Commensalism is an association between unrelated organisms, where one partner , the commensal, benefits while the other, the host, is unaffected. The host is said to be neutral since it neither gains benefit from nor is harmed by the association.
In many examples of commensalism, one partner feeds on the surplus or discarded food of the other, giving rise to the description 'eating on the same table'. This is illustrated By the association between the shark sucker or remora and the sharker. The remora dorsal fin is modified into a holdfast like structure. By means of this , the remora attaches itself temporary to the underside of a shark. When the shark feeds, the remora eats the scraps that pass by it. In addition, the remora gets protection and a wide distribution. The shark , however, is unaffected by this association. Many bacteria in our large intestine are also commensals. They feed on the unwanted food and get protection, while we are usually unaffected.
The association between an epiphyte and a tree may be regarded as commensalism. Here, the epiphyte gets a site where it can get enough sunlight to carry out photosynthesis . the advantage here is positional.
