{'fraction_non_alphanumeric': 0.035445258487256215, 'fraction_numerical': 0.029873078113713755, 'mean_word_length': 4.8594316807738815, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 1, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 5, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Effects of fragmentation on the seed predation and dispersal by rodents differ among species with different seed size

Abstract Fragmentation influences the population dynamics and community composition of vertebrate animals. Fragmentation effects on rodent species in forests may, in turn, affect seed predation and dispersal of many plant species. Previous studies have usually addressed this question by monitoring a single species, and their results are contradictory. Very few studies have discussed the fragmentation effect on rodent–seed interaction among tree species with different seed sizes, which can significantly influence rodent foraging preference and seed fate. Given that fruiting periods for many coexisting plant species overlap, the changing foraging preference of rodents may substantially alter plant communities. In this study, we monitored the dispersal and predation by rodents of 9600 seeds, belonging to 4 Fagaceae species with great variation in seed size, in both the edge and interior areas of 12 tropical forest fragments ranging in area from 6.3 to 13872.9 ha in Southwest China. The results showed that forest fragmentation altered the seed fates of all the species, but the intensity and even the direction of fragmentation effect differed between species with large versus small seeds. For the seeds harvested, fragment size showed negative effects in forest interiors but positive effects at edges for the 2 large‐seeded species, but showed little effect for the 2 small‐seeded species. For the seeds removed, negative effects of fragment size only existed among the small‐seeded species. The different fragmentation effect on seed dispersal and predation among plant species may, in turn, translate into the composition differences of the regeneration of the whole fragmented forest.


INTRODUCTION
Fragmentation is a major threat to biodiversity in forests (Fahrig 2003;Laurance et al. 2006). Populations of many animals and plants have declined as forest fragmentation has increased (Laurance 1994;Cordeiro & Howe 2001;Da Silva Jr & Pontes 2008), and regional populations of several large mammals have been extirpated (Terborgh et al. 2001;Crooks 2002;Foley et al. 2005;Newbold et al. 2013). However, some small mammals, especially certain rodent species, may benefit from fragmentation because of the loss of predators and competitors, and their quick breeding ability (Laurance et al. 2002;Gibson et al. 2013;Morán-López et al. 2015;Mendes et al. 2016).
Rodents are both seed predators and seed dispersers in forests, thus influencing seedling regeneration, spatial distribution and diversity of trees Jansen et al. 2012;Xiao et al. 2013;Sidhu & Datta 2015;Zhang et al. 2016;Cao et al. 2017). Therefore, changes to rodent populations and their foraging preferences in fragments may influence the whole structure and diversity of plant communities (Cordeiro et al. 2009;Zhang et al. 2016). Fragment size and edge effects are usually considered as the 2 most important fragmentation parameters for plant-rodent interactions (Kollmann & Buschor 2003;Fleury & Galetti 2006;Aliyu et al. 2014;Mendes et al. 2016), but previous work on these interactions in forest fragments has yielded contradictory results. For example, in 2 separate studies in eastern Brazil, Andreazzi et al. (2012) showed that seeds of Attalea humilis were scatter-hoarded more frequently in the large fragments than small ones, but seed predation by rodents did not relate to fragment size, whereas Mendes et al. (2016) observed greater seed predation in smaller fragments. Aliyu et al. (2014) also found that seeds suffered more predation in small fragments and forest edges than in the continuous forest interior, which they attributed to greater fruit production at forest interior sites. Fleury and Galetti (2006) found that the seed predation was more common in medium-sized fragments than both small and large ones. Forest fragmentation also decreased the distance of seeds dispersed by rodents (Cramer et al. 2007;Aliyu et al. 2014; but see Morán-López et al. 2015).
As discussed above, the current studies do not tell a consistent story about how fragmentation affects seed predation and dispersal by rodents. This is very likely due to differences in the plant-animal systems being studied in these different locations. One source of variation is that fragmentation may change rodent community composition (Suzán et al. 2008), and different species of rodents often show different seed preferences during foraging (Munoz & Bonal 2008;Tamura & Hayashi 2008). A second source of variation may result from differences in seed characteristics of tree species studied at each site, as rodents predate seeds differently based on their characteristics. Numerous studies have demonstrated that seed size can significantly influence rodent foraging preference and, thus, seed fate (Moore et al. 2007;Wang & Chen 2009;Vander Wall 2010;Lichti et al. 2017). Most previous studies have targeted a single plant species in their experiments (Xiao et al. 2013;Mendes et al. 2016;Zhang et al. 2017). However, many coexisting species in forests fruit during similar periods, which may increase the role of rodent preference in seed fate, and, thus, forest composition (Garzon-Lopez et al. 2015;Yi & Wang 2015a). Changes of rodent foraging preference upon seed size may, in turn, lead to different effects on seed fate among plant species. However, very few studies have discussed this question. In this study, we monitored the seed dispersal and predation of 4 fagaceae species with great variation in seed size (2 large, 2 small), in 12 different sized tropical fragmented forests. We attempted to answer 2 questions. First, do forest fragmentation effects on rodent-plant interaction (i.e. seed dispersal and predation by rodents) differ significantly among plant species? Second, if so, does seed size partly explain this interspecific variation?

