SPECIES IN PERIL | SierraSun.com


The yellow-legged frog's Sierra Nevada habitat is shrinking, and the animal is battling the voracious trout and virulent fungal diseases that threaten to eradicate it. Associated Press

BERKELEY ” Amphibians are dying off in astounding numbers around the world, including in the Sierra Nevada, in a decline that UC Berkeley researchers are calling a “mass extinction spasm.”

Around Truckee and Tahoe, yellow-legged frog populations have crashed because of a rapacious trout populations and a virulent strain of fungus, according to the university researchers.

But the mass amphibian decline extends across the globe and to salamanders and other species.

“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,” said David Wake, professor of integrative biology at UC Berkeley.

The study ” co-authored by Wake and Vance Vredenburg, research associate at the Museum of Vertebrate Zoology at UC Berkeley and assistant professor of biology at San Francisco State University ” will appear in a special supplement to the journal featuring papers based on presentations from the December 2007 Arthur M. Sackler Colloquium of the National Academy of Sciences, “In the Light of Evolution II: Biodiversity and Extinction.”

New species arise and old species die off all the time, but sometimes the extinction numbers far outweigh the emergence of new species, experts say. Extreme cases of this 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 this may be 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, Wake said.

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

Wake and his colleagues study amphibians in the Sierra Nevada.

“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 high elevations 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 2 to 5 percent of its former size.

Originally, frogs living high elevation seemed to thrive, but recently, they also succumbed.

There are several frog killers in the Sierra Nevada, Wake said. The first hint of frog decline in this area came in the 1990s, and researchers originally thought that rainbow trout introduced to this area were the culprits ” they like to eat tadpoles and frog eggs.

The UC Berkeley team did experiments in which it physically removed trout from some areas, and the result was that frog populations started to recover.

“But then they disappeared again, and this time there were carcasses,” Wake said.

The culprit is a nasty pathogenic fungus that causes the disease 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. And the Sierra Nevada amphibians are also susceptible to winds carrying pesticides from Central Valley croplands.

“The frogs have really been hit by a one-two punch,” Wake said, “although it’s more like a one-two-three-four punch.”

The frogs are not the only victims in this mass extinction, Wake emphasized. Scientists studying other organisms have seen similarly dramatic effects.

“Our work needs to be seen in the context of all this other work, and the news is very, very grim,” Wake said.

The National Science Foundation and National Institutes of Health helped support this study.

Brook and rainbow trout could be removed from seven lakes in the Desolation Wilderness Area under a project proposed by the U.S. Forest Service.

The proposal ” developed in cooperation with the California Department of Fish and Game and the U.S. Fish and Wildlife Service ” is part of an attempt to restore Sierra Nevada yellow-legged frog populations to the wilderness area and could affect Ralston Lake, Tamarack Lake, Cagwin Lake, Margery Lake, Lucille Lake, Le Conte Lake, Jabu Lake and their associated ponds and streams, according to a statement from the U.S. Forest Service.

Forest Service staff will hike into the Desolation Wilderness and set gill nets, which they will leave in place over the winter and revisit the following season. They will use backpack electroshockers to remove fish from connecting streams, the statement says.

The proposed lakes were selected because of their proximity to current populations of the frogs, which are under consideration for Endangered Species Act listing.

Before the 1950s, alpine lakes in the Desolation Wilderness were fishless and supported viable frog populations. Predation by the introduced trout is the best documented reason for the elimination of the frogs from more than 90 percent of their native habitat, according to the statement.

Although the project will result in the loss of fishing opportunities in the seven proposed lakes, other lakes in Desolation Wilderness have been identified as recreational fishing lakes and will be stocked in the future by the California Department of Fish and Game, the statement indicates.

Comments should be submitted by Friday.

The proposed action, including information on how to provide comments and a map, is posted on the Lake Tahoe Basin Management Unit’s Web site at http://www.fs.fed.us/r5/ltbmu/projects.

For more information, contact Sarah Muskopf at (530) 543-2835 or smuskopf@fs.fed.us.

Under a separate proposal, the Forest Service also is considering the removal of the nonnative brook trout from the Upper Truckee River and associated streams and lakes from the bottom of Meiss Meadows to 3,000 feet above South Upper Truckee Road to help the recovery of the native Lahontan cutthroat trout.

Crews would use electrofishing to remove brook trout from streams and would use gill nets in Showers, Round, Dardanelles and Four Lakes, installing 10 to 15 gill nets per lake, according to a statement.

Implementation of the project would occur August through October over the next six years, the statement added.

” Sun News Service

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