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FACTORS IMPLICATED IN AMPHIBIAN POPULATION DECLINES IN THE US, AND AN EVALUATION OF THE CASE FOR INVASIVE SPECIES
Citation:
Bradford, D F. FACTORS IMPLICATED IN AMPHIBIAN POPULATION DECLINES IN THE US, AND AN EVALUATION OF THE CASE FOR INVASIVE SPECIES. Presented at Annual meeting of the Society for Northwestern Vertebrate Biology, Hood River, OR, April 4, 2002.
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:
Factors known or suspected to be adversely affecting native amphibian populations in the US were identified using information from 267 species accounts written in a standardized format by multiple authors in a forthcoming book. Land use was the most frequently implicated adverse factor for both anurans and caudates. The predominant land use factors were agriculture, urban development, and timber harvest/silviculture, followed by road construction/use, livestock grazing, altered fire regime, recreational use/development, and mining. Exotic animal species were the second most frequently implicated adverse factor for anurans, and third for caudates. Exotic taxa implicated consisted of a number of introduced fishes, American bullfrogs, crayfish, defoliating insects, and other amphibians. Chemical contamination ranked third for anurans and second for caudates, and included acid precipitation, pesticides/herbicides, and mine water pollution. A regional analysis revealed that exotic species were implicated significantly more frequently among anurans in the western US than elsewhere, whereas chemical contamination was implicated significantly more frequently among caudates in the non-western US. Less frequently implicated factors were disease, water source modification, collecting/harvesting, and UV-B radiation.
The case for invasive species as agents of amphibian population declines is frequently poorly substantiated, a situation that has impeded remediation. Even in thoroughly documented cases, however, such as the effects of introduced trout on the mountain yellow- legged frog in California, resource management agencies can be remarkably resistant to arguments for action. This situation begs for a better understanding of the effects of invasive species on amphibians, and further development of tools for restoration.