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Why amphibians matter
They form a key link in ecosystems worldwide. But they're dying off and global warming is a likely suspect.
By Moises Velasquez-Manoff | Contributor to The Christian Science Monitorfrom the June 21, 2007 edition
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Monteverde Cloud Forest Preserve, Costa Rica - Since the 1970s, three frog species have disappeared from Puerto Rico's mountain forests, all after unusually warm years. Between 1987 and 1988, the hottest year on record until then, the golden toad and Monteverde harlequin frog disappeared from the Monteverde Cloud Forest Preserve in Costa Rica. That same year, the jambato toad vanished from the highlands of Ecuador, which was also unusually hot and dry. "We have a tendency for species to disappear after warm years," says Alan Pounds, scientist-in-residence at Monteverde.
Scientists consider these extinctions part of an ongoing worldwide amphibian die-off. The World Conservation Union (IUCN) estimates that 32 percent of all amphibians are in danger of going extinct. Of 5,918 known species – and new species are constantly being discovered – 165 may have already disappeared. Two-thirds of all harlequin frogs, which range throughout New World tropics, are already gone, Dr. Pounds says. Scientists have blamed habitat loss, increased ultraviolet radiation, pollution, and chytrid, a fungus that humans may have inadvertently transported around the globe.
To that list of suspects, Dr. Pounds and many other scientists now add climate change. Scientists rarely expect animals to drop dead from heat exhaustion. Instead, they anticipate warming will do away with food sources and habitats or trigger outbreaks of disease – and not always in obvious ways. Pounds thinks that this is what happened at Monteverde. Warming helped the chytrid fungus kill off the golden toad.
The fungus, which grows on the skin of amphibians and is lethal to many of them, thrives in the relatively cool conditions found in tropical highlands. So how could global warming enable it? What if warming pushed average temperatures at Monteverde up into the fungus's optimal range, between 63 and 77 degrees F.? Rather than suppressing the cool-weather fungus, rising temperatures may have led to ideal growing conditions. "It's the opposite of what you would expect," Pounds says.
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