Drivers of amphibian declines: effects of ultraviolet radiation and interactions with other environmental factors

Abstract

As a consequence of anthropogenic environmental change, the world is facing a possible sixth mass extinction event. The severity of this biodiversity crisis is exemplified by the rapid collapse of hundreds of amphibian populations around the world. Amphibian declines are associated with a range of factors including habitat loss/modification, human utilisation, exotic/invasive species, environmental acidification and contamination, infectious disease, climate change, and increased ultraviolet-B radiation (UVBR) due to stratospheric ozone depletion. However, it is recognised that these factors rarely act in isolation and that amphibian declines are likely to be the result of complex interactions between multiple anthropogenic and natural factors. Here we present a synthesis of the effects of ultraviolet radiation (UVR) in isolation and in combination with a range of naturally occurring abiotic (temperature, aquatic pH, and aquatic hypoxia) and biotic (infectious disease, conspecific density, and predation) factors on amphibians. We highlight that examining the effects of UVR in the absence of other ecologically relevant environmental factors can greatly oversimplify and underestimate the effects of UVR on amphibians. We propose that the pathways that give rise to interactive effects between multiple environmental factors are likely to be mediated by the behavioural and physiological responses of amphibians to each of the factors in isolation. A sound understanding of these pathways can therefore be gained from the continued use of multi-factorial experimental studies in both the laboratory and the field. Such an understanding will provide the foundation for a strong theoretical framework that will allow researchers to predict the combinations of abiotic and biotic conditions that are likely to influence the persistence of amphibian populations under future environmental change.