HA3 Effects of Multiple Stressors on Marine Resources
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() From individuals to populations: Modeling toxicity data across levels of biological organization.

Raimondo, S.1, McKenney, Jr., C. 1, 1 U. S. Environmental Protection Agency, Gulf Breeze, FL, 32561

ABSTRACT- A critical step in estimating population and community -level effects of a toxicant is extrapolating individual-level response data across higher levels of biological organization. Often, individual-level responses measured in toxicity tests (altered survival and reproduction) are used as input for predictive population and community-level models. However, determining the relative roles of individual-level responses in population-level consequences provides a more informative, hierarchical approach to population toxicology. The mysid, Americamysis bahia , is a representative species used in toxicity tests to determine the potential ecological impacts of toxicants in estuaries. Individual-level responses of A. bahia to lethal (reduced survivorship) and sublethal (reduced reproduction or no effect observed) concentrations of five pesticides were determined from laboratory life-cycle tests and used as input for population matrix models. The individual-to-population gap was bridged using a combination of parametric statistics performed on individual-response data, sensitivity analysis of the population projection matrix, and nonparametric statistics performed on changes in population model parameters. As pesticide concentration increased the individual-level responses ranged from no significant effect to reproduction effects to survival effects, resulting in non-linear population-level responses throughout the ranges of concentrations measured. A significant population-level effect was measured as a change in population growth rate with increased concentration determined from either a linear or logistic regression, and was observed at every chemical concentration where significant lethal effects were measured. Population-level effects occurred at sublethal concentrations where a significant decline in reproduction occurred, indicating that population-level effects are not restricted to lethal concentrations. Our results show that at lethal concentrations the population growth reduced to less than one, which is indicative of eventual extinction. Additionally, significantly reduced reproduction can reduce population growth rate. This effect, although not great enough to drive a population to extinction, results in reduced biomass production and may find its consequences on the community level.

Key words: population-level effects, individual responses, matrix models, pesticides

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