Competition (biology)

Competition is an interaction between organisms or species in which both the organisms or species are harmed. Limited supply of at least one resource (such as food, water, and territory) used by both can be a factor.[1] Competition both within and between species is an important topic in ecology, especially community ecology. Competition is one of many interacting biotic and abiotic factors that affect community structure. Competition among members of the same species is known as intraspecific competition, while competition between individuals of different species is known as interspecific competition. Competition is not always straightforward, and can occur in both a direct and indirect fashion.[2]

According to the competitive exclusion principle, species less suited to compete for resources should either adapt or die out, although competitive exclusion is rarely found in natural ecosystems. According to evolutionary theory, this competition within and between species for resources is important in natural selection. However, competition may play less of a role than expansion among larger clades;[3] this is termed the 'Room to Roam' hypothesis.[2]

Clone war of sea anemones 2-17-08-2
Sea anemones compete for the territory in tide pools

By mechanism

Competition occurs by various mechanisms, which can generally be divided into direct and indirect. These apply equally to intraspecific and interspecific competition. Biologists typically recognize two types of competition: interference and exploitative competition. During interference competition, organisms interact directly by fighting for scarce resources. For example, large aphids defend feeding sites on cottonwood leaves by ejecting smaller aphids from better sites. In contrast, during exploitative competition, organisms interact indirectly by consuming scarce resources. For example, plants consume nitrogen by absorbing it into their roots, making nitrogen unavailable to nearby plants. Plants that produce many roots typically reduce soil nitrogen to very low levels, eventually killing neighboring plants.

Hirschkampf
Male-male competition in red deer during rut is an example of interference competition within a species.

Interference

Interference competition occurs directly between individuals via aggression etc. when the individuals interfere with foraging, survival, reproduction of others, or by directly preventing their physical establishment in a portion of the habitat. An example of this can be seen between the ant Novomessor cockerelli and red harvester ants, where the former interferes with the ability of the latter to forage by plugging the entrances to their colonies with small rocks.[4]

Exploitative

Exploitation competition occurs indirectly through a common limiting resource which acts as an intermediate. For example, use of resources depletes the amount available to others, or they compete for space.[5]

Apparent

Apparent competition occurs indirectly between two species which are both preyed upon by the same predator.[6] For example, species A and species B are both prey of predator C. The increase of species A may cause the decrease of species B, because the increase of As may aid in the survival of predator Cs, which will increase the number of predator Cs, which in turn will hunt more of species B.[7]

By size asymmetry

Competition varies from complete symmetric (all individuals receive the same amount of resources, irrespective of their size) to perfectly size symmetric (all individuals exploit the same amount of resource per unit biomass) to absolutely size-asymmetric (the largest individuals exploit all the available resource). The degree of size asymmetry has major effects on the structure and diversity of ecological communities, e.g. in plant communities size-asymmetric competition for light has stronger effects on diversity compared with competition for soil resources.

By taxonomic relationship

Competition can occur between individuals of the same species, called intraspecific competition, or between different species, called interspecific competition. Studies show that intraspecific competition can regulate population dynamics (changes in population size over time). This occurs because individuals become crowded as a population grows. Since individuals within a population require the same resources, crowding causes resources to become more limited. Some individuals (typically small juveniles) eventually do not acquire enough resources and die or do not reproduce. This reduces population size and slows population growth.

Species also interact with other species that require the same resources. Consequently, interspecific competition can alter the sizes of many species' populations at the same time. Experiments demonstrate that when species compete for a limited resource, one species eventually drives the populations of other species extinct. These experiments suggest that competing species cannot coexist (they cannot live together in the same area) because the best competitor will exclude all other competing species.

