Studying Stress: The Importance of Organism-Level Responses

The importance of studying the effects of stress on individual organisms is addressed by considering the use of individual-level information to: (1) elucidate the mechanistic bases of interpopulation variation; (2) predict population-level effects; and (3) monitor stress in natural communities. Examples discussed include interpopulation variation in the sensitivity of freshwater shrimps to zinc stress; the use of individual-based models to predict the effects of copper stress on earthworm populations; the use of single-species in situ assays to monitor pollution. It is contended that knowledge of organism-level responses is essential for understanding how stressors cause adverse biological effects and the strategies adopted by organisms to tolerate stress. It is also contended that the effects of stressors on populations can be predicted from a knowledge of the effects of stressors on individual energy budgets. Organism-level responses can be used to monitor stress in natural environments. In situ assays, based on the physiological energetics of ecologically relevant species, can provide sensitive and general stress indicators that are correlated with community-level responses.