Competition in Ecosystems

Competition describes an interaction between individuals within a community that both or all need a limited resource. As a result of the interaction, involved individuals suffer, experiencing reduced growth, survivorship or reproductive capability. Competition is frequently described as intraspecific or interspecific and is also potentially categorized as exploitation or interference.

When competition for resources occurs between organisms of different species, it is called interspecific competition. The more similar the resource needs of two species, the greater the competition between them. In order that both species might survive, interspecific competition often leads to one of two things: changes in the distribution of those species or the development of more distinct niches with less overlap. For example, one species of bird might primarily eat flying insects and berries from a certain tree species, while another species of bird sharing the same area might have evolved to consume mostly grass seeds and insects on the ground. These differences would limit the overlap of their niches.

When individuals are of the same species, they have very similar resource requirements and competition can be very fierce, especially if resources are limited. Competition between individuals of the same species is called intraspecific competition. Intraspecies competition can involve competing for food or water, and it can also take the form of fighting for a mate or defending a territory.

With exploitation or scramble competition, organisms use up resources directly. By using limited resources, an individual makes those resources even less available to other individuals. Two animals grazing in the same field might never directly come into contact with each other, but if they are eating the same plants, they are competing. Plants growing in a site might compete for water and nutrients without direct aggression. Preemptive competition occurs when an individual negatively affects another by using space, and overgrowth competition involves one species growing over another, reducing the amount of light reaching the species below.

Interference competition describes direct, aggressive interaction between two animals. A resource might not necessarily be very limited for interference competition to occur. An individual might be territorial, fighting or defending a space, or it might fight for a specific resource such as food, water, space or a mate. Although plants are generally considered passive, some can practice interference competition. For example, certain plants practice allelopathy, releasing toxins from roots or other parts to keep other plants from growing nearby.