CAN CHANGES IN FEMALE RELATEDNESS INFLUENCE MICROTINE POPULATION-DYNAMICS

We present a model relating fluctuations in density of vole and lemming populations to changes in the degree of relatedness among females. We propose that a high degree of relatedness prior to the spring decline causes more overlap between female home ranges and leads to a high density of breeding females in spring and vole outbreak densities in summer. Low relatedness in spring leads to competition for territories between females and to a severe spring decline. We suggest that severe mortality owing to predators or reduced mortality resulting from favorable environmental conditions that allow winter breeding may influence the genetic structure of a population and thus the intensity of competition for space among females. The predictions of our model are opposite to those of the Charnov-Finerty (1980) model. Charnov and Finerty predicted that the degree of relatedness would be inversely correlated with population density and that a decline in degree of relatedness at high density causes population crashes. We predict that relatedness fluctuates seasonally and is greatest at high density owing to the philopatry of juvenile females. We also predict that declines in relatedness are due to predation and immigration during the non-breeding season.