Why amphibians matter

They form a key link in ecosystems worldwide. But they're dying off and global warming is a likely suspect.

from the June 21, 2007 edition

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Disease isn't the only threat from warming. Steven Whitfield, a PhD candidate at Florida International University in Miami, analyzed 35 years of amphibian and lizard population data at La Selva Biological Field Station on Costa Rica's Caribbean plain. To his surprise, he found that researchers today catch one-quarter of the number of frogs and lizards they caught then.

"These declines were not subtle," he says. And Pounds's chytrid hypothesis doesn't explain them: The fungus doesn't grow well in the hot lowlands, and lizards don't get chytrid. That suggested something else. Mr. Whitfield guesses it is the leaves rotting on the jungle floor.

In those same 35 years, average temperatures at La Selva have risen. Higher temperatures, especially at night, perhaps make trees put out fewer leaves. But they also increase the decomposition rate of fallen leaves on the jungle floor, where frogs and lizards feed, lay eggs, and take shelter.

"If there's less leaf litter on the ground, then frogs and lizards have [fewer] hiding places," Whitfield says.

Both these hypotheses underscore global warming's indirect effect on wildlife. "I don't think that a single factor is going to explain all of the trends that we're seeing worldwide," Whitfield says. But "interaction between these factors is going to be hugely important."

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