gradient were, lake food web, metal contamination, Perca flavescens, stunting, Sudbury, yellow perch Introduction
Dams and downstream aquatic biodiversity: Potential food web consequences of hydrologic and geomorphic change
Power, M.E.; Dietrich, W.E.; Finlay, J.C. [Univ. of California, Berkeley, CA (United States)
Responses of rivers and river ecosystems to dams are complex and varied, as they depend on local sediment supplies, geomorphic constraints, climate, dam structure and operation, and key attributes of the biota. Therefore, {open_quotes}one-size-fits-all{close_quotes} prescriptions cannot substitute for local knowledge in developing prescriptions for dam structure and operation to protect local biodiversity. One general principle is self-evident: that biodiversity is best protected in rivers where physical regimes are the most natural. A sufficiently natural regime of flow variation is particularly crucial for river biota and food webs. We review our research and that of others to illustrate the ecological importance of alternating periods of low an high flow, of periodic bed scour, and of floodplain inundation and dewatering. These fluctuations regulate both the life cycles of river biota and species interactions in the food webs that sustain them. Even if the focus of biodiversity conservation efforts is on a target species rather than whole ecosystems, a food web perspective is necessary, because populations of any species depend critically on how their resources, prey, and potential predators also respond to environmental change. In regulated rivers, managers must determine how the frequency, magnitude, and timing of hydrologic events interact to constrain or support species and food webs. Simple ecological modeling, tailored to local systems, may provide a framework and some insight into explaining ecosystem response to dams and should give direction to mitigation efforts. 78 refs.
Food Web Changes over Fourteen Years Following Introduction of Rainbow Smelt into a Colorado Reservoir
Brett M. Johnson; John P. Goettl Jr
Rainbow smelt Osmerus mordax were introduced into Horsetooth Reservoir, Colorado, in 1983 to increase prey availability for walleyes Stizostedion vitreum. The introduction was highly successful. Rainbow smelt abundance reached at least 0.4 fish\\/m within 6 years, and walleye growth improved by 50%. Zooplankton sampling provided the first clues that the Horsetooth Reservoir food web was undergoing dramatic changes in response
Detritus fuels ecosystem metabolism but not metazoan food webs in San Francisco estuary's freshwater delta
Sobczak, W.V.; Cloern, J.E.; Jassby, A.D.; Cole, B.E.; Schraga, T.S.; Arnsberg, A.
Detritus from terrestrial ecosystems is the major source of organic matter in many streams, rivers, and estuaries, yet the role of detritus in supporting pelagic food webs is debated. We examined the importance of detritus to secondary productivity in the Sacramento and San Joaquin River Delta (California, United States), a large complex of tidal freshwater habitats. The Delta ecosystem has low primary productivity but large detrital inputs, so we hypothesized that detritus is the primary energy source fueling production in pelagic food webs. We assessed the sources, quantity, composition, and bioavailability of organic matter among a diversity of habitats (e.g., marsh sloughs, floodplains, tidal lakes, and deep river channels) over two years to test this hypothesis. Our results support the emerging principle that detritus dominates riverine and estuarine organic matter supply and supports the majority of ecosystem metabolism. Yet in contrast to prevailing ideas, we found that detritus was weakly coupled to the Delta's pelagic food web. Results from independent approaches showed that phytoplankton production was the dominant source of organic matter for the Delta's pelagic food web, even though primary production accounts for a small fraction of the Delta's organic matter supply. If these results are general, they suggest that the value of organic matter to higher trophic levels, including species targeted by programs of ecosystem restoration, is a function of phytoplankton production. ?? 2005 Estuarine Research Federation.
Columbia River food webs: Developing a broader scientific foundation for river restoration
Alldredge, J. Richard; Beauchamp, David; Bisson, Peter A.; Congleton, James; Henny, Charles; Huntly, Nancy; Lamberson, Roland; Levings, Colin; Naiman, Robert J.; Pearcy, William; Rieman, Bruce; Ruggerone, Greg; Scarnecchia, Dennis; Smouse, Peter; Wood, Chris C.
