Oct. 29 (Bloomberg) -- Frogs and salamanders, considered by scientists bellwether species demonstrating global warming, are declining as Yellowstone National Park's wetlands dry out, Stanford University researchers said.

Climate monitoring over six decades and surveys of 49 ponds in Yellowstone, where the Old Faithful geyser, native bison and hot springs have enthralled visitors since the park was created in 1872, show ``climatic warming already has disrupted one of the best-protected ecosystems on our planet,'' said a study published in the Oct. 27 the journal Proceedings of the National Academy of Sciences.

``Our study adds to the growing body of evidence that amphibian populations are threatened and declining worldwide,'' including tiger salamanders, the most common salamander in the U.S., said Sarah McMenamin, a biologist at Stanford, in California, and lead author of the study, in an e-mail. ``These results are particularly startling because they are occurring in one of the most highly protected areas in the United States.''

Drought is more common and severe than at any time in the part century and the number of permanently dry ponds in northern Yellowstone has increased four-fold in 15 years, the study showed. Yellowstone, the world's oldest national park, is mostly in Wyoming and edges into Idaho and Montana.

Pollution, pathogens, invasive species and solar radiation are contributing to the world's declining amphibian population in addition to climate change. Rising temperatures, pond desiccation and decreasing rainfall have affected breeding habitats and prevented spawning, McMenamin and two collegues wrote.

Rising temperatures are also thought to be increasing the amphibians' susceptibility to deadly diseases including chytridiomycosis and ranavirus, McMenamin said.

``These diseases may have caused two of the mass extirpations I witnessed,'' she said. ``Last year and the year before, I found two ponds with hundreds of salamanders floating at the surface, dead for no apparent reason.''

Besides the tiger salamanders, the species under threat in the park included the Colombia spotted frog, boreal chorus frog and the boreal toad, the study said.

To contact the reporters on this story: Randall Hackley in London via rhackley@bloomberg.net

Last Updated: October 29, 2008 13:27 EDT