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 (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 bioticand abiotic factors that affect communitystructure. 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 plays a very relevant role 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]
Types of competition
By mechanism
The following terms describe mechanisms by which competition occurs, which can generally be divided into direct and indirect. These mechanisms apply equally to intraspecific and interspecific competition.
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.
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. Also known as exploitative competition.
Apparent competition
Occurs indirectly between two species which are both preyed upon by the same predator. 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.[4]
By species
Intraspecific competition
Main article: Intraspecific competition
Intraspecific competition occurs when members of the same species compete for the same resources in an ecosystem. The organism that obtains less resources, will usually perform less well than if it lives alone, Although in this situation it may actually be more useful to think in terms of resource availability than competition.
Interspecific competition
Main article: Interspecific competition
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, and this phenomenon is 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).[5]
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 reptiles and mammals. 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]