Interspecific competition
Interspecific competition, in ecology, is a form of competition in which individuals of different species compete for the same resources in an ecosystem (e.g. food or living space). This can be contrasted with mutualism, a type of symbiosis. Competition between members of the same species is called intraspecific competition.
If a tree species in a dense
Competition is only one of many interacting
Types
All of the types described here can also apply to intraspecific competition, that is, competition among individuals within a species. Also, any specific example of interspecific competition can be described in terms of both a mechanism (e.g., resource or interference) and an outcome (symmetric or asymmetric).
Based on mechanism
Exploitative competition, also referred to as resource competition, is a form of competition in which one species consumes and either reduces or more efficiently uses a shared limiting resource and therefore depletes the availability of the resource for the other species.[1] Thus, it is an indirect interaction because the competing species interact via a shared resource.
Interference competition is a form of competition in which individuals of one species interacts directly with individuals of another species via antagonistic displays or more aggressive behavior.
In a review and synthesis of experimental evidence regarding interspecific competition, Schoener[2] described six specific types of mechanisms by which competition occurs, including consumptive, preemptive, overgrowth, chemical, territorial, and encounter. Consumption competition is always resource competition, but the others cannot always be regarded as exclusively exploitative or interference.
Separating the effect of resource use from that of interference is not easy. A good example of exploitative competition is found in
This type of competition can also be observed in forests where large trees dominate the
Based on outcome
Scramble and contest competition refer to the relative success of competitors. Scramble competition is said to occur when each competitor is equal suppressed, either through reduction in survival or birth rates. Contest competition is said to occur when one or a few competitors are unaffected by competition, but all others suffer greatly, either through reduction in survival or birth rates. Sometimes these types of competition are referred to as symmetric (scramble) vs. asymmetric (contest) competition. Scramble and contest competition are two ends of a spectrum, of completely equal or completely unequal effects.
Apparent competition
Apparent competition is actually an example of predation that alters the relative abundances of prey on the same
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
Competitive exclusion
The competitive exclusion principle, also called "
A well-documented example of competitive exclusion was observed to occur between Dolly Varden charr (Trout)(
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
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
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 zooplankton in artificial rock pools, local extinction rates were significantly higher in areas of interspecific competition.[10] 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
Competitive 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 and β are the relative competition coefficients.[11] 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.
An equivalent formulation of these models[12] is:
In these formulae, is the effect that an individual of species 1 has on its own population growth rate. Similarly, is the effect that an individual of species 2 has on the population growth rate of species 1. One can also read this as the effect on species 1 of species 2. In comparing this formulation to the one above, we note that , and .
Coexistence between competitors occurs when and . We can translate this as coexistence occurs when the effect of each species on itself is greater the effect of the competitor.
There are other mathematical representations that model species competition, such as using non-polynomial functions.[13]
Interspecific competition in macroevolution
Interspecific competition is a major factor in macroevolution.[14] Darwin assumed that interspecific competition limits the number of species on Earth, as formulated in his wedge metaphor: "Nature may be compared to a surface covered with ten-thousand sharp wedges ... representing different species, all packed closely together and driven in by incessant blows, . . . sometimes a wedge of one form and sometimes another being struck; the one driven deeply in forcing out others; with the jar and shock often transmitted very far to other wedges in many lines of direction." (From Natural Selection - the "big book" from which Darwin abstracted the Origin).[15] The question whether interspecific competition limits global biodiversity is disputed today,[16] but analytical studies of the global Phanerozoic fossil record are in accordance with the existence of global (although not constant) carrying capacities for marine biodiversity.[17][18] Interspecific competition is also the basis for Van Valen's Red Queen hypothesis, and it may underlie the positive correlation between origination and extinction rates that is seen in almost all major taxa.[14]
In the previous examples, the macroevolutionary role of interspecific competition is that of a limiting factor of biodiversity, but interspecific competition also promotes niche differentiation and thus speciation and diversification.[19][20] The impact of interspecific competition may therefore change during phases of diversity build-up, from an initial phase where positive feedback mechanisms dominate to a later phase when niche-peremption limits further increase in the number of species; a possible example for this situation is the re-diversification of marine faunas after the end-Permian mass extinction event.[21]
See also
References
- ^ Tilman, D. (1982). Resource Competition and Community Structure. Princeton, NJ: Princeton University Press.
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- ^ Roesti, M., Groh, J.S., Blain, S.A., Huss, M., Rassias, P. & Bolnick, D.I. et al. (2023) Species divergence under competition and shared predation. Ecology Letters, 26, 111–123. Available from: https://doi.org/10.1111/ele.14138
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- ^ Gotelli, N.J. 2008. A Primer of Ecology, 4th ed. Sinauer Associates, Sunderland, MA, USA.
- ^ Stevens, M. H. H. (2009). A Primer of Ecology with R. (R. Gentleman, Hornik K., & G. Parmigiani, Eds.). Springer.
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Further reading
- Begon, M., C.R. Townsend and J.L. Harper. 2006. Ecology: From Individuals to Ecosystems. Blackwell Publishing, Malden, MA.
- Connell J.H. (1961). "Factors on the distribution of the barnacle Chthamalus stellatus". Ecology. 42 (4): 710–723. JSTOR 1933500.
- 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. https://www.nsf.gov/
- Inbar M., Eshel A., Wool D. (1995). "Interspecific competition among phloem-feeding insects mediated by induced host-plant sinks". Ecology. 76 (5): 1506–1515. S2CID 54686728.)
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: CS1 maint: multiple names: authors list (link - Schoener T.W. (1983). "Field experiments on interspecific competition". American Naturalist. 122 (2): 240. S2CID 85191738.
- Solomon, E. P., Berg, L. R., & Martin, D. W. (2002). Biology, sixth edition. (N. Rose, Ed.). Stamford, CT: Thomson Learning
- Taniguchi, Yoshinori; Nakano, Shigeru (2000). "Condition-Specific Competition: Implications for the Altitudinal Distribution of Stream Fishes". Ecology. 81 (7): 2027–2039. JSTOR 177290.
- 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)