FINFACTS (Ireland) 11 January 06 Dead frogs linked to global warming; Amphibians under worldwide threat
The science magazine Nature says that the mysterious disappearance of frog species throughout Central and South America has been linked to a fungal disease that is exacerbated by the changing climate.
"Disease is the bullet killing frogs, but climate change is pulling the trigger," says Alan Pounds, an ecologist at the Monteverde Cloud Forest Preserve and Tropical Science Center in Costa Rica.
Researchers warn that the fungus Batrachochytrium dendrobatidis, which lives on the frogs' skin, may be killing amphibians worldwide.
Tropical America is just one of many regions that have seen dramatic losses of amphibian species over the past few decades. In 2004, the first global assessment of amphibians revealed that almost a third of the world's known species are threatened with extinction.
Studies have pointed to a range of causes for these deaths, including infections, habitat loss and changing temperature or rain patterns; amphibians, with their moist, breathable skins, are thought to be particularly sensitive to environmental change. But the root of the problem in many places, often in seemingly pristine habitats, has remained elusive.
The magazine says that Pounds and his team set out to test whether fungal disease exacerbated by climate change could explain the loss of 70 or so species of harlequin frog (Atelopus) from the highlands of Central and South America. Many of them have vanished despite being in protected reserves.
The team first mapped the timing of species disappearances against changes in sea-surface and air temperature over the past few decades, and found that the frogs are disappearing almost exactly in step with climate change.
But it was not clear how the link between species loss and climate change worked: the world is generally warming, but the fungus is thought to be more deadly in cooler climes.
So the team looked at 50 sites from Costa Rica to Peru. It found that the frogs were doing worst in areas where night-time temperatures are getting warmer, but day-time temperatures are cooler - conditions that favour the fungus.
The most likely connection, say the researchers in Nature, is that large-scale warming is accelerating the formation of clouds. This in turn makes local conditions kinder on the fungus, and spells bad news for the frogs.
The extent to which the team's finding explains the global problem of amphibian deaths is not yet clear. But Pounds argues that because the chytrid fungus is known to exist in many regions, including Europe and Australia, "it is likely to be a key player on a global scale". Of course, it is still uncertain how global climate change will affect local weather patterns where frogs and toads live.
Camille Parmesan, an ecologist at the University of Texas, Austin, and an author of the third assessment report of the Intergovernmental Panel on Climate Change, applauds the study. She says it is "the first to show a whole group of extreme-environment species disappearing because of climate change on a large scale".
Pounds hopes his team's findings will ram home the global-warming message. "We have to reduce concentrations of greenhouse gases very soon if we are to avoid massive losses of biodiversity."
Five known extinction waves have been experienced by the Earth but this is the first one that has likely been triggered by human activity.
The World Conservation Union says that the rapid loss of bird, mammal and amphibian species in recent decades is estimated at being between 100 and 1,000 times higher than the "background" or expected natural extinction rate. In the last 500 years, human activity has forced 844 species to extinction, the group says.
The amphibians are the most vulnerable.
The world’s amphibian species are under unprecedented assault and are experiencing tens of thousands of years worth of extinctions in just a century, according to the most comprehensive study ever conducted. More than 500 scientists from over 60 nations contributed to the Global Amphibian Assessment, the key findings of which published in October 2004 in the journal Science.
Over the previous three years, scientists analyzed the distribution and conservation status of all 5,743 known amphibian species—which include frogs and toads, salamanders, and caecilians. Of these, 1,856—or 32 percent—are now considered threatened with extinction. In addition, sufficient data are lacking to accurately assess the status of nearly 1,300 other species, most of which scientists believe are also threatened.
Amphibians are widely regarded as “canaries in the coal mine,” since their highly permeable skin is more immediately sensitive to changes in the environment, including changes to freshwater and air quality.
“Amphibians are one of nature’s best indicators of overall environmental health,” said Russell A. Mittermeier, president of Conservation International (CI). “Their catastrophic decline serves as a warning that we are in a period of significant environmental degradation.”
Key findings of the study include:
• According to the IUCN Red List of Threatened Species, at least 1,856 amphibian species are threatened with extinction, representing 32 percent of all species. By comparison, only 12 percent of all bird species and 23 percent of all mammal species are threatened.
• At least nine species have gone extinct since 1980, when the most dramatic declines began. Another 113 species have not been reported from the wild in recent years and are considered to be possibly extinct.
• 43 percent of all species are in population decline; fewer than one percent are increasing. Twenty-seven percent are stable, and the rest are unknown.
• 427 species are considered Critically Endangered (CR), 761 are Endangered (EN), and 668 are Vulnerable (VU).
Dead frogs linked to global warming; Amphibians under worldwide threat