Demography of a Habitat Generalist, The White-Footed Mouse, in a Heterogeneous Environment

A population of white-footed mice (Peromyscus leucopus) in southeastern Massachusetts was lived-trapped monthly in five habitat types for 5 yr in order to study the demography of a habitat generalist. We identified three demographic groups (two of low density and one of high density), which differed primarily in density, adult survival, proportion of males breeding, and variability in the proportion of males. The low-density segments of this population were at times able to achieve demographic performance equivalent to the high-density segments. Several demographic variables were related linearly to microhabitat gradients derived from a principal components analysis of 24 habitat variables, but similar demographic structure was found in different habitat types. A simple model is presented that relates demography to environmental suitability in a habitat generalist. According to this model, population density, productivity, and survival increase, and numerical and demographic variability decrease, along a gradient of increasing environmental suitability. Intensity of intrinsic regulation also may increase with environmental suitability, which would contribute to population stability. We hypothesize that in habitat generalists such as Peromyscus leucopus, population numbers are regulated along a stable trajectory in areas of high suitability, but may show little or no intrinsic regulation in poorer habitats. Furthermore, demographic structure may shift as environmental conditions improve or decline in quality. This highly flexible demographic structure may enable populations of generalists to persist in poor habitats.