THE DECLINE OF AMPHIBIANS IN CALIFORNIA GREAT CENTRAL VALLEY

Declines in amphibian populations are rarely reported on the community or ecosystem level. We combined broad-scale field sampling with histo rical analyses of museum records to quantify amphibian declines in Cal ifornia's Great Central Valley. Overall, amphibians showed an unambigu ous pattern of decline, although the intensity of decline varied both geographically and taxonomically. The greatest geographical decline wa s detected in the counties of the Sacramento and San Joaquin Valleys. Two species, Rana aurora and Bufo boreas were identified as the most a ffected by decline, whereas Pseudacris regilla was the least affected. The Coast Range counties has little or no detectable decline. We prov ide new evidence implicating introduced predators as a primary threat. Introduced predators occur at lower elevations that native species, a nd our data indicate that for some native species there has been signi ficant restriction to higher elevation sites from a formerly broader d istribution. Our historical approach provides a strategy for identifyi ng declining amphibian communities that complements more detailed, lon g-term monitoring programs and provides an assessment of the pattern o f change that is a necessary prerequisite for the development of field experiments that test hypothesized mechanisms of change.