Commensalism: Definition, Types, and Examples

Definition of Commensalism

Commensalism is an association between two organisms where one organism gets benefits while the other remains unaffected. On the other hand, the other forms of symbiosis, such as mutualism and parasitism, are opposite of commensalism.

The key distinction between commensalism and other kinds of symbiosis is that the second organism or host is unaffected in commensalism. Many scientists believe that this is highly unlikely and that most commensalism may turn out to be either mutualism or parasitism after a thorough examination.

Others believe commensalism exists and influence on the host is invisible. In the natural world, there are several examples of apparent commensalism. Transportation, nourishment, protection, and a number of additional advantages may be achieved in a commensal relationship.

Many commensal organism hosts seem to be unharmed or are only mildly troubled by the presence of commensal organisms.

Commensalism Examples

1. Pseudoscorpions

The pseudoscorpion is a fascinating example of commensalism. These are very small scorpions (less than a centimeter in length) that ride on the backs of much bigger insects. A pseudoscorpion is stuck to the leg of a much bigger fly as shown in the figure above.

Unlike a regular scorpion, the pseudoscorpion does not have a stinger and cannot kill its host. In doing so, the pseudoscorpion can move from one place to another. In this example, the larger insect is slightly troubled by the pseudoscorpion.

The partnership is momentarily and gets over once the pseudoscorpion reaches to another destination. In certain situations, the fly may get overwhelmed when too many pseudoscorpions try to ride simultaneously.

In this situation, the fly spends too much energy flying, which turns into a parasitic relationship. There is minimal distinction between commensalism and parasitism and challenging to identify such differences.

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2. Bait Fish and Manta Rays

The commensalism is often observed between small baitfish as well as manta rays. In this situation, the baitfish are protected just by being near to the bigger fish. Usually, large schools of tiny fish are found under the fins of manta rays.

In this situation, the large fin acts like a protective umbrella for small fish else; they will be easy targets of birds or other prey. However, the manta ray is unharmed by the baitfish and may not even feel them around. Interestingly, most big marine creatures are followed or adhered to by one or smaller species.

Contrary to this, some associations are parasitic in nature, for example, lampreys, where they feed on their hosts. There are several situations of commensalism in which the host is completely unharmed. For instance, the smaller fish eat the leftovers after sharks kill.

Small barnacles that stick to whales are another example as long as they don’t harm the whale. In summary, a certain amount of commensalism may be tolerated without causing damage, but the condition can ultimately turn parasitic.

3. Dispersal of Seeds

Many plants have devised unusual methods of dispersing their seeds into new settings. Some of the most effective methods of seeds dispersal include sticky, barbed, or hooked. In practice, Velcro was developed after scientists examined how the seeds attach to clothes.

You will notice seeds sticking to your trousers after walking through a dense grassland. After some time, the seeds will fall off and may not cause any harm. However, this process will carry the seed to a new place or habitat similar to what we observed in the pseudoscorpion. Generally, the host does not notice the seeds and may continue their journey.

Related Biological Terms

• Symbiosis: A long-term, mutually beneficial interaction between two species.

• Mutualism: A sort of symbiosis that benefits both species.

• Parasitism: A sort of symbiosis that favors just one species.

Related Questions

1. A new kind of bacteria has been discovered in your stomach. These bacteria feed on the waste that you would typically expel during the process of energy generation. But the bacteria do not seem to help you in any way. What classification would you give this symbiotic relationship?

  • A. Mutualism
  • B. Parasitism
  • C. Commensalism

2. Anemonefish, also known as “clownfish,” are fish that live inside anemones. They are immune to the stings of the anemone’s tentacles, unlike all other fish. The anemonefish uses the anemone for protection and feeds on the scraps left behind by the anemone. Sometimes the anemone picks up parasites that the anemonefish can remove, and the anemonefish chases away fish that eat anemones. How would you categorize their symbiotic relationship?

  • A. Parasitism
  • B. Commensalism
  • C. Mutualism

3. The striped cuckoo is a South American bird. The striped cuckoo lays its eggs in the nests of other birds rather than raising its own young. The nest’s unknowing parent then raises the chick as their own. These chicks frequently consume more resources than the genetic offspring and, in some cases, kick them out of the nest or kill them. How would you categorize their symbiotic relationship?

  • A. Parasitism
  • B. Commensalism
  • C. Mutualism




Answers and Explanations

Q1. C is the right answer. This relationship is an example of commensalism since the bacteria does not affect you and benefits significantly from riding about in your gut. Mutualism would occur if the bacteria created a product that your body could utilize. It would be parasitism if the germs used your body to proliferate but killed it in the process.

Q2. C is the right answer. The connection is mutualistic because both sides profit from it. In reality, each of the 30 species of anemonefish has just one kind of anemone in which it may thrive. This shows that the species pairings have evolved as evolutionary friends for a long time.

Q3. A is the right answer. Cuckoo chicks deplete the reproductive capacity of the host birds by consuming more resources and harming other chicks. The cuckoo reaps all of the advantages while the host birds suffer a significant loss. The connection may be called commensalism if the cuckoo chicks were smaller and shared with the other birds.

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