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Frog, Lizard Extinctions Caused by Climate, Not Fungus, Study Suggests

Jonathan Franklin
for National Geographic News
April 17, 2007
 
A changing climate may be responsible for the sharp drop in more than a dozen species of lizards and frogs in Central America, according to a new long-term study.

The research adds another challenge to understanding the rapid extinctions observed in Central and South America, where more than a hundred amphibian species have disappeared since 1980.

The massive decline of frog populations in particular has been widely linked to a fungus known as BD, which can wipe out a species in months.

But the new study found slow, steady declines of both lizards and frogs in pristine, protected rain forests that are free of the BD fungus, researchers say.

"There was no reason that these species should be in decline. Populations in the lowlands of Central America were thought to be free of risk," said Steven M. Whitfield of Florida International University, the lead author of the study.

"This is particularly troubling, because if the species seen as least susceptible to risk show clear signs of decline, that is worrying."

The new study, published in the current issue of the Proceeedings of the National Academy of Sciences, reviewed data collected over 35 years at La Selva Biological Station in Costa Rica.

The scientists found a 75 percent drop in local amphibian and reptile numbers during that period.

Not only is BD fungus absent at La Selva, but BD is also not known to affect reptiles at all, Whitfield explained, so another factor must be to blame for the drop in numbers.

His team's findings suggest that increased rain and higher temperatures observed over the same 35-year period may be responsible. Hotter, wetter conditions speed decomposition of the fallen leaves that the animals depend on for their habitat, Whitfield said.

"One of the reasons the amphibian crisis is so alarming is that species are going extinct so rapidly, even in areas where there is no human impact or [where the impact is] minimal," he noted.

"Biologists can predict which are likely to go extinct," he added, citing a proposal to create captive populations for hundreds of amphibian species to save them from extinction.

(Read related story: "'Frog Hotel' to Shelter Panama Species From Lethal Fungus" [November 2, 2006].)

"But doing that is obviously expensive, so more funding is needed for amphibian conservation," he said.

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