Evol Ecol Res 2: 911-934 (2000)     Full PDF if your library subscribes.

Linking consumer–resource theory and digestive physiology: Application to diet shifts

Christopher J. Whelan,1 Joel S. Brown,2 Kenneth A. Schmidt,3 Benjamin B. Steele4 and Mary F. Willson5

1Illinois Natural History Survey, Midewin National Tallgrass Prairie, 30071 S. Route 53, Wilmington, IL 60481, 2University of Illinois at Chicago, 845 W. Taylor St, Chicago, IL 60607, 3Williams College, Williamstown, MA 01267, 4Colby-Sawyer College, New London, NH 03257 and 55230 Terrace Place, Juneau, AK 99801, USA

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We develop mathematical and graphical models of diet selection incorporating recent advances in digestive physiology – that is, the adaptive modulation of active nutrient transport and gut retention time in response to changes in diet composition – into an explicitly ecological context based on consumer–resource dynamics and optimal foraging theory. The models indicate that gut modulation causes the consumer to treat two resources that are perfectly substitutable (the benefit derived from consumption of one resource is a constant fraction of the benefit derived from consumption of the second resource) as if they are antagonistic resources (the benefit derived from consumption of either resource alone is greater than the benefit derived from joint consumption of both resources). This will tend to favour diet switching and specialization, and also suggests a definitive (laboratory or field) test of the models. The models also suggest that modulation ultimately leads to more efficient use of resources, although it incurs an initial cost. We further cast gut modulation in three ecological scenarios. In the first, the consumer species does not deplete its resources and the optimal modulation strategy is determined by the standing crop of resources. In the second, a fixed population size of consumers results in resource depletion and the standing crop of resources results from a dynamic equilibrium between resource renewal and resource consumption. Under this scenario, the optimal gut-modulation strategy is determined by this dynamic equilibrium between renewal and consumption. In the third, we let resource renewal, depletion and consumer population sizes equilibrate. In this last scenario, the optimal gut modulation strategy emerges from the combined effects of resource renewal and the intersection of the depletion trajectory with the consumer’s zero net growth isocline. We conclude that forging tighter links between gut physiology and foraging ecology will lead to greater understanding and predictability of diet selection and its ecological consequences.

Keywords: active nutrient transport, consumer–resource dynamics, digestive physiology, frugivory, gut modulation, insectivory, modulation isoleg, optimal foraging theory, passive nutrient absorption.

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