Distributional changes and population status of amphibians in the eastern Mojave Desert

Authors

David F. Bradford, U.S. Environmental Protection Agency, Landscape Ecology Branch, Las Vegas, Nevada
Jef R. Jaeger, University of Nevada, Las Vegas
Seth A. Shanahan, Southern Nevada Water Authority, Las Vegas, Nevada

Abstract

Several amphibian species historically inhabited sparsely distributed wetlands in the Mojave Desert of western North America, habitats that have been dramatically altered or eliminated as a result of human activities. The population status and distributional changes of amphibians were investigated over a 20,000-km² area in the eastern Mojave Desert in 2 ways. For upland sites (i.e., sites outside of major valleys and river floodplains), where wetland habitat is almost exclusively springs, encounter surveys were conducted at 128 sites in 1997–1999, and results were compared to historical (pre-1970) locality records. For lowland sites (i.e., sites within major valleys and river floodplains), locality records and field surveys in 1995–2004 were reviewed to detect changes in distribution over time. Amphibians were found at 79% of upland sites. By far the most common species was the red-spotted toad (Bufo punctatus, 73% of sites), followed by the Pacific chorus frog (Pseudacris regilla), Woodhouse's toad (B. woodhousii), relict leopard frog (Rana onca), and the introduced American bullfrog (R. catesbeiana). Taxa observed or collected in the lowlands since 1990 were Woodhouse's toad, Pacific chorus frog, American bullfrog, and the introduced tiger salamander (Ambystoma tigrinum). Four taxa (Vegas Valley leopard frog [Rana sp.], Arizona toad [B. microscaphus], Great Plains toad [B. cognatus], and Great Basin spadefoot [Spea intermontana]) had historical records but no evidence of occurrence in the study area within the past 5 decades. The amphibian fauna of the study area has changed dramatically in the past century, primarily at lowland sites where habitat loss and modification have been extreme. Striking changes are the nearly complete replacement of native leopard frogs (i.e., Vegas Valley and relict leopard frogs) with the introduced bullfrog, and the complete replacement of the Arizona toad in Las Vegas Valley with Woodhouse's toad or hybrids with predominantly Woodhouse's traits. In contrast, the distributions of 2 species characteristic of upland springs, red-spotted toad and Pacific chorus frog, appear to have changed little from their historical distributions, despite habitat modification at many sites.

Recommended Citation

Bradford, David F.; Jaeger, Jef R.; and Shanahan, Seth A. (2005) "Distributional changes and population status of amphibians in the eastern Mojave Desert," Western North American Naturalist: Vol. 65: No. 4, Article 5.
Available at: https://scholarsarchive.byu.edu/wnan/vol65/iss4/5