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Amerciamysis bahia Stochastic Matrix Population Model for Laboratory Populations
Citation:
THURSBY, G. B. Amerciamysis bahia Stochastic Matrix Population Model for Laboratory Populations. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-09/121, 2009.
Impact/Purpose:
EPA needs population modeling methods to support assessments of the risks from toxic chemicals to non-target populations of aquatic and terrestrial species (“wildlife”). This documentation shows an approach for using data from traditional organism-level toxicity tests to estimate population-level risks. The specific application being evaluated is risk to populations of the marine invertebrate Americamysis bahia. This is accomplished through a population model which is a mathematical representation using vital rates (e.g., survival and reproduction) to describe population dynamics, such as population growth rate (λ). Population risks from pesticides (and other chemicals and stressors) are projected using a population model integrating both acute and chronic toxicity data from standard organism-level toxicity tests into predictions of long term viability of a population. This model demonstrates the potential for routine use of population level endpoints in pesticide risk assessments, and paves the way for more detail modeling efforts that will be aimed at more field-like situations. The document not only describes the inner workings of the model, but also provides the necessary documentation of default model input parameters when such parameters are not readily available from the toxicity data.
Description:
The population model described here is a stochastic, density-independent matrix model for integrating the effects of toxicants on survival and reproduction of the marine invertebrate, Americamysis bahia. The model was constructed using Microsoft® Excel 2003. The focus of the model is on laboratory populations because neither biological variability of field populations nor variability associated with time-varying toxicant concentrations, as might be expected in field situations, are considered. The model employs several aspects of traditional population viability analysis (PVA), establishing a dose-response relationship between exposure concentrations and estimates of expected minimum population size. This documentation describes the model, and also provides the justification for various default parameters for use when the ideal toxicity data set may not be available.