Commensalism – Concept, examples and what is mutualism

We explain what commensalism is and its differences with mutualism. Also, examples and how it develops in the desert.

Remora - commensalism
The phoresis occurs when the commensal uses another species to transport itself.

What is commensalism?

Commensalism is known as a specific type of interspecific biological interaction, that is, interaction between individuals of different species, characterized by the benefit of only one of those involved, without the other party receiving any type of damage or harm.

The term commensalism comes from the Latin cum Mensa, which translates as “share the table”, and originally it was used for those cases in which one animal fed on the remains of another’s food, as scavengers do, waiting for the hunter to finish feeding. However, there are many other cases that can be understood as commensalism, such as:

  • Foresis. It occurs when the diner uses another species to move from one place to another.
  • Tenancy. In this case, the diner finds lodging in the member of the other species.
  • Metabiosis or thanatocresis. The diner takes advantage of the excrement, remains or corpses of another species to protect themselves, reproduce or help themselves in some way.

Commensalism and mutualism

Mushroom - commensalism
Some fungi live between the roots of certain trees exchanging nutrients.

Unlike commensalism, in which only one species involved benefits, in the case of mutualism, it is both species that benefit from their interaction. This type of case is typical among species that present biological characteristics compatible with each other, being able to provide positive feedback, that is, to give mutual benefit.

This is the case, to cite an example, of mycorrhizae: fungi that make life between the roots of certain trees, exchanging with them nutrients and organic matter (used by the fungus) in exchange for water (usable by the roots of the tree). Both organizations benefit.

Follow on: Mutualism

Examples of commensalism

Some common examples of commensalism are:

  • Remoras. Small saltwater fish capable of attaching itself to larger and stronger animals, such as sharks, to take advantage of their ability to swim quickly and move from one place to another quickly.
  • Sea acorns. A genus of immobile marine crustaceans, they make life on the shells of mussels, oysters and other bivalves, as tenants.
  • Hermit crabs. With a soft abdomen, they take advantage of the empty shells of sea snails to enter and protect themselves, as if it were their own.
  • Certain species of epiphytic plants, not parasites. They live on the branches of large trees, thus accessing levels of sunlight that are scarce at ground level.

Commensalism in the desert

Commensalism - mutualism - desert
Some burrows are abandoned and inhabited by other species.

The desert habitat is one of the most extreme in the world and its flora and fauna are adapted to its difficult climatic conditions. This does not prevent them from forming commensal relationships, although they certainly occur less frequently than in other more friendly environments. Examples of this are as follows:

  • Burrows dug underground by rodents are often abandoned, and then other species can inhabit them and flee into the sun, as certain types of snakes and scorpions do.
  • Desert owls and owls take refuge in holes made by other species within cacti, keeping their young there and gaining protection from the sun and other species.
  • Birds of prey are frequent in the desert, like certain species of vulture, and they feed on any organic debris resulting from the hunt of larger species.

Other types of interspecific relationships

Predation - commensalism
In predation, one individual kills another for nutritional benefit.

In addition to commensalism and mutualism, which we have already discussed, there are the following types of interspecific relationships:

  • Parasitism. It occurs when one species benefits from the other nutritionally or otherwise, that is, it obtains benefits from it, but in this case causing damage of some kind. A perfect example of this are mosquitoes, which feed on the blood of animals to incubate their eggs, and in return can transmit diseases to which it acts as a contagion agent.
  • Symbiosis. It is a very narrow degree of mutualism, in which the species involved end up becoming codependent, that is, needing the presence of the other to survive or to complete their life cycles. A good example of this is the relationship between an alga and a fungus to form a lichen, exchanging structure for moisture and nutrients.
  • Competence. Quite the opposite to commensalism, it occurs when two species compete or face each other for access to the necessary resources to survive, so that only one of them will be able to obtain a benefit. This is the case, for example, of the competition between hyenas and vultures, or other African scavengers, to devour the remains of the lion hunt.
  • Predation The fundamental type of interaction in the food chain is that one species (the predator) hunts and devours another (the prey), thus obtaining a nutritional benefit and ending the existence of the other. This is what happens when a fox hunts a rabbit and eats it.
  • Amensalism. In this case, the interaction between the species is detrimental to one of them, without the other obtaining any benefit in return. This is the case with trees such as Eucalyptus or Walnut, for example, which prevent the growth of other plant species around them, without being directly benefited in the process.