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POPULATION STATUS AND DISTRIBUTION OF A DECIMATED AMPHIBIAN, THE RELICT LEOPARD FROG (RANA ONCA)
Citation:
Bradford, D F., J R. Jaeger, AND R. D. Jennings. POPULATION STATUS AND DISTRIBUTION OF A DECIMATED AMPHIBIAN, THE RELICT LEOPARD FROG (RANA ONCA). SOUTHWESTERN NATURALIST 49(2):218-228, (2004).
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:
The relict leopard frog (Rana onca) was once thought to be extinct, but has recently been shown to comprise a valid taxon with extant populations. We delineate the minimum historical range of the species, and report results of surveys at 12 historical and 54 other localities to determine the current distribution and status of extant populations. The species was found in the 1990s at seven sites in three areas. By 1. 200 1, however, this number had declined to five sites in two areas: near the Overton Arm of Lake Mead, NV, and in Black Canyon along the Colorado River below Lake Mead, NV. These two areas encompass maximum linear extents of only 3.6 and 5.1 km, respectively. The five extant populations inhabit spring systems with largely unaltered hydrology and no introduced American bullfrogs (Rana catesbeiana) or game fishes. In a mark-recapture study conducted over two years in the Overton Ann area, the estimated I number averaged 36 frogs (95% conf. limits, 27-45) over 555 m of stream habitat, and estimated annual survivorship averaged 0.27. A mark-recapture estimate for the size of
the largest population, which occurs at a site in Black Canyon approximately 450 m in length, was 637 adult frogs (95% conf. limits, 381-1210). An estimate for the total number of Rana onca frogs at all sites, based on mark-recapture data, visual encounter surveys, and extent of habitat, was approximately II00 adults. The two recent population extinctions occurred concomitantly with encroachment of emergent vegetation into pools. We speculate that this occurred as a result of natural processes in one case, and anthropogenic processes in the other.