Physiological costs of combating chemical toxicants: ecological implications.

1. Evidence is presented that combating the poisoning effects of toxic chemicals is metabolically costly. 2. This has implications for relating physiological stress responses observed at the level of individual organisms to population effects, and needs to be incorporated explicitly into models making this link. 3. The cost hypothesis also has implication for the evolution of stress resistance either as a fixed or facultative (inducible) response. Optimization models incorporating these ideas are reviewed and discussed.