Secondary Consumer — Definition & Role

The cascade effect is when a key species goes extinct and then causes the extinction of many other species.

A well known instance of the cascade effect is when otters were overhunted in the Pacific. Otters ate sea urchins. Sea urchins ate kelp. When humans hunted the otters to near extinction, the urchins grew out of control because they were no longer being eaten. The urchins then ate the kelp to extinction. Since no more kelp was left, the urchins eventually died. This left large areas with no life in the ocean known as "urchin barriers".