Small‐Mammal Associations in Forested and Old‐field Habitats: A Quantitative Comparison

Population densities, physical condition, and several parameters (diversity, niche breadth, and ratio of dominance) of small—mammal communities were documented for two old—field and two forested sites from fall 1974 to spring 1977. White—footed mice (Peromyscus leucopus) were the most numerous species in forested habitats, and populations fluctuated asynchronously and were noncyclic. Physical condition indices were not significantly different between the two forested sites, but values were significantly higher for adults than juveniles and significantly different between different sample periods. Seasonal changes in physical condition were not correlated with population fluctuations. Meadow voles (Microtus pennsylvanicus) were the most numerous species in old—field habitats, and populations were cyclic and fluctuated synchronously with a 2—yr duration between peaks. Physical condition indices were not significantly different between different census periods, but were significantly higher for adults than juveniles. Seasonal changes in physical condition were not significantly correlated with population fluctuations. There was a negative correlation between average niche breadth and the number of species occurring in each census period for both Peromyscus— and Microtus—dominated communities, which suggested the occurrence of species packing. Niche breadth of species was positively correlated with their abundance of both forested and old—field habitats. Species diversity was negatively correlated with meadow vole density, suggesting that at high densities voles competitively excluded other species of small mammals. Species diversity of small—mammal communities in both habitats were extremely variable spatially and temporally. There were significant differences in diversity indices between sites within the same habitat but not between habitats.