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Amensalism: Examples & Definition

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  • 0:01 Definition of Amensalism
  • 1:00 Examples of Amensalism
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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.

Many types of relationships exist between species on Earth, but not all are positive. In this lesson, we will learn about amensalism to gain an understanding of how this unique type of relationship works.

Definition of Amensalism

There are a variety of relationships that occur between different species all over the world. In nature, no organism lives its life in complete isolation. They must interact with other organisms and their environment in some manner. One type of relationship that has been classified by biologists and ecologists is amensalism. Amensalism is any relationship between organisms of different species in which one organism is inhibited or destroyed while the other organism remains unaffected.

Examples of Amensalism

There are basically two types of amensalism: competition and antibiosis. In competition, a larger or more powerful organism excludes another organism from its source of shelter or food. In antibiosis, one organism secretes a chemical that kills the other organism, while the one that secreted the chemical is unharmed.

Two examples of antibiosis amensalism are provided by the bread mold Penicillium and black walnut trees. You probably do not like to think about it, but many types of bacteria and fungi are perfectly capable of growing on bread under the right conditions. The bread mold Penicillium commonly grows on any bread that has passed its shelf life. This mold is capable of producing penicillin, which destroys many of the forms of bacteria that would also like to grow on this bread. It is this understanding of the bacteria-killing properties of penicillin that led to the use of it as an antibiotic medicine. The Penicillium does not benefit from the death of the other bacteria, making this an example of antibiosis amensalism.

Large, towering black walnut trees can be found growing in many areas of the United States. If you have ever been around walnut trees or have them in your yard, you may have noticed that there is no grass growing under the trees. This is because they have evolved to secrete a chemical known as Juglone. This chemical acts as a natural plant and weed killer and kills most plants living in the root zone of the walnut trees. Since the plants are prohibited from living under the trees, and the walnut trees do not really benefit in any way, this is a perfect example of amensalism.

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