Intraspecific

Intraspecific competition occurs when members of the same species compete for the same resources in an ecosystem.[8]

Interspecific

Interspecific competition may occur when individuals of two separate species share a limiting resource in the same area. If the resource cannot support both populations, then lowered fecundity, growth, or survival may result in at least one species. Interspecific competition has the potential to alter populations, communities and the evolution of interacting species. An example among animals could be the case of cheetahs and lions; since both species feed on similar prey, they are negatively impacted by the presence of the other because they will have less food, however they still persist together, despite the prediction that under competition one will displace the other. In fact, lions sometimes steal prey items killed by cheetahs. Potential competitors can also kill each other, in so-called 'intraguild predation'. For example, in southern California coyotes often kill and eat gray foxes and bobcats, all three carnivores sharing the same stable prey (small mammals).[9]

An example among protozoa involves Paramecium aurelia and Paramecium caudatum. Russian ecologist, Georgy Gause, studied the competition between the two species of Paramecium that occurred as a result of their coexistence. Through his studies, Gause proposed the Competitive exclusion principle, observing the competition that occurred when their different ecological niches overlapped.[10]

Competition has been observed between individuals, populations and species, but there is little evidence that competition has been the driving force in the evolution of large groups. For example, mammals lived beside reptiles for many millions of years of time but were unable to gain a competitive edge until dinosaurs were devastated by the Cretaceous–Paleogene extinction event.[2]

Evolutionary strategies

In evolutionary contexts, competition is related to the concept of r/K selection theory, which relates to the selection of traits which promote success in particular environments. The theory originates from work on island biogeography by the ecologists Robert MacArthur and E. O. Wilson.[11]

In r/K selection theory, selective pressures are hypothesised to drive evolution in one of two stereotyped directions: r- or K-selection.[12] These terms, r and K, are derived from standard ecological algebra, as illustrated in the simple Verhulst equation of population dynamics:[13]

where r is the growth rate of the population (N), and K is the carrying capacity of its local environmental setting. Typically, r-selected species exploit empty niches, and produce many offspring, each of whom has a relatively low probability of surviving to adulthood. In contrast, K-selected species are strong competitors in crowded niches, and invest more heavily in much fewer offspring, each with a relatively high probability of surviving to adulthood.[13]

Competitive exclusion principle

Competitive-20Exclusion-20Principle
1: a smaller (yellow) species of bird forages across whole tree.
2: a larger (red) species competes for resources.
3: red dominates in middle for the more abundant resources. Yellow adapts to new niche, avoiding competition.

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.[14][15]

Character displacement

Geospiza fortis
Medium ground finch (Geospiza fortis) on Santa Cruz Island in the Galapagos

Competition can cause species to evolve differences in traits. This occurs because the individuals of a species with traits similar to competing species always experience strong interspecific competition. These individuals have less reproduction and survival than individuals with traits that differ from their competitors. Consequently, they will not contribute many offspring to future generations. For example, Darwin's finches can be found alone or together on the Galapagos Islands. Both species' populations actually have more individuals with intermediate-sized beaks when they live on islands without the other species present. However, when both species are present on the same island, competition is intense between individuals that have intermediate-sized beaks of both species because they all require intermediate sized seeds. Consequently, individuals with small and large beaks have greater survival and reproduction on these islands than individuals with intermediate-sized beaks. Different finch species can coexist if they have traits—for instance, beak size—that allow them to specialize on particular resources. When Geospiza fortis and Geospiza fuliginosa are present on the same island, G. fuliginosa tends to evolve a small beak and G. fortis a large beak. The observation that competing species' traits are more different when they live in the same area than when competing species live in different areas is called character displacement. For the two finch species, beak size was displaced: Beaks became smaller in one species and larger in the other species. Studies of character displacement are important because they provide evidence that competition is important in determining ecological and evolutionary patterns in nature.[16]

