Fungus Identified in Frog Population Decline
STEVE INSKEEP, host:
Climate change experts have warned that the world may not adjust smoothly to an increase in the Earth's temperature. Some have warned of unexpected epidemics while others warn of mass extinctions. There has not been much solid proof of this until now. A study in the journal Nature has linked widespread frog extinctions in Central and South America to an epidemic of fungus, and the fungus is triggered by increasing temperatures. NPR's John Nielsen has more.
JOHN NIELSEN reporting:
Costa Rica's Monteverde Cloud Forest used to be full of exotic-looking amphibians. Among the most numerous were the red, black and yellow Harlequin frogs found only in these forests. Alan Pounds, chief biologist at the Monteverde Cloud Forest Reserve and Science Center, says it used to be impossible to take a walk and not see these frogs near the stream beds.
Mr. ALAN POUNDS (Chief Biologist, Monteverde Cloud Forest Reserve and Science Center): And in fact, you had to be careful not to step on them as you walked along the streams in certain areas and certain sites.
NIELSEN: Then in 1988, these frogs began to vanish. The few that remained were being killed by the so-called chytrid fungus, a pathogen never before found in these forests. Pounds was stunned by the speed with which the fungus killed the frogs.
Mr. POUNDS: It's now been missing since the late 1980s, and we suspect that it's extinct.
NIELSEN: The Harlequin is far from the only frog to go extinct. Last year an international team of scientists published a harrowing report on the global decline of amphibians. Thousands of species are in trouble, and hundreds are either gone or on the brink of extinction. The report blames habitat loss and pollution for some of the declines. It also blames the sudden and mysterious spread of the frog-killing chytrid fungus. But what could turn a previously harmless fungus lethal on a global scale? Pounds says one clue came when scientists studying the disappearance of more than a hundred other frog species compared temperature records against the timing of local extinctions.
Mr. POUNDS: We have an almost lockstep pattern of changing temperature and disappearing amphibians, so frogs tend to be seen for the last time immediately after a very warm year.
NIELSEN: Pounds says the chytrid fungus tends to thrive in places where the days are not too hot and the nights are not too cold. Global warming has expanded the range of the fungus by raising nighttime temperatures and lowering daytime highs by bringing on more cloudy days. Fungal attacks unleashed by these changes have wiped out a hundred and ten different species of frogs, he says. Experts on the links between diseases and climate change are hailing this paper as a breakthrough. Andy Dobson of Princeton University says that's because this paper explains why frog species separated by thousands of miles have all suffered the same fate.
Mr. ANDY DOBSON (Princeton University): The other examples people have tried to look at have usually only involved one pathogen and one host. And the evidence has been relatively ambiguous.
NIELSEN: Dobson thinks this paper will draw lots of public interest, in part because it isn't about a mere mass extinction. It's about frogs, and people love frogs.
Mr. DOBSON: And, you know, those are the sort of the classic things you see pictures of in children's books. They're the first animal that most kids can recognize after their teddy bear. And for most of the kids, looking at those books is the only chance they're ever going to get to see one now.
NIELSEN: Pounds says the so-called chytrid fungus is continuing to spread around the world. Recent outbreaks have been reported in several different parts of Europe. John Nielsen, NPR News, Washington.
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