Interspecific Relationships - Positive Interactions > Commensalism

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Estimated time: 11 minutes

CBSE: Class 12
Maharashtra State Board: Class 12
CISCE: Class 12

Definition: Commensalism

An interspecific relationship in which one organism benefits, while the other is neither benefited nor harmed.

CBSE: Class 12
Maharashtra State Board: Class 12
CISCE: Class 12

Introduction

Commensalism is an interspecific relationship where one species (commensal) benefits and the other (host) is neither benefited nor harmed.Sign Notation: (+, 0)

Role	Species	Effect
Commensal	Benefits	Gets food, shelter, support, or transport
Host	Unaffected	Neither helped nor harmed

CBSE: Class 12
Maharashtra State Board: Class 12
CISCE: Class 12

Types of Commensalism

Type	Description	Example
Phoresy	Commensal attaches to host for transport/dispersal	Barnacles on whale; Remora on shark
Inquilinism	Commensal uses host's body or structure as a home	Clownfish in sea anemone; birds nesting in tree hollows
Metabiosis	Commensal uses an environment modified by the host	Hermit crab using empty gastropod shell
Microbiota	Harmless microorganisms colonising host surfaces	Skin microbiota on mammals

CBSE: Class 12
Maharashtra State Board: Class 12
CISCE: Class 12

Examples

Example	Commensal (+)	Host (0)	Why it benefits
Orchid & Mango Tree	Orchid	Mango Tree	Gets support and sunlight. Note: It is an epiphyte; it does not steal nutrients from the tree.
Barnacles & Whale	Barnacles	Whale	Gains free ocean transport and access to plankton-rich waters (Phoresy).
Cattle Egret & Cattle	Cattle Egret	Cattle	Feeds easily on insects flushed out of the grass by the grazing cattle.
Clownfish & Anemone	Clownfish	Sea Anemone	Gets protection from predators by hiding in stinging tentacles.
Remora & Shark	Remora	Shark	Attaches for free transport and eats leftover food scraps from the shark (Phoresy).
Lianas & Forest Trees	Lianas	Forest Tree	Climbs the tree to reach sunlight. It does not penetrate the tree's tissues.

CBSE: Class 12
Maharashtra State Board: Class 12
CISCE: Class 12

Key Points: Commensalism

Commensalism (+/0) is an interaction where one species (the commensal) gains a benefit - such as food, shelter, or transport - while the other (the host) remains completely unaffected.
It occurs in various forms, such as phoresy for transport (e.g., barnacles on a whale) or inquilinism for shelter (e.g., clownfish living safely inside a stinging sea anemone).
Epiphytic plants, like orchids, grow on host plants (such as a mango tree) strictly for physical support and better sunlight, without absorbing any of the host's nutrients.
Cattle egrets exhibit this relationship by closely following grazing cattle to easily catch insects that are flushed out of the grass by the cattle's movement.
Remora fish attach themselves to the underside of sharks to gain free oceanic transport and scavenge leftover food scraps, causing absolutely no impact on the shark.