Assessing Competition Between Forest Rodents in a Fragmented Landscape of Midwestern USA
Abstract
Forests of the agricultural midwestern United States are highly fragmented, and species of small mammals that rely on the remaining forest fragments exhibit non-random distributions. We tested the extent to which interspecific competition between pairs of five species of granivorous forest rodents has influenced the structure of local assemblages occupying forest patches. We used a regression technique and incorporated patch and landscape variables in addition to local habitat variables. After accounting for variation in focal species density explained solely by local habitat variables, significant levels of interspecific competition were implicated for Sciurus niger-Tamias striatus. T. striatus also had a negative effect on densities of Peromyscus leucopus in forest patches > 10 ha. Inclusion of patch and landscape variables increased the explanatory power of regressions for T. striatus and S. carolinensis, two species generally regarded as sensitive to agriculturally induced fragmentation of forest habitat. Even when allowing for habitat selection at larger spatial scales, our results indicated competitive effects comparable to the analysis incorporating only local habitat variables. One difference was a marginal negative effect of S. carolinensis on Tamiasciurus hudsonicus after accounting for multi-scale selection. Overall, interspecific competition explained a significant proportion of the variation in densities for only three of the 24 potential interactions. In contrast, habitat and landscape features explained 0.37-0.71 of the variation in densities for all species except S. niger (0.09-0.20). We discuss the roles of competition and habitat fragmentation in mediating the coexistence of forest granivores.