Animals behave in bouts, and the process that causes feeding bouts to end is called satiation. Bout size or, in the case of feeding, meal size is the result both of the costs of food resources and the consequences of consuming a particular resource. Meal size increases as a function of increasing resource access cost; in this way, meal size is part of a strategy that economizes on time and energy spent acquiring food resources, thereby making time and effort available for competing activities. Meal size also varies as a function of the amount of the resource consumed and the animal's requirements for that resource. The paradox of satiation is that it is both a tool for economizing and a consequence of feeding.