Body length and mass growth of the brown bear (Ursus arctos) in northern Canada: model selection based on information theory and ontogeny of sexual size dimorphism

Abstract

We compared four nonlinear growth functions in modeling body length and mass size-at-age data for the brown bear ( Ursus arctos L., 1758) in northern Canada of wide-ranging body sizes and ages. Then, we analyzed the sex differences in patterns of growth and ontogeny of sexual dimorphism in this species revealed by the best model from these alternatives. The von Bertalanffy function proved to be the most parsimonious model because it was easy to fit, with higher fitting degrees, lower root mean squared standard deviation of data points about fitted growth curve, larger Akaike weight, and fewer parameters derived directly from metabolic laws that accurately estimated the observed body length and mass growth profiles. Our growth models indicated an association between sexual growth divergence and the onset of reproduction in females, together with more rapid and prolonged male growth. These findings suggest that sexual size dimorphism develops in part by constraints on female growth from high energetic costs of reproduction. In contrast, males do not experience a comparable energetic trade-off after reaching sexual maturity and apparently allocate available energetic resources to growing faster and longer to produce larger body size, which benefits more competitive males in terms of increased reproductive success.