Competitive exclusion principle
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2008-04-14T21:57:10Z
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Reverted edits by [[Special:Contributions/76.19.3.63|76.19.3.63]] ([[User talk:76.19.3.63|talk]]) to last version by SieBot
{{Citations missing|date=August 2007}}
In [[community ecology]], the '''competitive exclusion principle'''<ref>[[Garrett Hardin|Hardin, G.]] (1960). The Competitive Exclusion Principle. ''Science'' '''131''', 1292-1297.</ref>, sometimes referred to as '''[[Georgii Frantsevich Gause|Gause's]] Law of competitive exclusion''' or just '''Gause's Law'''<ref>[[Georgii Frantsevich Gause|Gause, G. F.]] (1934). ''The struggle for existence''. Baltimore, MD: Williams & Wilkins.</ref>, is a theory which states that two [[species]] [[competition (biology)|competing]] for the same resources cannot stably coexist, if the ecological factors are constant. Either of the two competitors will always take over the other which leads to either the extinction of one of the competitors or its [[evolution]]ary or behavioural shift towards a different [[ecological niche]]. <!-- The following is a good point, but confusingly executed here; it could do with expansion away from the introduction; plus some sources: As a consequence, [[interspecific competition|competing related species]] often evolve distinguishing characteristics in areas in which they coexist. This aids in [[mate recognition]], thus maintaining each species' superiority in exploiting slightly different ecological niches. -->
==Experimental basis==
Russian ecologist [[Georgii Frantsevich Gause]], formulated the law of competitive exclusion based on laboratory competition experiments using two species of ''[[Paramecium]]'', the ''Paramecium aurelia'' and ''Paramecium caudatum''. Following a lag phase, the ''Paramecium aurelia'' was consistently able to drive the other to extinction. The conditions were to add fresh water everyday and input a constant flow of food.
On the other hand, Gause was able to let the ''Paramecium caudatum'' survive by driving differently the environmental parameters (food, water): that explains why the Gause law is valid only if the ecological factors are constant.
==Prediction==
Competitive exclusion is predicted by a number of mathematical and theoretical models, such as the [[Lotka-Volterra model]]s of competition. However, for reasons that are poorly understood, competitive exclusion is rarely observed in natural [[ecosystem]]s, and many biological communities appear to violate Gause's Law. The best known example is the ''[[paradox of the plankton]]'' (or short ''diversity paradox''): All [[plankton]] species live on a very limited number of resources, primarily [[solar energy]] and minerals that are dissolved in the water. According to the competitive exclusion principle, only a small number of plankton species should be able to coexist on these resources. Nevertheless, large numbers of plankton species coexist within small regions of open sea.
==Paradoxical traits==
A partial solution to the paradox lies in raising the dimensionality of the system. Spatial [[heterogeneity]], multiple [[resource competition]], [[competition-colonization trade-off]]s, and lag prevent exclusion (ignoring stochastic extinction over longer time-frames). However, such systems tend to be analytically intractable. In addition, many can theoretically support an unlimited number of species. A new paradox is created: Most well-known models that allow for stable coexistence allow for unlimited number of species to coexist, yet in nature, any community contains just a handful of species.
==Re-definition==
Recent studies that address some of the assumptions made for the models predicting competitive exclusion have shown that these assumptions need to be reconsidered. For example, a slight modification of the assumption of how growth and body size are related leads to a different conclusion, namely that for a given ecosystem a certain range of species may coexist while others become outcompeted<ref>Rastetter, E. B. & Ågren, G. I. (2002). Changes in individual allometry can lead to coexistence without niche separation. ''Ecosystems'' '''5''', 789-801.</ref>.
==References==
{{reflist}}
* Vaurie, Charles (1950): Notes from the Walter Koelz Collections, Number 6. Notes on some Asiatic nuthatches and creepers. ''American Museum Novitates'' '''1472''': 1-39. [http://digitallibrary.amnh.org/dspace/bitstream/2246/4241/1/N1472.pdf PDF fulltext]
[[Category:Biological interactions]]
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