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(kəmĕn`səlĭz'əm), relationship between members of two different species of organisms in which one individual is usually only slightly benefited, while the other member is not affected at all by the relationship. For example, some flatworms live attached to the gills of the horseshoe crab, obtaining bits of food from the crab's meals; the crab is apparently unaffected. In many cases commensalism cannot be distinguished from parasitism (see parasiteparasite,
plant or animal that at some stage of its existence obtains its nourishment from another living organism called the host. Parasites may or may not harm the host, but they never benefit it.
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). See also competitioncompetition,
in biology, relationship between members of the same or different species in which individuals are adversely affected by those having the same living requirements, such as food or space. Intraspecific competition, i.e.
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; symbiosissymbiosis
, the habitual living together of organisms of different species. The term is usually restricted to a dependent relationship that is beneficial to both participants (also called mutualism) but may be extended to include parasitism, in which the parasite depends upon
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inquilinism, the cohabitation of animals of different species, whereby one (the commensal) benefits permanently or temporarily from the other without causing the latter any damage.

A commensal may use the other organism for protection or transportation, or it may take advantage of the latter’s food supply. Characteristically commensal animals are divided into three groups, according to the character of the interrelationship:

(1) The commensal limits itself to the use of the food of the organism of the other species; for example, the annelid Nereis lives in the coils of the shell occupied by the hermit crab and eats the crab’s leftover food.

(2) The commensal attaches itself, temporarily or permanently, to the body of the other species, in this case called the host; for example, the remora attaches itself by the dorsal fin, which has developed into a sucker, to sharks and other large fishes and uses them for transportation; certain marine hydroids settle on the skin of fish and feed on their excrement; and certain crustaceans (such as acorn barnacles) live on the skin of whales and the shells of mollusks.

(3) The commensal settles in the viscera of the host; for example, the infusorians of subclass Protociliata live in the rectum of frogs, and certain flagellates live in the intestines of mammals.

Parasitism may have originated evolutionarily from commensalism in which the commensal settles in the organs of the host. Symbiosis may also have been an elaboration of commensalism. However, commensalism is not an obligatory transitional step to parasitism or symbiosis; these forms of interrelationship may have originated independently of commensalism in the historical development of the given organisms.


An interspecific, symbiotic relationship in which two different species are associated, wherein one is benefited and the other neither benefited nor harmed.
References in periodicals archive ?
Pseudo-Code of SOS Algorithm 2 Symbiotic Organisms Search 1: Initialization 2: For iter = 1 to maximum iteration 3: For each organism in the ecosystem 4: Interact with random organism within mutualism phase 5: Interact with random organism within commensalism phase 6: Interact with random organism within parasitism phase 7: Memorize the best organism 8: End for 9: End for Resource Leveling Problem
The SOS optimization strategy is performed in three search-and-update phases (i.e., mutualism, commensalism, and parasitism) as presented subsequently.
considered the dynamic competition of mobile phone subscription in Korea and applied the Lotka-Volterra model to show the commensalism relationship [22].
The interaction between the chemotherapeutics and immune system resembles a commensalism. The presence of tumor infiltrating lymphocytes is associated with increased response of CT, whereas some agents like gemcitabine, paclitaxel, cyclophosphamide, and 5-fluorouracil may improve immunity by suppressive T-cell depletion and cytotoxic T-cell activation [71-74].
The event generates a non-festive commensalism for which appropriate codes and standards for food at the time are set.
All fungi most often interact directly or indirectly through neutralism, commensalism, mutualism, competition, parasitism and synergism, in order to survive in their habitat [2].
(43) In her recent ethnography of a Cambodian village (Forest of struggle), Eve Zucker has also discussed the role of commensalism in creating powerful signs or displays of kin-like intimacy.
Humans have been distinguished from the animals first of all thanks to the system of rigid restriction of some instincts that was formed and fixed at a very early stage of human commensalism development, without which human evolution would take another path.
While potentially pathogenic GI tract microbes are kept in check by a homeostatic commensalism, their increased abundance has been associated with diseases that include anxiety, autoimmune-disease, diabetes, metabolic-syndrome, obesity, and stress-induced and progressive neuropsychiatric diseases including autism, schizophrenia and AD (22, 24).
Then the students were to identify the type of symbiosis (i.e., mutualism, commensalism, or parasitism) they discovered for each relationship.