Keystone Species

Paine's starfish experiment: disproportionate community impact relative to biomass

Food Web

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Community Metrics

Species present
Keystone present
Dominant competitor
Diversity H
Paine 1966: removed Pisaster ochraceus (sea star) from rocky intertidal. Mussels (Mytilus) took over, driving 15→1 species. Keystone impact >> biomass. Introduced: Power et al. 1996 formal definition.