To minimize foraging time, use high-efficiency, energy-expensive search and capture methods when food is abundant but...

Based on a mathematical model, I show that the amount of food in the habitat determines which among alternative methods for search of prey, respectively, for pursuit-and-capture give the shortest daily foraging time. The higher the locomotor activity, the higher the rate of energy expenditure and the larger the habitat space a predator can search for prey per time unit. Therefore, I assume that the more efficient a foraging method is, the higher its rate of energy expenditure. Survival selection favors individuals that use foraging methods that cover their energy needs in the shortest possible time. Therefore, I take the optimization criterion to be minimization of the daily foraging time or, equivalently, maximization of the rate of net energy gain. When time is limiting and food is in short supply, as during food bottleneck periods, low-efficiency, low-cost foraging methods give shorter daily foraging times than high-efficiency, energy-expensive foraging methods. When time is limiting, food is abundant and energy needs are large, as during reproduction, high-efficiency high-cost foraging methods give shorter daily foraging times than low-efficiency low-cost foraging methods. When time is not limiting, food is abundant, and energy needs are small, the choice of foraging method is not critical. Small animals have lower rates of energy expenditure for locomotion than large animals. At a given food density and with similar diet, small animals are therefore more likely than large ones to minimize foraging time by using high-efficiency energy-expansive foraging methods and to exploit patches and sites that require energy-demanding locomotion modes. Survival selection takes place at food shortages, while low-efficiency low-cost foraging methods are used, whereas reproduction selection occurs when food is abundant and high-efficiency energy-expensive foraging methods do better. In seasonal environments, selection therefore acts on different foraging methods at different times. Morphological adaptation to one method may oppose adaptation to another. Such conflicts select against foraging and morphological specialization and tend to give species-poor communities of year-round resident generalists. But a stable year-round food supply favors specialization, niche narrowing, and dense species packing.