Final answer:
The competitive exclusion principle states that two species cannot coexist in the same habitat if they have identical niches due to resource competition.
Step-by-step explanation:
Competitive Exclusion Principle and Coexistence
According to the competitive exclusion principle, two different species can coexist in the same habitat if they have different ecological niches. Resources are often limited, leading to competition among species. The niche encompasses how a species uses resources and how it interacts with other organisms in the ecosystem. When two species occupy identical niches, the one that uses the resources more efficiently may drive the other to extinction. However, coexistence can occur if one or both species undergo character displacement, where they evolve to exploit different resources, reducing competition.
An empirical example involves the protozoan species Paramecium aurelia and Paramecium caudatum. Grown separately, each thrives; together, competition leads to the exclusion of P. caudatum by P. aurelia. This demonstrates the principle in action. Yet, through character displacement, species can specialize and coexist by utilizing different aspects of the environment, a key part of the evolutionary process and a facilitator of biodiversity.