Amensalism - Defination & Examples

Amensalism-Defination & Examples

Edited By Irshad Anwar | Updated on Jul 02, 2025 05:22 PM IST

Amensalism is the interaction between organisms wherein one is inhibited or killed while it does not affect the other. This topic is an important part of the Class 12 chapter Organism and Population. Amensalism involves the release of chemical substances or other forms of inhibition of one from the other affecting ecosystems and population dynamics. Amensalism meaning, amensalism examples, and comparison with commensalism are discussed in this article. This topic is important for the students preparing for CBSE or entrance exams with biology as a major subject like NEET, and AIIMS.

This Story also Contains

What is Amensalism?
Amensalism Meaning and Definition
Modes of Amensalism
Amensalism Examples class 12
Difference between Commensalism and Amensalism
Tips, Tricks and Strategies to Prepare Amensalism for Exams
Types of Questions and Weightage of Amensalism in Exams
Recommended Video on Amensalism

What is Amensalism?

Amensalism is the affiliation 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.

Read More:

Amensalism Meaning and Definition

Amensalism 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.

Amensalism 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 class 12

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.

NEET Highest Scoring Chapters & Topics

Know Most Scoring Concepts in NEET 2024 Based on Previous Year Analysis.

Know More

Difference between Commensalism and Amensalism

The major difference between commensalism and amensalism is described below:

Feature	Commensalism	Amensalism
Definition	A type of relationship where one organism benefits while the other is unaffected.	A type of relationship where one organism is harmed and the other is unaffected.
Effect on Organisms	Positive for one organism, neutral for the other.	Negative for one organism, neutral for the other.
Purpose of Interaction	Often for transportation, shelter, or access to resources.	Usually involves the inhibition or destruction of one organism by another.
Organism Involvement	One organism benefits from the relationship.	One organism is inhibited, destroyed, or otherwise harmed.
Presence in Ecosystems	Often seen in relationships where one species provides a habitat or mode of transport for another.	Often involves competitive or defensive actions that limit the growth of other organisms.
Example	Barnacles attaching to whales: barnacles benefit by getting access to food, while whales are unaffected.	Penicillium mould releases antibiotics that inhibit bacteria: bacteria are harmed, but the mould is unaffected.

Tips, Tricks and Strategies to Prepare Amensalism for Exams

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.

Types of Questions and Weightage of Amensalism in Exams

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

Exam Type	Types of Questions	Weightage
CBSE	Short answers on amensalism examples, definitions, and diagrams	4-6%
NEET	MCQs on amensalism interactions, differences from other interactions	2-3%
AIIMS	Assertion and reason questions on types and effects of amensalism	2-3%
Nursing Entrance Exams	Scenario-based questions on ecological relationships	1-3%
Paramedical Exams	True/False questions on examples and modes of amensalism	1-3%

Read More:

Symbiosis Definition	Parasitic Definition
Predators	Population Growth
Difference between Mutualism and Commensalism	Variations

Recommended Video on Amensalism

Frequently Asked Questions (FAQs)

1. What is amensalism, and how does it work?

Amensalism is the interaction between two creatures in which one of them suffers harm. The antibacterial effect of penicillin is a prime example of amensalism. Penicillin, which is secreted by the bread mold Penicillium, finally kills germs.

2. Is amensalism a good or bad thing?

Amensalism is not a good thing.

Amensalism is a bad kind of organism-organism interaction. The advantage only benefits one organism. The advantage is not received by the interacting organism. The interactions with another organism are unaffected.

3. What distinguishes amensalism from commensalism?

In contrast to amensalism, which is an interaction between two separate creatures in which one is always hurt but the other is neither harmed nor benefited, commensalism is a relationship in which one of the organisms always benefits.

4. What sort of bond is an amensalism?

A sort of biological interaction known as amensalism occurs when one species harms another without incurring any costs or advantages for itself.

5. Who gains from amensalism?

A sort of interaction between two species known as amensalism occurs in ecology and involves one species, the amensal, gaining an advantage at the expense of the other, the mutualist.

6. How does allelopathy relate to amensalism?

Allelopathy is a form of amensalism where plants release chemicals (allelochemicals) that inhibit the growth or reproduction of other plants. It's an example of antibiosis and plays a crucial role in plant community dynamics and succession.

