Ecological processes and the ecology of stress: the impacts of abiotic environmental factors

Rapid, effective and enduring responses of physiology and behaviour to perturbations of the environment are key to robustness of an organism (ability to resist perturbations) and resilience (ability to resist and recover quickly from perturbations) so that the normal life cycle can be resumed quickly. Perturbations of the environment can be labile (i.e. eventually subside) or permanent such as when human activity changes the environment in the long term, for example, deforestation, urbanization, etc. Hormonal responses to labile perturbation factors (LPFs) allow organisms to cope during the perturbation and then return to the normal life cycle. These hormonal responses are called stress responses especially in cases when major changes in physiology and behaviour occur (emergency life-history stage). Permanent perturbations require more than just temporary acclimation resulting in changes in range, adaptation or in some cases local extinction. Perturbations can be abiotic, biotic and social, but these are not mutually exclusive. Here I focus on the effects of abiotic perturbation factors and their effects on the hypothalamo-pituitaryadrenal/interrenal axis in vertebrates. There is a great need for more field investigations of responses of free-living populations to perturbations of the environment, especially now that it appears the frequency and intensity of these events is increasing. However, such studies will require a high degree of opportunism on the part of the investigators to take advantage of unpredictable events when they occur.