Ecophysiological Studies on Desert Mammals: Insights From Stress Physiology.

Abstract

Ecophysiology is the study of the physiological responses of animals living in their natural environment and can provide information substantially different from that obtained in laboratory situations where animals are constrained by artificial surroundings. Recent work with arid-living mammals in WA has focussed on the measurement of seasonal responses of free-ranging individuals to drought and has involved measurements of rates of turnover of water, together with changes in kidney function and circulating levels of antidiuretic hormone (ADH), the pituitary hormone essential for the conservation of water. Central to these studies has been an attempt to identify periods when animals in the field may be exposed to physiological stress due to a lack of adequate supplies of water, and to document their responses to this. Stress is here defined as "...the physiological resultant of demands that exceed an organism's regulatory capacities" (Bradshaw, 1986) and is detected through the combination of a significant perturbation of the milieu interieur of the animal, despite the maximum deployment of normal homeostatic responses (e.g. substantial dehydration despite maximal circulating levels of ADH; see Bradshaw, 1992). This approach also raises the possibility of determining the vulnerability to extinction of threatened and endangered species by comparing their actual rates of water turnover in the dry part of the year with allometric predictions. One predicts that species which display a profligate pattern of water usage would be much more susceptible to any environmental changes that might reduce the availability of water.