Linking global climate and temperature variability to widespread amphibian declines putatively caused by disease

Abstract

The role of global climate change in the decline of biodiversity and the emergence of infectious diseases remains controversial, and the effect of climatic variability, in particular, has largely been ignored. For instance, it was recently revealed that the proposed link between climate change and widespread amphibian declines, putatively caused by the chytrid fungus Batrachochytrium dendrobatidis ( Bd ), was tenuous because it was based on a temporally confounded correlation. Here we provide temporally unconfounded evidence that global El Niño climatic events drive widespread amphibian losses in genus Atelopus via increased regional temperature variability, which can reduce amphibian defenses against pathogens. Of 26 climate variables tested, only factors associated with temperature variability could account for the spatiotemporal patterns of declines thought to be associated with Bd . Climatic predictors of declines became significant only after controlling for a pattern consistent with epidemic spread (by temporally detrending the data). This presumed spread accounted for 59% of the temporal variation in amphibian losses, whereas El Niño accounted for 59% of the remaining variation. Hence, we could account for 83% of the variation in declines with these two variables alone. Given that global climate change seems to increase temperature variability, extreme climatic events, and the strength of Central Pacific El Niño episodes, climate change might exacerbate worldwide enigmatic declines of amphibians, presumably by increasing susceptibility to disease. These results suggest that changes to temperature variability associated with climate change might be as significant to biodiversity losses and disease emergence as changes to mean temperature.

Temperature variability and moisture synergistically interact to exacerbate an epizootic disease

“…The Temperature Variability Hypothesis described by Rohr & Raffel [2] postulates that delays in host acclimation following temperature shifts could drive increased infection rates in fluctuating temperature environments, assuming that parasite acclimation responses occur more rapidly than those of their hosts [8]. This study adds support for host acclimation effects postulated by this hypothesis.…”

“…[1]). However, climate change is also projected to cause changes in the magnitude and frequency of extreme weather events, including variability in temperature on multiple timescales [2][3][4][5]. The importance of short-term climate variability to species interactions remains an important open question in ecology [6], and recent studies suggest that temperature shifts on diurnal, daily and weekly timescales influence host-parasite interactions in ways that can be overlooked by constant-temperature experiments [7][8][9].…”

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

“…The NDVI is often a surrogate for the dynamics of ground moisture and temperature, which might affect the survival of many pathogens, including Bd, which is known to be sensitive to moisture and temperature [19]. Vegetation might increase moisture by reducing evaporation and might reduce temperature extremes preventing high-temperature clearance of Bd [23].…”

“…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.…”

A System for Assessing Vulnerability of Species (SAVS) to Climate Change

“…Disease exposure may be altered if climate becomes more, or less, favorable to vectors (Figure 8) (Benning and others 2002;Freed and others 2005). A number of studies relate the recent emergence and reemergence of many wildlife diseases to the effects of warming trends on vector species (Githeko and others 2000; Epstein 2001; Harvell and others 2002) as well as host immunity (Rohr and Raffel 2010). Climate-related disruptions to plant-pollinator interactions and mutualisms have profound implications for ecosystem function (Gilman and others 2010;Memmott and others 2007).…”