Study site
This study was conducted in the dry season (from December 2015 to April 2016) in the Xishuangbanna region, the northern edge of tropical Southeast Asia where the largest tropical rainforest in China is found. The annual mean temperature is 15.10-21.70 °C, and the annual precipitation is 1200-2500 mm, more than 80% of which occurs in the rainy season between May and October (Cao et al. 2006). Twelve fragmented forests were selected around Xishuangbanna Tropical Botanical Garden in Xishuangbanna Dai Autonomous Prefecture, Yunnan Province, Southwest China (21°55′N, 101°15′E). Our target fragments ranged in size from 6.30 to 13 872.87 ha and contained all the dominant forest types in this region (tropical rainforest, seasonal broadleaf forest and monsoon forest over limestone) (Table  S1) (Cao & Zhang 1997;Liu & Slik 2014).

Study species
Four fagaceae species were selected for the study, including 2 large-seeded species, Quercus acutissima (seed mass 3.91 ± 1.01 g, mean ± SD, n = 2400) and Castanopsis mekongensis (3.37 ± 0.89 g); and 2 small-seeded species, Castanopsis hystrix (0.74 ± 0.21 g) and Castanopsis echidnocarpa (0.51 ± 0.13 g). All the species are common in our study area, except Q. acutissima, for which seeds were collected in Menghai County, ap-proximately 80 km away from our study fragments. All the species have similar fruiting phenology and share the same rodent seed dispersal agents (e.g. Niviventer confucianus, Niviventer fulvescens, Rattus flavipectus and Maxomys surifer; Chen & Huang 1998;. All the experimental seeds were weighed and tagged using a modification of the methods of Xiao et al. (2006). A 0.6-mm diameter hole was drilled at the base of each seed, and a small white plastic tag (2.5 × 3.6 cm) with an individual number was tied through the hole with a thin steel thread (15 cm in length). When rodents cached the seed in the soil, the tags were usually left on the forest floor, making the seeds or seed fates easy to detect.

Experimental design
In each fragmented forest, 2 parallel transects were established in both the edge and interior area. The 2 edge transects were parallel to the forest fragment edge, with the distances being 3 and 18 m to the edge, respectively. The interior transects were at least 200 m from each edge of the forest, while for small fragments, the interior transects were established in the center of the forest with a distance to the edges being approximately 100 m. Five 20 × 20-cm plots were set up at intervals of 20 m along each transect.
At each plot, 40 tagged seeds (10 seeds × 4 plants species) were placed along a circle (approximately 15 cm in diameter), and then an infrared-triggered camera (Ltl-6210MC) was positioned at a height of 10 to 50 cm above ground to monitor the visiting animals. All the debris in the vision of the cameras was cleaned up to avoid false triggers. All the cameras were taken back after 20 days, and the seed fates were checked. Small rodents (88.8%, n = 9018 camera triggers), especially the nocturnal species (96.9%, n = 8008 camera triggers), were the dominant predators and dispersers of our experimental seeds. Seed fates were considered at several hierarchical levels: first, seeds were divided into those ignored and those harvested by rodents; next harvested seeds were divided into those eaten in situ and those removed by rodents; then removed seeds were divided into: seeds cached; seeds eaten after being transported; and missing seeds that were not found within a 20-m radius of the seed release plot (Wang & Yang 2014). For each removed seed that could be located, we also measured the distance to its original release plot.

