Species that have a significant impact on their natural environment with their absence or presence. A small impact on keystone species can cause major disruption for the entire ecosystem. The removal of a keystone species from the environment causes many deficiencies in biomass, productivity, continuity of the food web and sustainable life. For example, blue jays carry the acorns that enable oak forests to form. Without them, oak forests cannot regenerate naturally. Without forests, no other species in the ecosystem can survive.