Effects of forest edge on populations of white‐footed mice <i>Peromyscus leucopus</i>

Abstract

Several studies have reported higher densities of white‐footed mice in small fragments than in large fragments of eastern deciduous forests. The edge hypothesis states that higher densities in smaller fragments reflect an increase in relative amount of edge habitat, which supports higher densities of mice because of its higher quality. To test this hypothesis we live trapped white‐footed mice along edge‐to‐interior gradients in forest fragments of east‐central Illinois. Our results indicated a greater abundance of mice in the forest interior than near the edge, which did not support the edge hypothesis. This pattern could occur because dominant adults hold larger territories of higher quality habitat, thereby reducing density and increasing fitness near the edge (an ideal despotic distribution). We found some evidence of increased reproductive success (juveniles per female) at the edge, but this could reflect density‐dependent demographic processes rather than habitat quality. Furthermore, other indicators of dominance (body weight, and reproductive activity) did not show an increase at the edge, and other studies indicate higher prevalence of natural enemies at edges, which could account for lower densities there. Reduced competition from larger rodents and reduced predation could cause higher densities in small fragments but the distributions of competitors and predators do not strongly support these hypotheses. We suggest two additional hypotheses that could account for greater densities in smaller fragments: 1) estimates of high densities could be artifacts of the large effect that a few captures can have on density estimates for very small fragments, and 2) densities in smaller fragments are overestimated because mice use a relatively larger area of surrounding habitat as fragment size decreases.