commensalism

Commensalism is a relationship between two species of organisms, such as plants, animals, and fungus, in which one species benefits while the other is unaffected, as in Scientists have studied the commensalism of fleas that feed on birds’ feathers. 

A well-known example of commensalism is the relationship between the remora, commonly known as a suckerfish, and a shark. The  remora uses its suction cup–like head to attach itself to a shark. The remora benefits from the speed, protection, and leftover food from the shark. The shark gets nothing from the remora. It isn’t hurt by the remora, but the remora doesn’t help the shark in any way.

You can think of commensalism as a “+/0” relationship: One species benefits while the other remains the same. This is what sets commensalism apart from the other types of relationships between organisms, such as mutualism, parasitism, and amensalism.

In mutualism, both species benefit from the relationship. For example, a bird might pick food out of the teeth of an alligator, which prevents the teeth from becoming infected. Mutualism is a “+/+” relationship because the bird gets food to eat and the alligator gets cleaner teeth.

In parasitism, one species (the parasite) benefits at the expense of the other species, a “+/-” relationship. For example, when a  mosquito bites you, it has drunk some of your blood, which nourishes it. You, however, get an itch bite and possibly a disease carried by mosquitoes, such as Eastern equine encephalitis (EEE).

In amensalism, one species harms another species while remaining unaffected, a “-/0” relationship. For example, the black walnut tree secretes a substance that is harmful to other plants. The tree isn’t harmed by either the substance or the other plants.

The first records of the word commensalism come from around 1870. It combines commensal, meaning “living with, on, or in another without either being harmed,” and the suffix -ism, which creates nouns that denote an action or practice.

Commensalism happens frequently in nature. For example, an animal might seek shade underneath a large tree or a small animal might stay near a larger herbivore to discourage predators. The key to commensalism is that one species (called the commensal) benefits in some way, while the other isn’t affected, as when a monkey rides on an elephant to travel faster and safer.

Commensalism also occurs between humans and other organisms. Some examples include bacteria that live inside us but don’t harm or help us and tiny mites that eat our dead skin or hair.

The word commensalism is more likely to be used by natural scientists or biology students.

Yuccas (e.g., century plants, Joshua trees) rely on moths for pollination and the moths themselves could not exist if it wasn't for Yucca flowers. What started as an opportunistic parasite-host relationship has since evolved into an extremely specific co-dependent commensalism. pic.twitter.com/7uHkrrmGxj

— Eric Schniter (@esworldwide) July 19, 2019

Plain-backed Sparrow(F) one of several species of bird that visit my garden & collect insects from the "scars" that Freckle-breasted Woodpeckers leave on the bark of trees. An example of commensalism where one species benefits another without causing harm to either. @Avibase pic.twitter.com/V9moEMf0WD

— Mike Rose (@NaturewatchTH) February 16, 2020

Indirect commensalism between dingoes and barn owls. Our new paper led by James Rees shows that dingoes facilitate barn owls because they promote the abundance of owls' small mammal prey by suppressing the predatory impacts of foxes and cats. https://t.co/XYbBYUzUeo pic.twitter.com/A7bsXc1F1B

— Mike Letnic (@mikeletnic) June 7, 2019

• species
• relationship
• ecology
• mutualism
• parasitism
• amensalism

Is commensalism used correctly in the following sentence?

Lice that feed on birds’ feathers without harming the bird is a type of commensalism.