Examining the effects of heterospecific abundance on dispersal in forest small mammals

The effects of conspecific densities on dispersal have been well documented. However, while positive and negative density-dependent dispersal based on conspecific densities often are shown to be the result of intraspecific competition or facilitation, respectively, the effects of heterospecific densities on dispersal have been examined far less frequently. This gap in knowledge warrants investigation given the potential for the analogous processes of interspecific competition and heterospecific attraction to influence dispersal patterns and behavior. Here we use a long-term live-trapping study of deer mouse (Perotnyscus maniculatus), eastern chipmunk (Tamias striaius), red-backed vole (Myodes gapperi), and jumping mice (Napaeozapus insignis and Zapus hudsonius) to examine the effects of variation in conspecific and heterospecific abundances on dispersal frequency. In terms of conspecific abundance, jumping mice were more likely to disperse from areas with fewer conspecifics, while red-backed voles and chipmunks did not respond to variation in conspecific abundances in their dispersal frequencies. While there were no statistically significant effects of variation in heterospecific abundances on dispersal frequency, some effect sizes for heterospecific abundance effects on dispersal met or exceeded those of conspecific abundances. Conspecific abundances clearly can affect dispersal by some species in this system, but the effects of heterospecific abundances on dispersal frequency are less clear. Based on effect sizes, it appears that there may be potential for heterospecific effects on dispersal by some species in the community, although the strength and causes of these relationships remain unclear.