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

Background/Question/Methods

Harlequin frogs (Bufonidae: Atelopus) are a species-rich genus of Neotropical toads that has experienced disproportionately severe population declines and extinctions caused by the amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd). The genus Atelopus is of high conservation concern, but relatively little is known about the population dynamics and life histories of the majority of species. Studies of Atelopus population dynamics are therefore a critical component of ongoing research and recovery programs. We quantified demographic parameters of one population of Atelopus zeteki and two populations of A. varius in central Panama using three to six years of mark-recapture data collected prior to and during an epidemic of Bd. Both A. varius populations were located within the Parque Nacional G. D. Omar Torrìjos in tropical moist forest from 500–700 m elevation, while the A. zeteki population was located at about 300 m elevation in tropical dry forest. We estimated sex-specific survival probabilities and population sizes for these three populations using state-space Bayesian population models. We used our estimates to describe natural fluctuations in survival and abundance over time and to quantify patterns of decline across the three populations. 

Results/Conclusions

We found that mean monthly apparent survival probabilities were higher for A. varius (0.89 – 0.96) than for A. zeteki (0.59) until the arrival of Bd, and recaptures among years were low in both species, with lower rates in A. zeteki compared to A. varius. Density of both species varied over time and declined rapidly after the arrival of Bd. Abundances were highest in the A. zeteki population, and were different between the two A. varius populations. Male densities were generally greater than female densities, though female densities were higher or equivalent to males after the arrival of Bd. Estimates of survival and abundance over time reflected different use of stream habitat by the two sexes and three populations, both during and between breeding seasons. The A. zeteki population exhibited explosive breeding during two months of the dry season, while the A. varius populations used stream transects year-round and held established breeding territories. These estimates provide key baseline population information that can be used in reintroduction studies, captive assurance colonies, and in studies of extant Atelopus populations as part of conservation and management programs.