Amensalism-Defination & Examples

What is Amensalism?

Amensalism is the interaction of organisms from two distinct species, in which one is prevented from thriving or is wiped out while the other is untouched. Different animals on Earth have a wide variety of interactions. Not all of them, though, are good. One such instance of a bad association between two species is amensalism.

Amensalism is the term used to describe an ecological relationship between two species, although, in this association, one species' creatures are killed out or hindered while the other is untouched. Asymmetrical competitive engagement is also frequently referred to as amensalism.

Amensalism Meaning and Definition

Definition in Biology: Amensalism is the phenomenon where one species is adversely affected while the other remains unaffected in the interaction between two species. This relation is mainly negative for one species but neutral for the other.

Meaning: It is a type of relationship in which one organism is inhibited or destroyed by the action of another organism that is left uninhabited.

Modes of Amensalism

There are two main modes of Amensalism, which are divided into Antibiosis and Competition. In both types of amensalism, one organism is harmed, while the other one is unharmed.

Antibiosis

Definition: Antibiosis, from the French term "antibiosis," refers to an antagonistic relationship that involves harming one organism by chemicals or actions from another organism. The term was first introduced by Vuillemin in 1889–1890.

Mechanism: It works by releasing chemicals or toxins that inhibit or kill other organisms.

Examples of Antibiosis

Penicillium mould and bacteria: Penicillin is bactericidal, produced by the mould Penicillium. It is due to this discovery that penicillin was developed as an antibiotic against bacterial infections.

Black walnut trees and other plants: Juglone is the toxin found in the black walnut tree that stops the growth and kills the plants within the root zone of the tree. This reduces competition.

Interaction of microbes and antibiotics: The mechanism through which specific antibiotics act on bacterial cells thus involves interference with the synthesis process of their cell walls, which also occurs in antimicrobial relationships.

Competition

Definition: In amensalism competition, two species compete with scarce resources. For one organism, the other one will cause damage as it is not affected.

Mechanism: It occurs due to organisms competing over limiting resources, like food, space, or light, which may not be available to all the competitors.

Types of Competition

Intraspecific Competition: Individuals belonging to the same species in competition for resources. This includes competition amongst the plants of the same species for sunlight.

Interspecific Competition: competition of different species for the same resource, such as plants from different species competing for water.

Interference Competition: where direct interference to another species accessing resources is experienced (for example one plant releasing chemicals to prevent another close plant from growing).

Exploitation Competition: indirect competition of species by depleting the pool of shared resources (for example, animals consuming the same food source and reducing its availability for others).

Amensalism Examples

Here are some examples of amensalism:

• Penicillin, produced by penicillium, kills a variety of microorganisms.

• Black walnut roots exude juglone, a poisonous substance that kills other herbaceous plants in their vicinity.

• The actinomycete streptomyces prevents bacterial development. Most commonly, antibiotics are used.

• Convolvulus arvensis prevents wheat from growing.

Difference between Commensalism and Amensalism

The major difference between commensalism and amensalism is described below:

Importance of Amensalism in Ecology

Amensalism plays a crucial role in maintaining ecological balance by regulating population sizes and controlling competition among species. It also influences the distribution of organisms and contributes to natural selection in ecosystems.

Key Importance:

• Population control: Prevents the overgrowth of certain species by suppressing them.

• Competition regulation: Stronger species can dominate without directly benefiting, ensuring balance.

• Chemical defense: Production of antibiotics and toxins (e.g., Penicillium) helps maintain microbial balance.

• Ecosystem stability: Helps reduce resource competition, allowing diverse species to coexist.

• Practical applications: Basis of antibiotic production in medicine and use of allelopathy in agriculture.

Tips, Tricks & Mnemonics

Here are some tips and tricks to prepare amensalism for different exams:

• Diagrams and Tables: Include diagrams of amensalism, as exemplified by the suppression by Penicillium of the growth of bacteria. Complete comparison tables on amensalism compared to commensalism.
• Mnemonics: Use simple phrases like "A-N: Affect None" to remind you that amensalism only affects one organism.
• Flashcards: This uses words such as Amensalism, Chemical Inhibition, and Juglone Release to learn those important terms.
• Visualization Tools: Observe animations to see how chemical from plants or fungi inhibits other organisms, with this providing a better understanding of amensalism.
• Real-Life Applications: Relate how the above issues apply to real-life situations, such as how certain trees inhibit the growth of other plants or how these can limit practices such as gardening and forestry.

Weightage in Exams

The table below indicates the weightage and types of questions asked from amensalism in different exams:

Amensalism NEET MCQs

Q1. Amensalism is an association between two species where:

1. One species is harmed and the other is benefitted.

2. One species is harmed and the other is unaffected.

3. One species is benefitted and the other is unaffected.

4. Both species are harmed.

Correct answer: 2) One species is harmed and the other is unaffected.