The objectives of this report are to provide a fundamental understanding of aquatic food webs in the Columbia River Basin and to illustrate and summarize their influences on native fish restoration efforts. The spatial scope addresses tributaries, impoundments, the free-flowing Columbia and Snake rivers, as well as the estuary and plume. Achieving the Council's vision for the Columbia River Fish and Wildlife Program (NPCC 2009-09) of sustaining a "productive and diverse community" that provides "abundant" harvest, is best accomplished through a time-prioritized action plan, one that complements other approaches while addressing important challenges and uncertainties related to the Basin's food webs. Note that the oceanic food webs, although of immense importance in sustaining fish populations, are not considered beyond the plume since they involve an additional set of complex and rapidly evolving issues. An analysis of oceanic food webs of relevance to the Columbia River requires a separately focused effort (e.g., Hoegh- Guldberg and Bruno 2010).
Luther, Douglas S.
FOOD WEB STRUCTURE AND TROPHIC DYNAMICS OF A SUBTROPICAL PLANKTON COMMUNITY, WITH AN EMPHASIS of a subtropical plankton community were investigated to assess the ecological importance of metazoan organisms community. The feeding capabilities of warrn- water appendicularians on natural plankton prey were
We are exploring the use of food web properties to characterize nearshore and offshore habitats in the Great lakes. We analyzed the stable isotope signatures of benthos (predominantly Diporeia hoyi) and plankton from Lake Superior habitats ranging from 20m to 300m depth......
Differential support of lake food webs by three types of terrestrial organic carbon
Berkowitz, Alan R.
across ecosystem boundar- ies can also affect the metabolic balance of the receiving system by providing and James R. Hodgson3 1 Institute of Ecosystem Studies, Box AB (65 Sharon Turnpike), Millbrook, NY 12545 Organic carbon inputs from outside of ecosystem boundaries potentially subsidize recipient food webs. Four
Mercury biomagnification in the food web of Lake Tanganyika (Tanzania, East Africa)
L. Campbell; Piet Verburg; D. G. Dixon; R. E. Hecky
Lake Tanganyika is a globally important lake with high endemic biodiversity. Millions of people in the lake basin depend on several fish species for consumption. Due to the importance of fish consumption as an exposure route of mercury to humans, we sampled Lake Tanganyika in 2000 to assess total mercury concentrations and biomagnification of total mercury through the food web.
Bioaccumulation of 137Cs in pelagic food webs in the Norwegian and Barents Seas
Hilde Elise Heldal; Lars F°yn; Per Varskog
Knowledge and documentation of the levels of radioactive contamination in fish stocks important to Norwegian fisheries is of major importance to Norwegian consumers and fish export industry. In the present study, the bioaccumulation of caesium-137 (137Cs) has been investigated in marine food webs in the Barents and Norwegian Seas. The contents of 137Cs in the different organisms were generally low
Quantification of Bt-endotoxin exposure pathways in carabid food webs across multiple transgenic events
Julie A. Peterson; John J. Obrycki; James D. Harwood
Despite the reported specificity of Bacillus thuringiensis proteins against target pests, a number of studies have indicated that the uptake of Bt-endotoxins from bioengineered crops could have negative effects on natural enemies. It is therefore essential to quantify exposure pathways in non-target arthropod food webs across multiple transgenic events. Adult ground beetles (Coleoptera: Carabidae) were collected from transgenic corn fields
Positive complexity¢stability relations in food web models without foraging adaptation
Boris Kartascheff; Christian Guill; Barbara Drossel
May's [1972. Will a large complex system be stable? Nature 238, 413¢414] local stability analysis of random food web models showed that increasing network complexity leads to decreasing stability, a result that is contradictory to earlier empirical findings. Since this seminal work, research of complexity¢stability relations became one of the most challenging issues in theoretical ecology. We investigate conditions for
