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

Abstract

Atelopus is 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 endangered Atelopus species endemic to Venezuela, Atelopus cruciger is the only one that can be located at present. To assess the status of remnant populations of A. cruciger and to provide the demographic data for designing in situ management 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 in Atelopus, 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 of Atelopus are 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.

Overview of chytrid emergence and impacts on amphibians

“…To effectively manage Atelopus or other species where Bd is present, we need to know how disease has altered demographic rates of species such as survivorship, recruitment and transitions between life stages. Quantitative data from four species of Atelopus [45][46][47] can provide the baseline data for reintroductions and help understand stages limiting to natural population recovery. As in Australia, there is some evidence that warmer regions where environmental conditions could mitigate the impacts of disease [48] might be the best option for reintroductions.…”

The demography of Atelopus decline: Harlequin frog survival and abundance in central Panama prior to and during a disease outbreak

“…Territoriality and aggression by males of certain species have been well-documented (Crump, 1988;Lindquist and Hetherington, 1996), and males appear to exhibit high site fidelity (Crump, 1986). In two recent studies, researchers have quantified population parameters for a remnant Atelopus cruciger population in Venezuela (Lampo et al, 2012), and a rediscovered Atelopus spumarius population in Ecuador (Tarvin et al, 2014). These estimates provide a baseline for comparing demographic rates to other South American Atelopus species.…”

“…These estimates provide a baseline for comparing demographic rates to other South American Atelopus species. Analyses such as these can provide information on demographic rates in rediscovered Atelopus populations where Bd has been present (Tarvin et al, 2014), as well as on demographic responses to Bd outbreaks across species, populations, and time periods (Lampo et al, 2012). Additionally, they can help with designing monitoring programs, and can provide critical demographic information to inform captive breeding programs and potential reintroduction efforts in critically endangered species.…”

“…By tracking individuals, researchers can estimate survival, recruitment, and other population parameters of interest while accounting for probability of detection, where raw counts of individuals are corrected for imperfect detection (Schmidt et al, 2002;Funk et al, 2003;Mazerolle et al, 2007). Detection probabilities are rarely constant over time, so indices of population size like visual counts often do not capture true population dynamics (Lampo et al, 2012;Guimarães et al, 2014). Capture-recapture studies are relatively rare in the amphibian literature (Mazerolle et al, 2007), and are particularly infrequent in studies of amphibian populations in tropical systems (Guimarães et al, 2014).…”

Assessing host extinction risk following exposure to Batrachochytrium dendrobatidis

“…Its invasion can have devastating effects on host populations [6], and chytridiomycosis is currently linked to the decline or local extinction of over 200 amphibian species [7]. Nevertheless, many amphibian populations currently seem to be in a long-term endemic state with the fungus [8][9][10], often with a substantial reduction in survival [11].…”