Commensalism is a type of symbiosis where one kind of organism benefits from another organism. However, the other organism does not benefit or get harmed at all.
Because one organism is positively impacted by this association and the other party unaffected, this association is neutral for them.
This kind of interaction can occur among organisms that are of similar biological origins or completely different origins.
The term “commensalism” was coined by Pierre-Joseph van Beneden in 1876. A symbiotic association qualifies as commensalism only when it fulfills some important factors:
- Whether one of the engaging parties benefits
- The other organism is neither benefited nor harmed by the interaction
- The association happens continuously and is consistent i.e., it is a long-term based interaction. It is not something that happens only once or twice, based on chance.
Commensalism can be of multiple types:
- Metabiosis (It is the interaction that majorly happens between organisms that are often dead and other different types of organisms like microorganisms which take advantage of the dead organism and exploits their body for habitat and resources).
- Inquilinism (It is the condition where one organism acts as the permanent habitat for another organism, birds living in the trees is a popular example of such interactions).
- Phoresy (Here majority of the organisms use another organism as a carrier. They get transported from one place to another without spending any kind of energy of their own and it provides them with newer food resource options as well).
There are many instances of commensalism in nature and here are 15 such examples of commensalism that exist among different animals and plants:
1. Animals and Trees
2. Jackals and Tigers
3. Burdock Plants and Animals
4. Maggots and Dead Animals
5. Hermit Crabs and Dead Gastropods
6. Millipedes and Birds
7. Humans and Dogs
8. Barnacles and Sea Turtles
9. Bromeliads and Other Animals
10. Cattle Egrets and Livestock
11. Woodpeckers and Other Animals
12. Butterflies and Milkweed
13. Army Ants and Birds
14. Sea Cucumbers and Emperor Shrimp
15. Fungus and Humans
How these Animals Affect One Another
1. Animals and trees
There are a variety of animals that live trees and use them as their habitat. Many of these organisms even use the trees as a form of defense against their predators.
For example, tree frogs use the giant leaves of trees in forests as a cover against heavy rain. It also allows them to shelter conveniently in the wild.
Similarly, birds live in holes in tree trunks.
Many insects like termites often feed on the flowers and fruits falling from the trees and build their nests using the fallen twigs, leaves, and branches of the trees.
These organisms do not end up affecting the tree in any positive or negative manner but get benefits for themselves. Hence, this is an example of commensalism.
Another great example in this regard is the association of orchids and large trees in dense tropical forests. The orchids use the larger trees as anchors for their growth.
Growing along the branches and trunks of the tree allows them to get a better supply of sunlight. They also collect rainwater flowing on the outer body of the tree.
However, they do not depend on the tree for any kind of nutrition as they have their photosynthesis process, so they do not harm the tree in any way but get immense benefits from the tree.
2. Jackals and tigers
Golden Jackals hunt in packs or at least in pairs. However, often times they get expelled out of their pack.
In such instances, they find it hard to survive on their own as hunting all by themselves is something that is not their strong suit.
To solve this issue, many of these jackals are found to demonstrate a commensal relationship with the tigers living in their habitat.
Golden jackals who operate on their own are often found to follow tigers on their hunts. Once the tigers have feasted on their prey, the jackal then eats all the leftover remains of the prey.
3. Burdock plants and animals
Seed dispersal is an important part of a plant’s life. Burdock plants have developed a unique way to enhance the better dispersal of their seeds.
Their seeds have a long, curved, and sharp-looking structure that easily gets attached to the fur of animals moving past the Burdock plants.
The seeds are incredibly lightweight and quite sharp in nature which allows them to attach themselves to the body of the fast-moving animals but are not sharp enough to hurt or pierce through their skin.
4. Maggots and dead animals
Maggots demonstrate metabiosis commensalism where they build their habitat within the body of dead organisms.
They feed onto the nutrients and remains of the dead animals. The moist inner chambers of the body provide them with the perfect condition to lay their eggs.
The maggots coming out of the eggs will feed onto the flesh and later on they will move out of the body of the dead organism.
A sudden influx of maggots in the house is often a signal that there is a dead animal, most probably rodents or lizards, in the house that has been decaying for the past few days.
5. Hermit crabs and dead gastropods
Hermit crabs depend on shells for their survival. It is an important defense mechanism that protects them from a variety of predators both on land and in water.
However, they do not naturally contain these shells. They need to acquire them from other sources.
They are majorly found to acquire the dead shells of gastropods and then they start to use these shells as their cover.
So these crabs are dependent upon the gastropod shells for their better survival and this symbiosis doesn’t affect the gastropods in any way or other as the hermit crabs only acquire the shells of dead gastropod snails and not of living ones.
6. Millipedes and birds
This is an example of a transport commensalism association, also termed phoresy, where one organism attaches itself to another organism with the sole purpose of getting transported from one place to another.
Millipedes are little organisms belonging to the arthropod phylum and they sometimes attach themselves to the bird feathers to get a free ride from one place to another.
When the bird goes into a new location comes off the bird’s body and goes out looking for newer food resources.
7. Humans and dogs
Remains dating back 33000 years show that dogs and humans have shared a close relationship even way before humans have settled down and started agriculture.
