ECOLOGICAL AND DEMOGRAPHIC EFFECTS ON INTRASPECIFIC VARIATION IN THE SOCIAL SYSTEM OF PRAIRIE DOGS

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 variat ions in population densities, in addition to resource distributions, o n both the social system and the individual mating strategies of Gunni son's prairie dogs. Specifically, we predicted that monogamy would be associated with uniform resources, regardless of population density, g iving way to polygyny with increasing resource patchiness at intermedi ate densities, and to multiple males and females at high population de nsities. In addition, we predicted inbreeding at low densities and out breeding at high densities on the basis of naturally low levels of gen etic heterogeneity in this species. We tested these predictions by com paring social systems and mating strategies at two prairie dog colonie s 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-populati on density model.