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.Gause, G.F. (1934). The struggle for existence. Baltimore, MD: Williams & Wilkins.
