Variation in cadmium uptake, feeding rate, and life-history effects in the gastropod potamopyrgus antipodarum: linking toxicant effects on individuals to the population level.

A life-table response experiment was performed to investigate the effects of sediment-bound cadmium on individual life-history traits and feeding rates of four clones of Potamopyrgus antipodarum. Demographic effects were evaluated using a simple two-stage model to estimate population growth rate (lambda). Decomposition analysis was performed to investigate the contributions of each of the affected life-history traits to the effects observed on lambda, and elasticity analysis was applied to examine the relative sensitivity of lambda to changes in each of the life-history traits. Interclonal differences in tolerance to sediment-bound cadmium were statistically significant but were within an order of magnitude. There were no consistent patterns among clones in terms of which individual life-history trait was most or least sensitive to cadmium exposure. The relative performance of clones did not rank consistently across the cadmium gradient and was dependent on which trait was measured. Although lambda was most sensitive to changes in survival terms, the effects of cadmium on time to first reproduction and reproductive output were the major causes of reductions in lambda. Large percent reductions in some of the individual life-history traits were attenuated at the population level, but very small effects on population growth rate were statistically significant.