Competition (biology)
Competitive exclusion principle

To explain how species coexist, in 1934 Georgii Gause proposed the competitive exclusion principle which is also called the Gause principle: species cannot coexist if they have the same ecological niche. The word "niche" refers to a species' requirements for survival and reproduction. These requirements include both resources (like food) and proper habitat conditions (like temperature or pH). Gause reasoned that if two species had identical niches (required identical resources and habitats) they would attempt to live in exactly the same area and would compete for exactly the same resources. If this happened, the species that was the best competitor would always exclude its competitors from that area. Therefore, species must at least have slightly different niches in order to coexist.
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