A male Blackbird (
Turdus merula) singing.
Bird song
often functions as a
signal in territory defense.
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). This can be contrasted with Interspecific competition, in
which different species compete.
For example, two trees of the same species growing close together will compete for light, water
and nutrients in the soil. Getting less resources, they will perform poorer than if they grew by themselves (for example lowered
growth rates and fewer seed output). Trees have therefore adapted to grow taller or develop larger root
systems through natural selection.
Grasshoppers provide an animal 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 (known
as density dependent inhibition) 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.
Further reading
Solomon, E. P., Berg, L. R., & Martin, D. W. (2002). Biology, sixth edition. (N. Rose, Ed.). Stamford, CT: Thomson
Learning.
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