Commensalism (+/0): Definition and Examples (Epiphytes, Cattle Egret)
Biology · Organisms and Populations · NEET
Commensalism is a population interaction where one species is benefited (+) and the other is neither harmed nor helped (0). NEET's fixed examples are: an orchid (epiphyte) growing on a mango branch, barnacles on a whale, the cattle egret with grazing cattle, and the sea anemone with the clown fish. Memory hook: think "one wins, one shrugs" — the (+/0) sign pair is the whole answer.
Commensalism (+/0): the epiphytic orchid benefits from the mango branch (support, light, space) while the mango tree is neither harmed nor helped. The same one-way benefit pattern applies to barnacle-whale, cattle egret-cattle, and clown fish-sea anemone.
Your doubts, answered
Is the cattle egret and cattle interaction commensalism or mutualism?
It is commensalism (+/0). The egret walks beside grazing cattle and eats the insects that the moving cattle stir up from the grass, so the egret benefits. The cattle are neither harmed nor helped, so their sign is 0. Because only one side gains, it is NOT mutualism (which needs both to gain, +/+).
Why is sea anemone and clown fish commensalism and not mutualism in NEET?
NCERT lists sea anemone-clown fish as commensalism (+/0): the clown fish lives among the anemone's stinging tentacles and gets protection from predators, while the anemone is unaffected. Even though some real-world biology books call it mutualism, for NEET you must follow the NCERT example and mark it commensalism.
Is an epiphyte (orchid) growing on a mango tree parasitism or commensalism?
Commensalism (+/0). An epiphyte only uses the tree branch for support, space, sunlight and air moisture; it does NOT draw food or sap from the tree. So the orchid benefits and the mango tree is unaffected. A parasite (+/-) would harm the host by taking nutrients — an epiphyte does not, so it is never parasitism.
What is the difference between commensalism and mutualism?
In commensalism only one species benefits and the other is unaffected, so the sign pair is (+/0). In mutualism BOTH species benefit, so the sign pair is (+/+). One 0 versus two + is the fastest way to tell them apart in a NEET question.
What are the two signs for commensalism?
Commensalism is (+/0): a plus for the species that benefits and a zero for the species that is neither harmed nor benefited. It is never (+/-), which is predation or parasitism, and never (-/0), which is amensalism.
⚠️ The NEET trap ✗ Marking sea anemone and clown fish (or cattle egret and cattle) as mutualism because 'both seem to gain'. ✓ NCERT places both under commensalism (+/0) — only one clearly benefits and the other is unaffected. Follow the NCERT example list, not outside biology books. 🧠 For NEET, the example decides the sign — memorise NCERT's four commensalism examples exactly.
Real NEET questions
2025
Epiphytes that are growing on a mango branch is an example of which of the following?
A · Predation
B · Amensalism
C · Commensalism ✓
D · Mutualism
Solution: An epiphyte such as an orchid on a mango branch benefits by getting support, space and light, while the mango tree is neither harmed nor benefited. This (+/0) interaction is commensalism, not predation, amensalism or mutualism.
2023 (Odisha)
Between which among the following, the relationship is not an example of commensalism?
A · Orchid and the tree on which it grows
B · Cattle Egret and grazing cattle
C · Sea Anemone and Clown fish
D · Female wasp and fig species ✓
Solution: Orchid on a tree, cattle egret with grazing cattle, and sea anemone with clown fish are all commensalism (one benefits, other unaffected). The female wasp and fig relationship is obligate mutualism (both benefit — fig is pollinated, wasp larvae are fed), so it is NOT commensalism.
2023 (Phase 1)
Match List I (Interacting species) with List II (Name of Interaction): A. Leopard and Lion; B. Cuckoo laying egg in a Crow's nest; C. Fungi and root of a higher plant in Mycorrhizae; D. Cattle egret and Cattle. (I. Competition, II. Brood parasitism, III. Mutualism, IV. Commensalism)
A · A-I, B-II, C-III, D-IV ✓
B · A-I, B-II, C-IV, D-III
C · A-III, B-IV, C-I, D-II
D · A-II, B-III, C-I, D-IV
Solution: Leopard and Lion compete for prey (Competition, I). Cuckoo in crow's nest is Brood parasitism (II). Mycorrhizae fungi and root both benefit (Mutualism, III). Cattle egret benefits while cattle are unaffected (Commensalism, IV). So A-I, B-II, C-III, D-IV.
Solved Organisms and Populations NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is an interaction between two species where one gets a benefit and the other neither gains nor loses anything. Its sign notation is (+/0).
What are the four NEET examples of commensalism?
Orchid (epiphyte) on a mango branch, barnacles growing on the back of a whale, the cattle egret with grazing cattle, and the sea anemone with the clown fish. These are the fixed NCERT examples.
Is barnacle on a whale commensalism?
Yes. Barnacles get a place to attach and a free ride to food-rich waters, while the whale gets no apparent benefit or harm, so it is commensalism (+/0).
How is commensalism different from amensalism?
Commensalism is (+/0) — one benefits, the other is unaffected. Amensalism is (-/0) — one is harmed, the other is unaffected. The difference is whether the affected species gains or loses.
Which population interaction is NOT commensalism among common NEET options?
The fig and fig wasp relationship is mutualism, not commensalism, because both species benefit. This is a repeated NEET trap option.
