THE EFFECTS OF PREDATION ON THE AGE AND SIZE OF MATURITY OF PREY

The effects oi nonselective predation on the optimal age and size of m aturity of their prey tire investigated using mathematical models of a simple life history with juvenile and adult stages. Fitness is measur ed by the product of survival ro the adult stage and expected adult re production, which is usually an increasing function of size at maturit y. Size is determined by both age at maturity and the value of costly traits that increase mean growth rate (growth effort), The analysis in cludes cases with fixed size but flexible time to maturity, fixed time but flexible size, and adaptively flexible values of both variables. In these analyses, growth effort is flexible. For comparison with prev ious theory, models with a fixed growth effort are analyzed, In each c ase, there may he indirect effects of predation on the prey's food sup ply. The effect of increased predation depends on (I) which variables are flexible; (2) whether increased growth effort requires increased e xposure to predators; and (3) how increased predator density affects t he abundance of Pc,od for juvenile prey; Ii there is no indirect effec t of predators on prey food supply, size at maturity will generally de crease in response to increased predation. However, the indirect effec t from increased food has the opposite effect, and the net result of p redation is often increased size. Age at maturity may either increase or decrease, depending on functional forms and parameter values; this is true regardless of the presence of indirect effects. The results ar e compared with those of previous theoretical analyses. Observed shift s in life history in response to predation am reviewed, and the role o f lie-selective predation is reassessed.