Amphibians face raised extinction threat

Many of the world's amphibians, which include frogs, toads, newts and salamanders, could die out faster than expected this century, a study has found.

Conservationists think about a third of the estimated 6,000 amphibian species in existence are in peril. The study predicts that climate change and habitat loss will combine to boost the rate at which species become extinct.

Scientists analysed the geographical spread of the main threats to frogs, toads and other amphibians and found that the richest regions in terms of biodiversity are also the ones that are under the greatest threat from climate change and the loss of habitats caused by changes to the way land is used.

The researchers found that instead of acting independently of one another, climate change and habitat loss combined as a "double whammy" to hit amphibians particularly hard, making it difficult for them to recover if their populations crash.

"We looked at three major threats to amphibians – climate change, land-use and fungal disease – and mapped the level of the threats on a global scale," said Professor Carsten Rahbek of Copenhagen University, who led the study, which is published in the journal Nature.

"We found there is nowhere to go, no where to hide. The three threats cover the globe. We found that habitat destruction and climate change are additive effects and they go hand in hand. They also hit the places on Earth where there are the most species," Professor Rahbek said.

"Our assessment shows that amphibian declines are likely to accelerate over the next decades, as multiple drivers of extinction could jeopardise their populations more than previous, mono-causal assessments have suggested."

Amphibians are thought to be particularly vulnerable to human activities because they rely on both terrestrial and aquatic habitats for survival and have a porous skin that easily absorbs environmental pollutants. They are also being attacked by the chytrid fungus, which may be spread by the commercial trade in frogs and toads.

"Regions where climate and land-use change have the highest projected impact on amphibians tend to overlap. By contrast, the threat posed by the fungal disease shows little spatial overlap with the other two threats," said Christian Hof of Copenhagen University.

Professor Tim Halliday, an amphibian expert at the Open University who was not part of the study, said other researchers have shown that the areas of the world with the highest concentrations of amphibians are experiencing the greatest changes to the landscape.

"In my view, amphibians are indicators of a much larger problem, the global deterioration of freshwater habitats. The WWF Living Planet Report has shown that biodiversity is declining faster in freshwater than in any other biome, including coral reefs and tropical forest," Professor Halliday said.

Under threat: Species on the danger list

Granular poison frog (Oophaga granulifera)

Listed as vulnerable on the Red List of Threatened Species, mainly because its severely fragmented range covers an area of less than 20,000sqkm in Costa Rica and Panama, and is getting smaller due to farming, logging and human settlements.

Darwin's frog (Rhinoderma darwinii)

Lives in the forest streams of Chile and Argentina. The males raise their tadpoles in the baggy skin folds of their vocal sacs, allowing the young froglets to hop out when ready. Some closely related species have not been seen for several decades.

Atelopus

Nearly 100 frog species belong to the genus Atelopus (right). They are brightly coloured and active by day, living mainly at high altitudes in Central American and northern South America.

The purple frog (Nasikabatrachus sahyadrensis)

First described in 2003, it is found in the Western Ghats region of India and has a distinctive snout. It lives underground, emerging during the monsoon for two weeks to breed.

Rainbow burrowing frog (Scaphiophryne gottlebei)

Only recently discovered in the dry, hilly regions of the Vallée des Singes in Madagascar. It lives mainly below ground to avoid the heat, but its finger pads suggest that it may also climb. Many amphibians of Madagascar are threatened by habitat loss.