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Foraging Strategies of Insects

The evolutionary fitness of an animal depends significantly upon an optimal diet in both quantity and quality. Foraging strategies are therefore rigorously shaped by natural selection and should be considered in terms of the degree to which they maximize the net nutrient gain from feeding, and to which they minimize the risks to survival. Any discussion offoraging behavior is complicated by the forager's perceiving the environment at several hierarchical levels. We endeavor to categorize these, being fully aware that any such framework is bound to be plagued with exceptions and examples of blurred boundaries. Our classification includes three such levels: the habitat, the patch, and the food item. Of these, the food items are generally the easiest to define. They are the prey of predators, the hosts of parasitoids, the leaves for caterpillars, the feeding sites for mosquitoes, the nectaries and anthers for bees, and so on. Such items are almost invariably heterogeneous in their spatial distribution, which makes it appropriate for us to identify an aggregation of food items-a "patch"-as the next level in the hierarchy. The definitions of what should and should not constitute a patch have been various (174, 179). We look upon patches as spatial subunits of the foraging area in which aggregations of food items occur. A patch is most readily identified when the food items are distributed among discrete natural units, as are, for exam­ ple, prey on leaves. But we must beware of identifying a patch solely by what we perceive or consider reasonable. The forager itself defines the patch, and we should look to changes in the forager's behavior to identify patch boundaries. A patch in these terms is therefore an area containing a stimulus or stimuli that at the proper intensity elicit a characteristic foraging activity in a r esponsive forag er (174). Such a definition, rather than one based on the forager's response itself, avoids attributing more patches to the environment of a responsive forager than to that of an unrespon­ sive one.