Competitive exclusion principle
In ecology, the competitive exclusion principle,[1] sometimes referred to as Gause's law,[2] is a proposition that two species which compete for the same limited resource cannot coexist at constant population values. When one species has even the slightest advantage over another, the one with the advantage will dominate in the long term. This leads either to the extinction of the weaker competitor or to an evolutionary or behavioral shift toward a different ecological niche. The principle has been paraphrased in the maxim "complete competitors cannot coexist".[1]
History
The competitive exclusion principle is classically attributed to Georgy Gause,[3] although he actually never formulated it.[1] The principle is already present in Darwin's theory of natural selection.[2][4]
Throughout its history, the status of the principle has oscillated between a priori ('two species coexisting must have different niches') and experimental truth ('we find that species coexisting do have different niches').[2]
Experimental basis
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".[5] 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 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.
Prediction
Competitive exclusion is predicted by mathematical and theoretical models such as the Lotka–Volterra models of competition. However, for poorly understood reasons, competitive exclusion is rarely observed in natural ecosystems, and many biological communities appear to violate Gause's law. The best-known example is the so-called "paradox of the plankton".[6] All plankton species live on a very limited number of resources, primarily solar energy and minerals 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.
Some communities that appear to uphold the competitive exclusion principle are MacArthur's warblers[7] and Darwin's finches,[8] though the latter still overlap ecologically very strongly, being only affected negatively by competition under extreme conditions.[9]
Paradoxical traits
A partial solution to the paradox lies in raising the dimensionality of the system. Spatial
Redefinition
Recent studies addressing some of the assumptions made for the models predicting competitive exclusion have shown 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.[10][11]
One of the primary ways niche-sharing species can coexist is the
Support for a model of
Phylogenetic context
An ecological community is the assembly of species which is maintained by ecological (Hutchinson, 1959;[15] Leibold, 1988[16]) and evolutionary process (Weiher and Keddy, 1995;[17] Chase et al., 2003). These two processes play an important role in shaping the existing community and will continue in the future (Tofts et al., 2000; Ackerly, 2003; Reich et al., 2003). In a local community, the potential members are filtered first by environmental factors such as temperature or availability of required resources and then secondly by its ability to co-exist with other resident species.
In an approach of understanding how two species fit together in a community or how the whole community fits together, The Origin of Species (Darwin, 1859) proposed that under homogeneous environmental condition struggle for existence is greater between closely related species than distantly related species. He also hypothesized that the functional traits may be conserved across phylogenies. Such strong phylogenetic similarities among closely related species are known as phylogenetic effects (Derrickson et al., 1988.[18])
With field study and mathematical models, ecologists have pieced together a connection between functional traits similarity between species and its effect on species co-existence. According to competitive-relatedness hypothesis (Cahil et al., 2008[19]) or phylogenetic limiting similarity hypothesis (Violle et al., 2011[20]) interspecific competition[21] is high among the species which have similar functional traits, and which compete for similar resources and habitats. Hence, it causes reduction in the number of closely related species and even distribution of it, known as phylogenetic overdispersion (Webb et al., 2002[22]). The reverse of phylogenetic overdispersion is phylogenetic clustering in which case species with conserved functional traits are expected to co-occur due to environmental filtering (Weiher et al., 1995; Webb, 2000). In the study performed by Webb et al., 2000, they showed that a small-plots of Borneo forest contained closely related trees together. This suggests that closely related species share features that are favored by the specific environmental factors that differ among plots causing phylogenetic clustering.
For both phylogenetic patterns (phylogenetic overdispersion and phylogenetic clustering), the baseline assumption is that phylogenetically related species are also ecologically similar (H. Burns et al., 2011[23]). There are no significant number of experiments answering to what degree the closely related species are also similar in niche. Due to that, both phylogenetic patterns are not easy to interpret. It's been shown that phylogenetic overdispersion may also result from convergence of distantly related species (Cavender-Bares et al. 2004;[24] Kraft et al. 2007[25]). In their study[citation needed], they have shown that traits are convergent rather than conserved. While, in another study[citation needed], it's been shown that phylogenetic clustering may also be due to historical or bio-geographical factors which prevents species from leaving their ancestral ranges. So, more phylogenetic experiments are required for understanding the strength of species interaction in community assembly.
Application to humans
Evidence showing that the competitive exclusion principle operates in human groups has been reviewed and integrated into
Another recent application: in his work Historical Dynamics,
See also
References
- ^ PMID 14399717. Archived from the original(PDF) on 2017-11-17. Retrieved 2016-11-24.
- ^ ISBN 978-94-017-9014-7.
- ^ Gause, Georgii Frantsevich (1934). The Struggle For Existence (1st ed.). Baltimore: Williams & Wilkins. Archived from the original on 2016-11-28. Retrieved 2016-11-24.
- ISBN 1-4353-9386-4.
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- ^ Lack, D.L. (1945). "The Galapagos finches (Geospizinae); a study in variation". Occasional Papers of the California Academy of Sciences. 21: 36–49.
- PMID 24750315.
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- ^ ISBN 978-1-78374-403-9.
- ^ Turchin, Peter (2019). Historical Dynamics: Why States Rise and Fall. NJ: Princeton University Press. pp. 50–77.
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: CS1 maint: date and year (link) - ^ Byim, Martin (3 December 2019). "Implementing Turchin's Metaethnic Frontier Theory With NetLogo". Retrieved 21 February 2024.