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 are threatened, and many of the non-threatened species are on the wane.
Our own backyard provides a striking example, Wake said. He and his colleagues study amphibians in the Sierra Nevada, and the picture is grim there, as well.
"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 2 to 5 percent of its former size. Originally, frogs living atop the highest, most remote peaks 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 snack on 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
|Contact: Rachel Tompa|
University of California - Berkeley