What is the essence of Gause's principle of competitive exclusion?

The correct answer is Option (2) → Two species cannot occupy the same niche indefinitely when competing for the same limited resources.

Competition happens when two species use the same limited resources. Gause studied this and stated the Competitive Exclusion Principle: two closely related species competing for the same resources cannot co-exist indefinitely. The weaker competitor is eliminated in the end. This may be true when resources are limiting.

Option (1) Species with different food preferences are excluded due to competition for the same resources. — Incorrect. Species with different food preferences do not compete for the same resource, so there is nothing to exclude them. The principle is about species that need the same resources.

Option (2) Two species cannot occupy the same niche indefinitely when competing for the same limited resources. — Correct. Two species that compete for the same limited resources cannot share them forever. In time, the competitively inferior one is eliminated.

Option (3) Smaller organisms are excluded by larger ones through competition. — Incorrect. The principle says nothing about body size. The loser is the competitively inferior species, which need not be the smaller one.

Option (4) Less abundant species are excluded by more abundant species through competition. — Incorrect. Abundance is not the test either. The species that is eliminated is the one that competes less well for the limited resource, whatever its numbers.

NCERT Extract:
Population Interactions – “… Gause’s ‘Competitive Exclusion Principle’ states that two closely related species competing for the same resources cannot co-exist indefinitely and the competitively inferior one will be eliminated eventually. This may be true if resources are limiting, but not otherwise.”