28.10:
Competition
Ecosystems are populated by many organisms but harbor a finite amount of the resources that organisms require for survival and reproduction. Competition is an interaction that arises between individuals when the resources they need are limited.
Different types of competition are categorized by the identity of the organisms competing, the same species or different species, or by the way in which the organisms interact, directly or indirectly.
Competition is more likely to occur when there is an overlap between ecological niches, the roles of organisms within their environment. Organisms with similar niches will require more of the same resources, while those with very different niches may have no reason to compete.
Interspecific competition occurs when individuals of different species, such as coyotes and wolves, compete for a common resource, such as prey or territory. In areas where gray wolf and coyote populations overlap, competition between the two species may limit the number of coyotes in the wolf's territory.
One possible consequence of interspecific competition is competitive exclusion. If two species compete for the same limiting resources, the most efficient competitor will dominate over the long term.
The worst competitor would need to adjust its behavior to use other resources within its niche, for example, coyotes could establish a new territory away from the gray wolf, or evolve to occupy a different niche, otherwise, it may die out.
Intraspecific competition, on the other hand, occurs between individuals of the same species. This type of competition is common because the individuals occupy the same niche in the ecosystem, and thus require the exact same resources.
Two male deer fighting for the ability to mate with a female deer is an example of intraspecific competition. This behavior is a type of direct competition, a mechanism by which an individual prevents others from using a resource. Marking the territory is another type of behavior that aims to control access to a resource.
Indirect competition happens when a resource is used up by one individual and is therefore unavailable for the other. When one deer consumes a plant, no other deer are able to use that resource.
28.10:
Competition
When organisms require the same limited resources within an environment, they may have to compete for them. Competition is a net-negative interaction. Even if two competing individuals or populations do not interact directly, the overall fitness of both competitors is lowered as a result of not having full access to the limited resource.
Intraspecific competition, which occurs between individuals of the same species, serves as a natural mechanism for regulating population size. Too much population growth can lead to crowding and diminished resources. Stronger members of the population may outcompete weaker individuals for resources, leading to reduced reproduction or death for the weaker individuals and keeping the population size in check.
Competitive exclusion may occur as a consequence of competition between species, where one is better suited to use a resource and forces out the other, but this is not the only possible outcome when a resource is not abundant. Organisms can also find ways to share limited resources. Competing populations may engage in resource partitioning, dividing the resource in a spatial manner by keeping to non-overlapping territories or using the resource at different times of the day. Alternatively, one population might differentiate its niche so that it no longer has to compete.
Many similar species of anole lizard coexist on islands around the Caribbean Sea, and the anoles of each island avoid competition with each other by residing in slightly different locations within their habitat, an example of spatial resource partitioning. The lizards then prey only upon the insects that enter their preferred territory, effectively dividing up available food sources. This diminishes competition for food and reduces direct conflicts between the different species.
Ultimately, competition provides an evolutionary selection pressure both within and between species when resources are not plentiful, forcing organisms to adapt or risk dying out if they cannot successfully compete.
Suggested Reading
Bolnick, Daniel I., Travis Ingram, William E. Stutz, Lisa K. Snowberg, On Lee Lau, and Jeff S. Paull. "Ecological release from interspecific competition leads to decoupled changes in population and individual niche width." Proceedings of the Royal Society B: Biological Sciences 277, no. 1689 (2010): 1789-1797. [Source]