Theory of Marine Communities: The Intermediate Disturbance Hypothesis

The theoretical validity of the intermediate disturbance hypothesis is investigated with a model for hierarchical competition between marine species that have space-limited, benthic adults and pelagic larvae. The model explicitly incorporates larval and adult dynamics for two species, one of which overgrows the other. Conclusions include: (1) The subordinate must be a stress tolerator or ruderal for coexistence with a competitive dominant. (2) The intermediate disturbance principle is a moderate-to-high settlement phenomenon: coexistence is possible at sufficiently low settlement even without the aid of disturbance, but at high settlement, a dominant with greater benthic ability excludes the subordinate at all levels of disturbance. (3) Given coexistence, increasing disturbance drives the dominant extinct first. (4) For a fixed level of disturbance, an “intermediate recruitment hypothesis” holds: at low settlement only the subordinate exists, at intermediate settlement there is coexistence, and at high settlement the dominant excludes the subordinate. (5) A gradient in settlement is sufficient to generate benthic zonation, so negative covariation between settlement and disturbance accentuates disturbance’s effect, and positive covariation diminishes it. (6) The effects of area and settlement on coexistence in this model are equivalent. (7) Coexistence is favored when the subordinate body size is small compared to the dominant, conditional on larval production.