Frogs are croaking, study warns

Amphibians are in crisis, and scientists are alarmed.
LOS ANGELES TIMES
Almost 150 species of amphibians have apparently gone extinct and at least one-third of the rest are facing imminent threats that could soon wipe them out, according to a worldwide assessment by scientists published Thursday.
The severity of the global threat to thousands of species of frogs, salamanders and other amphibians makes them perhaps the most endangered class of animals on Earth, with their rapid decline outpacing that of mammals and birds.
David B. Wake of the University of California-Berkeley's Museum of Vertebrate Zoology, one of the world's leading amphibian experts, called the prospects for their survival "very grim."
"These are simply stunning results," Wake said of the report, published in the online version of the journal Science. "Nearly one-third of all the species are in the three top categories of endangerment, and nearly half the declines for unknown causes."
An array of threats
For two decades, scientists have been trying to figure out why amphibian populations worldwide are vanishing. Studies have documented an array of threats, varying from place to place, including infectious disease, destruction of freshwater and rain forest habitats, introduction of nonnative predators such as trout, pesticides, parasites, global climate change and the thinning ozone layer.
The findings of more than 500 scientists were included in the first global amphibian assessment, a three-year effort by researchers with IUCN-The World Conservation Union, the Center for Applied Biodiversity Science of Conservation International and NatureServe.
Sentinels for problems
Scientists say amphibians serve as sentinels for environmental problems that might be jeopardizing entire ecosystems. They spend much of their lives in water and breathe through permeable skin, which leaves them vulnerable to pesticides and changes in climate and water quality.
"Amphibians are one of nature's best indicators of overall environmental health," said Russell A. Mittermeier, president of Conservation International. "Their catastrophic decline serves as a warning that we are in a period of significant environmental degradation."
The report evaluated the status of all known species of amphibians -- 5,743 of them -- and concluded that 1,856, or 32 percent, were critically endangered, endangered or vulnerable to extinction.
Too little is known about 1,300 of the species to determine their status, but scientists believe that most of them are in peril, too. That means as many as 55 percent of all known amphibians, more than 3,000, could be on the verge of extinction, plus scores of species that have yet to be identified. Only 359 are considered not threatened.
"Amphibians are indeed telling us that our planet is being harmed right where you and I live," said Andrew Blaustein, director of the Graduate Program in Environmental Sciences at Oregon State University.
Extinction rate
Nine of 34 known amphibian extinctions have occurred since 1980 -- the onset of what is considered an age of accelerated, unnatural extinction driven by human activities. An additional 113 species have not been seen recently in the wild and probably are extinct, according to the report's lead author, Simon Stuart. Evolutionary biologists say species naturally disappear at a much slower pace.
Amphibians have inhabited Earth in their modern form for at least 150 million years, surviving the mass extinction of the dinosaur age virtually unscathed.
"The fact that this tough survival group is checking out on our watch should concern us all," said Wake, whose research focuses on the evolution and decline of salamanders. "The fate of every species is extinction, but they have a chance to give rise to other species before they go extinct. These species are going extinct in a blink -- not even a blink in geological time."
Underestimated numbers
Scientists say the rate of extinction is so rapid that the report probably underestimates the numbers threatened. Perhaps hundreds of varieties of frogs and salamanders are being wiped out before they are even discovered, Wake said. For example, more than 90 percent of Sri Lanka's rain forest is gone and the fragment that is left "is literally filled with undescribed species," he said. "Who knows what we have lost?"
Similar evaluations of birds and mammals found smaller percentages at risk -- 23 percent for mammals and 12 percent for birds.