Response of the Eastern Chipmunk, Tamias Striatus, to Sex Ratio Manipulations

We hypothesize that male and female eastern chipmunks compete for different resources during the breeding season. We predict that the availability of breeding opportunities is a major factor setting male density, whereas female density is set by competition for other resources. This hypothesis was tested by removal of all residents of one sex or the other from experimental grids. When males were removed, survival of resident females was unaffected, density of females increased slightly because of recruitment, and large numbers of males from adjacent areas immediately moved onto the plot. When females were removed, male density and survival declined rapidly and a similar number of new females dispersed onto the plot. We conclude that breeding density in eastern chipmunks is set by adult females, probably on the basis of food resources. Adult females set their density independently of adult male availability. Adult males set their density by spacing behaviour according to density of breeding females.