THIS TYPE OF RELATIONSHIP IS ESTABLISHED WHEN TWO OR MORE ORGANISMS LIVE TOGETHER WITHOUT HAVING ANY PHYSIOLOGICAL UNION. THE RELATION IS UNEQUAL IN THAT ONLY ONE INDIVIDUAL GETS THE BENEFIT FROM THE ASSOCIATION WHILE THE OTHER REMAINS UNAFFECTED.
THE CHIEF BENEFITS OF THIS ASSOCIATION ARE SHELTER, ANCHORAGE , TRANSPORTATION AND FOOD SUPPLY. A COMMENSAL THAT ATTACHES OR LIVES UPON THE HOST'S BODY IS CALLED ECTOCOMMENSAL. A COMMENSAL THAT LIVES INSIDE THE BODY OF THE HOST IS REFFERED TO AS AN ENDOCOMMENSAL. SUCKER FISH IS AN ECTOCOMMENSAL THAT ATTACHES ITSELF TO THE BODY OF A SHARK. ALL THE ECTOCOMMENSALS ARE SMALL IN SIZE AND NOT BURDENSOME TO THE HOST. THE HARMLESS PROTOZOAN IN THE INTESTINAL TRACT OF MAMMALS AND MICRO-ORGANISMS IN THE CANAL SYSTEM OF SPONGES ARE EXAMPLES OF ENDOCOMMENSALS.
MANY LARGE TROPICAL TREES PROVIDE HABITATS FOR NUMEROUS COMMENSAL PLANTS AND ANIMALS. TRUNKS AND BRANCHES PROVIDE ATTACHMENT SITES FOR PLANTS SUCH AS ORCHIDS. ATTACHMENT HARBOURAGE IS PROVIDE BY THE TREES FOR BATS, TREE FROGS, LIZARDS, INSECTS AND MANY OTHER ANIMALS. WHALES PROVIDE ATTACHMENT SITES FOR BARNACLES, ALGAE, ETC. THESE PLANTS AND ANIMALS ARE NOT PARASITIC.
ANOTHER COMMON TYPE OF COMMENSALISMS OCCURS WHEN VARIOUS SPECIES OF PLANTS AND ANIMALS USE BURROWS OR NESTS CONSTRUCTED BY OTHER SPECIES . TERMITE NESTS PROVIDE ECOLOGIC NICHES FOR MORE THAN A HUNDRED SPECIES OF OTHER ANIMALS SUCH AS ANTS, BEETLES AND MILLIPEDS.
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