Adaptive Responses to Accelerating Costs of Movement: A Bioenergetic Basis for the Type-III Functional Response

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Abstract
An investigation of the bioenergetic basis of the type-III functional response reveals that increases in the velocity of filtering or in the velocity of prey search occurring with increased food density may lead to type-III responses and are adaptive if rates of energy expenditure above the standard metabolite rate accelerate with velocity. Such costs are typical of movement in water, suggesting possible differences in the dynamics of aquatic and terrestrial foraging. When type-III responses are driven by changes in the optimal value of foraging-effort variables, the "stabilizing range" of the response for one food type is accompanied by increases in the rate of feeding on all other food types in the optimal diet. These indirect interactions between prey species sharing a common predator resemble competition and may therefore counteract any direct stabilizing effect that the type-III response has on the population dynamics of the prey.