Commensalism
கூட்டுவாழ்வு (ஒன்றுக்கு மட்டும் நன்மை)
Do not confuse Commensalism with Mutualism. In Commensalism, the interaction is one-sided, not a partnership. If you assume both species benefit, you will lose four marks.
The idea
Commensalism is a population interaction where one species benefits and the other remains unaffected. The benefited species is the commensal, while the host is neither harmed nor helped. Classic examples include the orchid growing as an epiphyte on a mango branch and barnacles growing on the back of a whale.
Why it matters
It allows species to utilize the habitat or resources of another organism without imposing a metabolic cost on the host, increasing survival chances.
NEET lens
NEET focuses on the (+, 0) notation for this interaction. Memorize the specific examples: orchid-mango, barnacle-whale, and cattle egret-grazing cattle. Expect a matching-type question where you must distinguish (+, 0) from (+, +) or (+, -).
Clinical significance
In the human gut, commensal bacteria like E. coli exist in a state of commensalism or mutualism depending on the strain. When this balance is disrupted, pathogenic bacteria colonize the space, leading to dysbiosis and gastrointestinal disease.
Introduction
Commensalism is an interaction in which one species benefits and the other is neither harmed nor benefited (+, 0).
Core concept
Examples (NCERT): an orchid growing as an epiphyte on a mango branch; barnacles growing on the back of a whale; the cattle egret and grazing cattle in close association — the egrets always forage close to where the cattle are grazing because the cattle, as they move, stir up and flush out insects from the vegetation that otherwise might be difficult for the egrets to find and catch; sea anemone with stinging tentacles and the clown fish that lives among them — the fish gets protection from predators, which stay away from the stinging tentacles, while the anemone does not appear to derive any benefit.
Go deeper
Commensalism and amensalism both have one partner unaffected; the difference is whether the other gains (+) or loses (−).
From Class 10
A small plant growing on a tree branch for support gets a benefit, while the tree is not affected — that is commensalism.