Herpetofauna III

Contributed Oral Presentations

Contributed paper sessions will be available on-demand for the duration of the conference, then again at the conclusion of the conference.


Carryover Effects of Pesticide Exposure and Pond Drying on Locomotor Ability and Avoidance Behavior in a Vernal Pool-Breeding Amphibian
Cassandra Thompson; Megan Sweeney; Viorel Popescu
Neonicotinoids are a common class of systemic pesticides used in the US that often have sublethal effects on amphibian growth, development, and behavior. Imidacloprid, a neonicotinoid pesticide, is extensively applied throughout the eastern US to control the spread of invasive hemlock wooly adelgids (Adelges tsugae), without fully understanding the impacts on the aquatic and terrestrial stages of pool-breeding amphibians and how it may interact with additional aquatic stressors. As hydroperiod (how fast a pond dries) varies widely across vernal pools and wetlands and can have direct negative impacts on amphibian development and terrestrial fitness, we sought to understand the combined effects of these stressors on larval development and survival and juvenile locomotor performance and behavior of the wood frog (Rana sylvatica). We manipulated hydroperiod length (nondrying vs drying) in 1000 liter cattletank mesocosms with and without Imidacloprid exposure (10 ppb) for a total of four aquatic treatments. While we did not find any significant differences in morphology (mass/SVL) of metamorphs from the four treatments, larval survival to metamorphosis was lowest in the pesticide x hydroperiod treatment. Juveniles from pesticide treatments performed significantly better during initial endurance trials, however, after exposure to a low concentration of the pesticide, individuals from pesticide treatments experienced greater declines in performance compared to non-pesticide treatments. The biological and physiological insights from this work can be used to better understand the impacts multiple aquatic stressors have on amphibian larval development and help to better the risks of the application and use of such systemic pesticides.
A Demographic PVA to Support Conservation Decision Making for an Endangered Snake with Limited Monitoring Data
Anna M. Tucker; Conor McGowan; Eneilis Mulero; Nicole Angeli; Jan Zegarra
Conservation planning for rare and threatened species is often made more difficult by a lack of research and monitoring data. In such cases, managers may rely on qualitative assessments of species risk that lack explicit acknowledgement of uncertainty. Snakes are a group of high conservation concern that are also notoriously difficult to monitor. Here we demonstrate a quantitative population projection for a data-deficient species, the Puerto Rican boa (Chilabothrus inornatus) using expert knowledge and published information about species life history and threats to persistence. Using this model, we simulated population dynamics over 30 years under four scenarios of future urbanization and found that there was an increased probability of population decline as urbanization rates increased. We conduct a sensitivity analysis to evaluate the sensitivity of outcomes to model inputs, a practice that may also be useful in recovery planning. The sensitivity analyses also provide insight into how the future trajectories would change if the elicited demographic rates are incorrect. Even when data are sparse, quantitative methods can often be used to produce rigorous and reproducible estimates of future status with quantifiable uncertainty.
Population Genetic Analyses of Western Massasauga Rattlesnakes Provide Little Support for Recognized Desert and Prairie Subspecies
Rian Bylsma; Toby Hibbits; Wade Ryberg; J. Andrew DeWoody
The Western Massasauga rattlesnake (Sistrurus tergeminus) is a small, North American rattlesnake found west of the Mississippi River. S. tergeminus is divided into two putative subspecies, Desert (S. t. edwardsii) and Prairie Massasaugas (S. t. tergeminus) based upon variation in morphology, coloration, and habitat. The Desert Massasauga subspecies is in consideration for federal listing under the Endangered Species Act. We generated whole genome sequence data for both putative subspecies and then developed curated suites of genetic markers from different fractions of the genome to test for population structure across much of the Western Massasauga range. FST results indicate little differentiation (inter-subspecific FST = 0.0239) between subspecies groups. Our population genetic analyses reveal only equivocal evidence for two taxonomic entities (i.e., subspecies) within S. tergeminus, but we did identify isolation by distance. Overall, our genomic and population genetic analyses provide little support that formal taxonomic protection is warranted.
Optimal Foraging and Multiscale, Behavior-Mediated Habitat Use in Timber Rattlesnakes
William E. Peterman; Annalee M. Tutterow; Andrew S. Hoffman
Habitat use and selection are central to our understanding of species’ ecology and resource requirements. Numerous studies have thoroughly described habitat selection and use in rattlesnakes generally, and timber rattlesnakes (Crotalus horridus) specifically. However, these studies rarely differentiate the behaviors of rattlesnakes in relation to habitat use. In this study, we assessed multiscale habitat use as a function of four distinct behaviors: foraging, digestion, ecdysis, and gestation. Using telemetry data collected for 43 snakes over four years and fine-scale spatially continuous LiDAR data describing topographic features and forest structure, we fit mixed effects models to determine the landscape and habitat features that best predicted each observed behavior. We assessed spatial variables at multiple scales, ranging from 5-105-m. Additionally, we modeled the distribution of rattlesnake prey, small mammals, using observation data collected from camera traps deployed at 242 unique locations across our focal landscape over two years. Our best models of small mammal distribution were then projected across the landscape. Finally, we assessed whether snakes foraged optimally in relation to small mammal distributions. Our analyses revealed that rattlesnakes are uniquely selecting topographic and habitat features at different scales for different behaviors, and that these multiscale models outperformed single-scale models. Snake foraging could only moderately be explained by multiscale habitat variables. However, the occurrence of small mammals was highly predictive of snake foraging, suggesting that snakes have the ability to maximize foraging efficiency in relation to prey availability. Our study provides a novel perspective of habitat use in timber rattlesnakes and adds to the limited knowledge of timber rattlesnake ecology in the Midwest. A clear understanding of the landscape and habitat features necessary for rattlesnakes will facilitate more effective and targeted habitat management.
