Amensalism – Definition, Types, Examples


Table of Contents

What is Amensalism (Antagonism)?

Amensalism is a sort of biological interaction in which one species harms another without incurring any costs or gaining any advantages. It is a form of interaction or competitive behaviour between organisms.

  • Haskell coined the term amensalism to describe a relationship in which one organism harms another without incurring any costs or receiving any benefits.
  • Amensalism refers to the negative impact that one organism has on another. This is a unidirectional process in which one organism releases a specific substance that has a harmful effect on another.
  • The microbial synthesis of antibiotics that can inhibit or kill other sensitive germs is a classic example of amensalism.
  • Sheep and cattle trampling grass is an obvious example of amensalism. While the presence of grass has little negative consequences on the animal’s hoof, the grass is negatively affected by being crushed.
  • Amensalism is frequently used to characterise highly asymmetrical competitive interactions, such as those observed between the Spanish ibex and Timarcha weevils that feed on the same type of plant.
  • While the presence of weevils has a negligible effect on food availability, the presence of ibex has a devastating effect on weevil populations, as ibex devour large quantities of plant matter and unintentionally consume weevils along with it.
  • Amensalisms can be fairly intricate. Attine ants (New World ant tribe) are able to profit from the interaction between an actinomycete and a parasite fungus of the genus Escovopsis.
  • This amensalistic interaction permits the ant to sustain a mutualistic relationship with members of the Leucocoprinus genus. Amazingly, these ants develop a Leucocoprinus fungus garden for their own sustenance.
  • Ants support the growth of an actinomycete of the genus Pseudonocardia, which produces an antibiotic chemical that inhibits the growth of the parasitic Escovopsis fungi.

Modes of Amensalism or Types of Amensalism

1. Competition

  • When two species require a finite resource, the presence of one species affects the resource’s availability for the other.
  • A “negative/negative” relationship exists. Examples of resources include food, water, and space
  • If there are adequate resources to meet the requirements, there is no competition.
  • Only a few resources are anticipated to be limited and so subject to competition.


  • When an organism, such as a goat, consumes the same type of shrub as an insect, mutualism occurs (such as a beetle). The goat is unharmed when it consumes the bush, but the beetle loses substantial amounts of food and may be consumed by accident. This form of amensalism is referred to as competition.

2. Antibiosis

  • Antibiosis is a type of amensalism in which one species is destroyed by a chemical secretion while the other remains unharmed.
  • Antibiosis is derived from the French word antibiose, which refers to the hostile relationship between organisms that occupy identical biological niches.
  • As a protection mechanism against potential predators, one of the species involved in the species produces antibiotics. Certain species may generate toxins.
  • Therefore, antibiotics may be detrimental to certain animals that inhabit the same environment as the antibiotic producer.
  • Thus, antibiosis is seen as an instance of interference competition, in which one species inhibits the growth of another to gain access to more food and resources.
  • This interaction occurs in both prokaryotes and eukaryotes, and it has been studied for its potential to protect people from a number of infectious diseases.
  • Examples of antibiosis include the relationship between antibiotics and bacteria and between animals and disease-causing pathogens.


  • Antibiosis is illustrated by the relationship between Penicillium and bacteria. Penicillin, which is particularly harmful to bacteria, is produced by the fungus Penicillium. This discovery served as the foundation for the first real antibiotic, penicillin.

Examples of Amensalism

  • A simple example of Amensalism is cows and bugs that graze. When cattle eat grass, birds eat the bugs, but they don’t hurt the cattle. “0” means “cattle,” while “-” means “insects.”
  • Most of us have heard of the example of Amensalism where Penicillium and Staphylococcus work together. Staphylococcus is a type of bacteria, while Penicillium is a type of fungus. They have a (0,-) relationship with each other. In this process, penicillium makes a poison called penicillin that kills bacteria.
  • Weeds can’t grow near crops with a smooth surface, like barley, sorghum, and sunflower. In this case, the crop doesn’t change, but the weeds do.
  • Juglone is a chemical that the black walnut tree makes (Juglans regia). This poison stops plants from growing in the area. This poison is bad for apple, tomato, and alfalfa plants.
  • Aspergillus and Trichoderma: Aspergillus can’t grow as well when Trichoderma is around. In organic farming, Trichoderma is used as a biocontrol agent for this reason.
  • Nematodes in the soil are hurt by the toxins that Tagetes makes.
  • Many different kinds of fish can die because of algal blooms. On the other hand, the loss of these animals doesn’t help the algae in any way.
  • When elephants step on ants, they kill the ants but don’t help the elephants.
  • Pine trees make an allopathic chemical that stops other plants from growing in the area. Other crops are hurt, but Pine neither gets hurt nor gets better.

In the Ocean, Examples of Amensalism

Many different kinds of fish could die from algal blooms. On the other hand, the loss of these animals doesn’t help the algae in any way.


  • Kitching, R. L., & Harmsen, R. (2008). Amensalism. Encyclopedia of Ecology, 160–162. doi:10.1016/b978-008045405-4.00640-6
  • Veiga, José. (2016). Commensalism, Amensalism, and Synnecrosis. Encyclopedia of Evolutionary Biology. 10.1016/B978-0-12-800049-6.00189-X. 

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