The Decline of Amphibians in California’s Great Central Valley

Abstract

Declines in amphibian populations are rarely reported on the community or ecosystem level. We combined broad‐scale field sampling with historical analyses of museum records to quantify amphibian declines in California’s Great Central Valley. Overall, amphibians showed an unambiguous pattern of decline, although the intensity of decline varied both geographically and taxonomically. The greatest geographical decline was detected in the counties of the Sacramento and San Joaquin Valleys. Two species, Rana aurora and Bufo boreas were identified as the most affected by decline, whereas Pseudacris regilla was the least affected. The Coast Range counties had little or no detectable decline. We provide new evidence implicating introduced predators as a primary threat. Introduced predators occur at lower elevations than native species, and our data indicate that for some native species there has been significant restriction to higher elevation sites from a formerly broader distribution. Our historical approach provides a strategy for identifying declining amphibian communities that complements more detailed, long‐term monitoring programs and provides an assessment of the pattern of change that is a necessary prerequisite for the development of field experiments that test hypothesized mechanisms of change.

Effective population size is strongly correlated with breeding pond size in the endangered California tiger salamander, Ambystoma californiense

“…A. californiense breeds in seasonal and permanent ponds that are free of fish and other introduced predators (Fisher and Shaffer 1996;Shaffer and Trenham 2005;Ryan et al 2009). Aquatic larvae grow and develop in these pools for 3-6 months, at which time they metamorphose and disperse onto the surrounding terrestrial landscape.…”

“…Pondbreeding amphibians provide especially good study systems for examining the effects of aquatic breeding habitats on population parameters, because breeding ponds have quantifiable features and often demarcate discrete yearly cohorts of breeding populations. Additionally, amphibians are facing local and global declines (Fisher and Shaffer 1996;Houlahan et al 2000;Collins and Storfer 2003;Stuart et al 2004) and are often sensitive to anthropogenic habitat alteration (Guerry and Hunter 2002;Zamudio and Wieczorek 2007). Thus, studies linking breeding habitat and population persistence may play a critical role in conservation and management strategies (Gibbs 1998;Guerry and Hunter 2002;Funk et al 2005;Rittenhouse and Semlitsch 2006).…”

The origin of tiger salamander (Ambystoma tigrinum) populations in California, Oregon, and Nevada: introductions or relicts?

“…Non-indigenous species have been identified as a major threat to global amphibian diversity (e.g., Blaustein and Wake 1990;Beebee and Griffiths 2005;Kraus 2009) and particularly California amphibian diversity (Bury and Luckenbach 1976;Fisher and Shaffer 1996). Well-known examples of non-indigenous species that negatively affect California's native amphibians through competition and predation include bullfrogs (Rana catesbeiana ;Moyle 1973;Kupferberg 1997;Kiesecker and Blaustein 1998;Pearl et al 2004), crayfishes (Gamradt and Kats 1996) and fishes (Hayes and Jennings 1986;Bradford 1989;Gamradt and Kats 1996;Lawler et al 1999;Knapp and Matthews 2000).…”

Crayfish Predation on Tadpoles : A Comparison Between a Native (Austropotamobius Pallipes) and an Alien Species (Procambarus Clarkii).

“…It is well documented that mortality during the aquatic stage regulates both the extent and the diffusion of the amphibian populations (SMITH, 1983). In North America, their decline has been related also to the introduction of alien aquatic predators (FISHER and SHAFFER, 1996 ;GAMRADT and KATS, 1996).…”