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Declines in amphibian populations around the globe remain a real concern, but the cause is not increasing UV radiation, according to Wendy Palen, lead author and a Simon Fraser University ecologist who conducted the research while earning her doctorate from the UW, and Daniel Schindler, UW professor of aquatic and fishery sciences. The work is being published in the Proceedings of the National Academy of Sciences May 25, and is now available online.
Papers published in the late 1990s and early 2000s raised the alarm that UV exposure was triggering amphibian declines, with many of the findings based on Pacific Northwest amphibians. Previous research wasn't wrong: some species proved extremely sensitive to UV radiation -- with especially high mortality for eggs and larvae -- as shown in physiological studies done mostly in highly controlled laboratory experiments or at just one or two natural ponds or sites, Palen says.
But conditions in labs or a few isolated sites are not what the animals typically encounter in the wild and they do not behave in labs as they do in their natural habitat, the new study of a large number of breeding sites, 22 altogether, revealed.
"When simple tests of species physiology are interpreted outside of the animal's natural environment, we often come to the wrong conclusions," Palen says.
For one thing there are lots of "natural sunscreens" in the water. They are in the form of dissolved organic matter -- remnants of leaves and other matter from wetlands and terrestrial areas that are dissolved in the water, much like tea dissolved in a mug of water. The more dissolved organic matter, the less UV exposure.