When Bob Paine chucked starfish into the Pacific Ocean in 1963, he was also throwing bombs into the heart of ecology. Back then, the prevailing view was that communities of animals and plants were fairly stable, provided that they contained a diverse set of members. But Paine showed that some species are disproportionately influential. Take the ochre starfish. When Paine prised them from a stretch of Washington shore and pitched them into the surf, the mussels that the starfish ate advanced over the shore like a black glacier. They crowded out other creatures and radically remodelled the coastline.

Paine described crucial species like the starfish as “keystones”, after the central stone that stops an arch from collapsing. The whole community