Describe what happens when a keystone species is removed from a population.

A keystone species is a vital element for the entire ecosystem (not for its abundance but for its influence). As such, if it were to be extinct, it would cause a domino effect among dependent species: lowering the presence of a keystone species will lead to a decline of its dependent species, then the overpopulation of the latter's usual prey, and then the lowering of the latter's preys and so on: a trophic cascade.