Projecting population-level responses of mysids exposed to an endocrine disrupting chemical

To fully understand the implications of a chemical's effecton the conservation of a species, effects observed at the physiologicalor individual level must be expressed in terms of the population.Since long-term field experiments are typically not feasible,vital rates such as survival and reproduction of individualorganisms are measured in life table response experiments (LTRE)and employed to extrapolate the effects of a pollutant on thepopulation. The population-level response of the mysid, Americamysisbahia, to varying concentrations of methoprene (0, 4, 8, 16,31, 62 µg/L) was determined using age-structured populationmodels. Models were parameterized from the results of an LTREconducted throughout the entire mysid life cycle. A density-independentmatrix model with time invariant demographic parameters wasdeveloped to measure the change in population growth rate, ,with change in methoprene concentration. The values of weregreater than one for all methoprene concentrations, indicatingthat populations exposed to the concentrations reported herewould not become extinct. However, a general decrease in occurredwith increasing methoprene concentration and would result inreduced population sizes. Sensitivity and decomposition analyseswere conducted to determined the relative roles of the vitalrates on altered population growth rates and determined thatimpaired reproduction was the primary influence on the observeddecrease in . The model constructed was a useful tool for linkingthe individual-level effects to the population-level consequencesof methoprene exposure on mysids, as well as defining the mechanism(reduced reproduction) responsible for the observed effectson population.