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OCR for page 316
Issues in Risk Assessment Application of Stress-Response Analysis In Case Studies The group found that some form of stress-response analysis was used in nearly all the case studies, most obviously in the chemical-related assessments. Both laboratory-derived and field-derived stress-response information was used in the TBT studies. The agricultural chemical case study used various kinds of stress-response information, from biochemical studies to field experiments, although all focused on individual species populations. Consideration of multiple stressors would be useful. The TCDD modeling studies were driven by human health considerations and, therefore, used individual-level stress-response information. In the spotted owl case, the stress-response relationship applies to habitat loss as the stressor and population viability as the response. In the case of harvesting, fishing is clearly the stressor, and yield and future recruitment are the end points. The latter study in particular was a good example of potential discontinuities in stress-response relationships, in that the Georges Bank haddock population, once depressed by overharvesting, did not recover after fishing pressure was relaxed. It is not clear whether the concept of stress-response relationships applies to species introductions. Modeling Needs for Stress-Response Relationships The group agreed that models are needed to deal with changes of state (e.g., shifts from bicarbonate to aluminum buffering), to incorporate multiple nonlinearities and discontinuities in multispecies systems, to extrapolate across ecological levels of organization (e.g., to assess the ecosystem consequences of a loss of a population or the population consequences of a loss in ecosystem function), and to make use of knowledge about synergies.