Landscape-level correlates of small-mammal assemblages in forest fragments of farmland

We studied effects of forest fragmentation on 15 species of small mammals, including 6 species of forest-dwelling granivorous rodents, in the Indian Pine watershed of west-central Indiana. Presence-absence and population densities of small mammals were assessed in spring in 35 woodlots of various sizes (0.1-150 ha) and 2 continuous forest sites (>1,000 ha) using live traps in 1992-1996. Presence-absence and population density were related to landscape attributes using logistic and multiple linear regression models, respectively. Species richness of forest-dwelling small mammals increased with area and was highest in continuous forest sites. Nested subsets of the full complement of species were found in smaller woodlots. White-footed mice (Peromyscus leucopus) were ubiquitous, and eastern chipmunks (Tamias striatus) were nearly ubiquitous across the landscape; densities of both species were related inversely to forested area. Fox squirrels (Sciurus niger) were found at 84% of study sites, and they did not respond negatively to isolation of forest patches. Red squirrels (Tamiasciurus hudsonicus) were unevenly distributed across the landscape and were found most often in woodlots with large core areas and simple shapes, possibly indicating sensitivity to edge. Southern flying squirrels (Glaucomys volans) and gray squirrels (S. carolinensis) were restricted to continuous forest sites and >4.6-ha woodlots adjacent to other wooded habitat. Species of small mammals differ appreciably in their sensitivities to agriculturally induced fragmentation of forests. Interspecific differences within this assemblage were not due solely, or even primarily, to body size. Rather, differential responses of species to fragmentation likely resulted from variation in habitat breadth and ability to move through an agricultural matrix.