Life History and the Relationship Between Food Availability and Foraging Effort

Simple theoretical models are used to explore the effect of changed food density on optimal foraging effort when a forager faces a trade—off between energy (nutrient) gain and risk of mortality. Models of simple iteroparous and semelparous life histories show that the optimal effort or amount of risk may increase or decrease with increasing food density. Increases are more likely for iteroparous than for semelparous life histories, and are more likely when the increase in food availability is of short duration. The possibility of starvation makes it more likely that foraging effort will decrease with increasing food density. Organisms whose foraging goal is to minimize mortality are especially unlikely to increase effort in response to increased food availability. If there is a cost associated with the amount of food ingested, effort is more likely to decrease with increasing food. Some limitations of previous theoretical treatments of the foraging effort question are discussed. Previous experimental results illustrate the full range of responses to food density predicted here.