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ELASTICITY ANALYSIS OF AMPHIBIAN LIFE HISTORIES
Citation:
Heppell, S. ELASTICITY ANALYSIS OF AMPHIBIAN LIFE HISTORIES. Presented at Ecological Society of America, Tucson, AZ, August 4-9, 2002.
Description:
By comparing life history parameters (e.g., age at metamorphosis, age at sexual maturation, egg number, longevity) and phenology of different species, we gain valuable insight into why growth rates differ across populations. Although the demography of most amphibians is lacking, it is possible to determine generally which life stages have the greatest effect on population growth and the potential effects of perturbations on those life stages. I have used matrix models to compare the relative contributions of survival and reproduction to deterministic population growth rates. The proportional sensitivity (= elasticity, de Kroon et al. 1986) of a population growth rate to changes in life stage-specific survival or reproduction is primarily dependent on generation time and the proportion of life spent in each stage (egg, larva, juvenile, adult). By comparing the elasticities across a life history ?space? defined by randomly generated matrices, I have found patterns in amphibian life histories that identify which species may be highly sensitive to certain kinds of perturbations. For Willamette Valley amphibians, this analysis provides clues for why some species seem to be particularly affected by reduction in survival of specific life stages, including hydrological modifications and wetland degradation, predation by fish or bullfrogs, and increased road density. This analysis does not identify the causes of decline, but does permit a broad classification scheme that may be useful for prioritizing conservation activities.