Global declines of amphibians refer to the phenomenon of the population declines and even extinctions of amphibian species around the world. Assessments of the world's amphibians found that nearly a third of the known species of amphibians are globally threatened with extinction and that at least 42% of known amphibian species are experiencing population losses. The rapidity and extent of these declines, far more dramatic than those described for birds, mammals, or reptiles, forecast impending extinction of numerous amphibian species during the coming decades. Many of these declines have occurred in protected areas where the causes have remained enigmatic. Other declines are due to obvious reasons, particularly habitat destruction, but the number of species experiencing enigmatic declines is increasing and these have caused the greatest alarm. Although climate change has been invoked as a potential contributing factor, evidence is mounting that epidemics of infectious disease may be primarily responsible for many of these catastrophic declines. The greatest threat is presented by a virulent fungal pathogen that can cause the infectious disease chytridiomycosis, which has decimated entire assemblages of amphibians worldwide. This pathogen, Batrachochytrium dendrobatidis, is responsible for what may well be the greatest disease-caused loss of biodiversity in recorded history, having caused population crashes or extinctions (often within a single year) of at least 200 species of frogs, even in relatively undisturbed, remote habitats. Compounding the crisis, amphibians suffer from relatively low levels of conservation effort compared to other vertebrate taxa. Although amphibians have survived a number of mass global extinctions throughout their 200 million year history, the speed and magnitude of this loss in amphibian biodiversity supports the idea that the earth may be now in the midst of a sixth mass extinction, similar to that which wiped out the nonavian dinosaurs.
Encyclopedia of Biodiversity (Second Edition), 2013, Pages 691-699,