Spatial variation in trophic ecology of small mammals in wetlands: support for hydrological drivers

Food webs composed of similar consumers can vary based on nutrient input, habitat structure, and other factors. For wetland‐associated species, fluctuating water levels can potentially affect habitat quality, which in turn can affect trophic diversity. Our objective was to determine spatiotemporal variation in the trophic structure of small mammals at two wetland complexes (floodplain and mineland) in southern Illinois. We live‐trapped small mammals during 2011–2013 at nine wetland patches on the Mississippi River floodplain and 14 patches at a reclaimed mineland. We collected hair samples from six species of small mammals ( n  =   428) at these wetland complexes. We analyzed C and N stable isotopes for three mammal taxa ( Oryzomys palustris , Peromyscus spp., Microtus ochrogaster ) to compare diet between species, sites, and times. Food sources (vegetation and invertebrates) were collected to form the isotopic baseline. We found no seasonal difference in diet composition, but isotopic values varied between sites and species. At the floodplain site, both δ 15 N and δ 13 C isotopic values for Oryzomys were more variable and completely enclosed that of Peromyscus . At the mining site, Peromyscus were at a lower trophic level (δ 15 N) and had a separate and less variable δ 13 C values from Oryzomys . Microtus was at a lower trophic position than the other two species at both sites. These results point to reduced niche overlap between Oryzomys and Peromyscus at the mining site, perhaps due to lower habitat quality and limited suitable resources. At the floodplain site, we conclude that more dynamic hydrology gave rise to higher biodiversity and more resources allowing small mammals to use similar food items.