Spatial variation in trophic position of small mammals between two wetland complexes

Background/Question/Methods

Wetlands vary greatly spatially and temporally in hydrology, and differences in hydrology between wetland complexes should be reflected in the trophic diversity of the communities occupying these areas. In particular, wetlands occurring on natural floodplains will have more dynamic hydrology compared to wetlands associated with reclaimed minelands. Wetlands are occupied by a suite of small mammals including rice rats (Oryzomys palustris) and white-footed and deer mice (Peromyscus spp).Our main objective was to investigate the spatio-temporal variation in community-wide trophic diversity at 2 wetland complexes (floodplain and mineland) in southern Illinois. We collected hair samples from small mammals (n=416 ) occurring at these wetland complexes.  We used analysis of C and N stable isotopes to compare food use between species, between sites, and across time.  Food sources (vegetation and invertebrates) were collected at each site to form the isotopic baseline. 

Results/Conclusions

Using stable isotope mixing models, we found no seasonal difference in isotope signatures, but signatures did differ between sites. Rice rats at both wetland complexes incorporated primarily (70-80%) invertebrates in their diet, and used more C₄ vegetation (30%) than C₃ (0%). Isotope signatures of mice varied greatly between the 2 sites. Mice at the floodplain site had diets similar to that of rice rats with ~80% invertebrates, and >C₄ vegetation than C₃ vegetation (~20% and 0% respectively). However, at the mining site, mice were at a much lower trophic level than rice rats and only incorporated 30% invertebrates in their diet. Vegetation consumption was also different with C₃ plants making up a greater part of their diet than C₄ vegetation (50% and 20% respectively). These isotope results point to niche-partitioning taking place at the mining site, perhaps due to lower habitat quality and limited suitable resources. At the floodplain site, the more dynamic hydrology might give rise to higher biodiversity and consequently provide more resources to allow small mammals to use similar food items.