It is thought to believe that the relationship between dogs and humans started initially as a commensal relationship. However slowly with time, it became a mutualistic one.
The ancestor of the present-day dogs may have followed the humans and once they have captured their prey and feasted on them, the dogs used to serve their appetite by eating the remains and leftovers.
So with time they became more fearless of the humans and started to be closer with them which ultimately converted the relationship from commensalism to a mutualistic one as the dogs used to further help out the humans in hunting and in defending them from all kinds of danger out in the wild.
8. Barnacles and sea turtles
Barnacles are organisms that attach themselves to different organisms like whales, turtles, etc and display a commensal relationship.
In adult forms, barnacles follow a sessile lifestyle, which means they do not move on their own. They not only attach themselves to other living organisms but to non-living items (like big rocks, ships, etc.) as well.
The barnacles belonging to the Chelonibia genus are more commonly known to attach themselves to sea turtles. They attach themselves to the turtles using a cup-shaped attachment organ present in their body.
Barnacles serve their appetite by catching tiny organisms moving around them and hence they need to attach themselves to organisms or items that are constantly moving through the water as it will enhance their chances of catching newer prey.
Barnacles are lightweight and as such pose, no threat to the turtles and hence have a symbiotic relationship with the turtles. But in certain instances, they can end up harming the turtles, and in such instances, the relationship changes from commensalism to parasitism.
9. Bromeliads and other animals
Bromeliads do an effective job of capturing water from their adjacent environment and then storing that water.
This retention capability of excess water ends up attracting a variety of insects and larger animals.
These organisms use the plant as their shelter and depend on the water storage system of the plant. The animals do not affect the plant adversely. So they exhibit a commensal relationship with the plant.
10. Cattle egrets and livestock
Cattle egrets are birds that move along with various kinds of livestock. The movement of the larger organisms stirs up the vegetation which further leads to the movement of insects that were residing in that particular location.
The egrets take the advantage of this chaos among the insects and feed onto these little organisms.
They often sit onto the body of the livestock animals and move from place to place using the livestock as a carrier and hence end up saving loads of energy. The whole process doesn’t affect the livestock in any form hence this is a widely observed commensal behavior.
11. Woodpeckers and other animals
Woodpeckers are noted for their special skills in drilling small compact holes in the trees. They use these holes as nests and lay their eggs there during the breeding season.
However, once the babies grow up and leave the nest, the place remains vacant for a while after which other kinds of birds and different other organisms like squirrels make these places their home.
They do not only drill holes for making their nests but often they drill smaller holes in the trees to look for bugs. So even smaller organisms then use these holes as their habitat.
12. Butterfly and milkweed
There is this particular variety of butterflies, called the Monarch butterflies which is very common in the northern part of America.
The larvae of the Monarch butterflies attach themselves to specific varieties of Milkweed plants which are known to contain a certain poisonous component named cardiac glycoside.
Owing to the presence of such toxic substances, most birds and other organisms avoid being around these plants.
The larvae of these butterflies are resistant to this poisonous compound and they even end up extracting the cardiac glycoside into their body from the plant.
They end up storing the poison in their body throughout their life. Because of this reason, birds and other organisms avoid preying on this variety of butterflies.
13. Army ants and birds
In hindsight, it may look odd that ants and birds can share any kind of a commensal relationship as they have a prey and predator relationship as per the ecological hierarchy.
However, army ants and birds are often found to share a distinct relationship where the birds do not harm the ants but follow their trail.
By doing so they often end up finding dead insects or in some cases nests of living insects which then acts as the perfect source of food for the birds. The ants here are not getting harmed in any manner but the birds are getting benefited by finding food for themselves.
It is also believed that the reason the birds are not attacking the ants is that the army ants are known to be very ferocious in nature, they can attack in large numbers and their bites can be very painful.
14. Sea cucumbers and emperor shrimp
Sea cucumbers are stronger ocean organisms in comparison with the emperor shrimps and hence the shrimps often attach themselves to the sea cucumber body as that provides them with an added layer of security.
Moreover, the sea cucumbers act as underwater transport for the shrimps as they get to travel from one place to another without spending any energy.
They are known to attach themselves to the body of a sea cucumber and then detach themselves to look for food in that zone. Later on, when they again need to go to another location, they look out for sea cucumbers and again attach themselves to their body.
15. Fungus and Humans
There are many kinds of fungal species that live within the human body and exhibit a symbiotic relationship with the host. Most of them demonstrate a commensal relationship with the host.
However, a handful of them are also capable of causing diseases and then they switch from a commensal relationship to a parasitic one.
Candida and Cryptococcus are fungus varieties that are perfect examples of such fungi that can switch from commensalism to parasitic relationships at opportune moments, particularly when the host immune system is not performing well.
Commensialim is a form of symbiosis that has had hugely positive impacts on animals, plants, and the evolution of ecosystems. It is a way in which animals and plants can rely on other organisms in their ecosystems without harming them. This often leads to coevolution and peaceful coexistence of organisms within an ecosystem.
It’s also a reminder to us that the loss of one organism from an ecosystem can have devastating collateral effects because organisms in an ecosystem often have other organisms relying on them for sustenance, shelter, reproduction, and protection.