Keystone Predator

Paine (1966): Pisaster ochraceus (sea star) preferentially preys on mussels, the competitive dominant. Without the sea star, mussels (Mytilus) monopolize the substrate, eliminating barnacles, chitons, limpets, and algae — reducing species richness from ~15 to ~1. The sea star is a keystone species: its effect on community structure is disproportionately large relative to its own biomass. Indirect effects propagate: removing one predator cascades through 3+ trophic levels.