See also

References

  1. ^ Begon, M.; Harper, J. L.; Townsend, C. R. (1996) Ecology: Individuals, populations and communities Blackwell Science.
  2. ^ a b c Sahney, S.; Benton, M.J.; Ferry, P.A. (2010). "Links between global taxonomic diversity, ecological diversity and the expansion of vertebrates on land". Biology Letters. 6 (4): 544–547. doi:10.1098/rsbl.2009.1024. PMC 2936204. PMID 20106856. Archived from the original on 2015-11-06. Retrieved 2010-09-30.
  3. ^ Jardine, P.E.; Janis, C.M.; Sahney, S.; Benton, M.J. (2012), "Grit not grass: Concordant patterns of early origin of hypsodonty in Great Plains ungulates Glires", Palaeogeography, Palaeoclimatology, Palaeoecology, 365-366: 1–10, doi:10.1016/j.palaeo.2012.09.001
  4. ^ Barton, Kasey E.; Sanders, Nathan J.; Gordon, Deborah M. (2002). "The Effects of Proximity and Colony Age on Interspecific Interference Competition between the Desert Ants Pogonomyrmex barbatus and Aphaenogaster cockerelli". American Midland Naturalist. 148 (2): 376–382. doi:10.1674/0003-0031(2002)148[0376:TEOPAC]2.0.CO;2.
  5. ^ Tilman, D. (1982) Resource competition and community structure. Princeton university press.
  6. ^ Holt, Robert D. (1977). "Predation, apparent competition, and the structure of prey communities". Theoretical Population Biology. 12 (2): 197–229. doi:10.1016/0040-5809(77)90042-9. PMID 929457.
  7. ^ Van Nouhuys, S.; Hanski, I. (2000). "Apparent competition between parasitoids mediated by a shared hyperparasitoid". Ecology Letters. 3 (2): 82–84. doi:10.1046/j.1461-0248.2000.00123.x.
  8. ^ Townsend, Colin R.; Begon, Michael (2008). Essentials of Ecology. pp. 103–105. ISBN 978-1-4051-5658-5.
  9. ^ .Fedriani, J. M., T. K. Fuller, R. M. Sauvajot and E. C. York. 2000. Competition and intraguild predation among three sympatric carnivores. Oecologia, 125:258-270.
  10. ^ Gause, G.F. (1934). The struggle for existence. Baltimore, MD: Williams & Wilkins.
  11. ^ MacArthur, R. and Wilson, E. O. (1967). The Theory of Island Biogeography, Princeton University Press (2001 reprint), ISBN 0-691-08836-5.
  12. ^ Pianka, E. R. (1970). On r and K selection. American Naturalist '104' , 592-597.
  13. ^ a b Verhulst, P. F. (1838). Notice sur la loi que la population pursuit dans son accroissement. Corresp. Math. Phys. '10' , 113-121.
  14. ^ Hardin, Garrett (1960). "The competitive exclusion principle" (PDF). Science. 131 (3409): 1292–1297. doi:10.1126/science.131.3409.1292. PMID 14399717.
  15. ^ Pocheville, Arnaud (2015). "The Ecological Niche: History and Recent Controversies". In Heams, Thomas; Huneman, Philippe; Lecointre, Guillaume; et al. (eds.). Handbook of Evolutionary Thinking in the Sciences. Dordrecht: Springer. pp. 547–586. ISBN 978-94-017-9014-7.
  16. ^ Brown, W. L., and E. O. Wilson. 1956. "Character displacement". Systematic Zoology 5:49–65.

External links

Agonistic behaviour

Agonistic behaviour is any social behaviour related to fighting. The term has broader meaning than aggressive behaviour because it includes threats, displays, retreats, placation, and conciliation. The term "agonistic behaviour" was first implemented by J.P Scott and Emil Fredericson in 1951 in their paper "The Causes of Fighting in Mice and Rats" in Physiological Zoology. Agonistic behaviour is seen in many animal species because resources including food, shelter, and mates are often limited.

