PARENT SESSION
Oral Session #1: Conservation Ecology: Threatened and Endangered Species. Presiding: W. Bond.
Monday, August 6, 2001. 8:00 AM to 12:15 PM. Madison Ballroom C.

Assessing the population-level consequences of UV-B radiation induced mortality in amphibians.

VONESH, JAMES¹, DE LA CRUZ, OMAR¹, ¹

ABSTRACT- It has been suggested that increased embryonic mortality induced by exposure to solar ultraviolet-B radiation (UV-B) has contributed to the decline of amphibian populations from some relatively undisturbed habitats. However, the connection between UV-B and population dynamics has not been examined explicitly. Connecting stage-specific mortality to population declines may be complicated by density-dependence in one or more life history stages, and there is considerable evidence suggesting that density dependence can play an important role in amphibian systems. This study examines the population-level implications of UV-B induced egg-stage mortality when there is density dependence in the larval stage. We focus on four species known to be vulnerable to UV-B, Bufo bufo, Bufo boreas, Rana cascadae, and Ambystoma macrodactylum. We developed a stage-structured demographic model to examine the sensitivity of population size to changes in a number of life history parameters, including egg survival. Our model suggests that the effect of embryonic mortality on amphibian populations depends upon the functional form of larval density dependence, and suggests that density dependence can moderate the population-level consequences of mortality early in life history for some species. In addition, while many recent studies have focused on species-specific differences in UV sensitivity, our model suggests that variation among species in their population-level responses to egg-stage mortality could also be explained simply by differences in the density dependence experienced in their life histories.

KEY WORDS: amphibian declines, UV sensitivity hypothesis, density dependence, population model