How Ecosystems Got a Keystone

One day in 1963, ecologist Bob Paine started plucking sea stars off rocks and tossing them into the sea. His study helped show how a species may be small in number but significant in its impact.

Published November 6, 2015

Leave baking soda out of a cake and all hell breaks loose—the cake comes out of the oven flat, not fluffy, and you’ve got a failed kitchen-chemistry experiment simply because you omitted a pinch of a key ingredient—a keystone ingredient.

Ecologist Bob Paine might not appreciate the analogy. He coined the term keystone species as an elegant descriptor for a species—in his case, the sea star Pisaster ochraceus—that plays a disproportionately large role in an ecosystem. He came up with the phrase after spending years prying sea stars off a study site on Washington’s Tatoosh Island and observing the long-term impact that the presence or absence of one predator can have on the ecosystem. More than 50 years on, you can’t crack open a biology textbook or take an ecology course without learning about keystone species—sea stars, sea otters, wolves, and more—whose influence far exceeds their abundance. But, for better or worse, the term has been co-opted in all sorts of other ways, too. (As far as we know, this is its first use to describe baking that’s gone sideways.)

In this video, Paine, professor emeritus of biology at the University of Washington, explains how he conducted his groundbreaking work and developed the idea of a keystone species.

(For further reading, check out this story by Ed Yong, who turns the analogy of a keystone species back on Paine, a man “whose disproportionate influence equals that of any starfish or sea otter” and who “changed the ecosystem of scientists.”)