Biological Response to Stress:
| Organisms are subjected to a number and variety of stressors in the environment, therefore multiple measures of health are needed to help identify and separate anthropogenic-induced effects of stress from those effects caused by natural stressors. |
| Multiple measures of health include responses that represent different levels of biological organization, response time to stressors, and sensitivity and specificity to stressors. |
| Environmental stressors can have direct (through metabolic pathways) and indirect (through food and habitat availability) effects on organisms. |
| Bioindicators that can be measured to characterize the physiological condition of organisms in each stress zone (see above figure). Indicators in zone 1 are more sensitive to environmental stressors, while those indicators in zone 3 are less sensitive, but have higher ecological relevance. |
| The physiological condition of organisms can be characterized by three major stress zone based on the level of disability caused by environmental stressors. |
| If properly calibrated to higher level responses, the lower-level responses can be effectively used in environmental management and in the ecological risk assessment process. |