Ecological and Demographic Effects on Intraspecific Variation in the Social System of Prairie Dogs

Abstract

Gunnison's prairie dogs (Cynomys gunnisoni) are social North American ground squirrels whose social system has been shown to vary with food resource distributions, as predicted by the habitat variability–mating system model. We expanded this model to include the effects of variations in population densities, in addition to resource distributions, on both the social system and the individual mating strategies of Gunnison's prairie dogs. Specifically, we predicted that monogamy would be associated with uniform resources, regardless of population density, giving way to polygyny with increasing resource patchiness at intermediate densities, and to multiple males and females at high population densities. In addition, we predicted inbreeding at low densities and outbreeding at high densities on the basis of naturally low levels of genetic eity in this species. We tested these predictions by comparing social systems and mating strategies at two prairie dog colonies near Flagstaff, Arizona, during a 3—yr period of population increase. We observed variations in sociality to vary in the predicted fashion at both colonies, providing support for the plant patchiness–population density model.