Competitive exclusion principle
Encyclopedia
In ecology
, the competitive exclusion principle, sometimes referred to as Gause's
law of competitive exclusion or just Gause's law, is a proposition which states that two species
competing
for the same resources cannot coexist if other ecological factors are constant. When one species has even the slightest advantage or edge over another, then the one with the advantage will dominate in the long term. One of the two competitors will always overcome the other, leading to either the extinction of this competitor or an evolution
ary or behavioral shift towards a different ecological niche
. The principle has been paraphrased into the maxim "complete competitors cannot coexist".
formulated the law of competitive exclusion based on laboratory competition experiments using two species of Paramecium
, the Paramecium aurelia and Paramecium caudatum. Although the following says that caudatum dominated, the aurelia recovered shortly and attacked the caudatum, completely annihilating the other species. It was a complete surprise, making no sense whatsoever. 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. However, Gause was able to let the Paramecium caudatum survive by driving differently the environmental parameters (food, water). This explains why the Gause law is valid only if the ecological factors are constant. Gause also studied competition between two species of yeast, Saccharomyces cerevisiae
and Schizosaccharomyces kefir, and found that Schizosaccharomyces kefir consistently out-competed Saccharomyces cerevisiae by producing a higher concentration of ethyl alcohol.
s, and many biological communities appear to violate Gause's Law. The best known example is the paradox of the plankton
. 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. Some communities that uphold competitive exclusion are MacArthur's Warblers and Darwin's Finches
.
competition
, competition-colonization trade-offs, 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.
One of the primary ways that niche-sharing species can coexist is the competition-colonization trade-off. In other words, species that are better competitors will be specialists, while species that are better colonizers are more likely to be generalists. Host-parasite models are effective ways of examining this relationship, using host transfer events. There seem to be two places where the ability to colonize differs in closely ecologically related species. In feather lice, Bush and Clayton provided some verification of this by showing that two closely related genera of lice are nearly equal in their ability to colonize new hosts pigeons once transferred. Harbison continued this line of thought by investigating whether the two genera differed in their ability to transfer. This research focused primarily on determining how colonization occurs and why wing lice are better colonizers than body lice. Vertical transfer is the most common occurrence, between parent and child, and is well studied and understood. Horizontal transfer is difficult to measure, but in lice seems to occur via phoresis or one species "hitchhiking" on another. Harbison found that body lice are less adept at phoresis and excel competitively, while wing lice excel in colonization.
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
, the competitive exclusion principle, sometimes referred to as Gause's
Georgii Frantsevich Gause
Georgii Frantsevich Gause, was a Russian biologist who proposed the competitive exclusion principle, fundamental to the science of ecology. He would devote most of his later life to the research of antibiotics.-Early life:...
law of competitive exclusion or just Gause's law, is a proposition which states that two species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
competing
Competition (biology)
Competition is an interaction between organisms or species, in which the fitness of one is lowered by the presence of another. Limited supply of at least one resource used by both is required. Competition both within and between species is an important topic in ecology, especially community ecology...
for the same resources cannot coexist if other ecological factors are constant. When one species has even the slightest advantage or edge over another, then the one with the advantage will dominate in the long term. One of the two competitors will always overcome the other, leading to either the extinction of this competitor or an evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
ary or behavioral shift towards a different ecological niche
Ecological niche
In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food...
. The principle has been paraphrased into the maxim "complete competitors cannot coexist".
Experimental basis
Russian ecologist Georgii Frantsevich GauseGeorgii Frantsevich Gause
Georgii Frantsevich Gause, was a Russian biologist who proposed the competitive exclusion principle, fundamental to the science of ecology. He would devote most of his later life to the research of antibiotics.-Early life:...
formulated the law of competitive exclusion based on laboratory competition experiments using two species of Paramecium
Paramecium
Paramecium is a group of unicellular ciliate protozoa, which are commonly studied as a representative of the ciliate group, and range from about 0.05 to 0.35 mm in length. Simple cilia cover the body, which allow the cell to move with a synchronous motion at speeds of approximately 12 body...