Carbon steady-state model of the planktonic food web of Lake Biwa, Japan
SUMMARY 1. A steady-state model of carbon flows was developed to describe the summer planktonic food web in the surface mixed-layer of the North Basin in Lake Biwa, Japan. This model synthesised results from numerous studies on the plankton of Lake Biwa. 2. An inverse analysis procedure was used to estimate missing flow values in a manner consistent with known
Identification of Bacterial Micropredators Distinctively Active in a Soil Microbial Food Web
Tillmann Lueders; Reimo Kindler; Anja Miltner; Michael W. Friedrich; Matthias Kaestner
The understanding of microbial interactions and trophic networks is a prerequisite for the elucidation of the turnover and transformation of organic materials in soils. To elucidate the incorporation of biomass carbon into a soil microbial food web, we added 13C-labeled Escherichia coli biomass to an agricultural soil and identified those indigenous microbes that were specifically active in its mineralization and
Trophic efficiency of the planktonic food web in a coastal ecosystem dominated by Phaeocystis colonies
V. Rousseaua; S. Becquevort; J.-Y. Parent; S. Gasparini; M.-H. Darob; M. Tackxb; C. Lancelot
The trophic efficiency of the planktonic food web in the Phaeocystis-dominated ecosystem of the Belgian coastal waters was inferred from the analysis of the carbon flow network of the planktonic system subdivided into its different trophodynamic groups. A carbon budget was constructed on the basis of process-level field experiments conducted during the spring bloom period of 1998. Biomass and major
Food-web structure in low-and high-dimensional trophic niche spaces
Dieckmann, Ulf
in each column indicating a consumer's diet, can then be derived. A niche-overlap graph (Cohen 1977 that their foraging niches (figure 1a) overlap. If the niche-overlap graph of a food web can be represented by the overlaps of foraging niches given by intervals along a line, the graph is said to be interval (Benzer 1959
BSAFs and Food Web Modeling for Establishing Contaminant Relationships between Biota and Sediment
The presentation will cover how to measure and evaluate BSAFs (biota-sediment accumulation factors), and how to construct, calibrate, validate, and evaluate food web models. The presentation will also discuss the advantages of the two approaches for establishing contaminant rel...
Contribution of Allochthonous Carbon Subsidies to the Minho Estuary Lower Food Web
To study the contribution of autochthonous and allochthonous organic matter (OM) sources fuelling the lower food web in Minho River estuary (N-Portugal, Europe), we characterized the carbon (?13C) and nitrogen (?15N) stable isotope ratios of zooplankton and their potential OM sou...
Plankton are traditionally viewed as the basis for limnetic food webs, with zooplankton acting as an energy gateway between phytoplanktonic primary producers and fish. Often, benthic production is considered to be important primarily to the benthos and in shallow systems, such as...
Grazing food web view from compound-specific stable isotope analysis of amino acids
Technology Transfer Automated Retrieval System (TEKTRAN)
Knowledge of the trophic position (TP) of organisms in food webs allows ecologists to track energy flow and trophic linkages among organisms in complex networks of ecosystems. Compound-specific stable isotope analysis (CSIA) of amino acids has been employed as a relatively new method with the high p...
Camille McNeely; Jacques C. Finlay; Mary E. Power
We investigated the effect of grazing by a dominant invertebrate grazer (the caddisfly Glossosoma penitum) on the energy sources used by other consumers in a headwater- stream food web. Stable isotope studies in small, forested streams in northern California have shown that G. penitum larvae derive most of their carbon from algae, despite low algal standing crops. We hypothesized that
Evolutionary food web model based on body masses gives realistic networks with permanent species turnover
Allhoff, K. T.; Ritterskamp, D.; Rall, B. C.; Drossel, B.; Guill, C.
