Interspecific competition
Encyclopedia
Interspecific competition, in ecology
, is a form of competition
in which individuals of different species
compete for the same resource in an ecosystem (e.g. food or living space). The other form of competition is intraspecific competition
, which involves organisms of the same species.
If a tree species in a dense forest
grows taller than surrounding tree species, it is able to absorb more of the incoming sunlight. However, less sunlight is then available for the trees that are shaded by the taller tree, thus interspecific competition. Cheetah
s and lion
s can also be in interspecific competition, since both species feed on the same prey, and can be negatively impacted by the presence of the other because they will have less food.
Competition is only one of many interacting biotic
and abiotic factors that affect community structure. Moreover, competition is not always a straightforward, direct, interaction. 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 population
s, communities
and the evolution of interacting species. On an individual organism level, competition can occur as interference or exploitative competition.
Direct 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, between amphibians, reptiles and mammals.
es or weasel
s. A violent interaction between two of these species would likely result in victory for the larger predator. The stability of some mammalian carnivore populations is maintained through these conflicts over prey resources.
An example of interference competition in which only one party is negatively affected is allelopathy
, in which plants of one species release toxic chemicals that inhibit the germination and survival of other potential competitors. Some animals utilize a similar strategy. For example, algae in the feces of the common frog, Rana temporaria, inhibit the tadpoles of the competing natterjack toad, Bufo calamita.
species competing over the sap in plant phloem
. Each aphid species that feeds on host plant sap uses some of the resource, leaving less for competing species. In one study, Fordinae geoica was observed to out-compete F. formicaria to the extent that the latter species exhibited a reduction in survival by 84%.
This type of competition can also be observed in forests where large trees dominate the canopy
and thus allow little light to reach smaller competitors living below. These interactions have important implications for the population dynamics
and distribution of both species.
affect shared natural enemies in a higher trophic level
. If two species share a common predator, for example, apparent competition can exist between the two prey items as they attempt to make themselves less available for consumption.
. The changes of these species over time can also change communities as other species must adapt.
A well documented example of competitive exclusion was observed to occur between Dolly Varden charr (Salvelinus malma) and white spotted char (S. leucomaenis
) in Japan. Both of these species were morphologically similar but the former species was found primarily at higher elevations than the latter. Although there was a zone of overlap, each species excluded the other from its dominant region by becoming better adapted to its habitat over time. In some such cases, each species gets displaced into an exclusive segment of the original habitat. Because each species suffers from competition, natural selection favors the avoidance of competition in such a way.
There have been several well documented cases in birds where species that are very similar change their habitat use where they overlap. For example, they may consume different food resources or use different nesting habitat or materials. On the Galapagos Islands
, finch
species have been observed to change dietary specializations in just a few generations in order to utilize limited resources and minimize competition.
In some cases, third party species interfere to the detriment or benefit of the competing species. In a laboratory study, coexistence between two competing bacterial species was mediated by phage parasites. This type of interaction actually helped to maintain diversity in bacterial communities and has far reaching implications in medical research as well as ecology. Similar effects have been documented for many communities as a result of the action of a keystone predator that preys on a competitively superior species.
in artificial rock pools, local extinction rates were significantly higher in areas of interspecific competition. In these cases, therefore, the negative effects are not only at the population level but also species richness of communities.
to the United States, Purple-loosestrife. This plant when introduced to wetland communities often outcompetes much of the native flora and decreases species richness, food and shelter to many other species at higher trophic levels. In this way, one species can influence the populations of many other species as well as through a myriad of other interactions. Because of the complicated web of interactions that make up every ecosystem and habitat, the results of interspecific competition are complex and site-specific.
In these formulae, N is the population size, t is time, K is the carrying capacity, r is the intrinsic rate of increase and α is the competition coefficient. The results show the effect that the other species has on the species being calculated. The results can be graphed to show a trend and possible prediction for the future of the species. One problem with this model is that certain assumptions must be made for the calculation to work. These include the lack of migration and constancy of the carrying capacities and competition coefficients of both species. The complex nature of ecology determines that these assumptions are rarely true in the field but the model provides a basis for improved understanding of these important concepts.
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...
