ABSTRACT
Models support several aspects of chemical risk assessment, including characterizing exposures and predicting the effects of exposures on assessment endpoints. Population level ecological risk assessment requires that the composite characteristics of groups of individual organisms be considered rather than the more traditional approach of using organism-level attributes, such as the chemical concentration causing death, in the risk assessment. A fair amount has been written elsewhere about population models, and certainly with respect to their use in risk assessment. Unstructured population models are perhaps the simplest form for assessing population-level risk. Metapopulation models developed primarily to explore general relationships among patch configuration, dispersal characteristics and population persistence are most useful in early tiers of population-level ecological risk assessment. An alternative tiered approach involves population-level assessment endpoints only within certain tiers of the assessment. Classical metapopulation modeling approaches describe physically disparate subunits that may perform differently, sometimes as a result of varying environments or habitats.
