dramatic cascading effects alters trophic dynamics food web connections cause extinction species ref name fisher ref name libralato sea otters ''enhydra lutris'' commonly cited example keystone species limit density sea urchins feed kelp sea otters removed system urchins graze kelp beds disappear dramatic effect community structure ref name mills hunting sea otters example thought led indirectly extinction steller 's sea cow ''hydrodamalis gigas'' ref name anderson keystone
Natural science Biology Ecology