Editing Competitive exclusion principle (section)

==Experimental basis==

[[File:Graph of competitive exclusion principle.jpg|thumb|''[[Paramecium aurelia]]'' and ''[[Paramecium caudatum]]'' grow well individually, but when they compete for the same resources, ''P. aurelia'' outcompetes ''P. caudatum''.]]

Based on field observations, [[Joseph Grinnell]] formulated the principle of competitive exclusion in 1904: "Two species of approximately the same food habits are not likely to remain long evenly balanced in numbers in the same region. One will crowd out the other".<ref>{{Cite journal |last=Grinnell |first=J. |year=1904 |title=The Origin and Distribution of the Chestnut-Backed Chickadee |url=http://sora.unm.edu/node/7930 |journal=[[The Auk]] |publisher=American Ornithologists' Union |volume=21 |issue=3 |pages=364–382 |doi=10.2307/4070199 |jstor=4070199}}</ref> [[Georgy Gause]] formulated the law of competitive exclusion based on laboratory competition experiments using two species of ''[[Paramecium]]'', ''P. aurelia'' and ''P. caudatum''. The conditions were to add fresh water every day and input a constant flow of food. Although ''P. caudatum'' initially dominated, ''P. aurelia'' recovered and subsequently drove ''P. caudatum'' extinct via exploitative [[Resource (biology)|resource]] competition. However, Gause was able to let the ''P. caudatum'' survive by differing the environmental parameters (food, water). Thus, Gause's law is valid only if the ecological factors are constant.