Some forms of agonistic behaviour are between contestants who are competing for access to the same resources, such as food or mates. Other times, it involves tests of strength or threat display that make animals look large and more physically fit, a display that may allow it to gain the resource before an actual battle takes place. Although agonistic behaviour varies among species, agonistic interaction consists of three kinds of behaviours: threat, aggression, and submission. These three behaviours are functionally and physiologically interrelated with aggressive behaviour yet fall outside the narrow definition of aggressive behaviour. While any one of these divisions of behaviours may be seen alone in an interaction between two animals, they normally occur in sequence from start to end. Depending on the availability and importance of a resource, behaviours can range from a fight to the death or a much safer ritualistic behaviour, though ritualistic or display behaviours are the most common form of agonistic behaviours.

Biological dispersal

Biological dispersal refers to both the movement of individuals (animals, plants, fungi, bacteria, etc.) from their birth site to their breeding site ('natal dispersal'), as well as the movement from one breeding site to another ('breeding dispersal').

Dispersal is also used to describe the movement of propagules such as seeds and spores.

Technically, dispersal is defined as any movement that has the potential to lead to gene flow.

The act of dispersal involves three phases: departure, transfer, settlement and there are different fitness costs and benefits associated with each of these phases.

Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population genetics, and species distribution. Understanding dispersal and the consequences both for evolutionary strategies at a species level, and for processes at an ecosystem level, requires understanding on the type of dispersal, the dispersal range of a given species, and the dispersal mechanisms involved.

Biological dispersal may be contrasted with geodispersal, which is the mixing of previously isolated populations (or whole biotas) following the erosion of geographic barriers to dispersal or gene flow (Lieberman, 2005; Albert and Reis, 2011).

Dispersal can be distinguished from animal migration (typically round-trip seasonal movement), although within the population genetics literature, the terms 'migration' and 'dispersal' are often used interchangeably.

Cascade effect (ecology)

An ecological cascade effect is a series of secondary extinctions that is triggered by the primary extinction of a key species in an ecosystem. Secondary extinctions are likely to occur when the threatened species are: dependent on a few specific food sources, mutualistic (dependent on the key species in some way), or forced to coexist with an invasive species that is introduced to the ecosystem. Species introductions to a foreign ecosystem can often devastate entire communities, and even entire ecosystems. These exotic species monopolize the ecosystem's resources, and since they have no natural predators to decrease their growth, they are able to increase indefinitely. Olsen et al. showed that exotic species have caused lake and estuary ecosystems to go through cascade effects due to loss of algae, crayfish, mollusks, fish, amphibians, and birds. However, the principal cause of cascade effects is the loss of top predators as the key species. As a result of this loss, a dramatic increase (ecological release) of prey species occurs. The prey is then able to overexploit its own food resources, until the population numbers decrease in abundance, which can lead to extinction. When the prey's food resources disappear, they starve and may go extinct as well. If the prey species is herbivorous, then their initial release and exploitation of the plants may result in a loss of plant biodiversity in the area. If other organisms in the ecosystem also depend upon these plants as food resources, then these species may go extinct as well. An example of the cascade effect caused by the loss of a top predator is apparent in tropical forests. When hunters cause local extinctions of top predators, the predators' prey's population numbers increase, causing an overexploitation of a food resource and a cascade effect of species loss. Recent studies have been performed on approaches to mitigate extinction cascades in food-web networks.

Competition (disambiguation)

Competition is any rivalry between two or more parties.

Competition may also refer to:

Competition (companies), competition between multiple companies

Competition (biology), interaction between living things in which the fitness of one is lowered by the presence of another

Competition (economics), two or more businesses competing to provide goods or services to another party

Competition (1915 film), a short film directed by B. Reeves Eason

"Competition" (The Spectacular Spider-Man), an episode of the animated television series The Spectacular Spider-Man

Competition, Missouri, United States, a town in south-central Missouri, about 50 miles northeast of Springfield

Chatham, Virginia, formerly named Competition, a town in Pittsylvania County, Virginia, United States

Competitor magazine, published by Competitor Group

Competitors, a 2008 science fiction novel by Sergey Lukyanenko

Dominance (ethology)

Dominance in ethology is an "individual's preferential access to resources over another".Dominance in the context of biology and anthropology is the state of having high social status relative to one or more other individuals, who react submissively to dominant individuals. This enables the dominant individual to obtain access to resources such as food or potential mates at the expense of the submissive individual, without active aggression. The absence or reduction of aggression means unnecessary energy expenditure and the risk of injury are reduced for both.

