High Turnover Rates in Remnant Populations of the Harlequin FrogAtelopus cruciger(Bufonidae): Low Risk of Extinction?

Abstract

AbstractAtelopusis among the most threatened of all amphibian genera. Most species of harlequin frogs disappeared more than two decades ago and only a few still exist. From ten critically endangeredAtelopusspecies endemic to Venezuela,Atelopus crucigeris the only one that can be located at present. To assess the status of remnant populations ofA. crucigerand to provide the demographic data for designingin situmanagement programs, we estimated: (1) the population size; (2) the apparent survival; and (3) the recruitment rates of one remnant population using mark‐recapture data. The adult population size varied (69–117), and this variation was not related to that of abundance indices based on visual counts at the river margins. Thus, caution is recommended when using visual counts as an index of abundance inAtelopus, because capture rates differ significantly among months and between seasons. Despite the observed variations, this population appears to be stable. Previous reports suggest that species ofAtelopusare long‐lived. For populations of long‐lived species to remain approximately constant, recruitment must be low. Our mark‐recapture study, however, showed that adults tend to remain in the population for approximately 15 mo, but an average of 165 new frogs are recruited every year. Although immigration and emigration are possibilities, the site fidelity and the absence of nearby streams suggests that movement in and out of the study area is less important than births and deaths. Under the proposed hypothesis of a short life expectancy/high recruitment, the risk of extinction must be lower than previously thought.