1) A keystone species is a plant or animal that plays a unique and crucial role in the way an ecosystem functions.Without them, the ecosystem would be dramatically different or cease to exist altogether.
2) Its disappearance could affect other species that rely on it for survival.Example for keystone species is sea otter. It feed on sea urchins and controls their population.
3) If sea urchins population is not controlled, it would eat up the seaweed, which is a major source of food for the ecosystemA keystone species is often, but not always, a predator.
4) Herbivores can also be keystone species.For example, In African savannas, elephants are a keystone species.
5) It controls the tree population which makes the grasses thrive and sustain grazing.