Changes in the Composition of a Ranid Frog Community Following Bullfrog Extinction

Abstract

-Natural experiments have often shown that lowered competition or predation results in patterns of ecological release, density compensation, or predatory release of target species. At Point Pelee National Park, Ontario, Canada, from 1992 to 1994, we conducted extensive surveys of habitats to document patterns of relative abundance and distribution of amphibians and to compare these patterns with those documented in studies conducted in 1972 and 1991. Bullfrogs (Rana catesbeiana) have not been observed since spring 1990 and are now considered to be locally extinct in the park. Relative abundance of the green frog (R clamitans) has increased 4X since bullfrog extinction. Similarities in the natural history of bullfrogs and green frogs suggest that interactions should be greatest between this pair. The predaceous habits of bullfrogs are well-documented, and the experimental literature suggests that bullfrogs and green frogs are competitors. Changes in the pattern of ranid relative abundance that we observed suggest that the bullfrog is important in structuring amphibian communities.