Tropical amphibian populations experience higher disease risk in natural habitats

Abstract

Habitat loss and disease are main drivers of global amphibian declines, yet the interaction between them remains largely unexplored. Here we show that paradoxically, habitat loss is negatively associated with occurrence, prevalence, and infection intensity of the chytrid fungus Batrachochytrium dendrobatidis (Bd) in amphibian populations in the tropics. At a large spatial scale, increased habitat loss predicted lower disease risk in amphibian populations across Costa Rica and eastern Australia, even after jointly considering the effect of potential biotic and abiotic correlates. Lower host-species richness and suboptimal microclimates for Bd in disturbed habitats are potential mechanisms underlying this pattern. Furthermore, we found that anthropogenic deforestation practices biased to lowlands and natural vegetation remaining in inaccessible highlands explain increased Bd occurrence at higher elevations. At a smaller spatial scale, holding constant elevation, latitude, and macroclimate, we also found a negative relationship between habitat loss, and both Bd prevalence and infection intensity in frog populations in two landscapes of the Brazilian Atlantic Forest. Our results indicate that amphibians will be disproportionately affected by emerging diseases in pristine environments, and that, paradoxically, disturbed habitats may act as shelters from disease, but only for the very few species that can tolerate deforestation. Thus, tropical amphibian faunas are threatened both by destruction of natural habitats as well as increased disease in pristine forests. To curb further extinctions and develop effective mitigation and restoration programs we must look to interactions between habitat loss and disease, the two main factors at the root of global amphibian declines.chytridiomycosis | species diversity | anurans | Neotropics | pathogen

Spatial distribution of Batrachochytrium dendrobatidis in South American caecilians

“…These results, combined with a recent report of lethal chytridiomycosis in wild-caught caecilians (Gower et al 2013), indicate that Gymno phiona are potentially experiencing silent population declines in the wild due to Bd. Spatial regressions are also consistent with the observed associations between macroclimate and Bd infection in anuran species (Becker & Zamudio 2011, James et al 2015, Becker et al 2016. Specifically, we detected a positive effect of precipitation and a negative effect of temperature variables on the likelihood of Bd infection in caecilian hosts.…”

“…Seasonal variations in temperature and precipitation strongly mediate Bd infections by changing optimal physiological conditions of hosts and pathogen (Piotrowski et al 2004, Becker & Zamudio 2011, Ruggeri et al 2015. These environmental constraints are revealed in several environmental niche models, in dicating that much of South America is unsuitable for Bd during at least part of the year Gower et al 2013, Rendle et al 2015.…”

“…Infection prevalence and zoospore loads are often positively correlated with elevation (Brem & Lips 2008, Gründler et al 2012, Catenazzi et al 2013), vegetation density (Puschendorf et al 2009, Becker & Zamudio 2011, Becker et al 2016, and preci pitation (Becker & Zamudio 2011), and negatively correlated with temperature (Becker & Zamudio 2011, Ruggeri et al 2015, Becker et al 2016. Because most caecilians are fossorial, they are likely exposed to lower microclimatic fluctuations dictated by land cover, insolation, and humidity.…”

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

“…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]. Earlier studies have postulated that the distribution and abundance of Bd is affected by climate [15,17,19,20], elevation [21], vegetation [22,23], host species richness [22,24], exotic species introductions [25], frog leg trade [26], human movement [27] and the human footprint index [28]. Consequently, it is important to consider these plausible drivers concurrently because, if these factors are looked at independently, it could give the impression that particular factors are driving the distribution of Bd when in fact the causal driver might be another correlated factor.…”

Joint effects of habitat, zooplankton, host stage structure and diversity on amphibian chytrid

“…geothermal ponds, undisturbed forests) but not others (e.g. non-geothermal ponds, disturbed forests) [1][2][3][4][5][6]. Why?…”