Effects of ultraviolet radiation on montane amphibians of the Pacific Northwest: A comparison across scales

The decline of amphibians in protected areas across the globe has been a major conservation concern in the last decade and has stimulated a tremendous amount of research to identify specific causes. Increasing levels of ultraviolet-B radiation (UVB) resulting from anthropogenic ozone depletion has been a leading hypothesis for declines in western North America, and may affect individuals, populations, or species at local to regional scales. My dissertation research sought to improve our understanding of the risk that current levels of UV-B pose to montane amphibians of the Pacific Northwest (PNW) by critically evaluating the role of UV-B across a range spatial scales and levels of biological organization. Prior research from the PNW has been central to the debate surrounding declining amphibian populations and has focused primarily on identifying differences in species' physiological sensitivity to UV-B using laboratory assays and field experiments at a limited number of sites, but lacks a broader ecological context and a rigorous quantitative evaluation of risk. Here I improve upon the predictions of risk posed by UV-B by incorporating (1) differences in species' underlying physiological capabilities to withstand and repair UV-B induced damage, (2) the spatial heterogeneity in UV-B attenuating organic matter (DOM) in the water at amphibian breeding sites, (3) variation in individual oviposition behavior that directly influences embryonic UV-B exposure, (4) the results of field incubation experiments identifying thresholds of UV-B exposure associated with larval mortality at natural sites, and (5) an assessment of terrestrial features of watersheds correlated with pond-level UV-B transparency. The high variability in UV-B transparency among amphibian breeding ponds means that experiments conducted at any one site do not accurately characterize the importance of UV-B for populations distributed over heterogeneous landscapes. However, when related to the spatial scales relevant to population declines, these factors predict that fewer than 10% of all embryos and fewer than 15% of all breeding sites are likely to experience levels of UV-B known to reduce embryonic survival. These results allow us to make more informed decisions about the protection of amphibian species and refine our research priorities in the context of declining amphibian populations.