Recruitment Limitation as a Consequence of Natural Selection for Use of Restricted Feeding Habitats and Predation Risk Taking by Juvenile Fishes

Abstract

Juvenile fishes generally have spatial refuges from predation, and forage in limited but risky areas near refuges. Models of food density dynamics within such limited foraging areas predict that food availability and consumption per time spent feeding should depend strongly on Juvenile 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 proportional to the minimum needed to reach viable sizes for later survival and reproduction plus an additional time inversely proportional to the predation risk per time. Combining the food availability and optimal foraging time predictions leads to stock–recruitment patterns similar to classic Beverton–Holt and Ricker forms, depending on how food organisms respond over time. Very strong density-dependent mortality can occur even without noticeable changes in juvenile growth rates or average food densities over large spatial scales, but intraspecific competitive effects should always be evident through density-dependent changes in foraging time.