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Ecosystems contain many organisms, but they have a limited amount of the resources needed for survival and reproduction.

Competition is an interaction between individuals that happens when resources like food, water, shelter, and mates are limited.

Competition can be categorized by the identity of the organisms involved—either intraspecific, within the same species, or interspecific, between different species. It can also be categorized as direct or indirect competition based on whether the organisms interact directly or indirectly.

Competition is more likely to happen when there is an overlap between ecological niches. Organisms with similar niches need many of the same resources, while those with very different niches may not compete at all.

Interspecific competition happens when individuals of different species, such as coyotes and wolves, compete for a common resource, such as prey or territory. In territories where gray wolf and coyote populations overlap, competition between the two species may limit the number of coyotes within those territories.

One possible consequence of interspecific competition is competitive exclusion. If two species compete for the same limiting resource over time, one species may outcompete the other.

The weaker competitor may need to adjust its behavior to use other resources within its niche. For example, coyotes may move to a new territory away from gray wolves or, over many generations, evolve to occupy a different niche. Otherwise, they may die out.

Intraspecific competition, on the other hand, happens between individuals of the same species. This type of competition is common because individuals occupy the same niche in the ecosystem and require the same resources.

Direct competition happens when individuals of the same or different species interact directly. For example, two male antelopes fight for the opportunity to mate with a female. In this mechanism, one individual prevents others from using a resource, in this case, a mate. Marking territory is another behavior that helps control access to a resource.

Indirect competition happens when individuals use up a shared resource, leaving less available for others. For example, elephants and other animals use a common water source, such as a pond. Elephants may drink more water, leaving less available for other animals.