RECRUITMENT LIMITATION AS A CONSEQUENCE OF NATURAL-SELECTION FOR USE OF RESTRICTED FEEDING HABITATS AND PREDATION RISK-TAKING BY JUVENILE FISHES

Juvenile fishes generally have spatial refuges from predation, and for age in limited but risky areas near refuges. Models of food density dy namics with in such limited foraging areas predict that food availabil ity and consumption per time spent feeding should depend strongly on j uvenile density. Selection should act on the time that juveniles spend foraging, so as to strike a balance between growth and predation risk ; we predict that optimum balance will occur at foraging times proport ional to the minimum needed to reach viable sizes for later survival a nd reproduction plus an additional time inversely proportional to the predation risk per time. Combining the food availability and optimal f oraging time predictions leads to stock-recruitment patterns similar t o classic Beverton-Holt and Ricker forms, depending on how food organi sms respond over time. Very strong density-dependent mortality can occ ur even without noticeable changes in juvenile growth rates or average food densities over large spatial scales, but intraspecific competiti ve effects should always be evident through density-dependent changes in foraging time.