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The term commensalism ( Latin commensalis , table companion ) is used for a form of interaction between individuals of different species that is positive for members of one species and neutral for members of the other species. The term is used in different areas with slightly different definitions.

  • In the original definition, which goes back to the work of the Belgian parasitologist and paleontologist Pierre-Joseph van Beneden , a commensal is a "blackhead" that is dependent on an organism of another species for its nourishment by participating in its nourishment, this one but (unlike a parasite) does not harm. In the case of close spatial coexistence, the giving organism is called the host and the co-nourishing commensal. There are no advantages or disadvantages for the host. Only the commensal is the beneficiary of coexistence and is mostly dependent on the host. The commensal mostly feeds on waste materials or the host's excess food, but does not deprive it of any essential substances.
  • Derived from this meaning, the term was applied to any type of interaction between two types that is neutral for one partner and positive for the other. In this case, it can also be an interaction independent of food relationships (technical term: "trophic" relationships). The possible relationships sorted according to positive (+), negative (-) and neutral (0) effects are arranged in the form of an interaction matrix. There are five possible relationship pairs - or six, if one wants to consider the trivial case that the species do not interact at all (pairing 0/0). According to this definition, commensalism is the pairing (+ / 0), i.e. H. positive / neutral. Since at least one partner also benefits, this interspecific interrelationship represents a form of probiosis . The relationship is not defined here according to the mechanisms (e.g. food relationships), but exclusively according to the effects. This use of the term goes back to the influential American ecologist Warder Clyde Allee .
  • When considering mammals, it has become common practice to refer to species as commensals that are directly dependent on humans and their supplies for their nutrition.


In humans, the commensals include those microorganisms that colonize various microbiotopes as ecto- or endocommensals and are referred to in their entirety as the respective normal flora . However, this is partly also a question of mutualism , since many of the microorganisms ensure a protective environment for people and an imbalance in the flora brings health problems with it and, strictly speaking, these cannot be counted among the commensals. It is this


A typical example of commensalism are e.g. B. the scavengers of the steppes and deserts who follow the larger hunters. Occasionally, commensals can become indirect competitors through crowds or food shortages .


A well-known example is the spread of the seed heads of burdock , which attach themselves with their long, hook-tipped spines to the fur of animals passing by or to people's clothing and fall off or be pulled off the wearer elsewhere. The temporary use of other organisms as a means of transport is also known as phoresia .

Individual evidence

  1. ^ Eugenius Warming : Textbook of ecological plant geography. An introduction to the knowledge of plant associations. German, reviewed and enlarged edition by Emil Knoblauch, approved by the author. Borntraeger, Berlin 1896, p. 106 ff.
  2. Joseph Boch, Rudolf Supperer (founder), Thomas Schnieder (ed.): Veterinary Parasitology. 6th, completely revised and expanded edition. Parey, Stuttgart 2006, ISBN 3-8304-4135-5 , p. 16 ff.
  3. GCL Bertram: Aliee, WC, Emerson, AE, Park, O., Park, T. and Schmidt, KP Principles of Animal Ecology. Philadelphia and London, 1949. WB Saunders & Co. Pp. 837, 263 text figures and photographs. Price 70s . In: The Eugenics Review . tape 43 , no. 2 , July 1951, p. 101 , PMC 2973284 (free full text) - (review).
  4. ^ Jean-Pierre Gautier, Sylvain Biquand: Primate commensalism . In: Revue d'Ecologie . tape 49 , January 1994, ISSN  0249-7395 , p. 210–212 ( full text (PDF; 177 kB) ).
  5. Thomas M. Smith , Robert L. Smith : Ecology. German edition, 6th, updated edition, edited and supplemented by Anselm Kratochwil. Pearson Studium, Munich et al. 2009, ISBN 978-3-8273-7313-7 , p. 427.


  • Pierre J. van Beneden : The parasites of the animal kingdom. (= International Scientific Library. 18). Brockhaus, Leipzig 1876, ( digitized version ).
  • Claus D. Zander: Parasite-host relationships. Introduction to ecological parasitology. Springer, Berlin et al. 1998, ISBN 3-540-62859-2 .

See also