STRENGTHS OF INDIRECT EFFECTS GENERATED BY OPTIMAL FORAGING

Models of a three-species food chain are used to explore the strengths of the indirect effects between the chain's top and bottom species caused by adaptive foraging by the middle species. Foraging effort by the middle species is adjusted based on the benefits (primarily reproduction) of increased intake and the costs (primarily predation risk) of increased effort. This paper extends an earlier analysis of this question by: (1) deriving results for general rather than specific cost and benefit functions; and (2) exploring the effect of the adaptive forager's life history on the magnitude of indirect effects. Large indirect effects are more likely to be transmitted by iteroparous species with high survival and low reproductive rates than by semelparous species. Indirect effects on the basal species are likely to be large when cost and benefit functions have gradual curvature, and are likely to be small when the adaptive forager decreases its foraging effort in response to increased food density. The indirect effect on the top species will often be larger than the direct effect when nonforagers are relatively immune from predation.