Warming Tied To Extinction Of Frog Species
Thursday, January 12, 2006
Rising temperatures are responsible for pushing dozens of frog species over the brink of extinction in the past three decades, according to findings being reported today by a team of Latin American and U.S. scientists.
The study, published in the journal Nature, provides compelling evidence that climate change has already helped wipe out a slew of species and could spur more extinctions and the spread of diseases worldwide. It also helps solve the international mystery of why amphibians around the globe have been vanishing from their usual habitats over the past quarter-century -- as many as 112 species have disappeared since 1980.
Scientists have speculated that rising temperatures and changing weather patterns could endanger the survival of many species, but the new study documents for the first time a direct correlation between global warming and the disappearance of around 65 amphibian species in Central and South America.
The fate of amphibians -- whose permeable skin makes them sensitive to environmental changes -- is seen by scientists as a possible harbinger of global warming's effects. Rising temperatures are threatening the survival of flora and fauna worldwide, including coral reefs in the Caribbean, which serve as critical fish nurseries, and South African rhododendrons, which cannot move to a cooler climate.
J. Alan Pounds -- the resident scientist at the Tropical Science Center's Monteverde Cloud Forest Preserve in Costa Rica and the study's lead author -- worked with 13 other researchers to pin down the link between rising tropical temperatures and the spread of the deadly chytrid fungus that has wiped out dozens of species of harlequin frogs in recent years.
"Disease is the bullet killing frogs, but climate change is pulling the trigger," Pounds said. "Global warming is wreaking havoc on amphibians and will cause staggering losses of biodiversity if we don't do something first."
The paper helps explain how global warming has allowed the chytrid fungus -- which kills frogs by growing on their skin and attacking their epidermis and teeth, as well as by releasing a toxin -- to thrive in Costa Rica and neighboring countries. The higher temperatures result in more water vapor in the air, which in turn forms a cloud cover that leads to cooler days and warmer nights. These conditions favor the fungus, which grows and reproduces best at temperatures between 63 and 77 degrees Fahrenheit.
At least 110 species of the vibrantly colored amphibians once lived near streams in the Central and South American tropics, but about two-thirds disappeared in the 1980s and 1990s, including the golden toad. While researchers had previously identified the fungus as a major reason for the frogs' demise, they have been trying determine why the disease has taken such a major toll in recent years.
Looking at more than 65 harlequin frog species that had vanished, researchers found that 80 percent of the time there was a correlation between higher temperatures and the species' disappearance. After a warm peak in 1987, for example, five species died off.
"There's a coherent pattern of disappearances, all the way from Costa Rica to Peru," Pounds said in an interview. "Here's a case where we can show that global warming is affecting outbreaks of this disease."
Amphibians are experiencing a precipitous decline in Africa, Asia and North America, according to a comprehensive 2004 survey, which cited climate change as well as deforestation, pollution and habitat loss as key factors.
"We have a biodiversity crisis," said Andrew Blaustein, director of Oregon State University's graduate programs in environmental science. "Amphibians seem to be harder hit than other groups."
Michael Totten, senior director for climate and water initiatives at the environmental group Conservation International, said humans have made it more difficult for animal and plant species to adapt to the shifting climate by fragmenting natural habitat. "Traditionally species have been resilient and capable of going through dramatic climate change, but with humans changing the face of the landscape, we've created lots of prisons for species, and that's the major problem they face," he said.
Stanford University climatologist Stephen Schneider said the new research represents "a creative step in the right direction, but it's still early in the game to sound the 'solved' bell." He added that the study is "just further evidence" that global warming is linked to accelerating extinctions worldwide.
While Pounds and his colleagues are still researching the harlequin frogs' disappearance, their findings are prompting even some scientists who had been skeptical about climate change's impact on amphibians to reassess their position.
James Collins, who studies harlequin frogs at Arizona State University, called the paper "an intriguing contribution" to understanding what is happening to amphibians worldwide. He said the study shows that when it comes to climate change, "these forces don't all move in one direction," since some habitats are becoming drier while others are becoming wetter.
Collins and a team of researchers are trying to determine if the chytrid fungus is surfacing in areas where it had never thrived before.