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11 Jan 05
Climate change drives widespread amphibian extinctions
PlanetArk 12 Jan 06
Climate-Change Fungus is Wiping out Frogs – Study told
Story by Patricia Reaney
LONDON - An infectious fungus aggravated by global warming has killed entire populations of frogs in Central and South America and driven some species to extinction, scientists said on Wednesday.
In research that showed the effects of rising temperatures on delicate ecosystems, a team of researchers found that a warming atmosphere encouraged the spread of a fungus that has wiped out species of harlequin frogs and golden toads.
"This is the first clear evidence that widespread extinction is taking place because of global warming," Dr Alan Pounds, an ecologist of the Monteverde Cloud Forest Preserve in Costa Rica, said in an interview.
"Climate change is already altering the dynamics of infectious disease and causing species to disappear."
Pounds and his team established the link between global warming and the disappearance of frogs in the cloud forests of Costa Rica by analysing sea surface and air temperatures, which rose by 0.18 degrees per decade between 1975 and 2000. Warmer temperatures increased cloud cover over the tropical mountain which the scientists believe promoted conditions to spur the growth of the chytrid fungus that kills frogs.
They are confident that global warming is a key factor in the disappearance of many amphibian populations in tropical forests. "There is absolutely a linkage between global warming and this disease - they go hand-in-hand," said Dr Arturo Sanchez-Azofeifa, of Canada's University of Alberta and a co-author of the research published in the journal Nature.
"With this increase in temperature, the bacteria has been able to increase its niche and wipe out large populations of amphibians in the Americas," he added in a statement.
About a third of the 5,743 known species of frogs, toads and other amphibians are classified as threatened, according to the Global Amphibian Assessment. Up to 167 species may already be extinct and another 113 species have not been found in recent years.
Habitat loss is the greatest threat to amphibians but fungal disease is also a serious problem. Andrew Blaustein, of Oregon State University, and Andy Dobson, of Princeton University in New Jersey, described the research as a breakthrough.
"The powerful synergy between pathogen transmission and climate change should give us cause for concern about human health in a warmer world," they said in a commentary in Nature.
"The frogs are sending an alarm call to all concerned about the future of biodiversity and the need to protect the greatest of all open-access resources - the atmosphere," they added.
EurekAlert 11 Jan 05
Climate change drives widespread amphibian extinctions
Warmer temperatures enhance growth conditions of fatal fungus
Results of a new study provide the first clear proof that global warming is causing outbreaks of an infectious disease that is wiping out entire frog populations and driving many species to extinction.
Published in the Jan. 12 issue of the journal Nature, the study reveals how the warming may alter the dynamics of a skin fungus that is fatal to amphibians.
The climate-driven fungal disease, the author's say, has hundreds of species around the world teetering on the brink of extinction or has already pushed them into the abyss.
"Disease is the bullet that's killing the frogs," said J. Alan Pounds, the study's lead scientist affiliated with the Tropical Science Center's Monteverde Cloud Forest Preserve in Costa Rica.
"But climate change is pulling the trigger. Global warming is wreaking havoc on amphibians, and soon will cause staggering losses of biodiversity," he said.
"The good news, if there is any, is the new findings will open up avenues of research that could provide scientists with the means to save the amphibians that still survive," said Bruce Young, a zoologist at NatureServe who took part in the study. "If this cloud has any silver lining, that's it."
The new theory for the frogs' decline "leaps over a major roadblock in our understanding," said Sam Scheiner, program director for the National Science Foundation (NSF)'s ecology of infectious diseases program, which funded the research.
"This study demonstrates the complex nature of global climate change, including how climate affects the spread of disease, and why these must be integrated if we are to understand and reduce threats to species extinctions."
But the message goes beyond amphibians, says Scheiner: global warming and the accompanying emergence of infectious diseases are a real and immediate threat to biodiversity and a growing challenge for humankind.
The decline of amphibians in apparently pristine, protected habitats in Costa Rica and elsewhere has perplexed conservation biologists since 1990, when the problem was first recognized.
At least 110 species of brightly colored harlequin frogs once lived near streams in the tropics of Central and South America, but about two-thirds vanished in the 1980s and 1990s. In the famed Costa Rican cloud forests, for example, the Monteverde harlequin frog disappeared in the late 1980s, as did the golden toad, whose much-publicized extinction, said Pounds, "was the first sign of this emerging threat to species survival."
Using records of sea-surface and air temperatures, Pounds and colleagues show that harlequin frogs are disappearing in near lockstep with changing climate. According to the scientists, the Earth's rising temperatures enhance cloud cover on tropical mountains, leading to cooler days and warmer nights, both of which favor the chytrid fungus. The organism grows and reproduces best at temperatures between 63 to 77 degrees Fahrenheit (17 to 25 degrees centigrade). The fungus kills frogs mostly in cool highlands or during winter, implying that low temperatures make it more deadly. So the idea that it flourishes in warm years, which the evidence now supports, is new.
The study results come at a time of growing concern about the future of amphibians. The Global Amphibian Assessment, published in 2004, found that nearly one-third of the world's 6,000 or so species of frogs, toads and salamanders face extinction--a figure far greater than that for any other group of animals.
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