Home-Range Size as a Predictor of Mating Systems in Microtus

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Abstract
Breeding populations of Microtus pennsylvanicus and M. ochrogaster were studied for approximately 4 weeks each in central Pennsylvania and south-central Illinois, respectively. Identical radio-telemetric and live-trapping techniques were combined in each study to examine the possible causes of interspecific and intraspecific variation in range size. M. pennsylvanicus exhibited sexually diethic ranging behavior, whereas M ochrogaster did not. Specifically, male M pennsylvanicus had significantly larger ranges than conspecific females, and the sexual difference in range size was larger for heavier males and scrotal males. Sex, body mass, and reproductive status were not similarly related to ranging patterns in M. ochrogaster. These results are argued to be a reflection of the divergent course of sexual selection in these two species. If correct, this view suggests that sex-specific patterns of range size may serve as indicators of the prevailing mating system.