Historically, the determinants of meal initiation and termination have been investigated primarily with a focus on the momentary physiological state of the animal and the mechanisms which detect and respond to this state. A functional analysis suggests an alternative approach. Eating in meals, and performing other behaviors in bouts, makes possible the exploitation of resources (food, water, mates, nest sites, etc.) that are distributed discontinuously, that is, in patches. Given a world of limited resources and the need to satisfy multiple requirements, each animal must efficiently allocate its time and effort among resources and activities or be outcompeted by individuals that do. Each of the activities involved in the use of a resource (discovery, selection, procurement and consumption) is constrained by 1) the costs associated with that activity, 2) the animal's regulatory requirements for that resource, and 3) its requirements for other resources and other activities. Animals have developed, through natural selection, behavioral and physiological mechanisms that are sensitive to these constraints; together, these permit the animal's many requirements to be satisfied efficiently. The behavioral mechanisms by which animals respond to these constraints are largely unknown, however, as is the manner in which behavioral and physiological mechanisms interact. Also unknown is how animals acquire and integrate the vast amount of information about potential resources, including their costs and benefits, that is necessary to regulate efficiently. Finally, the contributions of taste and central neurotransmitter systems to this result have yet to be determined. These are the questions that the proposed research seeks to answer. To this end, we will use a foraging paradigm involving a naturalized laboratory setting in which freely feeding animals can respond to various simulated constraints. Animals are housed 24 hours per day in an environment that offers food resources which differ in calorie and nutrient content, temporal patterns of availability and abundance, and the time and effort required to find, acquire, and consume them. In this experimental habitat, both the energetic demands on the animal and the availability of other biologically-relevant resources can be varied. This paradigm allows the exploration of how, and in what form, animals acquire estimates of the current structure of their habitat while regulating intake effectively. Using this paradigm, we have already been highly successful in elucidating many of the rules of meal initiation, meal termination, and choice among food sources. The proposed research will extend our understanding of how regulation is achieved over the long term in the face of competing activities and fluctuating resources. Knowledge of the fundamental processes by which environmental and physiological factors interact to affect behavioral choice is prerequisite for a complete analysis of human feeding and regulation and their associated disorders.