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Population Status and Distribution of a Decimated Amphibian, the Relict Leopard Frog (Rana Onca)

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Abstract: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.
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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).
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Contact: Chris Siebert - (702) 798-2234 or siebert.christopher@epa.gov
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Division: Environmental Sciences Division
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Branch: Landscape Ecology Branch
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Product Type: Journal
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Published: 07/10/2004
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Related Entries:
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Bullet Item Development of Landscape Indicators for Use in Regional Ecological Risk Assessments
spacer Relationship Reason:   A Project of the Product
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