Frog die-off a global problem, UC researchers say

0 Comments | Oakland Tribune, Aug 12, 2008 | by Aaron Morrison

For years, California developers have been struggling to find ways to not disturb the endangered red-legged frog.

Now, research led by two UC Berkeley biologists finds frogs and other amphibians worldwide need help because they are dying at alarming rates.

The researchers found that some frog populations are at 2 percent to 5 percent of their former size, which they argue is a warning sign of a larger global issue.

An article published this week in the journal "Proceedings of the National Academy of Sciences" reports that scientists are not yet sure what the long-term implications might be.

They are sure, however, of the varied causes of the die-off and say human beings are to blame for most of them.

According to David Wake, professor of integrative biology at UC Berkeley, the die-off can be pinned to three factors -- habitat destruction, which even local developers in Contra Costa and Alameda counties have been taking measures to stem; a naturally occurring fungus, which researchers say is not unique to dead frogs they found in the Sierra; and introduced species, which present an imbalance in amphibious habitats. For example, the first hint of frog decline in the state came in the 1990s, when scientists believed rainbow trout introduced in the area by humans were feeding on tadpoles and frog eggs.

"It's not a one-two punch," Wake said. "It's more of a one, two, three, four punch."

The "fourth punch," Wake said, is climate change, which is showing dramatic effects on aquatic-dwelling species worldwide. "There is no place in California where frogs are still thriving," Wake said.

Fewer frogs eating insects -- such as West Nile-carrying mosquitoes -- is just one example of how a major blow to global ecology could cause a shift in the food chain, though Wake would not equate the possible spreading of West Nile virus to the frog die- off.

Wake and his colleague Vance Vredenburg studied amphibian populations in the Sierra and say they have observed frogs carcasses in remote peaks -- places they are expected to thrive. In 2004, researchers found that one-third of amphibian species around the world are threatened with extinction, according to a UC Berkeley release at that time.

Wake suggested mass extinctions should prompt more focus on the study of pathology, as decimated frog populations could easily mean a change in the ways diseases are transmitted in human populations. "We've got to invest a lot more in research of the ecology of infectious disease," Wake said. Drastic shifts in the ecology affects "how it spreads through the environment."

Aaron Morrison can be reached at amorrisonj@bayareanewsgroup.com.