What Is Commensalism?

Category: Feeding Behavior.

Commensalism is a relationship in nature where one organism benefits from another without harming it. Just as man is a social creature and has to have a certain type of relationship with everything around him, wild things work on a similar principle. Many different species share their environment with a variety of relationships. Today, I will talk about how commensalism works, and the animals that live this way.

Moss on trees. © pfly.

Moss and trees

One of the purest forms of this can be found in areas where moss grows on trees. The moss gets to share the light and the nutrients produced by the tree without causing harm to the tree. Many birds benefit from following the raids of army ants. The ants stir up the foliage on the forest floor causing insects to swarm upward and the birds have a feast. This is the same way that the cattle egret and the cows, sheep and other livestock share their habitats.

Lizards and barnacles

In desert areas, you will commonly see creosote bushes growing in the shade of the holly shrubs. The fringe-toed lizard takes advantage of dens abandoned by the desert rat. In the oceans, the barnacle and the whale are a prime example of commensalism. A barnacle is a crustacean that attaches itself to a host before hardening. It travels with the animal wherever it goes, getting its sustenance from the animal, all without apparent harm to its host.

Nurse shark with remoras. © Duncan Wright.

Remoras and sharks

The same is true of the remoras. It attaches itself to its host and survives by cleaning away any parasites that the host has picked up. Then there is the pilot fish, this one swims in front of sharks without any fear of being eaten. As the shark feeds, these brave little fish feed on any scraps that are too small for the shark.

Pilot fish and the Whitetip shark. © Peter Kölbl.

Caribous and foxes

Even in places like the Artic tundra, this relationship can be found, the caribou and arctic fox is one example. The fox follows the caribou and after it has dug through the snow and ice to uncover its meal of lichen plants, the fox will dig into the ground to hunt for small mammals.

How about insects?

This type of relationship can be observed in the insect world. the viceroy butterfly mimics the look of the monarch for protection from frogs and other predators. The monarch contains a poison that is lethal and predators know this. Human beings also have a commensalism relationship with the bacteria that lives on the skin. We have millions of bacteria colonies on our skin on a daily basis and are unaffected by them.

There are some gray ares

Commensalism is much harder to demonstrate than other types of relationships in that it is much harder to determine if the host is truly unaffected. For instance, barnacles will attach themselves to scallops. Since they both eat the same diet, it is hard to gauge whether there is a competition for food among them. Then again, the barnacle covering could possibly offer the scallop protection from natural predators. These, however, are only theories and will require further study to prove or disprove.

It is not true all of the time

Scientists are starting to label the symbiotic relationship between humans and the bacteria that grow in their digestive tracts as commensalism. The fact that neither species is harmed by the relationship is the main reasoning behind this. There are of course exceptions as in the case of ingesting E. coli. This bacteria can do serious harm, including the death of the host. This then would make the relationship more on the lines of parasitism. The study of biology is wide and varied field and a lot of the theories are still being investigated.

Relationship between organisms

  1. Cannibalism
  2. Kleptoparasitism
  3. Mutualism
  4. Parasitism
  5. Symbiosis

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