Global warming-fungus spell deadly combo for frogs

FROM Costa Rica to Peru, a fungal epidemic fuelled by global warming may have wiped out dozens of frog species in otherwise pristine environ...

FROM Costa Rica to Peru, a fungal epidemic fuelled by global warming may have wiped out dozens of frog species in otherwise pristine environments, a new study concludes. In the past 20 years, about two-thirds of central and South America’s 110 brightly colored harlequin frog species have vanished.

A killer fungus with a worldwide range and an affinity to amphibian skin had previously been indicted as the prime suspect in the frogs’ disappearance. But a study published in Nature concludes that the fungal epidemic has been stoked by global warming, a finding that may have broad implications for at-risk species.

‘‘The message is that global warming is causing species extinction, and a lot of them,’’ co-author J. Alan Pounds said over phone at the Monteverde Cloud Forest Preserve and Tropical Science Center in Costa Rica where he serves as resident scientist. In this case, he said, disease may be the bullet, but climate change is ‘‘pulling the trigger.’’

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A hypothesis blaming the fungus and climate change had been a conundrum for researchers, because the fungus is known to prefer relatively cool temperatures, between about 63 and 77 degrees Fahrenheit. Perhaps, as some suggested, global warming may benefit frogs by keeping their habitats too hot for the fungus to thrive. ‘‘But paradoxically, the losses of harlequin frogs were taking place in unusually warm years,’’ Pounds says.

He and his collaborators found a solution to the conundrum in detailed records of the region’s weather trends: Although night temperatures in the hard-hit mountain habitats went up, daytime temperatures went down, perhaps caused by global warming’s ability to increase cloud cover in mountainous areas. Before the upward creep of global temperatures in the ’70s, Pounds said the fungus was checked by normal fluctuations that made the day too hot or night too cold. But many harlequin frog habitats—especially in the middle elevations where most extinction occurred—have been moderated by global warming, enough to create the right temperature for the fungus.

Researchers have long maintained that amphibian declines may be a warning of greater perils. And scientists have hinted that global climate changes could pose a big threat to cold-weather species as polar bears, reindeer and penguins. Andrew Blaustein, a herpetologist at Oregon State University, said Pounds’ study goes beyond making predictions by showing ‘‘global climate change is making an unequivocal impact on animals.’’ ‘‘What we have here,’’ he said, ‘‘is real animals getting extinct with real climate change documented.’’ (LAT-WP )