Dominance may be a purely dyadic relationship, i.e. individual A is dominant over individual B, but this has no implications for whether either of these is dominant over a third individual C. Alternatively, dominance may be hierarchical, with a transitive relationship, so that if A dominates B and B dominates C, A always dominates C. This is called a linear dominance hierarchy.

Some animal societies have despots, i.e. a single dominant individual with little or no hierarchical structure amongst the rest of the group. Horses use coalitions so that affiliated pairs in a herd have an accumulative dominance to displace a third horse that normally out-ranks both of them on an individual basis.

The opposite of dominance is submissiveness.

Intraspecific competition

Intraspecific competition is an interaction in population ecology, whereby members of the same species compete for limited resources. This leads to a reduction in fitness for both individuals.

By contrast, interspecific competition occurs when members of different species compete for a shared resource. Members of the same species have very similar resources requirements whereas different species have a smaller contested resource overlap, resulting in intraspecific competition generally being a stronger force than interspecific competition.Individuals can compete for food, water, space, light, mates or any other resource which is required for survival or reproduction. The resource must be limited for competition to occur; if every member of the species can obtain a sufficient amount of every resource then individuals do not compete and the population grows exponentially. Exponential growth is very rare in nature because resources are finite and so not every individual in a population can survive, leading to intraspecific competition for the scarce resources.

When resources are limited, an increase in population size reduces the quantity of resources available for each individual, reducing the per capita fitness in the population. As a result, the growth rate of a population slows as intraspecific competition becomes more intense, making it a negatively density dependent process. The falling population growth rate as population increases can be modelled effectively with the logistic growth model. The rate of change of population density eventually falls to zero, the point ecologists have termed the carrying capacity (K). The carrying capacity of a population is the maximum number of individuals that can live in a population stably; numbers larger than this will suffer a negative population growth until eventually reaching the carrying capacity, whereas populations smaller than the carrying capacity will grow until they reach it.

Intraspecific competition doesn't just involve direct interactions between members of the same species (such as male deer locking horns when competing for mates) but can also include indirect interactions where an individual depletes a shared resource (such as a grizzly bear catching a salmon that can then no longer be eaten by bears at different points along a river).

The way in which resources are partitioned by organisms also varies and can be split into scramble and contest competition. Scramble competition involves a relatively even distribution of resources among a population as all individuals exploit a common resource pool. In contrast, contest competition is the uneven distribution of resources and occurs when hierarchies in a population influence the amount of resource each individual receives. Organisms in the most prized territories or at the top of the hierarchies obtain a sufficient quantity of the resources, whereas individuals without a territory don’t obtain any of the resource.

Limiting factor

A limiting factor is a variable of a system that, if subject to a small change, causes a non-negligible change in an output or other measure of the system. A factor not limiting over a certain domain of starting conditions may yet be limiting over another domain of starting conditions, including that of the factor.

Metapopulation

A metapopulation consists of a group of spatially separated populations of the same species which interact at some level. The term metapopulation was coined by Richard Levins in 1969 to describe a model of population dynamics of insect pests in agricultural fields, but the idea has been most broadly applied to species in naturally or artificially fragmented habitats. In Levins' own words, it consists of "a population of populations".A metapopulation is generally considered to consist of several distinct populations together with areas of suitable habitat which are currently unoccupied. In classical metapopulation theory, each population cycles in relative independence of the other populations and eventually goes extinct as a consequence of demographic stochasticity (fluctuations in population size due to random demographic events); the smaller the population, the more chances of inbreeding depression and prone to extinction.

