Abstract
An increase in ultraviolet-B (UV-B) radiation has been posited to be a potential factor in the decline of some amphibian population. This hypothesis has received support from laboratory and field experiments showing that current levels of UV-B can cause embryo mortality in some species, but little research has addressed whether UV-B is influencing the distribution of amphibian populations. We compared patterns of amphibian presence to sitespecific estimates of UV-B dose at 683 ponds and lakes in Glacier, Olympic, and Sequoia‐Kings Canyon National Parks. All three parks are located in western North America, a region with a concentration of documented amphibian declines. Sitespecific daily UV-B dose was estimated using modeled and field-collected data to incorporate the effects of elevation, landscape, and water-column dissolved organic carbon. Of the eight species we examined (Ambystoma gracile, Ambystoma macrodactylum, Bufo boreas, Pseudacris regilla, Rana cascadae, Rana leuteiventris, Rana muscosa, Taricha granulosa), two species (T. granulosa and A. macrodactylum) had quadratic relationships with UV-B that could have resulted from negative UV-B effects. Both species were most likely to occur at moderate UV-B levels. Ambystoma macrodactylum showed this pattern only in Glacier National Park. Occurrence of A. macrodactylum increased as UV-B increased in Olympic National Park despite UV-B levels similar to those recorded in Glacier. We also found marginal support for a negative association with UV-B for P. regilla in one of the two parks where it occurred. We did not find evidence of a negative UV-B effect for any other species. Much more work is still needed to determine whether UV-B, either alone or in concert with other factors, is causing widespread population losses in amphibians.
Highlights
IntroductionRoy 1993) is one factor contributing to the global decline in amphibian populations (Blaustein and others 1994)
Ecologists have hypothesized that a recent increase in surface ultraviolet-B radiation (UV-B) resulting from thinning of the ozone layer (Kerr and McEl-This article is a U.S government work, and is not subject to copyright in the United States.roy 1993) is one factor contributing to the global decline in amphibian populations (Blaustein and others 1994)
Estimated mean daily UV-B dose at 1-cm depth on the summer solstice ranged from 3.4 to 25.8 W h/ m2 in Glacier (x = 18.5, n = 391 ponds), 4.4 to 25.0 W h/m2 in Olympic (x = 19.2, n = 215 ponds), and 15.4 to 26.5 W h/m2 in Sequoia–Kings Canyon National Park (Sequoia) (x = 24.6, n = 83 ponds) (Figure 1)
Summary
Roy 1993) is one factor contributing to the global decline in amphibian populations (Blaustein and others 1994). This hypothesis is supported by experiments that show higher rates of embryonic mortality and larval deformities under ambient levels of UV-B compared to reduced UV-B levels (reviewed by Corn 2000; Blaustein and others 2003; Boone and others 2003; Licht 2003). UV-B exposure can be strongly influenced by factors such as shading and, for aquatic species, attenuation of UV-B by dissolved organic carbon (DOC) (Schindler and Curtis 1997). These factors operate at the scale of individual amphibian habitats and were not addressed by Middleton and others (2001)
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