The time window of feeding.

This paper contrasts the traditional depletion/repletion model of food intake with a longer-term perspective which focuses on function rather than mechanism. We review naturalistic observations as well as the economic relationships we have discovered in the laboratory by a cost/benefit analysis of feeding in a closed economy. We have manipulated feeding costs by means of operant methodology and have explored two classes of cost, the cost of initiating meals and the cost of consuming food. We conclude that when an animal can detect the cost/benefit structure of its habitat, its feeding behavior will tend to maximize benefits relative to cost in apparent anticipation of its nutritional requirements and environmental conditions. The time window over which these feeding decisions are integrated may be minutes, hours, months, or seasons depending upon the animal's niche and current habitat. Feeding mechanisms based on momentary deficits and repletions are inadequate to explain these strategies, leaving the field of feeding mechanisms open for major discovery and revision.