7. Can you provide an example of competition amensalism in nature?

A classic example of competition amensalism is the relationship between certain shade-tolerant trees and understory plants. The large trees block sunlight, preventing the growth of sun-loving plants beneath them, while remaining unaffected by the presence of the smaller plants.

8. Can you explain antibiosis with an example?

Antibiosis occurs when one organism produces chemicals that harm another. A classic example is the production of penicillin by the Penicillium mold. The antibiotic kills or inhibits the growth of certain bacteria, while the mold itself is unaffected.

9. What role does amensalism play in microbial communities?

In microbial communities, amensalism often occurs through antibiosis. Some microorganisms produce antibiotics or other inhibitory compounds that suppress the growth of competing microbes, helping to shape the composition of the microbial community.

10. How does amensalism contribute to ecological balance?

Amensalism can help maintain ecological balance by controlling populations of certain species. For example, some plants release allelopathic compounds that inhibit the growth of competing plants, which can help prevent overgrowth and maintain biodiversity in an ecosystem.

11. What is amensalism in ecology?

Amensalism is a type of interspecific interaction where one species is harmed or inhibited while the other species is unaffected. It's a one-sided negative relationship where one organism suffers while the other experiences no significant impact.

12. Can amensalism occur between microorganisms and larger organisms?

Yes, amensalism can occur between microorganisms and larger organisms. For example, human skin produces antimicrobial peptides that inhibit the growth of certain bacteria. The human is unaffected, but the bacteria are harmed, exemplifying amensalism.

13. What role does amensalism play in coral reef ecosystems?

In coral reefs, some corals and sponges produce chemical compounds that inhibit the growth of competing organisms. This amensalistic interaction helps maintain space on the reef and contributes to the complex community structure of these ecosystems.

14. What are some limitations in our current understanding of amensalism?

Limitations in our understanding of amensalism include:

15. How does amensalism relate to the concept of keystone species?

A keystone species exhibiting strong amensalistic effects could significantly shape community structure. By inhibiting certain species without being affected itself, it could maintain biodiversity and influence ecosystem functions, similar to more commonly discussed keystone roles.

16. How does amensalism differ from competition?

In amensalism, only one species is negatively affected while the other is neutral. In competition, both species are negatively impacted as they compete for the same resources. Amensalism is a one-sided interaction, while competition is mutual.

17. Can amensalism occur between individuals of the same species?

Typically, amensalism refers to interactions between different species. Interactions within the same species that resemble amensalism are usually classified as intraspecific competition or other forms of social interaction.

18. How does amensalism differ from commensalism?

In amensalism, one species is harmed while the other is unaffected (0/-). In commensalism, one species benefits while the other is unaffected (+/0). Both involve a neutral impact on one species, but the effect on the other species differs.

19. How does amensalism differ from parasitism?

In amensalism, one species is harmed while the other is unaffected (0/-). In parasitism, one species (the parasite) benefits at the expense of the other (the host), which is harmed (+/-). Parasitism involves a benefit to one party, while amensalism does not.

20. How does amensalism differ from antagonism?

Antagonism is a broader term that includes any negative interaction between species. Amensalism is a specific type of antagonism where one species is harmed and the other is unaffected. Other forms of antagonism, like competition or predation, involve mutual negative effects or benefits to one party.

21. What are the two main types of amensalism?

The two main types of amensalism are:

22. What is the difference between mechanical and chemical amensalism?

Mechanical amensalism involves physical interference, such as larger plants shading out smaller ones. Chemical amensalism, or antibiosis, involves the production of harmful chemical compounds. Both result in harm to one species while the other remains unaffected.

23. How does soil amensalism affect plant communities?

Soil amensalism occurs when certain plants or microorganisms in the soil release compounds that inhibit the growth of other plants. This can shape plant community composition, influence succession, and affect the distribution of species in an ecosystem.

24. How do scientists study amensalism in ecosystems?

Scientists study amensalism through field observations, controlled experiments, and molecular techniques. They may observe species interactions in natural settings, conduct lab experiments to isolate specific effects, or analyze chemical compounds involved in antibiosis.

25. Can amensalism occur between plants and animals?

Yes, amensalism can occur between plants and animals. For example, some plants produce toxic compounds that harm herbivores but don't benefit the plant directly. The plant is unaffected by the animal's presence, but the animal is harmed by the plant's toxins.

26. Is amensalism always a permanent relationship?

No, amensalism is not always permanent. Environmental changes or evolutionary adaptations can alter the relationship between species. For instance, a species might develop resistance to an allelopathic compound over time, changing the interaction.

