A keystone species can be defined as an animal or a plant that plays a fundamental role in impacting the ecosystem and its functions. McMillan et al. note that the ecosystem can be seen as dependent on keystone species to an extent where the absence of keystone species could either transform the ecosystem or cease it completely.
This occurs due to the fact that all elements of the habitat (or an ecosystem) rely on each other. Therefore, the impact of a keystone species is irreplaceable because of the presence of background factors, such as climate change. A decreased prevalence of keystone species could damage the environment and cause the habitat to collapse due to the inability to maintain a natural equilibrium.
One of the particularities of keystone species is that they are usually predators, but it is not a general rule. The absence of a keystone species in the region could make it easier for new animals and plants to come into the habitat and force out some of the native species. A perfect example of a keystone species is a gray wolf.
Their innate core responsibility is to keep the ecosystem healthy by revisiting the elk and deer populations recurrently. For the ecosystem and people in the region, this means that other animal and plant species could benefit from the existence of gray wolves through a well-kept balance within the environment.
This keystone species often leaves the carcasses of their prey untouched, which makes it possible to redistribute food and nutrients to other wildlife species that also seem to depend on gray wolves (for instance, scavengers and grizzly bears).