concept of dose-response assessment for ecological applications and then on the complexities that need to be addressed in practice. The group agreed immediately that for ecological assessments it is better to talk about stress-response than about dose-response relationships. Scientifically, the stress-response concept, as it applies to ecological risk assessment, is complex and involves many considerations that are absent from the usual understanding of dose-response relationships in human health risk assessment. The bulk of the session was devoted to identifying those considerations and discussing how assessments should be structured to address them.
Aspects of An Adequate Stress-Response Analysis for Ecological Risk Assessment
Selection of End Points
The group argued that end point definition is critical for ecological stress-response assessment. Responses can be assessed at all three hierarchical levels of ecological organization: population, community, and ecosystem. Because of the inherent linkages between the levels, it is important to assess how an effect at one level can affect the other levels. No standard methods exist for making those linkages. Because empirical studies of different levels of organization usually also involve different spatial and temporal scales, the decision about which levels to study must be made before studies are initiated.
Final end points must be expressed as measurable characteristics, such as minimal sustainable population or maximal damage that permits the continued viability of a complex ecosystem. Both structural end points and functional end points should be considered. Structural end points include descriptive characteristics of an ecosystem, such as abundance, species composition, and trophic structure. Functional end points include energy/material flows and other transformation processes (i.e., what the organisms do, as distinct from what they are). The choice of end points must be responsive to both technical and policy concerns, including the following:
Values (what do we really care about?),