What are keystone species?
Keystone species are species that can greatly affect population numbers and the health of an ecosystem. Sometimes keystone species are not abundant, and are usually plants and animals. e.g. sea otters, which feed on sea urchins. During the fur trade, the otters were being hunted, causing an increase in the sea urchins, which feed on kelp. The biomass of the kelp decreased, which then the fish that depended on kelp forests for habitats had a smaller population.