Age Distribution Patterns in a Small and a Large Population of Spotted Frogs (Rana luteiventris)

Abstract

Habitat fragmentation is one of the primary factors responsible for the decline of amphibians and has been shown to result in smaller and more isolated populations. In this study, a large and a small population of spotted frogs (Rana luteiventris) were studied in order to determine what effects, if any, patch size and isolation have on age structure and vital rates within populations of R. luteiventris. Individual frogs were captured, marked, and released. Skeletochronology was then used to determine individual age. Age structures were found to be significantly different between the populations, with the small population being composed mainly of older individuals and the large population being well represented by all age classes. Measurable vital rates were found to be comparable between sites, suggesting that the differences in age structure between the populations may be due to the isolation of the small population and subsequent inhibition of dispersal rates. This trend, coupled with drought conditions in the past three years, may explain why the small population has a significantly older population that may be susceptible to extinction. This finding may also indicate that the small population is characteristic of a sink population, dependent on immigration and recruitment for persistence.