Correlated factors in amphibian decline: Exotic species and habitat changein western Washington

Amphibian declines may frequently be associated with multiple, correlated f actors . In \western North America, exotic species and hydrological changes are often correlated and are considered 2 of the greatest threats to fresh water systems. Bullfrog (Rana catcsbeiana) introductions are frequently cit ed as a threat to lentic-breeding anurans native to western North America a nd are a suspected factor in the decline of red-legged frogs (Rana aurora) in California. Introduced fish and habitat change are cited less frequently but are equally viable hypotheses. I examined the relation among introduce d species, habitat, and the distribution and abundance of red-legged frogs in western Washington. Red-legged frog occurrence in the Puget Lowlands was more closely associated with habitat structure and the presence of exotic fish than with the presence of bullfrogs. The spread of exotics is correlat ed with a shift toward greater permanence in wetland habitats regionally. C onservation of more ephemeral wetland habitats may have direct benefits fat some native amphibians and may also reduce the threat of exotic fish and b ullfrogs, both of which were associated with permanent wetlands. Research a nd conservation efforts for lowland anurans in the West should emphasize th e complexities of multiple contributing factors to amphibian losses.