Data analysis
All statistical analyses were conducted using the R statistical software version 3.2.5 (R Development Core Team 2016, www.R-project.org). As our data was nested in random effects and mostly followed non-normal distributions, we using mixed effects models as formulated in the package lme4 (Bates et al. 2014). Three analyses were conducted to evaluate seed fate categories at different stages during the rodent scatter-hoarding process: first, seeds harvested versus ignored at the original plots (analysis I); second, of the harvested seeds, those removed versus eaten at the plot site (analysis II); third, of the removed seeds, those cached versus eaten (analysis III). A fourth analysis was conducted to evaluate how far removed seeds were transported from their original location (analysis IV). The first 3 analyses involved binomial responses, so these were fitted using a generalized linear mixed effects model (GLMM). The fourth analysis involved exponentially distributed continuous data, which was log-transformed and fitted using a linear mixed effects model (LMM). The fixed and random effects terms included in the models were identical in all 4 analyses: fixed effects were fragment size (numeric, log transformed), location of seeds released (factor, forest edge or interior) and species (factor, C. echidnocarpa, C. hystrix, C. mekongensis and Q. acutissima). Random effects were considered in a nested structure (seed release plot was nested in fragment, which was nested in forest type). Models were evaluated using likelihood ratio tests (LRTs) on nested models (all compared to χ 2 -values with appropriate degrees of freedom for the number of parameter changes). Model subsetting was terminated where significant interactions were encountered following the principle of marginality.

Fragment effects on seed fates
Likelihood ratio tests confirmed that there were significant 3-way interactions between species, fragment size and location in all 4 analyses conducted (Table 1, Fig. 1). Thus, the full interaction model was evaluated in each case. Seed harvesting of the 2 large-seeded species, C. mekongensis and Q. acutissima, decreased with increasing fragment size at interior plots and increased at edge plots, whereas the effect of fragmentation on seed harvesting was much weaker for the 2 small-seeded species (C. echidnocarpa and C. hystrix) in both edge and interior locations (analysis I) (Fig. 1). By contrast, fragment size had a negative effect on seed removal of the small-seeded species at edge locations but not at interior locations, whereas it had no effect on removal of the 2 large-seeded species in either edge or interior locations (analysis II) (Fig. 1). Fragment size had a negative effect on seed caching of Q. acutissima in both edge and interior locations, and on seed caching of C. mekongensis at edge locations, but had no effect on caching of the 2 small species at either edge or interior locations (Fig.  1). Fragment size had a negative effect on dispersal distance of C. echidnocarpa seeds in interior locations but a positive effect in edge locations; however, an opposite pattern was shown for seeds of Q. acutissima (analysis IV). Fragment size showed little effect on dispersal distance of C. hystrix and C. mekongensis (Fig. 2).

