Rob Grasso

Palatability and Antipredator Response of Yosemite Toad (Bufo canorus) to Nonnative Brook Trout (Salvelinus fontinalis) in the Sierra Nevada Mountains of California.

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ABSTRACT

Statement of the Problem - The global phenomenon of unexplained amphibian declines has been met with an increase of investigations into the possible anthropogenic as well as natural causes. Alien or introduced predators such as fish will often compete, displace or prey upon native amphibians. Amphibians that have evolved in fishless habitats often lack the necessary chemical defenses and behavioral responses to avoid predation and are thus unable to resist or co-occur with introduced predators due to the lack of a shared history. Toads, however possess noxious chemicals that may be adequate to deter non-native predators which may allow co-occurrence with alien predators, even when the same introduced predator has already been implicated in the decline of other amphibian species. Yosemite toads have experienced population declines throughout their range in which trout have been widely introduced, but it is not clear whether trout are responsible for the decline through direct predation of larval life stages.

Sources of the Data - Research was conducted June, 2004 and August, 2005 at the University of California Santa Barbara ’s Sierra Aquatic Research Laboratory (SNARL), part of the Valentine Eastern Reserve System. Brook trout were collected via hook-and-line from two alpine lakes in Inyo National Forest . Yosemite toad eggs (2004) and recently metamorphosed toads (2005) were collected by hand from Edith Lake area and Glacier Bench (Mono Co., CA). Through a series of no-choice palatability trials, antipredator response experiments and choice experiments I determined the level of threat brook trout pose to larval Yosemite toad life stages.

Conclusions -Two major conclusions can be drawn from my research. Firstly, brook trout found all early life stages of Yosemite toads to be unpalatable and unlikely rely on these stages as a primary food source in aquatic montane environments. Secondly, even though Yosemite toads were sampled by trout the toads did not suffer any ill effects.

 

Citation

Grasso, Robert Lawrence (2005) Palatability and Antipredator Response of Yosemite Toad (Bufo canorus) to Nonnative Brook Trout (Salvelinus fontinalis) in the Sierra Nevada Mountains of California. Masters thesis, Department of Biological Sciences, California State University, Sacramento.

Rob joined the lab in Fall 2003 and finished in December 2005.

For more information about amphibian declines check out this site: AmphibiaWeb

Also visit Save the Frogs

Current Position:

Robert Grasso
Aquatic Ecologist
USDA Forest Service
100 Forni Rd. Placerville, CA 95667

 

CSUS BIO SCI