Intraspecific Partitioning of Dietary Resources in a Common Generalist Snake
Micah W. Perkins; Perri K. Eason
Intrapopulation niche differentiation has important ecological consequences, in part because individual dietary differences can broaden species’ niches and reduce competition. Such individual dietary specialization can be a result of diets differing with body size, age class, sex, or some combination of these factors. We focused on dietary specialization in a generalist predator, the northern watersnake (Nerodia sipedon). We used stable isotope analyses to determine differences in dietary resource utilization patterns and intraspecific niche partitioning. Overall, females had enriched δ15N levels, indicating that they fed at higher trophic levels than males (F1=12.02, p=0.0008). Females also foraged over a larger range of trophic levels (δ15N; F1,109=11.24, P=0.001). Both isotopes became enriched as snake size increased (δ13C, F1 = 30.01, P<0.0001; δ15N, F1=71.59, P<0.0001), with longer snakes taking more prey from terrestrial habitats and feeding at higher trophic levels. However, the effects of size differed by sex for both isotopes. In males, δ13C enriched at a greater rate than in females (F1=8.36, P=0.005), indicating that males’ diets shifted more quickly to terrestrial prey as body size increased. In females, δ15N enriched at a greater rate (F1=7.47, P=0.007), suggesting females shifted more strongly to prey from higher trophic levels with increasing body size. δ13C variance tended to be greater in males (F1,109=3.67, P=0.058), with males possibly feeding across a wider range of habitats. In sum, sex, body size, and their interaction had complex effects on diet and intraspecific niche partitioning, likely reducing intraspecific competition and resulting in a broad dietary niche.
Factors Influencing Reproductive Success for Boreal Toads in the Southern Rockies
John Crockett; Larissa Bailey; Erin Muths
Populations of pond-breeding amphibians often have variable recruitment with large numbers of individuals metamorphosing in some years and none in other years (i.e., reproductive failure). Environmental processes, such as pond drying, and biological factors, such as disease and predators, can influence complete reproductive failure for local amphibian populations. We used multi-state occupancy models to explore factors influencing probability of breeding and successful metamorphosis (the complement of reproductive failure) in populations of boreal toads (Anaxyrus boreas boreas) in the southern Rocky Mountains. We fit both static and dynamic models to ten years (2001-2010) of detection-nondetection data from over 80 historic breeding sites to tested relationships between these probabilities and the presence of a pathogen (Batrachochytrium dendrobatidis), elevation, hydrology, relative snowpack in a given year, and the presence of trout. We found that the probability of breeding was higher at high-elevation sites and the probability of metamorphosis, given breeding, was influenced by an interaction between hydrology of the site and relative annual snowpack. The probability of metamorphosis was higher at ephemeral sites in years of relatively high snowpack, while at permanent sites, years of low snowpack lead to higher probabilities of metamorphosis. Our results suggest that both ephemeral and permanent sites likely to support successful reproduction in years of median snowpack, but conservation actions may be beneficial in low snowpack years and at sites with infrequent breeding.
Saving the Last Frogs in the Desert: Ecohydrological Complexity of Drought Mitigation
David S. Pilliod; Mark B. Hausner; Rick D. Scherer
Droughts that are so severe or long that they tip ecological systems beyond their natural range of variability are increasingly common as a result of climate change. Drought mitigation actions often attempt to alter the ecohydrology of a site. The objectives of this study were to examine the effectiveness of drought mitigation actions that aimed to reduce stream incision, increase surface water, improve riparian habitat, and increase populations of the Columbia spotted frog (Rana luteiventris) that had declined precipitously during multiple drought cycles in a semi-arid valley in central Nevada, USA. We assessed drought and mitigation responses using the Standardized Precipitation Evapotranspiration Index (SPEI) and Normalized Difference Vegetation Index (NDVI) derived from a 30-year time series of satellite imagery and gridded weather data. We then used a before-after analysis of a 23-year mark-recapture dataset to evaluate the effects of drought mitigation on the probability of survival and recruitment rates in frog populations. Preliminary results suggest that drought, as measured by SPEI in the summer, was detectable in our study meadows using NDVI as a response variable. Then, after accounting for interannual variation in precipitation, we found that NDVI increased significantly from before to after drought mitigation actions indicating that the management actions influenced the hydrology and vegetation of the meadows. Frog survival generally increased with NDVI, but habitat manipulation had an even stronger effect than NDVI where new ponds were excavated. Frog recruitment rates increased in years with higher NDVI, but responses to mitigation actions were more variable. We conclude that it is possible to mitigate some of negative effects of ecological drought through habitat manipulation, but also illustrate the ecohydrological complexity of drought mitigation given the inherent spatial and temporal variability in ecological systems.


Contributed Oral Presentations
Location: Virtual Date: Time: -