Habitat fragmentation and the distribution of amphibians: patch and landscape correlates in farmland

We studied the effects of agriculturally induced fragmentation of forests a nd wetlands on amphibian assemblages and their distribution in a landscape of the midwestern United States. Potential breeding pools and upland areas in 30 forest patches of various sizes and degrees of isolation were intensi vely sampled for amphibians during April through August 1996 and March thro ugh August 1997 in Indiana. Species presence was documented using pitfall t raps, anuran vocalization surveys, and cover-board sampling for adults and minnow traps and dip nets for larvae. Amphibian, anuran, and salamander ass emblages were nonrandomly distributed across the landscape. American toads (Bufo americanus) and gray treefrogs (Hyla versicolor) were ubiquitous, whe reas the distributions of several other species were ordered in a predictab le manner. Logistic regression was used to develop predictive models of pro babilities of occurrence for species in response to forest and wetland patc h and landscape variables. Occurrence of redback salamanders (Plethodon cin ereus) was positively associated with the area of a forest patch. Occurrenc e of ranid frogs was positively associated with proximity of wetlands for t hree of four species, and occurrences of smallmouth salamanders (Ambystoma texanum), spring peepers (Pseudacris crucifer), and western chorus frogs (P seudacris triseriata) were related to the degree of wetland permanency. Mul tiple linear regression revealed that species richness was greatest for wet lands with intermediate degrees of permanency. The observed nonrandom distr ibution exhibited by several amphibians suggests that they respond to lands cape-level attributes. Moreover, species differed substantially in the natu re of their responses to fragmentation, consistent with differences in thei r life history and ecology.