Exploitative competition

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Introduction

Exploitative competition occurs when consumption of a limiting resource by one species makes that resource unavailable for consumption by another. Such resources including space, food, water, safe space, light, soil nutrients, and mates. Exploitative competition may occur withing species (intraspecific competition) or between species (interspecific competition). Exploitative competition, a type of indirect ecological interaction, is the most common mechanism of competition in nature, and it is found in all terrestrial, aquatic, and marine communities.

Examples of exploitative competition

Examples of exploitative competition include (1) two individuals of the same zooplankton species competing for nutrients in the ocean, (2) lions and cheetahs competing for gazelles on the African plains, (3) two species of barnacles competing for space on a rocky shoreline, (4) two species of prairie grasses competing for light, soil moisture and soil nutrients, and (5) two males competing for females (when an egg is fertilized, it is effectively "consumed" because it can not be fertilized by a second male).

Importance exploitative competition

Exploitative competition within species can play an important role in limiting population sizes (see logistic growth). Exploitation competition among species can also influence the population sizes of competing species. In addition, competitive exclusion, as a result of exploitative competition, can be an influence on the number of species that can coexist in a community.

Exploitative competition among taxonomically diverse species

Because organisms compete exploitatively by consuming resources, and the same type of resource may be consumed by distantly related organisms, exploitative competition between taxonomically diverse organisms is common. For example, deserts seeds are consumed by insects (e.g., ants), birds (e.g., sparrows), and mammals (e.g., kangaroo rats). It doesn't matter to a kangaroo rat whether a seed was eaten by a member of its own species, another kangaroo rat species or by an unrelated sparrow or ant, because in any case the seed is not available for the kangaroo rat to eat.

Temporal separation of exploitative competitors

Because organisms can consume resources at different times of the year or different times of the day, it is possible for two species that are not present in the same time and place to compete exploitatively. For example, sparrows feed on seeds during the day while kangaroo rats feed at night. Thus, these two species can compete exploitatively even though they never come into direct contact with each other. Similarly, if a plant only produces its seeds in the Autumn, then an insect species that is active at that time of year will consume resources that are not available to another insect species that is only active in the spring. Thus, exploitative competition can occur between species that are not even alive at the same time.

Traits to win exploitative competition

Natural selection has produced a number of traits that help species win in exploitative competitive interactions. For example, because sunlight reaches taller plants first, forest trees are able to "consume" light before it reaches the understory plants. Thus, exploitative competition for light favors taller plant growth forms. Similarly, water infiltrates from the surface down into the soil. Thus, some species of plants have wide-spread shallow root systems that allow them to pick upt water before it reaches the roots of species with deeper root systems.

Reducing exploitative competition

Niche partitioning is an important mechanism that organisms use to try to reduce exploitative competition. Competition can be reduced if species with similar feeding strategies each specialize in slightly different resources, feed in different location, or feed at different times. For example, beetles that feed on the phloem of trees may feed at different locations (the roots tips, the root collar, the trunk).  Likewise, ant species that forage for caterpillar prey may do so at different times of day.

Further reading

  • Campbell, N.A., J.B. Reece, and L.G. Mitchhell. 2006. Biology. Addison Wesley Longman, Inc. Menlo Park, CA. ISBN: 080537146X
  • Raven, P.H., G.B. Johnson, J.B. Losos, K.A. Mason, and S.R. Singer. 2008. Biology, 8th edition. McGraw Hill, New York, NY. ISBN: 0073227390
Glossary

Citation

McGinley, M. (2008). Exploitative competition. Retrieved from http://www.eoearth.org/view/article/152711

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