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STATUS OF THE RELICT LEOPARD FROG (RANA ONCA): OUR LIMITED UNDERSTANDING OF THE DISTRIBUTION, SIZE, AND DYNAMICS OF EXTANT AND RECENTLY EXTINCT POPULATIONS
Citation:
Jaeger, J R., D F. Bradford, R. D. Jennings, AND B. R. Riddle. STATUS OF THE RELICT LEOPARD FROG (RANA ONCA): OUR LIMITED UNDERSTANDING OF THE DISTRIBUTION, SIZE, AND DYNAMICS OF EXTANT AND RECENTLY EXTINCT POPULATIONS. Presented at Annual Meeting of Declining Amphibian Task Force, Reno, NV, January 15-16, 2004.
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. Here, we discuss research from several studies, conducted between 1991 and 200 1, that represent the basis for our understanding of the distribution, size, and dynamics of extant and recently extinct relict leopard frog populations. We review phylogeographic findings that have been used to identify this taxon, discuss the delineation of a minimum historical range, report the findings from mark-recapture studies and visual encounter surveys, and describe the extinction of 2 of 7 populations extant in the 1990s and speculate on the causes for these extinctions. A minimum historical range for this taxon was based on records from 24 localities (> 1 km apart) along the Virgin and Muddy River drainages and adjacent portion of the Colorado River drainage in southern Nevada, northwestern Arizona, and southwestern Utah. These frogs currently exist naturally at only 5 spring sites distributed in 2 general areas: near the Overton Arm of Lake Mead, and in Black Canyon along the Colorado River below Lake Mead, Nevada. The loss of populations in the 1990's greatly reduced the extant distribution of this frog. These population extinctions occurred concomitantly with encroachment of emergent vegetation into pools. A rough estimate for the total number of frogs at all sites in 2001 was approximately 1100 adults (range 693-1833). Annual adult survivorship from a mark-recapture studyat one site was estimated at 0.27. The limited number and distribution of populations, the low estimated total population size, the high estimated population turnover, and the observations of recent population extinctions are reasons for concern about the continued existence of the relict leopard frog.