Commensalism is a long-term biological interaction in which members of one species benefit while those of the other species do not. A golden jackal (the commensal) that follows a tiger (the host) to eat on the leftovers from the tiger's kills is an example of commensalism. In the ecosystem, commensalism is crucial because it allows diverse species to interact and coexist without causing damage. This article will explain to you about Commensalism which will be helpful in preparing the Environment syllabus for the UPSC Civil service exam.

Commensalism - Concept

• Commensalism is a relationship between members of two species in which one derives food or other benefits from the other without harming or benefiting the latter.
• The commensal is defined as the species that benefit from the relationship.
• The commensal may acquire nourishment, shelter, support, or movement from the unaffected host species.
• Pierre-Joseph van Beneden, a Belgian palaeontologist and naturalist, coined the term commensalism, along with the term mutualism, in 1876.
• A larger host and a smaller commensal are frequently found in a commensal relationship.
• The contact leaves the host organism relatively unaltered, whilst the commensal species may exhibit significant morphological adaptation.
• Mutualism, on the other hand, is a partnership in which both species benefit.

Commensalism - Example

• The remora (family Echineidae), which rides on the backs of sharks and other fish, is a well-known example of a commensal.
• Remoras have evolved a flat oval sucking disc structure on the top of their heads that clings to the bodies of their hosts.
• Remoras and pilot fishes both eat the scraps leftover from their hosts' meals.

Remora And Pilot Fishes

• Other commensals include birds like the great egret (Ardea alba), which eat insects left behind by grazing mammals or soil organisms stirred up by ploughing.
• Biting lice, fleas, and louse flies are commensals, meaning they feed on the feathers of birds and the sloughed-off skin flakes of mammals without harming them.

Commensalism - Types

• All types of commensalism require one organism to profit from the interaction while the other remains unaffected.
• However, there are three primary types of commensalism within those parameters.

Inquilinism

• Inquilinism is when one organism acts as a permanent home for another.
• A woodpecker, for example, drills a hole in a saguaro cactus to utilise as a nesting place.
• The woodpecker reaps the benefits, but the cactus remains unharmed.

Metabiosis

• When an organism (typically a dead one) creates a habitat for another creature, such as bacteria growing in the remnants of a dead animal, this is known as metabiosis.
• Because the animal is dead, it cannot be damaged or benefited, but the germs get a home and food source.

Phoresy

• When one organism transports another, this is known as phoresy.
• Arthropods, such as mites that live on insects, are the most common examples of commensalism.
• Anemones attached to hermit crab shells, pseudoscorpions living on mammals, and millipedes travelling on birds are some other examples.
• Phoresy can be either obligatory or optional.

Microbiota

• Microbiota is a commensal organism that lives in communities within a host organism.
• The bacterial flora found on human skin is an example.
• Microbiota is debated by scientists as to whether it is genuinely a form of commensalism.
• There is evidence that bacteria provide some protection to the host in the case of skin flora, for example (which would be mutualism).

Conclusion

Although it can be difficult to prove that an organism's contact with another creature has no effect on it, there are several examples of commensalism in nature. Mutualism, parasitism, predation, amensalism, and competition are all types of symbiosis; commensalism is just one of them.

FAQs 

Q1: What is commensalism in ecology?

Q2: Can you give an example of commensalism in the environment?

Q3: How is commensalism different from mutualism and parasitism?

Q4: What role does commensalism play in ecosystems?

Q5: Are there any drawbacks to commensalism for the species involved?

MCQs 

1. In a commensal relationship, what happens to the host species?

A) The host benefits

B) The host is harmed

C) The host is unaffected

D) The host becomes extinct

2. Which of the following is an example of commensalism?

A) A bee pollinating a flower

B) A mosquito feeding on human blood

C) Birds feeding on insects disturbed by grazing animals

D) A tree providing shade to an animal

3. How does commensalism differ from mutualism?

A) Both species benefit in mutualism, while only one benefits in commensalism

B) One species benefits in commensalism, while both species benefit in mutualism

C) Commensalism is always harmful to the host

D) Mutualism involves no benefit to either species

4. Which of the following is a consequence of commensalism?

A) Both species grow stronger

B) One species is harmed

C) One species benefits, and the other is unaffected

D) Both species die

5. Which is an example of commensalism in the animal kingdom?

A) Lions and zebras

B) Mites living in the fur of mammals

C) Oxpecker birds and buffalo

D) Bees and flowers

GS Mains Questions and Model Answers

Q1: Explain the concept of commensalism and discuss its significance in ecological systems.

Answer: Commensalism is a type of symbiotic relationship in which one organism benefits from the relationship, while the other organism is neither helped nor harmed. This type of relationship plays a significant role in the dynamics of ecosystems, as it allows for resource utilization without negatively impacting the host species. Commensal relationships contribute to biodiversity and the overall balance of ecosystems by enabling different species to coexist and utilize available resources. For example, birds that follow grazing animals to catch insects do not harm the animals but gain an easy food source, benefiting the birds and leaving the animals unaffected. This relationship highlights the importance of resource-sharing and coexistence in natural systems.

Q2: How does commensalism contribute to the survival and adaptation of species in ecosystems?

Answer: Commensalism allows species to adapt to their environment and survive by providing them with resources or shelter without competing directly with other species. This relationship can provide species with a competitive advantage, as they can exploit resources that they might not have access to otherwise. For example, barnacles that attach themselves to whales benefit by being carried to nutrient-rich waters while the whale remains unaffected. This ability to gain resources without harming the host species can help species survive in challenging environments and adapt to different ecological niches.

Q3: Discuss how commensalism can impact biodiversity within an ecosystem.

Answer: Commensalism has a positive impact on biodiversity by promoting species coexistence. Since one species benefits without harming the other, multiple species can occupy the same environment, each utilizing different resources. This interaction can increase the number of species in an ecosystem, enhancing its biodiversity. For example, in coral reef ecosystems, various organisms, such as cleaner fish and host fish, engage in commensalism. The cleaner fish benefit by eating parasites from the host fish, which is unharmed. Such relationships increase species diversity and support the overall health of the ecosystem by preventing overpopulation of any single species and facilitating resource availability.

Previous Year Questions on Commensalism

1. UPSC CSE 2019

Question: "Explain the different types of symbiotic relationships in nature and provide examples of each."

Answer: Symbiotic relationships in nature can be classified into three main types: mutualism, commensalism, and parasitism. In mutualism, both species benefit from the relationship, such as the relationship between bees and flowers, where bees get nectar and flowers get pollinated. Commensalism involves one species benefiting while the other is unaffected, such as the relationship between cattle and cattle egrets, where the birds feed on insects disturbed by the grazing cattle. Parasitism is when one species benefits at the expense of the other, such as ticks feeding on the blood of mammals.

2. UPSC CSE 2020

Question: "Discuss the role of commensalism in enhancing ecological balance and resource sharing in ecosystems."

Answer: Commensalism plays an important role in maintaining ecological balance by enabling species to share resources without negatively impacting each other. It fosters coexistence in ecosystems by allowing organisms to access food, shelter, or transportation without direct competition or harm to the host. For example, remora fish attach themselves to larger fish or sharks, gaining free movement and food scraps without harming their hosts. This form of resource sharing helps maintain the balance of species populations and supports biodiversity by reducing the intensity of competition for limited resources.