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Study Finds Global Warming Is Killing Frogs

Study Finds
Global Warming
Is Killing Frogs By GAUTAM NAIK
January 12, 2006; Page B1

Conservationists have been puzzled for more than a decade by the mysterious disappearance of harlequin frogs from the pristine, high-altitude tropical forests of Costa Rica. Now a group of scientists believe they have pinpointed the likely cause: global warming that promotes a fungus that is fatal to the frogs.

The finding, 1, is likely to stoke the debate about whether climate change is affecting the dynamics of disease, and why amphibians are dying out in such massive numbers world-wide. Recent data indicates that, since 1980, as many as 122 amphibian species are likely to have become extinct and one-third of known amphibian species are threatened.

In Costa Rica, researchers found that the region's brightly-colored harlequin frogs were succumbing to a disease caused by the chytrid (KIT-rid) fungus, which also has been implicated in a wave of amphibian deaths elsewhere in the world. Using records of sea and air temperatures, the scientists discovered that the frogs were disappearing at a rate in near-lockstep with the changing climate.

"About 80% of the disappearances of frogs correspond to unusually warm years" when the fungus thrives, said J. Alan Pounds, the study's lead author and resident scientist at the Monteverde Cloud Forest Preserve in Costa Rica. The fungus grows on amphibians' skin, creating a dermatological condition for the creatures that is often fatal. About two-thirds of the harlequin species, which once thrived in the tropics of Central and South America, vanished in the 1980s and 1990s.

But establishing a causal link between large-scale, long-term global warming and the elimination of specific species in a particular region isn't easy. The fungus-related frog deaths in Costa Rica "could be a roll of the dice one time, or it could be several interconnected factors contributing to the problem," said Ben Orlove, a professor of environment science and policy at the University of California, Davis. Habitat destruction, pesticides and other factors have all been blamed for amphibian declines.

Still, the demise of amphibians is part of a far-larger pattern. The earth has witnessed five known extinction waves affecting many species. What makes the current one different, scientists have concluded, is that it is likely to have been triggered mainly by human activity.

Bird, mammal and amphibian species are disappearing in recent decades at a rate estimated at 100 to 1,000 times as high as the expected, natural extinction rate. In the past 500 years, human activity has forced 844 species to extinction, according to the World Conservation Union, a Switzerland-based agency whose members include some 82 states, 111 government agencies and other groups involved in ecology and conservation.

Amphibians are in the deepest trouble. They may be particularly vulnerable because they go through several life-cycle stages, making them prey to more predators and environmental shifts. And while they perform the nifty trick of absorbing oxygen through their skin, that probably makes them more susceptible to toxins and infection.

According to the Global Amphibian Assessment, a large, world-wide study that reported its findings in 2004, about 43% of amphibian species are declining, 27% are stable and less than 1% are increasing. The status of the rest isn't known.

Almost certainly, factors such as loss of habitat, pesticides and change in land-use patterns contribute to the decline in amphibian species across the globe. "The assumption, then, was that [amphibians] would do just fine in protected areas" such as Costa Rican cloud forests, said James P. Collins, a professor at Arizona State University in Tempe and chairman of the Declining Amphibian Populations Task Force. But since Costa Rica's harlequin-frog population is diminishing anyhow, "the climate-change explanation attracts attention," he said.

Last fall, scientists and conservationists met in Washington and drew up a global action plan to save the world's frogs, toads and salamanders from oblivion. The estimated cost over five years: more than $400 million to move their populations from threatened areas, breed them in captivity or conduct studies.

In Costa Rica, Mr. Pounds and his colleagues studied air and sea surface temperatures from 1973 to 2000 and found that rising temperatures enhanced cloud cover over tropical mountains, leading to warmer nights and cooler days. The change appears to have favored the chytrid fungus, which grows and reproduces best at temperatures from 63 to 77 degrees Fahrenheit. One solution for the harlequin frogs might be to move their populations to altitudes where the fungus doesn't thrive as well, Mr. Pounds says.

But key questions remain unanswered. "Climate change may be helping the fungus spread, but we don't know where the fungus came from" or whether it can survive without amphibians, Mr. Pounds says. "These are the parts of the story that aren't entirely clear."

Write to Gautam Naik at 2
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