Final answer:
The competitive exclusion principle states that different species cannot coexist in a community if they are competing for all the same resources. Natural selection favors traits that lessen reliance on shared resources, reducing competition. If a species cannot evolve to reduce competition, the more efficient species will drive the other to extinction.
Step-by-step explanation:
The competitive exclusion principle in biology states that two species cannot occupy the exact same niche in a habitat. This means that different species cannot coexist in a community if they are competing for all the same resources. If there is competition between two species for the same resources, natural selection will favor traits that lessen reliance on the shared resource, reducing competition. If one species cannot evolve to reduce competition, the species that most efficiently exploits the resource will drive the other species to extinction.
An example of the competitive exclusion principle is the case of two protozoan species, Paramecium aurelia and Paramecium caudatum. When grown individually, both species thrive. However, when placed together in the same habitat, P. aurelia outcompetes and drives P. caudatum to extinction.