Canopy cover and drought influence the landscape epidemiology of an amphibian chytrid fungus

Abstract

Abstract. Batrachochytrium dendrobatidis (Bd) is a globally distributed fungal pathogen of amphibians that has caused amphibian population declines. Prevalence and infection intensity of Bd should vary spatially across heterogeneous landscapes because survival of the pathogen depends on environmental conditions including humidity and temperature. Wetland temperatures should vary with forest canopy cover, but few studies have examined the relationship between Bd prevalence and canopy cover. We sampled anurans for Bd at 33 wetlands in Illinois across a canopy cover gradient during the severe drought of 2012 and during more typical weather in 2013. We hypothesized that anurans from closed canopy wetlands would have higher Bd prevalence than anurans from open canopy wetlands because high canopy cover would prevent temperatures from exceeding Bd's critical maximum temperature as often. We used occupancy modeling to examine how Bd prevalence varied spatially in relation to environmental covariates, and to determine if weather conditions altered such relationships. We analyzed all common species combined and Spring Peepers (Pseudacris crucifer) separately. Bd was widespread among the study wetlands. During the drought year of 2012, however, Bd prevalence and infection intensity were substantially reduced. Although wetland temperatures were related negatively to canopy cover, the influence of canopy cover on Bd was complex. Bd prevalence for Spring Peepers was related positively to canopy cover during the drought, but not in the non-drought year. Bd prevalence for all common species was not related positively to canopy cover in either year. Effects of other environmental covariates, such as water depth, also differed between years. Weather conditions had a large impact on Bd infection patterns, which makes predicting pathogen dynamics difficult. In the Midwest region of the United States, climate change models predict more frequent droughts, which may generally inhibit Bd while also altering the effect of environmental factors such as canopy cover on Bd prevalence for amphibians.

Refugia and connectivity sustain amphibian metapopulations afflicted by disease

“…), and one from the United States (Beyer et al . ). Connectivity among host populations should facilitate metapopulation persistence in this circumstance (Gog et al .…”

Identifying Species Conservation Strategies to Reduce Disease‐Associated Declines

“…Observational studies have documented the influence of environmental features (Beyer et al . ) and natural disturbances (Hossack et al . ; Roznik et al .…”

“…Mortality rates vary by species, life stage, infection intensity, the virulence of the fungal strain, and environmental factors (Van Rooij et al 2015). Observational studies have documented the influence of environmental features (Beyer et al 2015) and natural disturbances (Hossack et al 2013;Roznik et al 2015) on amphibian-Bd dynamics, but few mitigation strategies have been field tested and no single strategy is appropriate for all species threatened by Bd (Converse et al 2016;Garner et al 2016). Collectively, these limited studies form the foundation of knowledge regarding potential in situ strategies available to managers facing Bd-related declines.…”

Can Habitat Management Mitigate Disease Impacts on Threatened Amphibians?

“…The generality of this conclusion hinges on the generality of this phenomenon. Current evidence suggests that endemic infections are the norm following initial epizootics of Bd, with reservoir hosts and environmental transmission becoming the primary drivers of contagion (Beyer et al 2015;Stockwell et al 2015a;. As such, our conclusions regarding connectivity may hold for many anurans threatened by chytridiomycosis.…”

“…Current evidence suggests that endemic infections are the norm following initial epizootics of Bd , with reservoir hosts and environmental transmission becoming the primary drivers of contagion (Beyer et al . ; Stockwell et al . ; Scheele et al .…”