The hypothesis that increasing ultraviolet-B (UVB) radiation is a causal factor in the decline of amphibian populations has received considerable attention in the scientific and public media. To evaluate the validity of this hypothesis, it is necessary to examine the natural environmental factors and biological traits of amphibians that protect them from UVB radiation. A careful reading of the literature reveals that most published studies on the effects of ambient UVB radiation on amphibian embryos have found no increased mortality. Those few reports that show harmful effects employ experimental methods that do not place enough importance on the natural abiotic and biotic factors that provide UVB protection. In the laboratory, amphibian embryos are resistant to doses of UVB radiation far higher than those they would normally receive from ambient sunlight. The jelly surrounding amphibian eggs absorbs UVB radiation, as revealed by spectral measurements of absorbance; after UVB exposure, embryos with their jelly capsules removed show significantly higher mortality than those with the jelly intact. In light of this and other factors mitigating UVB absorption, the hypothesis that ambient UVB radiation causes amphibian mortality and population declines is without support.
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