Many generalized species are in fact composed of individual specialists that use a small subset of the population's resource use. The most proximate reason for why individuals will specialize on different resources is if they have different resource use efficiencies, that is, there are efficiency tradeoffs between different prey. Different resource use efficiencies may reflect variable morphological, behavioral, or physiological capacities to handle alternative resources. Individual diet specialization can occur in a number of ways - they can be related to sexual dimorphism, ontogenetic niches, or related to morphological or behavioral variation in the population. However, not all diet variation needs to be related to variation in efficiencies - diet variation may also be related to varia tion in social status, mating strategy, or territories. Studying diet variation is important both in ecology and evolution. Ecologically, diet variation is important not only when looking at predator-prey interactions and competitive interactions but also in population dynamical studies. In evolutionary studies, diets of an individual are equivalent to the energy acquisition of the individual and are thus strongly related to fitness. An individual with a relatively high rate of energy (high foraging rate) income will thus have a relatively higher fitness compared to the average individual. Thus, differential foraging rates on different prey types will have a big influence on both the ecological and evolutionary dynamics of populations.
See also: Ecological Niche; Fitness; Habitat Selection and Habitat Suitability Preferences; Optimal Foraging; Optimal Foraging Theory; Phenotypic Plasticity.
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