Science Inventory



Bradford, D F. AND R. A. Knapp. ALIEN SPECIES: THEIR ROLE IN AMPHIBIAN POPULATION DECLINES AND RESTORATION. Presented at International Symposium on Declining Amphibian Populations, Indianapolis, IN, June 30-31, 2001.


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.


Alien species (also referred to as exotic, invasive, introduced, or normative species) have been implicated as causal agents in population declines of many amphibian species. Herein, we evaluate the relative contributions of alien species and other factors in adversely affecting anuran populations in the USA, and then focus on the problems and potential solutions for a single native species. We accomplish the former by reviewing early-draft species accounts written in a standardized format by multiple authors for the book "Status and Conservation of U.S. Amphibians" (Lannoo, in press). For each species, factors implicated by the authors (i.e., known or suspected) as affecting persistence of populations were identified. Each species was also classified by status with regards to change in its historical geographic range or number of sites within the range, taxonomic family, and region of the US. Information was sufficient to classify the status of 71 (78%) of the 91 species native to the US. Relatively few species were classified as increasing (7%), whereas 25% were classified as no change, and almost half were classified as either minor decline (24%) or major decline (22%). The frequency of declining species was exceptionally high for ranids in the western US (i.e., 100% of 13 species restricted to the Rocky Mountains and west), whereas no differences in frequency of declining species were evident among non-westem ranids, western non-ranids, and non-western non-ranids. Specific adverse factors were identified for 51 (56%) of the 91 species and 36 (86%) of the 42 declining species (i.e., major- and minor-decline groups combined). Of the species with adverse factors implicated, alien species ranked second (43% of the 51 species; 53% of the 36 declining species) behind land use change (77% of the species; 81% of declining species). Factors implicated less frequently were disease, water source alteration, chemical contamination, increased UV-B, and collecting/harvesting. Alien species were implicated in anuran population declines significantly more frequently in the western US (88% of declining species) than in the other regions (24% of declining species), which suggests that alien species may be the major factor accounting for the high frequency of declining species among western ranids. Among alien, introduced fishes of many species were implicated most frequently, followed by American bullfrogs, crayfish, and other amphibians.

Record Details:

Product Published Date: 06/30/2001
Record Last Revised: 06/06/2005
Record ID: 59598