Experimenting with a food web
Paine joined the University of Washington in 1962. Beginning in 1963, he repeatedly removed the sea star Pisaster ochraceus from a Pacific Northwest rocky-shore plot and compared it with a control where sea stars remained.
The question concerned changes in prey and other organisms occupying the rock surface. Sustained removal and long observation made the predator’s role in community change experimentally testable.
Mussels and the keystone-species concept
Without the sea stars, California mussels, Mytilus californianus, expanded and displaced other organisms from space on the shore. Predation could therefore maintain coexistence indirectly by limiting a dominant competitor.
Paine reported food-web experiments in 1966 and used the term keystone species in 1969. The concept concerns a community effect disproportionate to a species’ abundance, rather than simply large size, high numbers or a position at the top of a food chain.
From predation to indirect effects
His research drew attention to effects transmitted through intervening species. A predator’s alteration of competition among its prey is one such indirect interaction.
Paine discussed trophic cascades in his 1979 Tansley Lecture and the paper that followed. This terminology came after the original sea-star experiment; the dates of the experiment and of the term should be distinguished.
References: [1]
Community change across space and time
With Simon Levin, Paine also investigated the creation, disturbance and recovery of patches. A shore contains changing areas of open rock and mussel cover rather than one uniform background.
These studies combined repeated field visits, manipulation and natural-history knowledge. They made keystone effects and cascades questions for investigation, rather than rules assigning the same controlling species to every ecosystem.
References: [1]