, is a form of competition
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...
in which individuals of different 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...
compete for the same resource in an ecosystem (e.g. food or living space). The other form of competition is intraspecific competition
Intraspecific competition
Intraspecific competition is a particular form of competition in which members of the same species vie for the same resource in an ecosystem...
, which involves organisms of the same species.
If a tree species in a dense forest
Forest
A forest, also referred to as a wood or the woods, is an area with a high density of trees. As with cities, depending where you are in the world, what is considered a forest may vary significantly in size and have various classification according to how and what of the forest is composed...
grows taller than surrounding tree species, it is able to absorb more of the incoming sunlight. However, less sunlight is then available for the trees that are shaded by the taller tree, thus interspecific competition. Cheetah
Cheetah
The cheetah is a large-sized feline inhabiting most of Africa and parts of the Middle East. The cheetah is the only extant member of the genus Acinonyx, most notable for modifications in the species' paws...
s and lion
Lion
The lion is one of the four big cats in the genus Panthera, and a member of the family Felidae. With some males exceeding 250 kg in weight, it is the second-largest living cat after the tiger...
s can also be in interspecific competition, since both species feed on the same prey, and can be negatively impacted by the presence of the other because they will have less food.
Competition is only one of many interacting biotic
Biotic component
Biotic components are the living things that shape an ecosystem. A biotic factor is any living component that affects another organism, including animals that consume the organism in question, and the living food that the organism consumes. Each biotic factor needs energy to do work and food for...
and abiotic factors that affect community structure. Moreover, competition is not always a straightforward, direct, interaction. 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
Fecundity
Fecundity, derived from the word fecund, generally refers to the ability to reproduce. In demography, fecundity is the potential reproductive capacity of an individual or population. In biology, the definition is more equivalent to fertility, or the actual reproductive rate of an organism or...
, growth, or survival may result in at least one species. Interspecific competition has the potential to alter population
Population
A population is all the organisms that both belong to the same group or species and live in the same geographical area. The area that is used to define a sexual population is such that inter-breeding is possible between any pair within the area and more probable than cross-breeding with individuals...
s, communities
Community
The term community has two distinct meanings:*a group of interacting people, possibly living in close proximity, and often refers to a group that shares some common values, and is attributed with social cohesion within a shared geographical location, generally in social units larger than a household...
and the evolution of interacting species. On an individual organism level, competition can occur as interference or exploitative competition.
Direct 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, between amphibians, reptiles and mammals.
Interference competition
Interference competition involves direct interactions between individuals such as fighting over limited resources. This form of competition is typically, though not always, detrimental to both individuals and both species involved. These interactions are usually asymmetric with one species having an advantage over the other, resulting in greater loss by one competitor. For example, large predators like canids have a significant size advantage over smaller predators such as foxFox
Fox is a common name for many species of omnivorous mammals belonging to the Canidae family. Foxes are small to medium-sized canids , characterized by possessing a long narrow snout, and a bushy tail .Members of about 37 species are referred to as foxes, of which only 12 species actually belong to...
es or weasel
Weasel
Weasels are mammals forming the genus Mustela of the Mustelidae family. They are small, active predators, long and slender with short legs....
s. A violent interaction between two of these species would likely result in victory for the larger predator. The stability of some mammalian carnivore populations is maintained through these conflicts over prey resources.
An example of interference competition in which only one party is negatively affected is allelopathy
Allelopathy
Allelopathy is a biological phenomenon by which an organism produces one or more biochemicals that influence the growth, survival, and reproduction of other organisms. These biochemicals are known as allelochemicals and can have beneficial or detrimental effects on the target organisms...
, in which plants of one species release toxic chemicals that inhibit the germination and survival of other potential competitors. Some animals utilize a similar strategy. For example, algae in the feces of the common frog, Rana temporaria, inhibit the tadpoles of the competing natterjack toad, Bufo calamita.
