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A titan triggerfish (Balistoides viridescens) creates feeding opportunities for smaller fish by moving large rocks too big for them to shift themselves.

In ecology, commensalism is a class of relationship between two organisms where one organism benefits without affecting the other. It compares with mutualism, in which both organisms benefit, amensalism, where one is harmed while the other is unaffected, and parasitism, where one benefits while the other is harmed.

Commensalism derives from the English word commensal, meaning "eating at the same table" in human social interaction, which in turn comes through French from the Medieval Latin commensalis, meaning "sharing a table", from the prefix com-, meaning "together", and mensa, meaning "table" or "meal".[1] Originally, the term was used to describe the use of waste food by second animals, like the carcass eaters that follow hunting animals, but wait until they have finished their meal.[citation needed]

The term "Commensalism" was introduced by Pierre-Joseph van Beneden in 1876.[2]

Examples of commensal relationships[edit]

Commensalism is harder to demonstrate than parasitism and mutualism, for it is easier to show a single instance whereby the host is affected than it is to prove or disprove that possibility. One example is a whale and barnacles. Another is the titan triggerfish (Balistoides viridescens) creates feeding opportunities for smaller fish by moving large rocks too big for them to shift themselves. Yet another example is the remora, which eats leftover food from a whale and "hitches a ride".[citation needed]


Whether the relationship between humans and some types of our gut flora is commensal or mutualistic is still unanswered.

Some biologists argue that any close interaction between two organisms is unlikely to be completely neutral for either party, and that relationships identified as commensal are likely mutualistic or parasitic in a subtle way that has not been detected. For example, epiphytes are "nutritional pirates" that may intercept substantial amounts of nutrients that would otherwise go to the host plant.[3] Large numbers of epiphytes can also cause tree limbs to break or shade the host plant and reduce its rate of photosynthesis. Similarly, phoretic mites may hinder their host by making flight more difficult, which may affect its aerial hunting ability or cause it to expend extra energy while carrying these passengers.


Phoretic mites on a fly (Pseudolynchia canariensis)
Phoresy, a pseudoscorpion on the leg of a crane fly

Like all ecological interactions, commensalisms vary in strength and duration from intimate, long-lived symbioses to brief, weak interactions through intermediaries.


Phoresy is one animal attached to another exclusively for transport, mainly arthropods, examples of which are mites on insects (such as beetles, flies or bees), pseudoscorpions on mammals[4] or beetles, and millipedes on birds.[5] Phoresy can be either obligate or facultative (induced by environmental conditions).


Inquilinism is the use of a second organism for permanent housing. Examples are epiphytic plants (such as many orchids) that grow on trees,[6] or birds that live in holes in trees.


Metabiosis is a more indirect dependency, in which one organism creates or prepares a suitable environment for a second. Examples include maggots, which feast and develop on corpses, and hermit crabs, which use gastropod shells to protect their bodies.

See also[edit]

  • Symbiosis - long-term interactions between different biological species, which can be mutualistic, commensal or parasitic
  • Mutualism - where both organisms experience mutual benefit in the relationship
  • Parasitism - where one organism benefits at the expense of another


  1. ^ Harper, Douglas. "commensalism". Online Etymology Dictionary. 
  2. ^ van Beneden, Pierre-Joseph (1876). Animal parasites and messmates. London, Henry S. King.[page needed]
  3. ^ Benzing, D.H. (1980) Biology of the Bromeliads. Eureka, California: Mad River Press.[page needed]
  4. ^ Durden, Lance A. (June 1991). "Pseudoscorpions Associated With Mammals in Papua New Guinea". Biotropica 23 (2): 204–6. JSTOR 2388309. 
  5. ^ Tajovský, Karel; Mock, Andrej; Krumpál, Miroslav (2001). "Millipedes (Diplopoda) in birdsˈ nests". European Journal of Soil Biology 37 (4): 321–3. doi:10.1016/S1164-5563(01)01108-6. 
  6. ^ C. Michael Hogan. 2011. Commensalism. Topic Ed. M.Mcginley. Ed-in-chief C.J.Cleveland. Encyclopedia of Earth. National Council for Science and the Environment. Washington DC

External links[edit]

Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Commensalism — Please support Wikipedia.
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