What is Amensalism?

Meaning of Amensalism

Amensalism or antibiosis is one of the ecological relationships in which only one of the beings benefits, and the other organism will be harmed. Simply put, one species is inhibited while the other is unaffected.

Ecological relationships are present within the ecosystems that we know, some may be beneficial to one or more organisms involved, while others may be harmful.

When we deal with living organisms that harm other organisms to survive, the first impression we have is that they are bad, and that is a false impression.

Each and every one of the interactions between living organisms that have the objective of survival of the species are the result of a long period of evolution and are essential for the balance of the planet.


Amensalism is an ecological relationship of an interspecific nature (between different species) and disharmonious (one species is favored in relation to another).

In amensalism, one species (animal or plant) harms the other to obtain benefits for itself in relation to the resources of the environment.


This relationship is very common in environments where environmental resources are scarce (space, water, light, food, etc.). Therefore, in amensalism there is a kind of competition.

Taking into account the basic functioning of a food chain would help to better deal with and understand this type of situation.

The fact is that the organism that produces amensalism  is harming other species, so the relationship is considered negative, but that organism needs to perform this type of interaction to keep its species alive.

It is a natural and survival process.

Organisms that practice amensalism or commensalism will produce toxic substances that harm the host or the amensal organism .

These toxic substances prevent the natural life cycle of amensal organisms from being fulfilled. They cannot develop and reproduce, the competition for space and organic matter becomes unfair.

The main practitioners of amensalism or commensalism are plants, but large animals and insects can also be considered practitioners of antibiosis .

Examples of amensalism or commensalism

  • The fungus, Penicillium notatum , produces a substance called penicillin (known as the oldest antibiotic) that prevents the growth of bacteria.
  • The eucalyptus secretes some substances through its roots that affect and prevent the growth of all the plants that surround it. This reduces local competition for water and nutrients, and gives eucalyptus a reputation for being an easy-to-adapt tree.
  • Tall, large trees can make the environment apotic (without light) for organisms at lower levels.

Amensalism in the Ocean

In marine and freshwater environments there is a problem called red tide or algal bloom , which is characterized by the presence of a large number of dinoflagellate microorganisms.

These in the appropriate climatic conditions, reproduce quickly, changing the aspect of the aquatic region .

The main effect of this phenomenon is the high mortality rate of animals in these regions, species of marine and coastal fish, birds, marine mammals (mainly manatees) and many other organisms.

There are studies that point to the red tide as a natural phenomenon and studies that point to the red tide as an anthropic problem.

The red tide would be a very beautiful phenomenon, were it not for the large number of animals affected by these toxins.

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