Exploitative competition
Exploitative competition is a form of competition in which one species either reduces or more efficiently uses a resource and therefore depletes the availability of the resource for the other species. A good example of exploitative competition is found in aphidAphid
Aphids, also known as plant lice and in Britain and the Commonwealth as greenflies, blackflies or whiteflies, are small sap sucking insects, and members of the superfamily Aphidoidea. Aphids are among the most destructive insect pests on cultivated plants in temperate regions...
species competing over the sap in plant phloem
Phloem
In vascular plants, phloem is the living tissue that carries organic nutrients , in particular, glucose, a sugar, to all parts of the plant where needed. In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Greek word "bark"...
. Each aphid species that feeds on host plant sap uses some of the resource, leaving less for competing species. In one study, Fordinae geoica was observed to out-compete F. formicaria to the extent that the latter species exhibited a reduction in survival by 84%.
This type of competition can also be observed in forests where large trees dominate the canopy
Canopy (forest)
In biology, the canopy is the aboveground portion of a plant community or crop, formed by plant crowns.For forests, canopy also refers to the upper layer or habitat zone, formed by mature tree crowns and including other biological organisms .Sometimes the term canopy is used to refer to the extent...
and thus allow little light to reach smaller competitors living below. These interactions have important implications for the population dynamics
Population dynamics
Population dynamics is the branch of life sciences that studies short-term and long-term changes in the size and age composition of populations, and the biological and environmental processes influencing those changes...
and distribution of both species.
Apparent competition
Apparent competition occurs when two or more species in a habitatHabitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
affect shared natural enemies in a higher trophic level
Trophic level
The trophic level of an organism is the position it occupies in a food chain. The word trophic derives from the Greek τροφή referring to food or feeding. A food chain represents a succession of organisms that eat another organism and are, in turn, eaten themselves. The number of steps an organism...
. If two species share a common predator, for example, apparent competition can exist between the two prey items as they attempt to make themselves less available for consumption.
Scramble competition
Scramble competition occurs when a resource is inadequate for the needs of all. Each competitor obtains an equal amount, but never the amount it needs, leading to a depression in population growth.Consequences
Many studies, including those cited previously, have shown major impacts on both individuals and populations from interspecific competition. Documentation of these impacts has been found in species from every major branch of organism. The effects of interspecific competition can also reach communities and can even influence the evolution of species as they adapt to avoid competition. This evolution may result in the exclusion of a species in the habitat, niche separation, and local extinctionLocal extinction
Local extinction, also known as extirpation, is the condition of a species which ceases to exist in the chosen geographic area of study, though it still exists elsewhere...
. The changes of these species over time can also change communities as other species must adapt.
Competitive exclusion
The competitive exclusion principle states that two species that use the same resource in the same way in the same space and time cannot coexist and must diverge from each other over time in order for the two species to coexist. One species will often exhibit an advantage in resource use. This superior competitor will out-compete the other with more efficient use of the limiting resource. As a result, the inferior competitor will suffer a decline in population over time. It will be excluded from the area and replaced by the superior competitor.A well documented example of competitive exclusion was observed to occur between Dolly Varden charr (Salvelinus malma) and white spotted char (S. leucomaenis
Salvelinus leucomaenis
Salvelinus leucomaenis is a Japanese trout in the genus of Salvelinus called Iwana in Japanese and whitespotted char in English. Iwana is widely fished in Japan....
) in Japan. Both of these species were morphologically similar but the former species was found primarily at higher elevations than the latter. Although there was a zone of overlap, each species excluded the other from its dominant region by becoming better adapted to its habitat over time. In some such cases, each species gets displaced into an exclusive segment of the original habitat. Because each species suffers from competition, natural selection favors the avoidance of competition in such a way.
Niche differentiation
Niche differentiation is a process by which competitive exclusion leads to differences in resource use. In the previous example, niche differentiation resulted in spatial displacement. In other cases it may result in other changes that also avoid competition. If competition avoidance is achievable, each species will occupy an edge of the niche and will become more specialized to that area thus minimizing competition. This phenomenon often results in the separation of species over time as they become more specialized to their edge of the niche, called niche differentiation. The species do not have to be in separate habitats however to avoid niche overlap. Some species adapt regionally to utilizing different resources than they ordinarily would in order to avoid competition.There have been several well documented cases in birds where species that are very similar change their habitat use where they overlap. For example, they may consume different food resources or use different nesting habitat or materials. On the Galapagos Islands
Galápagos Islands
The Galápagos Islands are an archipelago of volcanic islands distributed around the equator in the Pacific Ocean, west of continental Ecuador, of which they are a part.The Galápagos Islands and its surrounding waters form an Ecuadorian province, a national park, and a...
