Amphibians face a bleak future
Worldwide survey reveals a third of all species are in danger.
The world's frogs, newts and toads are dying. They are being over-harvested for food, their homes are being destroyed, and most worryingly, entire species are disappearing for no apparent reason.
That is the conclusion of more than 500 herpetologists around the world, reported in Science1 today. Although it has been known for some time that many amphibian species are in trouble, this is the first global assessment of the group's status.
Similar surveys of mammals and birds have been completed, and they were not short of bad news. But this comprehensive survey is the bleakest yet. Consulting local experts in a series of regional workshops, Simon Stuart and his team at Conservation International and the World Conservation Union (IUCN) examined the status of all 5,743 known species. They found that 1,856 of them - more than 30% - qualify as vulnerable, endangered or critically endangered under IUCN Red List Criteria.
IUCN/ Conservation International
For many of these species, the way forward is clear, say the researchers. Limits must be placed on harvesting, and protected areas must be established. But many creatures are undergoing what's known as 'enigmatic decline', where the cause of their demise isn't known. In these cases, the only way to save them may be to breed the animals in captivity, because we don't know how to help them where they are.
Scientists have argued for decades about what causes amphibians that seem unmolested and happy to just blink out overnight. Stuart says there is a growing consensus that blames both climate change and a nasty fungal disease called chytridiomycosis that attacks the skins of adult amphibians and the mouthparts of tadpoles.
The fungus may well have come from a species of amphibian with which it coexisted more or less peacefully. Human movement of organisms could then have spread it. "It is almost certainly an invasive fungus that spread out from its place of origin," says Stuart. Climate change may also create new weather patterns that promote the spread of the fungus.
The theory is gaining acceptance, but Blair Hedges, an evolutionary biologist at Pennsylvania State University in Philadelphia who helped with the survey, is not convinced that the fungus is causing the extinctions. "I haven't seen real hard evidence for it," he says.
He's also a little sceptical about how pristine some of the habitats described as such really are. While on a night-time ramble in apparently untouched Caribbean forest, listening for the telltale croaks of various frog species, a large European rat fell on his head. "Rats eat everything," he says. "I don't call that forest pristine."
The lag between the beginning of the amphibians' die-off and the beginning of understanding why - more than a quarter of a century - has taken its toll. For example, an entire family of Australian frogs called gastric breeding frogs is completely gone. These creatures swallowed their own eggs and then vomited up their young after they had passed the tadpole stage.
Since the first frogs began to die mysteriously in the 1970s, more than 100 amphibian species are have gone missing, and are presumed extinct.
Frog, salamanders and their ilk tend to be less robust than birds and mammals. Their ranges are smaller, their tolerance for dryness is low, and their porous skin is particularly sensitive. This helps explain why more amphibians die off than mammals and birds, but it also makes them useful as a marker of environmental disruption.
"There is the canary in the coalmine argument," says Stuart. "Because of their sensitivity, amphibians are the first species we would expect to show adverse reactions to climate change and new emerging diseases."
The news is bad, but the effort of assessing the situation has perhaps injected new life into the field. Many herpetologists met each other for the first time to compare information for the survey, and the meetings are producing a crop of new collaborative work, says Stuart.
- Stuart S., et al. Science, published online 10.1126/science.1103538 (2004).
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