Commensalism: Relationship Examples, Definition & Types

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  • 0:03 Definition of Commensalism
  • 0:29 Types of Commensalism
  • 1:25 Examples of Commensalism
  • 2:38 Lesson Summary
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Lesson Transcript
Instructor: Derrick Arrington

Derrick has taught biology and chemistry at both the high school and college level. He has a master's degree in science education.

Living organisms found in nature react and live with one another in a variety of ways. One of these interesting types of relationships between two organisms is called commensalism. In this lesson, we will explore commensalism and see how it works.

Definition of Commensalism

The relationships formed between organisms that interact in nature are referred to by ecologists as symbiotic relationships. One type of symbiosis is called commensalism. In commensalism, one organism benefits from the relationship while the other species involved neither benefits nor is harmed. The benefits for one organism can be in a variety of forms, including food, shelter, transportation and seed dispersal.

Types of Commensalism

Most experts in the field of ecology group commensal relationships into four main types: chemical, inquilinism, metabiosis and phoresy.

  • Chemical commensalism is most often observed between two species of bacteria. It involves one species of bacteria feeding on the chemicals produced or the waste products that are not used by the other bacteria.
  • Inquilinism involves one species using the body or a body cavity of another organism as a platform or a living space while the host organism neither benefits nor is harmed.
  • Metabiosis is a form of commensalism that occurs when one species unintentionally creates a home for another species through one of its normal life activities.
  • A phoresy takes place when one organism attaches to another organism specifically for the purpose of gaining transportation.

Examples of Commensalism

An example of inquilinism can be observed between barnacles and whales. Barnacles are normally sessile, or non-moving sea creatures. They rely on currents to bring food past them in order to eat. However, some barnacles have attached themselves to the sides of various sea life, such as whales, in order to have a more advantageous position in life. These barnacles benefit by receiving transportation all over the ocean, which exposes them to more currents and feeding opportunities than they would normally experience. The whale neither benefits nor is harmed by the barnacles.

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