The same edition of Ecology includes a second, corroborating study, by USGS researchers P. Stephen Corn and Erin Muths, that examines breeding of the boreal chorus frog at a Colorado pond.
The research by Palen's group used amphibian population and breeding information scientists collected at hundreds of Pacific Northwest sites from 1997 through 2000. The focus was narrowed to 136 sites that yielded the best information, and then water samples were collected from each of those sites, spread throughout the Olympic Mountains and the Cascade Range in Washington and Oregon.
The water samples were analyzed for dissolved organic matter produced primarily from terrestrial vegetation and soils that is leeched into lakes and streams by rain or melting snow. The research concluded that 85 percent of the amphibian habitats sampled are protected from harmful levels of UV-B by dissolved organics.
Using the water-sample approach allowed the scientists to bring the small scale at which experiments are done into line with the much larger scale at which conditions could affect entire populations.
Most of the previous research that implicated UV-B in amphibian mortality and deformity has been done in the Northwest, but the effects were thought to occur elsewhere as well. Now, Palen said, it appears that scientists need to keep looking for causes, and that they could include a number of factors that vary across geographic regions.
For instance, she noted that the mountain yellow-legged frog in California's Sierra Nevada has been declared endangered, but the reason has nothing to do with UV-B. Instead, the frog population has declined because of the introduction of non-native trout species that feed on frog eggs, juveniles and adults.
Such evidence suggests that the causes of amphibian population declines might be spe
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Contact: Vince Stricherz
vinces@u.washington.edu
206-543-2580
University of Washington
5-Dec-2002