Intraspecific competition

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Intraspecific competition is a particular form of competition in which members of the same species vie for the same resource in an ecosystem (e.g. food, light, nutrients, space).

For example, two trees growing close together will compete for light, water and nutrients in the soil. Therefore, getting less resources, they will usually perform less well than if they grew by themselves. To counter the effect of competition, they may grow taller (to reach the light, especially in forests), or develop a larger root system.

In animals, grasshoppers are an example. By eating grass, individual grasshoppers deprive their fellow conspecifics of food. This is an example of exploitation competition, which means that the grasshoppers do not interact directly with each other, but have a negative effect on others' growth and reproduction by their effect on a resource (in this case, grass). In other cases, intraspecific competition may be a case of interference competition, in which the animals interact directly. This is the case, most notably, in territorial animals: some individuals actively prevent others from exploiting a given resource, usually food or space.

Intraspecific competition is a major factor affecting the carrying capacity of a population (maximum population level supported by the environment). The levelling of population growth at high densities can be seen as an effect of intraspecific competition. Indeed, whereas at low densities organisms do not compete for resources, at higher densities resources become limiting, and the population size can no longer increase. In terms of population growth rate, this produces a sigmoidal curve, which is a familiar sight for ecologists.