Natal Philopatry and Breeding Systems in Voles (Microtus Spp.)

Abstract

We tested the hypotheses of Greenwood (1980) and Dobson (1982) by examining natal philopatry in males and females of five species of Microtus from live-trapping data collected from seven areas in North America. In all species, similar or larger proportions of males than females remained near the natal site as immature animals and both sexes moved similar distances from the natal site if they remained immature. In the four mainland species of voles.sbd.M. californicus, M. ochrogaster, M. pennsylvanicus, and M. townsendii.sbd.about twice as many females as males matured near their natal site regardless of whether the mating system was monogamous or polygynous. This evidence is consistent with the Greenwood hypothesis and suggests that females in both monogamous and polygynous species primarily compete for resources, and males compete for access to females. In the island species, M. breweri, and in enclosed populations (some with and some without an opportunity to disperse) of M. ochrogaster, M. pennsylvanicus, and M. townsendii similar proportions of males and females remained near the natal site as mature animals. Thus, preventing or reducing dispersal eliminated the bias towards female philopatry. Nevertheless, in all of these species, mature males still moved about twice as far from the natal sites as females. Males in polygynous species from control populations, if they did mature within the population, tended to move farther from the natal site than females; males in the one monogamous species showed no such difference. Thus, though male-male competition may be a primary cause of male dispersal, inbreeding avoidance may be a secondary cause. We suggest that the basic social organization in females all species is one based on female kin clusters.