ABSTRACT
The ecosystem remains a fundamental conceptual unit not only in basic ecological research,
but also in environmental assessment and management. The limitations of organism-level
ecological assessments raised decades ago remain (NRC 1981; O’Neill and Waide 1981;
Kimball and Levin 1985). To address these limitations, ecologists, environmental toxicolo-
gists, and risk assessors have continued to develop, apply, and evaluate methods and models
for characterizing ecosystem-level risks (Pastorok et al. 2002). Ecosystem modeling continues
to contribute importantly to assessing ecological risk.
