Life on the edge: the demography of short-season populations of deer mice

We documented populations of deer mice in the Kananaskis Valley, southweste rn Alberta, Canada from 1979 to 1997 to determine whether these short-seaso n populations were more, or less, variable than populations in more tempera te environments. We then examined patterns of reproduction, age-specific su rvival, and immigration to explain variation in summer population growth. P opulation densities showed no multi-annual periodicity and were generally l ow. At maximum, numbers doubled over the breeding season, but declined over the breeding season in 4 of 16 yr. Variability in population density was l ow, and similar to that of Peromyscus populations in more temperate environ ments. No demographic parameters were related to spring population densitie s, and immigration rates were low when conditions for survival of nestlings and adults were favorable. Variation in summer population growth was attri buted primarily to variation in nestling survival among years.