Distribution models for the amphibian chytrid Batrachochytrium dendrobatidis in Costa Rica: proposing climatic refuges as a conservation tool

Abstract

Aim We use novel data on the occurrence of the amphibian chytrid fungus Batrachochytrium dendrobatidis in Costa Rica to model its potential distribution in that country. Location Lowland and montane areas of Costa Rica. Methods We use published and new data on the presence of B. dendrobatidis on 647 amphibians (35 species). Screening was performed through histological techniques by which 156 sites were surveyed. Of these, 21 were found to have the amphibian chytrid. Maxent, a presence‐only distribution modelling technique, was used to create 100 predictions of B. dendrobatidis occurrence, of which the most accurate 10 (based on area under the receiver‐operating characteristic curve) were chosen to create a composite distribution model. This approach increased confidence in model predictions, distinguishing areas of high probability of occurrence and low variability across model runs (higher confidence) from those with high probability but high variability (lower confidence). Results Predicted distribution patterns were not uniform along Costa Rica's mountains, where most amphibian declines have occurred. The pathogen was predicted to occur with greater probability on the Caribbean slopes than on the Pacific slopes. While high temperature seems to constrain the distribution of the pathogen, areas that also have small amounts of rainfall during the driest period of the year were predicted to have low probability of B. dendrobatidis occurrence. Main conclusions The model predicts that the Santa Elena Peninsula and the Central Valley have low probabilities of B. dendrobatidis occurrence, suggesting that they could function as refuges for amphibians. In such refugial areas, one could expect B. dendrobatidis to be absent, or to be present in low abundance (rendering an epidemic outbreak of chytridiomycosis unlikely). Craugastor ranoides, which belongs to a group of frogs particularly sensitive to chytridiomycosis outbreaks, persists in the hot and seasonally dry Santa Elena Peninsula but disappeared in the nearby colder and more humid Guanacaste Volcanic Chain. This information suggests that climatic refuges, where environmental conditions prevent disease outbreaks, could be an important component in amphibian conservation.

DROUGHT REDUCES CHYTRID FUNGUS (BATRACHOCHYTRIUM DENDROBATIDIS) INFECTION INTENSITY AND MORTALITY BUT NOT PREVALENCE IN ADULT CRAWFISH FROGS (LITHOBATES AREOLATUS)

“…Variations in natural history, life history, behavioral, and immunologic traits among species can strongly affect the development and outcome of Bd infection (Voyles et al 2011). In addition, intraspecific variation in ecology (e.g., Puschendorf et al 2009), geography (e.g., Kriger et al 2007), and season (e.g., Lannoo et al 2011) can also influence infection prevalence, infection intensity, and host mortality. Batrachochytrium dendrobatidis infections are generally thought to be most intense in cool, humid habitats (e.g., Woodhams et al 2005) and in species that aggregate when threatened by dehydration (Longo et al 2010).…”

Global Amphibian Extinction Risk Assessment for the Panzootic Chytrid Fungus

“…However, to avoid model 'overfitting' [22] and multicollinearity of predictors, we restricted our study to the six 'bioclimate' variables mentioned which can be considered as biologically relevant parameters to Bd [10,11,14,16]. Also, these variables have been suggested to perform well in SDMs [23][24][25] including those for Bd [26]. We obtained 365 globally scattered Bd records (latitude/longitude) from www.spatialepidemiology.net/bd/ (accessed 15 August 2008).…”

Climate, vegetation, introduced hosts and trade shape a global wildlife pandemic

“…Bd is widely considered one of the principal drivers of the global decline of amphibians [13], the most threatened vertebrate taxon on the Earth [14]. There have been several SDMs for Bd that use environmental predictors to explain Bd occurrence patterns [15][16][17][18]. Although these studies are useful for predicting Bd risk and making relevant management strategies, they mostly focus on FN predictors, or only limited PP factors, such as human population density at a continental scale [15].…”

“…We constructed our global SDM using the MaxEnt model, one of the highest performing methods for modelling species' distributions [30], which was widely used as a robust approach to explore Bd potential distributions [15][16][17]. We simultaneously evaluated 22 variables probably affecting the FN of Bd and five variables that probably affected PP (see the electronic supplementary material, table S1) and their independent relative contributions of FN and PP to the global distribution of Bd.…”