structural:summarization
Interspecific

Interspecific competition may occur when individuals of two separate species share a limiting resource in the same area. If the resource cannot support both populations, then lowered fecundity, growth, or survival may result in at least one species. Interspecific competition has the potential to alter populations, communities, and the evolution of interacting species. An example among animals could be the case of cheetahs and lions; since both species feed on similar prey, they are negatively impacted by the presence of the other because they will have less food, however, they still persist together, despite the prediction that under competition one will displace the other. In fact, lions sometimes steal prey items killed by cheetahs. Potential competitors can also kill each other, in so-called ' intraguild predation '. For example, in southern California coyotes often kill and eat gray foxes and bobcats, all three carnivores sharing the same stable prey (small mammals).

An example among protozoa involves Paramecium aurelia and Paramecium caudatum. Russian ecologist, Georgy Gause, studied the competition between the two species of Paramecium that occurred as a result of their coexistence. Through his studies, Gause proposed the Competitive exclusion principle, observing the competition that occurred when their different ecological niches overlapped.

Competition has been observed between individuals, populations, and species, but there is little evidence that competition has been the driving force in the evolution of large groups. For example, mammals lived beside reptiles for many millions of years of time but were unable to gain a competitive edge until dinosaurs were devastated by the Cretaceous–Paleogene extinction event.