Editing Symbiosis (section)

=== Mutualism ===

{{main|Mutualism (biology)}}

[[File:Calcinus laevimanus hermit crab with Calliactis sea anemone. 2 frames in one.jpg|thumb|upright=1.25|[[Hermit crab]], ''Calcinus laevimanus'', with sea anemone]]

Mutualism or interspecies [[reciprocal altruism]] is a long-term relationship between individuals of different [[species]] where both individuals benefit.<ref name="Paracer-2000">{{Harvnb|Paracer|Ahmadjian|2000|p=6}}</ref> Mutualistic relationships may be either obligate for both species, obligate for one but facultative for the other, or facultative for both.

[[File:Bryolith (Banc d'Arguin, Mauritania).jpg|thumb|upright|[[Bryolith]]s document a mutualistic symbiosis between a [[hermit crab]] and encrusting [[bryozoans]].]]

Many [[herbivores]] have mutualistic [[gut flora]] to help them digest plant matter, which is more difficult to digest than animal prey.<ref name="Moran-2006"/> This gut flora comprises cellulose-digesting [[protozoans]] or bacteria living in the herbivores' intestines.<ref>"symbiosis." The Columbia Encyclopedia. New York: Columbia University Press, 2008. Credo Reference. Web. 17 September 2012.</ref> [[Coral]] reefs result from mutualism between coral organisms and various algae living inside them.<ref>{{Harvnb|Toller|Rowan|Knowlton|2001}}</ref> Most land plants and land ecosystems rely on mutualism between the plants, which [[carbon fixation|fix]] carbon from the air, and [[Mycorrhizal|mycorrhyzal]] fungi, which help in extracting water and minerals from the ground.<ref>{{Harvnb|Harrison|2005}}</ref>

An example of mutualism is the relationship between the [[ocellaris clownfish]] that dwell among the [[tentacle]]s of [[Heteractis magnifica|Ritteri sea anemone]]s. The territorial fish protects the anemone from anemone-eating fish, and in turn, the anemone stinging tentacles protect the clownfish from its [[predator]]s. A special [[mucus]] on the clownfish protects it from the stinging tentacles.<ref>{{Harvnb|Lee|2003}}</ref>

A further example is the [[goby]], a fish which sometimes lives together with a [[Caridea|shrimp]]. The shrimp digs and cleans up a burrow in the sand in which both the shrimp and the goby fish live. The shrimp is almost blind, leaving it vulnerable to predators when outside its burrow. In case of danger, the goby touches the shrimp with its tail to warn it, and both quickly retreat into the burrow.<ref>{{Harvnb|Facey|Helfman|Collette|1997}}</ref> Different species of gobies (''[[Elacatinus]] spp.'') also [[Cleaning symbiosis|clean up ectoparasites]] in other fish, possibly another kind of mutualism.<ref>{{cite journal |last1=Soares |first1=M. C. |last2=Côté |first2=I. M. |last3=Cardoso |first3=S. C. |last4=Bshary |first4=R. |title=The cleaning goby mutualism: a system without punishment, partner switching or tactile stimulation |journal=Journal of Zoology |date=November 2008 |volume=276 |issue=3 |pages=306–312 |doi=10.1111/j.1469-7998.2008.00489.x }}</ref>

A spectacular example of obligate mutualism is the relationship between the [[siboglinid]] [[tube worm (body plan)|tube worm]]s and symbiotic [[bacteria]] that live at [[hydrothermal vents]] and [[cold seep]]s. The worm has no digestive tract and is wholly reliant on its internal symbionts for nutrition. The bacteria oxidize either [[hydrogen sulfide]] or methane, which the host supplies to them. These worms were discovered in the late 1980s at the hydrothermal vents near the Galapagos Islands and have since been found at [[deep-sea]] hydrothermal vents and cold seeps in all of the world's oceans.<ref>{{harvnb|Cordes|Arthur|Shea|Arvidson|2005}}</ref>

Mutualism improves both organism's competitive ability and will outcompete organisms of the same species that lack the symbiont.<ref>{{cite journal |last1=Clay |first1=Keith |last2=Holah |first2=Jenny |title=Fungal Endophyte Symbiosis and Plant Diversity in Successional Fields |journal=Science |date=10 September 1999 |volume=285 |issue=5434 |pages=1742–1744 |doi=10.1126/science.285.5434.1742 |pmid=10481011 }}</ref>

A facultative symbiosis is seen in encrusting [[bryozoans]] and [[hermit crabs]]. The bryozoan colony (''Acanthodesia commensale'') develops a cirumrotatory growth and offers the crab (''Pseudopagurus granulimanus'') a helicospiral-tubular extension of its living chamber that initially was situated within a gastropod shell.<ref>{{cite journal |last1=Klicpera |first1=A. |last2=Taylor |first2=P. D. |last3=Westphal |first3=H. |title=Bryoliths constructed by bryozoans in symbiotic associations with hermit crabs in a tropical heterozoan carbonate system, Golfe d'Arguin, Mauritania |journal=Marine Biodiversity |date=December 2013 |volume=43 |issue=4 |pages=429–444 |doi=10.1007/s12526-013-0173-4 |bibcode=2013MarBd..43..429K }}</ref>