The networks of predator-prey interactions in ecological systems are remarkably complex, but nevertheless surprisingly stable in terms of long term persistence of the system as a whole. In order to understand the mechanism driving the complexity and stability of such food webs, we developed an eco-evolutionary model in which new species emerge as modifications of existing ones and dynamic ecological interactions determine which species are viable. The food-web structure thereby emerges from the dynamical interplay between speciation and trophic interactions. The proposed model is less abstract than earlier evolutionary food web models in the sense that all three evolving traits have a clear biological meaning, namely the average body mass of the individuals, the preferred prey body mass, and the width of their potential prey body mass spectrum. We observed networks with a wide range of sizes and structures and high similarity to natural food webs. The model networks exhibit a continuous species turnover, but massive extinction waves that affect more than 50% of the network are not observed. PMID:26042870
Seeking Emotional Involvement in Science Education: Food-Chains and Webs.
ERIC Educational Resources Information Center
Alsop, Steve
Documents a study of emotion in two grade 8 science classrooms. Describes a lesson on food-chains and webs designed with a conceptual and an emotional agenda. Discusses issues of emotion, sensation and relevance in science teaching. (Author/MM)
Atrazine effects on the microbial food web in tidal creek mesocosms
M. E. DeLorenzo; J. Lauth; P. L. Pennington; G. I. Scott; P. E. Ross
Atrazine effects on the microbial food web were assessed in mesocosms designed to simulate a southeastern tidal creek ecosystem. The test chambers simulate the major features unique to estuarine systems, such as tidal flow and salinity changes. Microbial communities were colonized on artificial substrates and analyzed for productivity, biomass, and community composition. Atrazine was found to reduce chlorophyll a, phototrophic
Structural and functional succession in the nematode fauna of a soil food web
H. Ferris; M. M. Matute
Soil microplots were amended with organic materials of varying nature and complexity but providing similar amounts of carbon. Materials were either placed on the soil surface or incorporated. Unamended and mineral fertilizer control plots were established. Plots were maintained vegetation-free so that the food web activity was fueled by resident soil organic matter and the input material. Enrichment-opportunist bacterivore nematodes
Effects of grassland plant species diversity on soil animal food web components
Alexandru Milcu; Stephan Partsch; Stefan Scheu
To investigate the feedback of the plant community to the soil food web we set up a greenhouse experiment manipulating both (1) the diversity of a model grassland community, consisting of 43 common plant species of a Central European Arrhenatherion grassland following \\
UV Effects on Marine Planktonic Food Webs: A Synthesis of Results from Mesocosm Studies
Claude Belzile; Serge Demers; Gustavo A. Ferreyra; Irene Schloss; Christian Nozais; Karine Lacoste; Behzad Mostajir; Suzanne Roy; Michel Gosselin; Emilien Pelletier; S¶nia M. F. Gianesella; Maria Vernet
UV irradiance has a broad range of effects on marine planktonic organisms. Direct and indirect effects on individual organisms have complex impacts on food-web structure and dynamics, with implications for carbon and nutrient cycling. Mesocosm experiments are well suited for the study of such complex interrelationships. Mesocosms offer the possibility to conduct well-controlled experiments with intact planktonic communities in physical,
The effects of energy input, immigration and habitat size on food web structure: a microcosm experiment
Matthew Spencer; Philip H. Warren
It has been hypothesised that larger habitats should support more complex food webs. We consider three mechanisms which could lead to this pattern. These are increased immigration rates, increased total productivity and spatial effects on the persistence of unstable interactions. Experiments designed to discriminate between these mechanisms were carried out in laboratory aquatic microcosm communities of protista and bacteria, by
Anadromous alewives ( Alosa pseudoharengus ) contribute marine-derived nutrients to coastal stream food webs
Annika W. Walters; Rebecca T. Barnes; David M. Post
Diadromous fish are an important link between marine and freshwater food webs. Pacific salmon (Oncorhyn- chus spp.) strongly impact nutrient dynamics in inland waters and anadromous alewife (Alosa pseudoharengus) may play a similar ecological role along the Atlantic coast. The annual spawning migration of anadromous alewife contributes, on average, 1050 g of nitrogen and 120 g of phosphorus to Bride