Keystone Species

Some species have disproportionate influence on their ecosystem relative to their abundance. These are keystone species — remove them and the entire structure changes dramatically. The concept was discovered when ecologist Robert Paine removed sea stars from a tidal ecosystem.

Not all keystones are predators. Beavers are ecosystem engineers whose dams create wetlands that support hundreds of species. Pollinators like bees are keystones too: they enable reproduction for seventy-five percent of flowering plants, including a third of the crops that feed humanity. Lose them, and whole layers of the web unravel.