Gause’s competitive exclusion principle states that:
No two species can occupy the same niche indefinitely for the same limiting resources.
According to Gause’s Competitive Exclusion Principle, two closely related species which are competing for the same resources cannot coexist indefinitely and the one which is inferior competitively will be eliminated eventually. This may be true if resources are limiting, but not otherwise.
More abundant species will not exclude the less abundant species if they are not competing for the same resources. However, if they are competing for the same resource, the number of competing organisms may play a role. The competing species may also undergo different specializations to diverge their feeding habits, in order to reduce the conflict.
The Principle is applicable only if the competition is for the same resource and not for the species with different food preferences.
Size of the organism is also irrelevant if the competition is not for the same resource.