Explanation:

An ecological relationship known as amensalism occurs when one species suffers harm while the other species is unscathed. This interaction can take many different forms, but it is frequently observed when one species physically prevents another from growing or surviving, or when one creature creates a material that is toxic to another.

The interaction between some plants and their environment is a well-known illustration of amensalism. Allelopathic compounds, for example, are released into the soil by certain plants and prevent the growth of competing plants in the vicinity. In this instance, the chemicals damage the rival plants but do not affect the plant that produces them.

Hence, the correct answer is an option (2) one species is harmed and the other is unaffected.

Q2. What is a conflict between members of two different species over the use of resources in the same territory known as?

1. Apparent competition

2. Interspecific competition

3. Interference competition

4. Intraspecific competition

Correct answer: 2) Interspecific competition

Explanation:

Interspecific competition refers to the competition between individuals of different species for the same resources, such as food, space, or light, within an ecosystem. This type of competition occurs when two or more species occupy similar ecological niches and rely on overlapping resources. Interspecific competition can lead to a variety of outcomes, including one species outcompeting the other, resource partitioning where species divide the resources, or the coexistence of species by utilizing different aspects of the environment. Over time, interspecific competition can drive evolutionary changes, such as the development of specific adaptations that reduce competition between species.

Hence the correct answer is option (2) Interspecific competition

Q3. Which one of the following interactions does NOT promote coevolution?

1. Commensalism

2. Mutualism

3. Parasitism

4. Interspecific competition

Correct answer: 1) Commensalism

Explanation:

An interaction between species or organisms in which the fitness of one organism is lowered by another organism is known as competition. Competition arises for the limited available resources such as water, food, or limited supply for the females. The competition between the organisms of the same species is called the intraspecific competition while the competition between the organisms of different species is called interspecific competition. According to the principle of competitive exclusion the species that is least suited for the resources either adapt or die and thus promote co-evolution.

A specific case of co-evolution is a host-parasite co-evolution, an adaptive and reciprocal genetic change of a parasite and a host through reciprocal selective pressures. The reciprocal genetic change and changes in the allele frequencies within the population characterize this.

This relationship is established based on the genetic changes that help both host and parasite to evolve reciprocally. Parasitism is a symbiotic relationship in which the parasite takes benefits from the host. The benefit is derived from the host in terms of nourishment and space. Different strategies are developed by the host to counter the invasion of parasites and thus promote co-evolution.

The symbiosis ranges from mutualism which is beneficial for both the involved species to the competition which is harmful or detrimental to both involved species. Coevolution includes different forms of mutualism, predator-prey, and host-parasite relationships between the species, as well as, intraspecific competition or interspecific competition.

Commensalism does not involve physiologic interaction or dependency between the two partners, the host and the commensal as one gets benefitted and the other derives neither benefitted nor harmed and thus does not promote coevolution.

Hence, the correct option is option (1) commensalism.

Read More:

• Practice MCQ on Population Interaction

• Biotic and Abiotic

• Predators

FAQs on Amensalism

Define amensalism.

Amensalism is an ecological interaction between two species in which one species is inhibited or harmed, while the other remains unaffected. It is a type of negative ecological relationship where one organism’s growth or survival is suppressed without any direct benefit to the other. Amensalism often occurs through the release of chemicals, antibiotics, or toxins into the environment. It plays an important role in regulating population growth and maintaining balance in ecosystems.

What are the modes of amensalism?

Amensalism generally occurs in two main modes, these modes highlight how amensalism can be both direct (through toxins) or indirect (through competitive exclusion):

1. Competition Amensalism: when a stronger species outcompetes and suppresses a weaker one, without gaining significant benefit itself.

2. Antibiosis: when one organism releases toxic substances (like antibiotics, alkaloids, or chemicals) that inhibit or kill another species.

What are examples of amensalism?

A classic example of amensalism is the production of penicillin by the fungus Penicillium, which inhibits the growth of nearby bacteria. Similarly, black walnut trees (Juglans nigra) release a chemical called juglone into the soil, preventing the growth of many plants nearby. Another example is bacterial production of antibiotics in soil, which suppresses competing microorganisms without directly benefiting the producer. These interactions maintain ecological balance and have practical uses in medicine and agriculture.

What is the difference between commensalism and amensalism?

The key difference lies in the effect on the interacting species. In commensalism, one species benefits while the other remains unaffected (e.g., epiphytic orchids growing on trees). In amensalism, one species is harmed or inhibited, while the other remains unaffected (e.g., Penicillium fungus inhibiting bacteria). Thus, commensalism is a + / 0 interaction, whereas amensalism is a – / 0 interaction in ecology. Both are important for ecosystem stability but have opposite outcomes.

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