, the Paramecium aurelia and Paramecium caudatum. Although the following says that caudatum dominated, the aurelia recovered shortly and attacked the caudatum, completely annihilating the other species. It was a complete surprise, making no sense whatsoever. 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. However, Gause was able to let the Paramecium caudatum survive by driving differently the environmental parameters (food, water). This explains why the Gause law is valid only if the ecological factors are constant. Gause also studied competition between two species of yeast, Saccharomyces cerevisiae
Saccharomyces cerevisiae
Saccharomyces cerevisiae is a species of yeast. It is perhaps the most useful yeast, having been instrumental to baking and brewing since ancient times. It is believed that it was originally isolated from the skin of grapes...
and Schizosaccharomyces kefir, and found that Schizosaccharomyces kefir consistently out-competed Saccharomyces cerevisiae by producing a higher concentration of ethyl alcohol.
Prediction
Competitive exclusion is predicted by a number of mathematical and theoretical models, such as the Lotka-Volterra models of competition. However, for reasons that are poorly understood, competitive exclusion is rarely observed in natural ecosystemEcosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
s, and many biological communities appear to violate Gause's Law. The best known example is the paradox of the plankton
Paradox of the plankton
In aquatic biology, the paradox of the plankton is the name given to the situation where a limited range of resources supports a much wider range of planktonic organisms...
. All plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
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. Some communities that uphold competitive exclusion are MacArthur's Warblers and Darwin's Finches
Darwin's finches
Darwin's finches are a group of 14 or 15 species of passerine birds. It is still not clear which bird family they belong to, but they are not related to the true finches. They were first collected by Charles Darwin on the Galápagos Islands during the second voyage of the Beagle...
.
Paradoxical traits
A partial solution to the paradox lies in raising the dimensionality of the system. Spatial heterogeneity, multiple resourceResource
A resource is a source or supply from which benefit is produced, typically of limited availability.Resource may also refer to:* Resource , substances or objects required by a biological organism for normal maintenance, growth, and reproduction...
competition
Competition
Competition is a contest between individuals, groups, animals, etc. for territory, a niche, or a location of resources. It arises whenever two and only two strive for a goal which cannot be shared. Competition occurs naturally between living organisms which co-exist in the same environment. For...
, competition-colonization trade-offs, 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.One of the primary ways that niche-sharing species can coexist is the competition-colonization trade-off. In other words, species that are better competitors will be specialists, while species that are better colonizers are more likely to be generalists. Host-parasite models are effective ways of examining this relationship, using host transfer events. There seem to be two places where the ability to colonize differs in closely ecologically related species. In feather lice, Bush and Clayton provided some verification of this by showing that two closely related genera of lice are nearly equal in their ability to colonize new hosts pigeons once transferred. Harbison continued this line of thought by investigating whether the two genera differed in their ability to transfer. This research focused primarily on determining how colonization occurs and why wing lice are better colonizers than body lice. Vertical transfer is the most common occurrence, between parent and child, and is well studied and understood. Horizontal transfer is difficult to measure, but in lice seems to occur via phoresis or one species "hitchhiking" on another. Harbison found that body lice are less adept at phoresis and excel competitively, while wing lice excel in colonization.
See also
- Ecological competitionCompetition (biology)Competition is an interaction between organisms or species, in which the fitness of one is lowered by the presence of another. Limited supply of at least one resource used by both is required. Competition both within and between species is an important topic in ecology, especially community ecology...
- Joseph GrinnellJoseph GrinnellJoseph Grinnell was a field biologist and zoologist. He made extensive studies of the fauna of California, and is credited with introducing a method of recording precise field observations known as the Grinnell System...
- Limiting factorLimiting factorA limiting factor or limiting resource is a factor that controls a process, such as organism growth or species population, size, or distribution. The availability of food, predation pressure, or availability of shelter are examples of factors that could be limiting for an organism...
- Limiting similarityLimiting similarityLimiting similarity is a concept in theoretical ecology and community ecology that proposes the existence of a maximum level of niche overlap between two given species that will allow continued coexistence....
- Paradox of the planktonParadox of the planktonIn aquatic biology, the paradox of the plankton is the name given to the situation where a limited range of resources supports a much wider range of planktonic organisms...
External links
- Competitive exclusion principle, KnolKnolKnol is a Google project that aims to include user-written articles on a range of topics. The project was led by Udi Manber of Google, announced December 13, 2007, and was opened in beta to the public on July 23, 2008 with a few hundred articles mostly in the health and medical field.Knol has no...
- Paradox of the plankton, KnolKnolKnol is a Google project that aims to include user-written articles on a range of topics. The project was led by Udi Manber of Google, announced December 13, 2007, and was opened in beta to the public on July 23, 2008 with a few hundred articles mostly in the health and medical field.Knol has no...