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A titan triggerfish (Balistoides viridescens)

In ecology, commensalism is a class of relationships between two organisms where one organism benefits without affecting the other. It can be compared 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.

The word commensalism is derived 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]

Pierre-Joseph van Beneden introduced the term "Commensalism" in 1876.[2]

Examples of commensal relationships[edit]

Commensalism is harder to demonstrate than parasitism and mutualism, as it is easier to show a single instance in which the host is affected than it is to disprove that possibility. One example is a whale and barnacles. Another is the titan triggerfish (Balistoides viridescens) which 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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6 news items

Lake County News
Wed, 22 Oct 2014 02:45:00 -0700

These organisms have already been recorded in Britain, and experts warn they will act as a gateway for further species due to favorable inter-species interactions that facilitate invasion, such as food provision and “commensalism” – in which one ...


Fri, 03 Oct 2014 08:33:45 -0700

Scientists have long believed that gene flow and species dispersal is only interrupted by physical barriers, like mountain ranges, rivers or even the complete disappearance of a suitable habitat. But new research into the distribution of two mouse ...

Tech Times

Tech Times
Tue, 14 Oct 2014 12:07:30 -0700

In part, this is due to commensalism, or the ability of species to thrive from the life cycles of other animals. This trait could set off an "invasion meltdown" throughout the United Kingdom, as the species help reinforce survivability of the non ...
Wed, 24 Sep 2014 14:56:15 -0700

For example, the team found that adding an opioid drug to the mix -- which mimics stress signals released by sick patients—could also switch behavior from a peaceful coexistence called commensalism to virulence for some microbe pairs. The team could ...
Science Codex
Thu, 18 Sep 2014 07:26:15 -0700

"It is heading in the direction of commensalism," says Regoes – a kind of ceasefire between two disparate partners. However, the two strategies have different evolutionary consequences: while tolerance tends to suppress the emergence of adaptations, ...

Gastroenterology Update

Gastroenterology Update
Mon, 29 Sep 2014 18:41:15 -0700

For example, the team found that adding an opioid drug to the mix could also switch behaviour from commensalism to virulence for some microbe pairs. The team could prevent this switch by feeding the worms a molecule that created high phosphate levels.

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