, finch
Finch
The true finches are passerine birds in the family Fringillidae. They are predominantly seed-eating songbirds. Most are native to the Northern Hemisphere, but one subfamily is endemic to the Neotropics, one to the Hawaiian Islands, and one subfamily – monotypic at genus level – is found...
species have been observed to change dietary specializations in just a few generations in order to utilize limited resources and minimize competition.
In some cases, third party species interfere to the detriment or benefit of the competing species. In a laboratory study, coexistence between two competing bacterial species was mediated by phage parasites. This type of interaction actually helped to maintain diversity in bacterial communities and has far reaching implications in medical research as well as ecology. Similar effects have been documented for many communities as a result of the action of a keystone predator that preys on a competitively superior species.
Local extinction
Although local extinction of one or more competitors has been less documented than niche separation or competitive exclusion, it does occur. In an experiment involving zooplanktonZooplankton
Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...
in artificial rock pools, local extinction rates were significantly higher in areas of interspecific competition. In these cases, therefore, the negative effects are not only at the population level but also species richness of communities.
Impacts on communities
As mentioned previously, interspecific competition has great impact on community composition and structure. Niche separation of species, local extinction and competitive exclusion are only some of the possible effects. In addition to these, interspecific competition can be the source of a cascade of effects that build on each other. An example of such an effect is the introduction of an invasive speciesInvasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
to the United States, Purple-loosestrife. This plant when introduced to wetland communities often outcompetes much of the native flora and decreases species richness, food and shelter to many other species at higher trophic levels. In this way, one species can influence the populations of many other species as well as through a myriad of other interactions. Because of the complicated web of interactions that make up every ecosystem and habitat, the results of interspecific competition are complex and site-specific.
Lotka-Volterra model
The impacts of interspecific competition on populations have been formalized in a mathematical model called the Competitive Lotka–Volterra equations, which creates a theoretical prediction of interactions. It combines the effects of each species on the other. These effects are calculated separately for the first and second population respectively:In these formulae, N is the population size, t is time, K is the carrying capacity, r is the intrinsic rate of increase and α is the competition coefficient. The results show the effect that the other species has on the species being calculated. The results can be graphed to show a trend and possible prediction for the future of the species. One problem with this model is that certain assumptions must be made for the calculation to work. These include the lack of migration and constancy of the carrying capacities and competition coefficients of both species. The complex nature of ecology determines that these assumptions are rarely true in the field but the model provides a basis for improved understanding of these important concepts.
Further reading
- Begon, M., C.R. Townsend and J.L. Harper. 2006. Ecology: From Individuals to EcosystemsEcology: From Individuals to EcosystemsEcology: From Individuals to Ecosystems is a 2006 higher education textbook on general ecology written by Michael Begon, Colin R. Townsend and John L. Harper. Published by Blackwell Publishing, it is now in its fourth edition. The first three editions were published by Blackwell Science under the...
. Blackwell Publishing, Malden, MA. - Giller, P. S. 1984. Community Structure and the Niche. Chapman & Hall, London.
- Holekamp, K.E. 2006. Interspecific competition and anti-predator behavior. National Science Foundation. http://www.nsf.gov/
- Inbar, M., A. Eshel and D. Wool. 1995. Interspecific competition among phloem-feeding insects mediated by induced host-plant sinks. Ecology. 76.5: 1506-1515.
- Solomon, E. P., Berg, L. R., & Martin, D. W. (2002). Biology, sixth edition. (N. Rose, Ed.). Stamford, CT: Thomson Learning
- Taniguchi Y. and S. Nakano 2000. Condition-Specific Competition: Implications for the Altitudinal Distribution of Stream Fishes. Ecology, 81. 7: 2027-2039
- Weiner, J. 1994. The Beak of the Finch. Cambridge University Press, New York.
External links
- Competition for Territory: The Levins Model for Two Species Wolfram Demonstrations Project — requires CDF player (free)