Commensalism

Commensalism

Commensalism is a type of symbiosis, specifically, a biological relationship in which one species benefits from an interaction, while the host species is neither positively or negatively affected to any tangible degree.

The most classic example of commensalism is that of scavengers, who benefit from predators killing prey in that the remaining scraps provide them with a source of food. The predator, however, is essentially unaffected by the behavior of scavenger cleaning up after it leaves its kill behind.

One type of commensalisms, known as inquilinism, occurs when an organism uses a second organism as a place to live. For example, epiphytic plants (which grow on other plants but are not parasitic) benefit from living on host plants, because the host provides a substrate (base) upon which to grow relatively high in the canopy. The host trees, however, are not affected in any significant way by this relationship. Some plants are specialized as epiphytes, for example, many species of air-plants or bromeliads (family Bromeliaceae), orchids (Orchidaceae), and ferns (Pterophyta). Many lichens, mosses, and liverworts are also epiphytes on trees.

Animal analogues (types or examples) of inquilinism also exist. Some sea anemones (order Actiniaria) benefit by growing on the upper carapace of a hermit crab (crustacean infraorder Anomura) because they are able to filter more water and acquire more food. However, the crab is apparently unaffected by the presence of the sea anemone.

A type of commensal relationship, known as phoresy, is similar to biological hitch-hiking in which one organism benefits through access to transportation while the animal providing this service is not significantly affected by its role. For example, many plants produce fruits that adhere to fur and are thereby dispersed by the movement of mammals. Some North American examples of such animal-dispersed plants are the burdock (Arctium lappa ), beggar-tick or stick-tight (Bidens frondosa ), and tick-trefoil (Desmodium canadense ). The fruits of these plants have special anatomical adaptations for adhering to fur–in fact, those of the burdock are the botanical model from which the idea for the very useful fastening material known as Velcro was developed.

A third type of commensalism, called metabiosis, describes a situation in which one animal uses something that a second animal has created. For example, some tube worms line their tunnels with shells left behind by clams.