Many the forms of bacteria that would

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.

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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.Common examples of competition amensalism include cattle trails and forest growth. If you have ever worked on a farm or ranch, you may have seen cattle trails. These are paths that cows walk when they are moving from one place to another as a group.

It’s not uncommon to see 20 or 30 cows walking in a line down the paths. These trails will be worn down dirt paths with no plant growth because they are frequently traveled by the herds. These paths serve as an example of competition-based amensalism because the presence of the large group of cattle moving through inhibits and destroys the plant life that would normally grow well in the space.We all know that plants need light in order to survive. Light allows them to complete the process of photosynthesis to obtain energy.

In dense forests all around the world, amensalism takes place frequently as large trees tower over shorter plants stealing most or all of the sunlight. When the trees get so large that hardly any light reaches the forest floor, they inhibit the growth of or cause the death of many plants. This makes them an example of amensalism.

Lesson Summary

Let’s review. Amensalism is any relationship in which one organism is harmed or killed while the other organism does not benefit in any particular way. Amensalism relationships can be seen all throughout the world and are particularly prevalent among plant species.

Learning Outcomes

Once you’ve finished with this lesson, you will have the ability to:

  • Define amensalism
  • Describe competition-based amensalism and antibiosis and provide examples of each

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