FUNCTIONAL-RESPONSES OF OPTIMAL CONSUMERS AND THE POTENTIAL FOR REGULATION OF RESOURCE POPULATIONS

A central issue in studies of consumer-resource interactions is whethe r consumers regulate resource dynamics. One condition for regulation i s that consumption rate of a resource increases positively with increa sing resource density, that is, that the consumer's functional respons e must be positively density dependent. Many mammalian consumers exhib it density-independent or inversely density-dependent functional respo nses, suggesting that regulation will not occur. However, most studies measure functional responses for a single consumer and resource speci es in specific feeding trials. Many real-world consumers use more than one resource and resource choices depend on the distribution and nutr itional quality of resources as well as abundances. Foragers also acti vely choose resources in ways that match predictions of optimal foragi ng theory, that is, they exhibit adaptive behaviour. This paper explor es the variety of functional responses of adaptive consumers that aris es from optimal choice of resources in a simple, single-consumer-two-r esource system to determine the potential for consumer regulation of r esource populations. Optimal consumer behaviour can generate four type s of functional responses: (2) density independent, (2) increasing, in verse density dependent, (3) increasing, positively density dependent, and (4) decreasing. A positive density-dependent functional response arises in 3 of 22 possible cases. Moreover, consumers may not exhibit the same functional response to all resources included in the diet, th at is, they exhibit mixed responses to resource densities. This sugges ts that studies that examine the potential for consumer regulation of resources must go beyond the traditional focus (interactions between a consumer and the most dominant or abundant prey) and consider the var iety of resource species selected by a consumer in a specified time pe riod.