Geographic variation in size, growth, and sexual dimorphism of Alaska brown bears, Ursus arctos

We modeled the growth in skull size of brown bears (Ursus arctos) using 11,651 individuals across 6 regions in Alaska with the von Bertalanffy function. The study areas varied greatly in habitat types and included coastal areas in south-central Alaska, interior regions, and the most northern reaches of the species' North American range. The top-ranking model supported region- and sex-specific growth curves. The large differences in parameter estimates of asymptotic size and the growth coefficient across regions were likely influenced by variation in habitat quality, especially the availability of salmon (Oncorhynchus spp.), and these differences relate to other known life-history traits. Contrary to other studies of North American bears, we found a strong hyperallometric relationship in sexual size dimorphism (SSD) where SSD increased with asymptotic size. This relationship supports sexual selection as the driving mechanism of SSD in brown bears. However, the variable intensity of sexual selection across these regions, as demonstrated through hyperallometry in SSD, is likely influenced by proximate factors such as variable food resources and population densities that vary by more than 2 orders of magnitude. The ecological implications of the variation in growth, size, and SSD of brown bears across their Alaskan range are substantial and need to be recognized and incorporated into area-specific management and conservation strategies.