Uinta Ground Squirrel Demography: Is Body Mass a Better Categorical Variable Than Age?

We compared the relative impact of age and body mass on fecundity and survival in a population of Uinta ground squirrels, and modeled the population using body—mass classes as stage categories of Lefkovitch stage transition matrices. Body mass was a better predictor of survival than was age, and was nearly as good a predictor of litter size. Mass—based stage transition matrices provided results similar to age—based transition matrices, but also indicated that larger and subsequently more fecund young were a consequence of a population reduction. We believe that mass—based analysis of ground squirrel populations is a viable alternative to traditional age—based analyses. Body mass is easy to measure in small—mammal populations and is linked to a variety of life—history characteristics.