Influence of habitat structure on demography of two rodent species in eastern Massachusetts

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Abstract
Populations of two rodent species (Peromyscus leucopus and Microtus pennsylvanicus) were livetrapped monthly for over 3 years at three study sites in eastern Massachusetts (U.S.A.) to examine relationships between microhabitat structure and demography. Measures of microhabitat structure–diversity gradients and an index of microhabitat heterogeneity were developed separately for each study site using principal components analysis. Relative densities of both species were ordered linearly along microhabitat gradients. Peromyscus densities increased along a woody habitat gradient, and Microtus densities generally decreased along woody gradients or increased along herbaceous gradients. Microhabitat structure appeared to influence population density more than it did other demographic characteristics. Where relationships between density and demographic variability existed, the most variable segments of a population were in the lowest density areas. It is suggested that this variability may be partitioned into biological effects (dispersal and response to environmental fluctuations) and density dependence of variability. Microhabitat heterogeneity, in contrast to gradients of microhabitat structure and diversity, was apparently unimportant in affecting demography of these rodent populations.