Impacts of small-scale habitat fragmentation on abundance and movments of sigmodon hispidus and microtus ochrogaster.

Abstract

Small mammals are impacted by habitat fragmentation resulting from habitat loss in a number of quantifiable ways. Remnant patches often become areas for breeding and resource acquisition for individuals that were members of the former continuous habitat. Vegetative cover is important for both hispid cotton rat (Sigmodon hispidus) and prairie vole (Microtus ochrogaster) population dynamics. I conducted field work at the John H. Nelson Environmental Study Area near Lawrence, Kansas, using a small mammal trapping grid (with 99 trapping stations) that had been in operation since 1973. I examined abundance of individuals in mowed areas (postM) after deliberate habitat removal (by mowing a checkerboard-like pattern) from a continuous landscape (and compared this to 27 years of pre-mowing data) to determine species responses to fragmentation. Iexaminedabundance of individuals in unmowed (postU) areas and movement subsequent to fragmentation to determine if postU patch size was appropriate. I examined variance-to-mean ratios of distributions of movements to determine if individuals changed the proportion of short-or long-distance movements made post fragmentation. I examined the responses by individuals to fragmentation for the following categories of both species: overall, sex, reproductive condition (reproductive and non-reproductive), and stage class (adult, sub-adult, and juvenile). Decreases in abundance occurred for all categories on the postM patches. Decreases in abundance occurred on postU patches together with decreases or no change in movement length between successive captures for the majority of the categories. Most individuals also moved a greater proportion of shorter distance movements within their distribution of movements post-mowing. Thus, patch size was appropriate for the individuals; however, there were fewer individuals traversing the grid subsequent to fragmentation. Thus, on a local scale, habitat fragmentation can alter abundance and movement patterns of individual small mammals. Key Words: abundance, habitat fragmentation, Microtus ochrogaster, movement, patch, removal, Sigmodon hispidus