Commensalism

Commensalism

Commensalism is a symbiotic relationship that benefit one species and neither hurts nor helps the other. in nature, individuals of one species are often physically attached to members of another. for example, epiphytes are plant that grow on the branches of other plant. in general, the host plant is unharmed, while the epiphyte that grows on its benefit. similarly, various marine animals, such as barnacles, grow on other, often actively moving sea animal like whales and thus are carried passively from place to place. these passenger presumably gain more protection from predation than they would if they were fixed in one place, and they also reach new resources of food. the increased water circulation that such animal receive as their host moves around may be of great importance, particularly if the passenger are filter feeders. the gametes of the passenger are also more widely dispersed than would be the case otherwise

Example of Commensalism

The best known examples of commensalism involve the relationship between certain small tropical fishes and sea anemone, marine animals that have stinging tentacles. these fish have evolved the ability to live among the tentacles of sea anemones, even though these tentacles would quickly paralize other fishes that touched them. the anemone fishes feed on the detritus left from the meals of the host anemone, remaining uninjured under remarkable circumstance. (See Picture 1)

On land, an analogous relationship exist between birds called oxpeckers and grazing animals such as cattle or rhinoceros. the birds spend most of their time clinging to the animals, picking off parasites and other insects, carrying out their life cycle in close association with the host animals. (See Picture 2)

When Is Commensalism Commensalism
In each of these instances , it is difficult to be certain whether the second partner receives a benefitor not; there is no clear-cut boundary between commensalism and mutualism. for instance, it may be advantageous to the sea anemones to have particle of food removed from tentacles; it may then be better able to catch other prey. similarly, while often thought of as commensalism , the association of grazing mammals and gleaning birds is actually an example of mutualism. the mammal benefit by having parasites and other insects removed from its body, but the birds also benefut by gaining a dependable source of food.
On the other hand, commensalism can easily transform into parasitism. for example oxpeckers are also known to pick not only parasites, but also scabs off their grazing host. once the scab is picked, the birds drink blood that flows from the wound. Occasionally the cumulative effect of persistant attacks can greatly weaken the herbivore, particularly when conditions are not favorable, such as during droughts.

So Commensalism is the benign use of one organism by another