Gause's competitive exclusion principle states that two species competing for the same limiting resources cannot stably coexist in the same ecological niche.In 1934, Soviet microbiologist Georgy Gause conducted an elegant experiment: he grew two species of paramecia (Paramecium caudatum and Paramecium aurelia) in test tubes with bacteria as their shared food. Separately, both species thrived, but together, P. aurelia always displaced P. caudatum. The reason wasn't predation but that P. aurelia reproduced faster and used the bacteria more efficiently. Gause formulated the principle: if two species occupy the same ecological niche (using resources identically), they cannot coexist—one will displace the other. Later this was generalized: for stable coexistence, species must differ in their niches by at least a 'threshold amount.' The principle became a cornerstone of ecology, explaining biodiversity through resource partitioning.
Georgy Frantsevich Gause, a young researcher at Moscow University, conducted a series of experiments with paramecia and yeast in 1932–1934, publishing the results in his book 'The Struggle for Existence' (1934). He mathematically described competition based on equations proposed by Volterra and Lotka, but it was his experimental verification that brought the principle fame. Similar ideas were independently expressed by American ecologist Joseph Grinnell, but the term 'Gause's principle' became established after the work of ecologist David Lack in the 1940s. Today, the principle is considered a special case of the broader niche theory, and its strict formulation is criticized for oversimplification.
Applied in ecology to predict invasion outcomes: an invader occupying the same niche as a native species will likely displace it if it uses the resource more efficiently. In agriculture, the principle justifies crop rotation and polycultures: plants with different needs (root depth, growing season) compete less. Limits of applicability: the principle is strict only for homogeneous environments and constant conditions; in heterogeneous landscapes, species can diverge into microhabitats, and in variable environments, a weak competitor can survive by colonizing disturbed patches.
Predicting the outcome of resource competition between invasive and native species, as well as selecting crops for mixed planting in agriculture.
Gause conducted his experiments in small test tubes, but his principle works on a continental scale: the North American gray squirrel is displacing the British red squirrel because it digests acorns more efficiently and carries a virus lethal to its competitor.










