Dying amphibians signal impending biodiversity crisis

August 13th, 2008 - 2:16 pm ICT by IANS  


Washington, Aug 13 (IANS) An alarming decline in amphibian species signals an impending biodiversity disaster or a new mass extinction threatening the planet, according to University of California researchers. “There’s no question that we are in a mass extinction spasm right now,” said David Wake, professor of integrative biology at University of California. “Amphibians have been around for about 250 million years. They made it through when the dinosaurs didn’t. The fact that they’re cutting out now should be a lesson for us.”

The global amphibian extinction is a particularly bleak example of this drastic decline. In 2004, researchers found that nearly a third of amphibian species are threatened, and many of the non-threatened species are on the wane.

The study, co-authored by Wake and Vance Vredenburg, research associate at UC Berkeley, said new species arise and old species die all the time, but sometimes the extinction numbers far outweigh the emergence of new species.

Such extreme cases are called mass extinction events, and there have been only five in the planet’s history, until now. The sixth mass extinction event, which Wake and others argue is happening currently, is different from the past events. “My feeling is that behind all this lies the heavy hand of Homo sapiens,” Wake said.

There is no consensus among the scientific community about when the current mass extinction started, Wake said. It may have been 10,000 years ago, when humans first came from Asia to the Americas and hunted many of the large mammals to extinction.

It may have started after the Industrial Revolution, when the human population exploded. Or, we might be seeing the start of it right now, Wake said. But no matter what the start date, empirical data clearly show that extinction rates have dramatically increased over the last few decades, he said.

“We have these great national parks here that are about as close as you can get to absolute preserves, and there have been really startling drops in amphibian populations there, too,” Wake said.

Of the seven amphibian species that inhabit the peaks of the Sierra Nevada, five are threatened. Wake and his colleagues observed that, for two of these species, the Sierra Nevada Yellow-legged Frog and the Southern Yellow-legged Frog, populations over the last few years declined by 95 to 98 percent, even in highly protected areas such as Yosemite National Park.

This means that each local frog population has dwindled to only two to five percent of its former size. Originally, frogs living atop the highest, most remote peaks seemed to thrive, but recently, they also succumbed.

But the culprit is a nasty pathogenic fungus that causes chytridiomycosis. Researchers discovered the fungus in Sierra Nevada frogs in 2001. Scientists have documented over the last five years mass die-offs and population collapses due to the fungus in the mountain range.

But the fungus is not unique to California. It has been wiping out amphibians around the world, including in the tropics, where amphibian biodiversity is particularly high. “It’s been called the most devastating wildlife disease ever recorded,” Wake said.

Global warming and habitat constriction are two other major killers of frogs around the world, Wake said. The frogs are not the only victims in this mass extinction. Scientists studying other organisms have seen similarly dramatic effects, he added.

These findings have been published online this week in Proceedings of the National Academy of Sciences.

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