Spatial and temporal disease dynamics of a Neotropical amphibian community 10 years after a chytridiomycosis epizootic
Disease dynamics vary over space and time and are influenced by the interactions of hosts, pathogens, and the habitat. For multi-host pathogens that can persist in the habitat, such as Batrachochytrium dendrobatidis (Bd), host population dynamics are influenced by pathogen prevalence, infection intensity, and transmission routes between hosts and between the host and habitat. To quantify the spatial and temporal dynamics of amphibians and Bd, we conducted surveys over two wet and dry seasons at Parque Nacional G. D. Omar Torrijos Herrera in El Copé, Panama. We resurveyed 24, 10-m sections six to eight times each. We quantified occupancy, detection, and habitat re-use for amphibians and Bd in the 10-m sections with a hierarchical Bayesian occupancy model, accounting for imperfect detection of both taxa. We assumed that if an amphibian was infected with Bd, then the 10-m section the frog was found in was occupied by chytrid. Two complications to this approach are that 10-m sections lacking captures may support Bd zoospores, and Bd may not be detected on individuals where it is present. By developing our own likelihood model accounting for amphibian and Bd detection, we were able to estimate amphibian and Bd occupancy of the 10-m habitats.
We captured between 1 and 14 amphibians per section per season, and amphibian density averaged 4.29 ± 3.15 per section (wet) and 2.84 ± 1.98 (dry). During both dry seasons, frog habitat occupancy was higher than Bd habitat occupancy (dry1: frog 93.7 ± 5.5%, chytrid 79.1 ± 14.2%; dry2: frog 84.2 ± 7.9%, Bd 67.5 ± 17.3%), suggesting that propagule pressure is reduced when chytrid occupancy is low or chytrid becomes limiting when frog populations grow. We found that if a frog was captured in a 10-m section, then the probability that we would find it in any survey was 26.70 ± 3.40% to 47.50 ± 5.10%. We found that if Bd was infecting frogs in a 10-m section, then the probability that we would find it in any future survey of that section was 49.30 ± 12.30% to 75.00 ± 13.90%. The probability of finding amphibians and Bd re-occupying the same 10-m section in a subsequent season was high (amphibian: 75.30 ± 9.10 to 94.70 ± 4.90%; Bd: 55.80 ± 20.90 to 81.00 ± 15.60%), indicating good habitats are consistently good. The spatial distribution of amphibians and Bd are consistent over spatial and temporal scales during the enzootic stage.