DISCUSSION
In this study, both fragment size and forest edge showed some effects on each step of the foraging processes of scatter-hoarding rodents, but these effects var-ied greatly among different plant species.
As discussed in the Introduction, many studies have shown that forest fragmentation has significant effects on seed dispersal and predation by rodents, but they have found contradictory results. Some studies found that seeds were more likely to be removed and cached in large fragments than small fragments (Andreazzi et al. 2012), possibly because there are more species of rodents in large fragments (Nupp & Swihart 2000;Johnson & Karels 2015), while other studies found the opposite result, and their explanation was that more rodents existed in small fragments because of increased seed production and decreased population of predators (Morán-López et al. 2015;Mendes et al. 2016). Some studies found that seeds were predated more frequently in fragment edges than in forest interiors, which they attributed to greater understory vegetation in fragment edges, providing harvesters increased shelter from predators (Matlack 1994;Kollmann & Buschor 2003), but other studies observed less seed removal at forest edges and proposed that this was due to lower cover at forest edges affording less protection from predators (Wolf . However, in our study we have shown that patterns of seed foraging differ among species when they are released simultaneously in fragments of different sizes and in edge versus interior locations, suggesting that parsimonious interpretations such as those provided previously are not tenable. Our study also provides some evidence that one seed characteristic that might mediate these patterns is seed size, as there were clear differences during the foraging behavior at each step (harvesting, removing and caching) between large-seeded and small-seeded species. Seed size has been demonstrated to play an important role in mediating rodent foraging behavior upon seeds (Wang & Chen 2009;Vander Wall 2010;Lichti et al. 2017). In our study, the 2 large-seeded species Q. acutissima and C. mekongensis were more likely to have their seeds being removed and cached and transported to a further distance than the small-seeded species, C. echidnocarpa and C. hystrix (Figs 1 and 2).
Why did forest fragmentation effects on seed fate differ between large-seeded and small-seeded species? Different species of rodents usually show different foraging preferences during their scatter-hoarding processes (Yi & Wang 2015b), and rodent body size has often been considered as an important factor influencing the seed size-foraging preferences of scatter-hoarding rodents (Munoz & Bonal 2008;Tamura & Hayashi 2008). Forest fragmentation may influence the rodent community. For example, in North America the density of small-bodied white-footed mouse (Peromyscus leucopus) and eastern chipmunks (Tamias striatus) declined with forest area, whereas large-bodied gray squirrels (Sciurus carolinensis) increased with forest area (Nupp & Swihart 2000;Johnson & Karels 2015). The changes of relative density of different rodent species in the fragments may, in turn, lead to different effects on seed fate among different plant species. In our study, the camera trap data showed that neither fragment size nor forest edge significantly affected the relative abundance of the whole rodent community (unpublished data from 8 of our 12 fragments). This does not exclude that possibility that species composition is affecting the seed fate at each site. There were at least 5 rodent species (i.e. Niviventer fulvescens, Rattus flavipectus, Maxomys surifer, Niviventer confucianus and 1 unidentified species) in our study fragments, with body mass ranging from 60.30 to 238.70 g (unpublished data). These different rodent species have been shown to have different preferences on different sized seeds, including the species used in this study ). However, we could not assess the effects of different rodent species compositions, because it was difficult to identify rodent species from our camera traps due to the low quality of the pictures. Live-traps or high definition cameras are recommended in future studies.
In this study, we have mainly discussed the effects of seed size, but other seed traits, such as germination schedule, nutrition level and secondary metabolites, could also influence seed predation and dispersal by rodents (Vander Wall 2010; Lichti et al. 2017;Zhang et al. 2017). Most of these traits differed among our study species, but there was no apparent relationship between seed size and any of these traits (Table 2). Furthermore, our results showed no obvious differences of forest fragmentation effects on seed fate between seeds with different levels of tannin, fat, starch, protein content or coat thickness. However, we could not test the difference in forest fragmentation effects on seed fate between seeds with different germination schedules, as all the species used in this study are recalcitrant seeds and show no apparent dormancy.
In our study, quite a number of seeds (especially for Q. acutissima and C. mekongensis) were cached by ro- Coat thickness (mm), crude protein (%), crude fat (%), crude starch (%) and tannins (%) . ‡ The crude starch (%) of Q. acutissima (Wang et al. 2016). dents. Because of resource limitations we did not monitor the germination and survival of the cached seeds to investigate the longer-term effects on juvenile tree recruitment. However, many studies have found that seed dispersal and predation by rodents can significantly affect the composition and distribution pattern of the seedling community Jansen et al. 2014;Garzon-Lopez et al. 2015).
In conclusion, we have shown a complex influence of forest fragmentation on the rodent-seed interaction. Forest fragmentation affected the seed fate of all the species; however, the intensity and even the direction of this effect differed greatly among different species, and differed between species with small versus large seeds. The different effects of fragmentation on seed dispersal and predation among plant species may, in turn, translate into the recruitment differences across the whole fragmented forest.  1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48  49  50  51