Intra-specific competition

Intra-specific competition is competition between members of a species (intra means within).

Since each member of a species needs practically the same as other members of the same species - and these needs overlap much more than with other species - there is a strong competition for resources, such as food, water, territory, and mates, which results in natural selection and the "survival of the fittest".

This is the basis for evolution. Effectively it ensures that organisms are well adapted for their environment.