Efficiency is affected by a number of constraints on energy and resource allocation. Clearly, selection should favor physiological and behavioral adaptations that improve overall efficiency. However, adaptive strategies reflect the net current result of many factors that have variable and interactive effects on survival and reproduction. Hence, individual responses to current conditions vary in efficiency. Whereas physiological, and many behavioral, responses are innate (genetically based, hence relatively inflexible), the capacity to learn can improve efficiency greatly, by reducing the time and resources expended in responding to environmental variation (Cunningham et al. 1998, A. Lewis 1986).
Hairston et al. (1960) stimulated research on the constraints of food quality on efficiency of herbivore use of resources by postulating that all plant material is equally suitable for herbivores. Just as plant chemical defenses can reduce herbivore efficiency, various animal defenses increase the resource expenditure necessary for predators to capture and assimilate prey. In addition to factors affecting the efficiency of resource acquisition, several factors affect the efficiency of resource allocation, including food quality, size, physiological condition, and learning.
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