Amensalism – Concept, examples and what is commensalism

We explain what amensalism is and some examples of this biological relationship. Also, what is commensalism?

In amensalism, the individual who is harmed is usually the smallest.

What is amensalism?

Amensalism is a biological relationship that is established between two organisms in which one prevents the other from growing and develop (or even survive).

In amensalism, the individual who is harmed is usually the smallest or weakest, while the other organism does not even register its presence.

This relationship it is the result of the survival instinct that many species have and that occurs at the moment in which a certain organism is installed in a habitat. Once there, it makes an effort so that other individuals or species cannot survive in the same space, which hurts these other species.

In general, this survival instinct is produced from the generation of toxic substances that come from microorganisms and that prevent other species from developing in nearby areas.

The term “amensalism” is not synonymous with competition. Although both are biological relationships that occur in nature, in the competition two individuals face each other to get the same resource, which is essential for the subsistence of both. In this relationship, always one of the individuals benefits and the other harmed. On the other hand, in amensalism the organism that carries out the delimiting action does not acquire any type of benefit.

Examples of amensalism

The toxicity of pine needles prevents the seeds in the area from germinating.
  • When pine leaves fall to the ground, their toxicity prevents the seeds in the area from germinating.
  • Fungi feed on organic matter, that is, they absorb nutrients from other populations that they harm, weaken or neutralize.
  • An animal crushes with its legs the grasses that grow in its habitat and this prevents the rest of the species from being able to use them for food.
  • The overpopulation of algae results in an increase in its toxicity and this harms the fish or plants that grow or develop around it.
  • The substance that eucalyptus produces complicates and even prevents other plants from developing near it.
  • Like eucalyptus, black walnut generates a toxin known as juglone, which disables other plants to develop, which generates very little competition for survival.
  • Redwoods block sunlight through their branches, causing plants to not grow near them.
  • Elephants’ urine and fecal matter contain substances that attract pathogens that pollute the soil and water, and make it difficult for other species to survive.

Commensalism and amensalism

Commensalism - amensalism
An example of commensalism is when bees build their honeycomb on a tree.

Commensalism and amensalism are two types of interactions that occur between different organisms in the environment.

The difference between commensalism and amensalism has to do with that, in the first case, one of the individuals is benefited of the relationship whereas, in amensalism, none of the members of the relationship derives any advantage from that bond.

In commensalism, one of the individuals is benefited while the other is neither benefited nor harmed: the link is neutral.

Some examples of commensalism may be when bees build their honeycomb on a tree, when remoras are mounted on sharks for transport or when birds build their nests in any tree.