Community structure and differential responses of aquatic turtles to agriculturally induced habitat fragmentation

Abstract

Several studies have shown that wetland loss and habitat fragmentation can alter diversity and abundance of herpetofauna, but taxonomic attention has been skewed towards amphibians. We assessed responses of aquatic turtles to features at multiple spatial scales in an intensively farmed region of the Midwestern United States. Spatially hierarchical sampling was conducted from 2001 to 2003 in 35 randomly selected 23-km2 cells throughout the upper Wabash River basin in Indiana. Hoop nets were used at wetlands to capture common snapping turtles (Chelydra serpentina serpentina) (n=258), midland painted turtles (Chrysemys picta marginata) (151), eastern spiny softshells (Apalone spinifera spinifera) (70), red-eared sliders (Trachemys scripta elegans) (59), northern map turtles (Graptemys geographica) (27), false map turtles (Graptemys pseudogeographica pseudogeographica) (6), Blanding’s turtles (Emydoidea blandingii) (3), and stinkpot turtles (Sternotherus odoratus) (3). We examined the degree to which these aquatic species were nonrandomly distributed in 14 landscapes. Assemblages of turtles generally were random and the extent of nestedness was influenced by the diversity of landcover, the proportion of grassland, and the total length of roads in each landscape. The occurrence and abundance of several species also were modeled to test hypotheses regarding the importance of site, patch, and landscape-level variables. Red-eared sliders appeared to be most sensitive to habitat fragmentation, whereas painted turtles, snapping turtles, map turtles, and spiny softshells were less affected. Factors at multiple spatial scales affect turtle distributions, suggesting differential responses to landscape fragmentation.