Latest research underlines the impact of three major threats to all Amphibian species

An adult male Ecnomiohyla rabborum, a species ravaged by chytridiomycosis in its native habitat. Image: Brian Gratwicke

A series of recent papers in Nature frame the key threats to amphibian species on the global scale.  IUCN classifies 30% of all amphibian species as threatened and establishing the cause of this trend is pressing priority for conservation science.

Widespread declines in amphibian populations were first noticed in the 1980s.  Habitat degradation through pollution, human land-use and climate change were initially identified as causal factors, but recent papers give more attention to the fungal disease chytridiomycosis.  This is caused by Batrachochytrium dendrobatidis and occurs mainly in cooler regions, with varying virulence in different species.  The disease was first discovered in amphibians in 1998 and is widespread: it is known to have caused local extinction in some frog species.  A current chytridiomycosis global pandemic is underway and may be responsible for many species becoming critically endangered. However, little is known about the overall effects of these major threats (chytridiomycosis, climate change and habitat degradation) and how they could interact to further endanger the global amphibian population.

Hof et al publish a letter in Nature addressing the issue of understanding how the fungal disease pandemic, climate change and land-use change are affecting amphibians worldwide.  In a model which takes into account the spatial distribution of these three threats, the interactions between them and the global distribution of all amphibian species, they predict that species in different regions will face varying levels of each threat, often not simultaneously.  All three orders of amphibian were included in this model, frogs, salamanders and caecilians, and the outlook for all is fairly poor.

Hof et al predict that by 2080 over half of the species in tropical regions (with the greatest amphibian diversity) will be facing drastic declines due to both climate change and habitat degradation.  The occurrence of chytridiomycosis will become more concentrated in temperate and mountainous areas.  What is most worrying is that the spatial distribution of these declines is very widespread and not particularly overlapping.  For example, amphibians in tropical areas such as Africa and South America will be most negatively impacted by climate change, but not so threatened by the disease pandemic.  Overall, more than half of the total geographic distribution for frogs, salamanders and caecilians will be highly affected by the three main threats.

Our beleaguered amphibian species are facing accelerating rates of decline over the next few years, Hof et al predicting that the interaction of climate change, disease and habitat degradation is far more damaging than each threat alone.  Amphibians can be found in almost every terrestrial habitat (apart from Polar Regions) and in some ecosystems are important apex predators.  They also play an important role in linking terrestrial and freshwater habitats in both tropical and temperate zones. It is important that future conservation takes into account all threats to amphibian species before making decisions on how best to ameliorate population decline.