Social Spacing in Small Mammals: Patterns of Individual Variation

Abstract

The pattern of social spacing in small mammals differs from that observed in many other vertebrates. Small mammals frequently have non-exclusive territories and tolerate a large amount of overlap with other conspecifics. The determinant factors of home range or territory size in small mammals are not known for most species. We carried out a study of the determinant factors of home range size in a model small mammal, the eastern chipmunk, Tamias striatus. The population was studied for five years. The effect of experimental perturbations on food supply and population density offered strong evidence that the mean home range size in the population was determined by resource abundance. Changes in population density had little or no measurable effect. We noted that even when mean home range size decreased significantly in response to an increase in available food, a great deal of variability in individual home range sizes remained. We hypothesized that this pattern of variation among individuals was also resource related; large home ranges would be located in areas of low resource density and small home ranges would be located in areas of high resource density. Our data to date do not offer support for this hypothesis; however our research has shown that the data needed to convincingly reject the null hypothesis are very complex. We discuss the evidence required to study patterns of individual variation, and how models of optimal territory size may be useful. Research that examines patterns of individual variation are few in number, yet studies of individual variation will ultimately provide the best insights on the dynamics of evolutionary ecology.