Citation:

Bradford, D F., J. R. Jaeger, AND S. A. Shanahan. DISTRIBUTIONAL CHANGES AND POPULATION STATUS FOR AMPHIBIANS IN THE EASTERN MOJAVE DESERT. Western North American Naturalist 65(4):462-472, (2005).

Impact/Purpose:

The primary objectives of this research are to:

Develop methodologies so that landscape indicator values generated from different sensors on different dates (but in the same areas) are comparable; differences in metric values result from landscape changes and not differences in the sensors;

Quantify relationships between landscape metrics generated from wall-to-wall spatial data and (1) specific parameters related to water resource conditions in different environmental settings across the US, including but not limited to nutrients, sediment, and benthic communities, and (2) multi-species habitat suitability;

Develop and validate multivariate models based on quantification studies;

Develop GIS/model assessment protocols and tools to characterize risk of nutrient and sediment TMDL exceedence;

Complete an initial draft (potentially web based) of a national landscape condition assessment.

This research directly supports long-term goals established in ORDs multiyear plans related to GPRA Goal 2 (Water) and GPRA Goal 4 (Healthy Communities and Ecosystems), although funding for this task comes from Goal 4. Relative to the GRPA Goal 2 multiyear plan, this research is intended to "provide tools to assess and diagnose impairment in aquatic systems and the sources of associated stressors." Relative to the Goal 4 Multiyear Plan this research is intended to (1) provide states and tribes with an ability to assess the condition of waterbodies in a scientifically defensible and representative way, while allowing for aggregation and assessment of trends at multiple scales, (2) assist Federal, State and Local managers in diagnosing the probable cause and forecasting future conditions in a scientifically defensible manner to protect and restore ecosystems, and (3) provide Federal, State and Local managers with a scientifically defensible way to assess current and future ecological conditions, and probable causes of impairments, and a way to evaluate alternative future management scenarios.

Description:

A number of 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 for amphibians were investigated in a 20,000 km2 area in the eastern Mojave Desert in two ways.
For upland sites, where wetland habitat consists almost exclusively of spring encounter surveys were conducted at 128 sites in 1997-1999, and these results were compared to historical (pre.: 1970) lacality records. For lowland sites, i.e., sites in the major valleys and river flood plains, locality records and field observations were reviewed and compared between recent and historical times. Amphibians were found at 79% of the upland sites. By far the most common species was the red-spotted toad (73% of sites), followed by the Pacific chorus frog, Woodhouse's toad, relict leopard frog, and the introduced American bullfrog. Taxa recently observed or collected in the lowlands were Woodhouse's toad, Pacific chorus frog, American bullfrog, and the introduced tiger salamander. Taxa with historical records but no evidence of occurrence in the study area within the past five decades are the Vegas Valley leopard frog, Arizona toad, Great Plains toad, and Great Basin spadefoot. 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) by the introduced bullfrog, and the complete replacement of the Arizona toad in Las Vegas Valley by Woodhouse ' s toad or hybrids with predominantly Woodhouse's traits. In contrast, the distributions of two species characteristic of upland springs, red-spotted toad and Pacific chorus frog, appear to have changed relatively little from their historic distributions, despite consiuderable habitat modification at many sites.

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