THEORY OF MARINE COMMUNITIES: COMPETITION, PREDATION, AND RECRUITMENT-DEPENDENT INTERACTION STRENGTH

Abstract

Of the marine animals that spend their adult lives inhabiting benthic communities, most have a planktonic larval phase. In this paper, we derive the relationship between the physical oceanographic processes that transport these larvae and the strength of species interactions in the benthic habitat. We review a model of hierarchical competition for space between two species with planktonic larvae and develop a model for predator–prey dynamics in which prey are space-limited. Lotka-Volterra approximations to these models are developed. The approximations provide per capita interaction strength (the effect of an individual of one species on the per capita growth rate of another) and population interaction strength (the effect of a population of one species on the per capita growth rate of another) as functions of parameters in the original model. Per capita and population interaction strengths of dominant competitors on subordinates decrease in magnitude as offshore advection of larvae increases. The per capita effect of prey on predators also decreases as offshore advection increases, but population interaction strength is independent of offshore advection rate. Conversely, the per capita effect of predators on prey is independent of offshore larval advection rate, but the population effect decreases as offshore advection increases. We also develop submodels that simulate experimental removals of competitors and predators. Measurements of interaction strength derived from these simulations decrease as offshore advection of larvae increases. These results predict that a latitudinal gradient in upwelling intensity in the northeast Pacific produces a gradient in the intensity of species interactions in rocky intertidal communities.