Amensalism (Antagonism) Interaction: Definition, Types, & Examples

Amensalism (Antagonism) Definition

  • A negative ecological relationship called Amensalism occurs when one species suffers harm or extinction while the other either gains or is unharmed.
  • Amensalism is typically considered a connection between creatures of two distinct species, but it can also occur between members of the same species.
  • The process of natural selection promotes organisms that can efficiently gather resources and energy for survival, making amensalism one of the phases of evolution.
  • Despite the fact that amensalism and antagonism are sometimes used interchangeably, one of the species obviously gains from hostile interactions at the expense of the other.
  • Amensalism is also known as asymmetrical competitive contact since it may not result in any advantages for either species.
  • The species that cause damage typically produces chemicals or other products that have a detrimental effect on the other species participating in amensalism interactions in nature. Such products are not produced in reaction to interactions but rather as part of the daily operation of the species.
  • Defending tactics in the form of chemical and physical deterrents are then used during antagonistic encounters, either to protect one another or to collect resources from the environment.

Types of Amensalism

Depending on the species involved and the outcome of the encounter, there are two main categories of amensalism.

1. Competition

  • Competition is a form of antagonistic interaction in which a larger or more powerful species denies a smaller species food or other resources.
  • The species involved in these interactions occupy the same ecological niche. This makes it difficult for the weaker species to find food and habitats.
  • The contact occurs due to having a shared biological niche, although the bigger species are unaffected by it.
  • When two creatures of the same species struggle with one another for survival, there might be competition between the two species.

Example of Competition

1. Goats and Insects

  • Goats and grasshoppers both occupy the same ecological niche in nature. As a result, the two species compete with one another for food supplies.
  • The same kind of grass and bushes are consumed by the goat. As a result, the insects have fewer food sources available to them.
  • The relationship has no negative effects on the goat, but it deprives the insects of numerous food sources.
  • In this type of competition, the stronger species have an adverse effect on the development of the weaker species existing in the same ecological niche.

2. Larger and Smaller Fishes

  • In aquatic settings, smaller fish and bigger fish compete for food sources. Both species of fish consume aquatic phytoplankton and zooplankton for food.
  • The resources are rare for the smaller fish since the larger fish can readily locate and dine on them.
  • The contact between smaller and larger fish has a detrimental impact on both of them where interspecies competition occurs.

2. Antibiosis

  • An essential kind of amensalism is called antibiosis, in which one species is killed by a chemical secretion while the other is untouched.
  • The word “antibiosis,” which refers to the antagonistic interaction of species occupying comparable ecological niches, is derived from the French word “antibiose.”
  • Antibiotics are produced by one of the species involved in the species as a mode of defense against potential predators. Some species may even produce poisons.
  • As a result, some animals that share the same environment as the antibiose producer may experience adverse effects from the antibiose.
  • As a result, antibiosis is viewed as an instance of interference competition, in which one species interferes with the growth of the other in order to obtain access to more food and resources.
  • Prokaryotes and eukaryotes frequently engage in this kind of interaction, which has been investigated for its potential to shield people against various infections.

You may also like to read: Stratified Cuboidal Epithelium

Examples of Antibiosis

1. Penicillium and Bacteria

  • The interaction of the fungus Penicillium with several bacterial species is a well-known example of antibiosis.
  • Penicillin is secreted by the fungus during growth as a secondary metabolite. The antibacterial activity of penicillin is effective against different bacterial species.
  • The development of penicillin as the first antibiotic was based on this interaction. Penicillium naturally generates the antibiotic as a secondary metabolite, but bacteria that coexist with the fungus are adversely impacted.
  • The interaction has now been employed to produce a number of important medicinal poisons and medicines.

2. Black Walnut and Herbaceous Plants

  • Juglone, a chemical produced by black walnut (Juglans nigra), has an antagonistic impact on a variety of herbaceous plants that are present in the plant’s root zone.
  • The molecule is produced by the walnut plant as a defense mechanism against several plant diseases.
  • The secretion affects the herbaceous plants that grow in the root zone, but the walnut plant is untouched.


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