Competition in an ecological sense can be defined as the use of any resource by one individual causing a reduction in the availability of that resource. In ecology, interactions between organisms are often classified in terms of the effect that these interactions have on fitness. Competition is an interaction between organisms in which the influence is negative for both players involved.
One method of classifying competition is by species. Thus, competition can be either intraspecific or interspecific. Intraspecific competition occurs between individuals of the same species. For example, individuals of the same species may have to compete with each other for mates, especially in monogamous populations in which mates are limited. Interspecific competition is between individuals of different species and can potentially lead to population depression and in the worst case, extinction.
Additionally, competition can be categorized by mechanism:
- Exploitative competition (also known as indirect competition). Individual A has a negative influence on individual B and vice versa.
- Interference competition (also known as direct competition). Individuals harm each other by taking up resources first.
Exploitative competition is the most common and occurs when a resource within an ecosystem is limited. Therefore, individuals must race to acquire the resource first. For example, exploitative competition is frequent in plant communities in which different species out-compete each other for resources such as light or soil nutrients like nitrogen.
Interference competition is when aggressive fighting/defence interactions take place between individuals. For example, black walnuts engage in interference competition with other plants in close proximity with them by secreting chemicals to inhibit the germination of these plants. This minimizes the competition between black walnuts and other plants for spreading their seeds.
This discussion only covers the basics of competition. It is a rather expansive theme in ecology which applies to a range of topics such as coexistence and evolution. Furthermore, competition is a process which is even modelled by equations such as the Lotka Volterra competition equations.
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