27. How does amensalism relate to the concept of ecological niche?

Amensalism can influence the realized niche of a species by restricting its distribution or abundance. The species experiencing the negative effects may be excluded from certain areas or resources, narrowing its niche compared to its fundamental niche.

28. Can amensalism be beneficial for ecosystem management?

Yes, understanding amensalism can be valuable for ecosystem management. It can be used to control invasive species, manage pests without harmful pesticides, or promote desired species compositions in restoration projects.

29. Can amensalism be used in sustainable agriculture practices?

Yes, amensalism can be applied in sustainable agriculture through:

30. How do amensalistic interactions change over ecological succession?

Amensalistic interactions may change over succession as:

31. How does amensalism differ from predation?

In amensalism, one species is harmed while the other is unaffected. In predation, one species (the predator) benefits by consuming the other (the prey). Predation is a +/- interaction, while amensalism is a 0/- interaction.

32. Can amensalism lead to evolutionary changes?

Yes, amensalism can drive evolutionary changes. Species negatively affected by amensalism may evolve mechanisms to resist or avoid the harmful effects, leading to adaptations over time. This can result in coevolution between the interacting species.

33. What are some challenges in identifying amensalism in nature?

Challenges include:

34. How does amensalism impact biodiversity?

Amensalism can both promote and reduce biodiversity. It may prevent certain species from dominating an ecosystem, allowing others to thrive. However, strong amensalistic effects can also exclude species entirely, potentially reducing local biodiversity.

35. Can amensalism play a role in biological control?

Yes, amensalism can be utilized in biological control strategies. For example, introducing organisms that produce antibiotic compounds can help control pathogenic microbes in agriculture or medicine without directly harming the crop or patient.

36. How does the study of amensalism contribute to our overall understanding of ecology?

Studying amensalism enhances our ecological understanding by:

37. How do allelopathic plants affect soil microbial communities?

Allelopathic plants release compounds that can inhibit the growth of certain soil microbes while potentially promoting others. This can alter the composition and function of soil microbial communities, indirectly affecting nutrient cycling and plant growth.

38. How can climate change affect amensalistic relationships?

Climate change can alter amensalistic relationships by:

39. What are some examples of amensalism in marine ecosystems?

In marine ecosystems, amensalism can be observed in:

40. How does amensalism contribute to community succession?

Amensalism can influence succession by:

41. Can amensalism occur across trophic levels?

Yes, amensalism can occur across trophic levels. For example, a plant producing toxins that harm herbivores but don't affect the plant's predators represents amensalism across trophic levels. The plant (producer) negatively affects the herbivore (primary consumer) without impacting higher-level consumers.

42. How might amensalism influence species coexistence?

Amensalism can promote species coexistence by:

43. What role does amensalism play in the rhizosphere?

In the rhizosphere, amensalism can occur through:

44. How does amensalism differ in aquatic versus terrestrial ecosystems?

While the basic principle is the same, amensalism in aquatic ecosystems often involves:

45. Can amensalism play a role in speciation?

Amensalism could contribute to speciation by:

46. How do amensalistic interactions change with environmental stress?

Environmental stress can alter amensalistic interactions by:

47. What are some examples of amensalism in human-modified environments?

In human-modified environments, amensalism can be seen in:

48. How does amensalism relate to the concept of ecosystem engineers?

Ecosystem engineers that create amensalistic conditions can significantly shape communities. For example, a tree species that produces allelopathic compounds can be considered an ecosystem engineer, modifying the environment in a way that inhibits certain other species.

49. Can amensalism influence the spread of invasive species?

Amensalism can affect invasive species spread by:

50. How might amensalism be relevant to conservation biology?

In conservation biology, understanding amensalism is important for:

51. What role does amensalism play in microbial biofilm formation?

In microbial biofilms, amensalism can:

52. How does amensalism relate to the concept of facilitation in ecology?

While amensalism and facilitation are different, they can be related. An amensalistic interaction that harms one species might indirectly facilitate another by reducing competition or creating favorable conditions. This highlights the complex, interconnected nature of ecological interactions.

53. Can amensalism contribute to the maintenance of genetic diversity?

Amensalism can maintain genetic diversity by:

54. How might amensalism influence ecosystem resilience?

Amensalism can affect ecosystem resilience by:

55. What are some potential applications of amensalism in biotechnology?

Amensalism could be applied in biotechnology through: