Keystone species

A species whose ecological effects are disproportionately large relative to its abundance. Its interactions can shape community structure and biodiversity.

Trophic cascade: A chain of indirect effects across multiple trophic levels, often triggered by changes in predator abundance. Predators can shape vegetation and prey communities through cascading effects.
Pisaster ochraceus: A predatory sea star found on the Pacific coast of North America. Robert Paine’s removal experiments showed that this sea star maintained diversity in rocky intertidal communities.
Robert T. Paine: An American ecologist who developed the keystone-species concept through experimental studies of rocky shores. Paine named the concept after documenting the outsized effects of Pisaster predation.
Foundation species: A species that creates or defines habitat and supports a community, often through high abundance or biomass. Foundation species typically shape ecosystems through abundance, unlike the disproportionate effects defining keystone species.
Trophic downgrading: The ecological disruption caused by losing large predators or other top consumers. The loss of a keystone predator can trigger cascading changes throughout an ecosystem.
Predation: An interaction in which one organism captures and consumes another. Predators can regulate abundant prey and indirectly preserve other species.
Sea otter: A marine mammal that feeds largely on invertebrates, including sea urchins. By consuming urchins, sea otters can protect kelp forests from intense grazing.
Keystone species experiment: Robert Paine’s removal study of the sea star Pisaster ochraceus in a rocky intertidal community. The experiment demonstrated that removing one predator could sharply reduce local species diversity.
Ecosystem engineer: An organism that modifies the physical environment, altering habitat or resource availability for other species. Engineering is a mechanism; an engineer is a keystone species only when its overall effect is disproportionate.
Rewilding: A conservation approach that restores ecological processes, often by reintroducing species or reducing intensive management. Restoring a keystone species can help revive interactions and ecosystem processes.

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