• Gause's competitive exclusion principle (CEP) states that two species with identical niches cannot coexist indefinitely as they compete for identical resources. A species' niche is basically its ecological role, which is defined by the set of conditions, resources, and interactions it needs.
• In nature, it's rarely the case that two species occupy exactly identical niches. However, the greater the extent to which two species' niches overlap, the stronger the competition between them will tend to be.• Competitive exclusion may be avoided if one or both of the competing species evolves to use a different resource, occupy a different area of the habitat, or feed during a different time of day. The result of this kind of evolution is that two similar species use largely non-overlapping resources and thus have different niches. This is called resource partitioning, and it helps the species coexist because there is less direct competition between them.