The Effects of Habitat Fragmentation on Small Mammal Populations

Abstract

We examined the population dynamics of small mammals in an experimentally fragmented, successional field over three years. Patches of three sizes (32 m2, 288 m2, and 5000 m2) were censused at biweekly intervals, and data for the three common species were grouped by patch size and analyzed for relative population density, persistence of individuals, and patterns of movement among patches. The three species sorted by patch size, with the largest (Sigmodon hispidus) most abundant on the largest patches, the smallest (Peromyscus maniculatus) most abundant on the smallest patches, and the intermediate-sized (Microtus ochrogaster) most abundant on medium patches. Our explanation for this spatial pattern in density involves the interplay of source-sink dynamics and interspecific interactions. Persistence times for the two larger species were highest on large patches, but P. maniculatus persisted equally well on all patch sizes. Eighty-five percent of individual moves for all species occurred within a patch size. Individuals that dispersed between patch sizes tended to move towards a larger size patch. Our results suggest that in the future, metapopulation theory and analyses of habitat fragmentation should consider in more detail the effects of intra- and interspecific density-dependent interactions.