I.1.4.C Gause’s rule

Gause’s rule ( Principle of Competitive Exclusion)

It is a proposition named for Georgy Gause.

Two species competing for the same limiting resource cannot coexist at constant population values.

If two species occur at same trophies level in an ecosystem, they are likely to compete with each other for food.

When one species has even the slightest advantage over another, the one with the advantage will dominate in the long term. This leads either to the extinction of the weaker competitor or to an evolutionary or behavioral shift toward a different ecological niche.

Gause’s law is valid only if the ecological factors are constant.

The principle has been paraphrased in the maxim “complete competitors cannot coexist”

The competition may result in

 1) Adaptive radiation of one or both species restricting them to separate niche and minimising competition.

 2) Within the same or overlapping niches, equilibrium situation may be reached where one of the competitors declines in numbers to the point of extinction.

This phenomenon called “Competitive Exclusion” was studied by Russian biologist Gause in several species of Paramoecium.


  1. Adaptive radiation is seen in finches in Galápagos Islands, which have undergone great diversification in their feeding habits.
  2. Paramecium aurelia and Paramecium caudatum grow well individually, but when they compete for the same resources, aurelia outcompetes P. caudatum.
  3. Increased cultures of duckweed (Lamna) species, L.gibba was capable of excluding L.polyrrhiza.

Application to humans ;

Evidence showing that the competitive exclusion principle operates in human groups has been reviewed and integrated into regality theory to explain warlike and peaceful societies. For example, hunter-gatherer groups surrounded by other hunter-gatherer groups in the same ecological niche will fight, at least occasionally, while hunter-gatherer groups surrounded by groups with a different means of subsistence can coexist peacefully.


Gause law speaks of parallel evolution in terms of structural adaptations but not in terms of physiological, protective animal association, biotic and organic adaptations.

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