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

Abstract

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 bodymass classes as stage categories in 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.