Principle of competitive exclusion, also called Gause’s principle, or Grinnell’s axiom, (after G.F. Gause, a Soviet biologist, and J. Grinnell, an American naturalist, who first clearly established it), statement that in competition between species that seek the same ecological niche, one species survives while the other expires under a given set of environmental conditions. The result is that each species occupies a distinct niche.

The Gause competitive exclusion principle, also known as Gause's law of competitive exclusion, is a concept in ecology that states that two species competing for the same limited resources cannot coexist indefinitely. Proposed by Russian biologist Georgy Gause in 1934, this principle suggests that when two species with similar ecological niches (roles in an ecosystem) compete for the same resources, one species will eventually outcompete and eliminate the other species from that particular habitat.

The principle is based on the assumption that resources in an environment are finite and limited. When two species occupy the same niche and require the same resources, they will face intense competition. This competition can take various forms, such as direct competition for food, water, or shelter, as well as indirect competition through the release of chemicals or interference behaviors.

Key factors of competitive exclusion principle:

1. Niche Overlap:
- The competitive exclusion principle is most likely to occur when two species have a high degree of niche overlap, meaning they have similar requirements and ecological roles.
- This overlap leads to direct competition for resources, reducing the chances of coexistence.

2. Competitive Advantage:
- In any given environment, one species may have certain traits or adaptations that give it a competitive advantage over the other species.
- This advantage could be in terms of better utilization of resources, higher reproductive rate, or more efficient defense mechanisms.

3. Competitive Exclusion:
- Over time, the species with a competitive advantage will outcompete the other species, leading to its dominance in the habitat.
- The species that loses the competition may either be driven to extinction or forced to adapt and occupy a different ecological niche.

Exceptions and Coexistence:

While the competitive exclusion principle generally holds true, there are exceptions and instances of coexistence among competing species. Some factors that can enable coexistence include:

1. Resource Partitioning:
- Species may evolve to occupy slightly different niches or utilize different resources within the same habitat, reducing direct competition.

2. Character Displacement:
- Natural selection can drive species to evolve different traits, such as beak size or feeding habits, that allow them to exploit different resources and minimize competition.

3. Disturbances or Environmental Variability:
- Fluctuations in environmental conditions or disturbances can create temporary opportunities for coexistence by altering resource availability.

In conclusion, the Gause competitive exclusion principle states that when two species with similar ecological niches compete for the same limited resources, one species will ultimately outcompete and eliminate the other. However, exceptions to this principle exist, and coexistence can occur through resource partitioning, character displacement, or environmental variability. Understanding competitive interactions is crucial for studying species dynamics and community ecology.