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Amphibian deaths may signal larger biodiversity disaster, researchers say

August 14, 2008 | 11:08 am


The death of frogs, salamanders and other amphibians could be a sign of a larger biodiversity disaster, according to an article published online this week by researchers from the University of California, Berkeley and San Francisco State University.

"Are we in the midst of the sixth mass extinction? A view from the world of amphibians" was co-authored by David B. Wake and Vance T. Vredenburg, and published online in the journal Proceedings of the National Academy of Sciences.

Wake and Vredenburg concluded the "substantial die-offs of amphibians and other plant and animal species add up to a new mass extinction facing the planet." A 2004 study by the researchers found that nearly one-third or more of roughly 6,300 amphibian species are threatened with extinction:

Amphibians have received much attention during the last two decades because of a now-general understanding that a larger proportion of amphibian species are at risk of extinction than those of any other taxon. Why this should be has perplexed amphibian specialists. A large number of factors have been implicated, including most prominently habitat destruction and epidemics of infectious disease; global warming also has been invoked as a contributing factor. What makes the amphibian case so compelling is the fact that amphibians are long-term survivors that have persisted through the last four mass extinctions.

The scientists study of frogs in California's Sierra Nevada Mountains showed that a disease caused by a fungal pathogen has had a "devastating" impact on the species -- in addition to the effects of pollution and new predators. The new disease, chytridiomycosis, may be spreading across the globe, including key tropic areas, and its effects may be worsened by global warming. The researchers believe the fungus may be linked to the serious declines and extinctions of more than 200 species of amphibians and "poses the greatest threat to biodiversity of any known disease," according to the article.

Of the Sierra Nevada's seven amphibian species, five are threatened. Two of these species, the Sierra Nevada yellow-legged frog and the Southern yellow-legged frog, had their populations decline by up to 98% over the last few years, even in highly-protected areas such as Yosemite National Park.

The National Science Foundation and National Institutes of Health helped fund the study.

-- Tami Abdollah

Photo: A mountain yellow-legged frog tadpole. Credit: Zoological Society of San Diego