COMBINED EFFECTS OF UV-B RADIATION AND NITRATE FERTILIZER ON LARVAL AMPHIBIANS

Abstract

As part of a global loss of biodiversity, amphibian populations are declining worldwide. Numerous factors may be involved in these declines, including environmental changes and the spread of contaminants. Ultraviolet-B (UV-B) radiation (280–315 nm) and chemical pollution are two factors that have become increasingly important as contributing to amphibian mortality and, perhaps, to amphibian population declines. Therefore, we studied the combined effects of ambient UV-B radiation and nitrate fertilizer pollution on larval amphibians in outdoor experiments at low and high elevation sites in Oregon. Recent studies have shown that UV-B radiation and nitrate fertilizer pollution have differential effects on amphibians. Some species are more susceptible than others when exposed to either UV-B or to nitrate. Moreover, depending upon other environmental conditions, UV-B levels are often greater in intensity at higher elevation sites compared to lower elevation sites. Therefore, our experiments were designed to include amphibians from both low and high elevations. Very little is known about interpopulational variation regarding the effects of environmental stressors. We tested the combined effects of UV-B and nitrate on larval survival, mass, and length in Pacific treefrogs (Hyla regilla) and long-toed salamanders (Ambystoma macrodactylum). In the low elevation experiment, we found that UV-B and nitrate together reduced the mass of larval H. regilla. In the high elevation experiment, we found that UV-B and nitrate together reduced the survival of larval H. regilla. In both the low elevation and the high elevation experiment, nitrate increased the mass of larval A. macrodactylum. However, in the high elevation experiment, this result occurred only when UV-B was blocked. This result indicates that the effects of nitrate addition could depend upon the presence of other factors such as UV-B. Results emphasize the importance of considering the effects of multiple stressors.