Growth rate and age at maturity in syntopic populations of Rana clamitans and Rana septentrionalis in central Ontario

Abstract

Populations of the green frog (Rana clamitans) and the mink frog (Rana septentrionalis) in Algonquin Provincial Park, Ontario, Canada, were studied from May 1985 through October 1987 and from May 1991 through September 1993. Parameters estimated from fitting logistic curves to growth data obtained from marked individuals were used to test for interspecies and intersexual differences in growth trajectories. Female R. septentrionalis had a significantly greater asymptotic length than males. We found no sexual size dimorphism in R. clamitans. Asymptotic size was significantly greater for R. clamitans than for R. septentrionalis. Age was estimated from a combination of extrapolation from size-frequency data and from production of size-specific growth curves from recapture data. Age-specific size and growth rate were measured to test the hypothesis that differences in growth trajectories could be predicted from differences in patterns of survivorship. Both R. septentrionalis and R. clamitans were larger at transformation, and older at maturity, than has been reported in previous studies. Although significantly larger at transformation, R. septentrionalis was significantly smaller than R. clamitans in all subsequent age-classes. The growth rate of R. clamitans was significantly greater than that of R. septentrionalis for all age-classes except 0 years post transformation. The observed differences in growth trajectories and age at maturity were consistent with predictions based on differences in the pattern of survivorship.