Growth Rate and Body Size at Maturity of Florida Black Bears

Abstract

Abstract Growth rate and body size at maturity are important life-history traits of interest because they represent a potential source of fitness variance within a species and provide information for understanding the nutritional condition, fecundity, and dynamics of populations. My objective here was to examine the growth rate and body size at maturity of Florida black bears Ursus americanus floridanus using body length, chest girth, and body weight measurements fitted to the nonlinear von Bertalanffy, Gompertz, and logistic size-at-age growth functions. The von Bertalanffy model had the largest Akaike weight, indicating the best fit for all measurements of both sexes. Growth models showed that females grew more slowly, with a younger age at maximum growth, faster rate at which maturity was reached, and attained significantly smaller asymptotic body length, chest girth, and weight than males. A more conservative growth strategy by females to invest available energy resources to costs of reproduction, together with intrasexual selection among males for larger body size to enhance intimidating and fighting ability to increase reproductive and survival success, are implicated as determinants of the male-biased direction and degree of sexual size dimorphism. In both sexes, the presence of human food in the diet increased the asymptotic body weight from the estimate for bears consuming a natural diet, but differences were insignificant. Females consuming human food had a slightly younger age at maximum growth and continued growth in body weight for a somewhat longer duration than did conspecifics that consumed a natural diet. In contrast, males that consumed human food had a slightly older age at maximum growth and decreased body weight growth somewhat earlier than did conspecifics consuming a natural diet. Florida black bears exhibited a larger asymptotic body size, faster growth rate, and younger age at maximum growth and maturity when compared with conspecifics in other mainland populations. Recognition of Florida black bear growth rate and adult body size provides wildlife managers a foundation for implementing measurable criteria to assess trends in population health.