Although individual populations have finite life-spans, the metapopulation as a whole is often stable because immigrants from one population (which may, for example, be experiencing a population boom) are likely to re-colonize habitat which has been left open by the extinction of another population. They may also emigrate to a small population and rescue that population from extinction (called the rescue effect). Such a rescue effect may occur because declining populations leave niche opportunities open to the "rescuers".

The development of metapopulation theory, in conjunction with the development of source-sink dynamics, emphasised the importance of connectivity between seemingly isolated populations. Although no single population may be able to guarantee the long-term survival of a given species, the combined effect of many populations may be able to do this.

Metapopulation theory was first developed for terrestrial ecosystems, and subsequently applied to the marine realm. In fisheries science, the term "sub-population" is equivalent to the metapopulation science term "local population". Most marine examples are provided by relatively sedentary species occupying discrete patches of habitat, with both local recruitment and recruitment from other local populations in the larger metapopulation. Kritzer & Sale have argued against strict application of the metapopulation definitional criteria that extinction risks to local populations must be non-negligible.Finnish biologist Ilkka Hanski of the University of Helsinki was an important contributor to metapopulation theory.

Size-asymmetric competition

Size-asymmetric competition refers to situations in which larger individuals exploit disproportionately greater amounts of resources when competing with smaller individuals. This type of competition is common among plants but also exists among animals. Size-asymmetric competition usually results from large individuals monopolizing the resource by "pre-emption". i.e. exploiting the resource before smaller individuals are able to obtain it. Size-asymmetric competition has major effects on population structure and diversity within ecological communities.

Texas Academy of Mathematics and Science

The Texas Academy of Mathematics and Science (TAMS) is a two-year residential early entrance college program serving approximately 375 high school juniors and seniors at the University of North Texas. Students are admitted from every region of the state through a selective admissions process. TAMS is a member of the National Consortium for Specialized Secondary Schools of Mathematics, Science and Technology.

Victory

The term victory (from Latin victoria) originally applied to warfare, and denotes success achieved in personal combat, after military operations in general or, by extension, in any competition. Success in a military campaign is considered a strategic victory, while the success in a military engagement is a tactical victory.

In terms of human emotion, victory accompanies strong feelings of elation, and in human behaviour often exhibits movements and poses paralleling threat display preceding the combat, which are associated with the excess endorphin built up preceding and during combat.

Victory dances and victory cries similarly parallel war dances and war cries performed before the outbreak of physical violence.

Examples of victory behaviour reported in Roman antiquity, where the term victoria originated, include: the victory songs of the Batavi mercenaries serving under Gaius Julius Civilis after the victory over Quintus Petillius Cerialis in the Batavian rebellion of 69 AD (according to Tacitus); and also the "abominable song" to Wodan, sung by the Lombards at their victory celebration in 579. The sacrificial animal was a goat, around whose head the Langobards danced in a circle while singing their victory hymn.

The Roman Republic and Empire celebrated victories with triumph ceremonies and with monuments such as victory columns (e.g. Trajan's Column) and arches. A trophy is a token of victory taken from the defeated party, such as the enemy's weapons (spolia), or body parts (as in the case of head hunters).

Mythology often deifies victory, as in the cases of the Greek Nike or the Roman Victoria. The victorious agent is a hero, often portrayed as engaging in hand-to-hand combat with a monster (as Saint George slaying the dragon, Indra slaying Ahi, Thor slaying the Midgard Serpent etc.). Sol Invictus ("the Invincible Sun") of Roman mythology became an epithet of Christ in Christianity. Paul of Tarsus presents the resurrection of Christ as a victory over Death and Sin (1 Corinthians 15:55).

The Latinate English-language word victory (from the 14th century) replaced the Old English equivalent term sige (cognate with Gothic sigis, Old High German sigu and Sieg in modern German), a frequent element in Germanic names (as in Sigibert, Sigurd etc.), cognate to Celtic sego- and Sanskrit sahas.

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