Effects of Introduced Mosquitofish and Bullfrogs on the Threatened California Red-Legged Frog

Exotic species have frequently caused declines of native fauna and may contribute to some cases of amphibian decline. Introductions of mosquitofish (Gambusia affinis) and bullfrogs (Rana catesbeiana) are suspected to have caused the decline of California red-legged frogs (Rana aurora draytonii). We tested the effects of mosquitofish and bullfrog tadpoles on red-legged frog tadpoles in spatially complex, speciose communities. We added 720 hatchling red-legged frog tadpoles to each of 12 earthen ponds. Three ponds were controls, 3 were stocked with 50 bullfrog tadpoles, 3 with 8 adult mosquitofish, and 3 with 50 bullfrogs plus 8 mosquitofish. We performed tests in aquaria to determine whether red-legged frog tadpoles are preferred prey of mosquitofish. Mosquitofish fed on a mixture of equal numbers of tadpoles and either mosquitoes, Daphnia, or corixids until