Restriction to a single host species is rare among epibiota, with many species found on multiple host species or even nonliving surfaces. For instance, many terrestrial epiphytes also grow at ground level on soil or rocks, and most mobile epifaunal taxa found on aquatic macrophytes will also colonize artificial plants, suggesting that for those epibiota there is nothing intrinsically special about the host. Obligate host-specificity is probably commonest among epibiota having a tight mutualistic relationship with their host, for example, coral-dwelling shrimps and crabs that derive shelter from and eat mucous released by their host in exchange for protecting it from crown-of-thorns starfish and other predators. There is little evidence for coevolution of such relationships.
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