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Commensalism: cattle egret eats insects stirred up by grazing Burchell’s zebra

A Burchell's zebra and a cattle egret at the Rietvlei Nature Reserve in South Africa

It is International Day for Biological Diversity and people ask what is commensalism. The search engine, Bing, has an example on the home page today which is a downloadable wallpaper photograph by Richard du Toit/Minden Pictures. It’s a great photograph of a Burchell’s zebra stirring up insects from the grass as it grazes with a cattle egret in close attendance. The egret is right up to the zebra’s head waiting to pounce for any insect which jumps up out of the grass. This is a great example of commensalism; a relationship in which one species benefits without helping or hurting the other.

A Burchell's zebra and a cattle egret at the Rietvlei Nature Reserve in South Africa

A Burchell’s zebra and a cattle egret at the Rietvlei Nature Reserve in South Africa. An example of commensalism. Please click on the image to see a larger version if you are using a desktop computer.

There are many other examples of animals working together to help in survival. Another is the way that the anemone’s tentacles protect crabs from predators and the crab’s mobility helps the anemone move around. And another is the way that Nile crocodiles have their teeth cleaned by the Egyptian plover bird as it picks food from their teeth.

Commensalism falls under the umbrella of symbiotic relationships which are close associations formed between pairs of species. They come in the form of parasitism where one species benefits and the other is harmed and in the form of commensalism where one species benefits and the other is neither harmed or helped. Another form is mutualism where both benefit. A mutually benefit interaction exists between the clownfish and anemone.

The anemone’s stinging cells protect the clownfish from predators and give pairs of clownfish a safe place to lay their eggs. The benefit is reciprocated when the clownfish drops food particles that provide nutrients for the anemone. Both organisms benefit from this relationship.

In writing this article it made me question what commensalism has to do with the animal-human relationship 😎. Well, the photograph was taken by a human! And it is an excellent photograph. If animals help each other to survive it takes some of the responsibility away from people to help nature. Humans have a duty to protect nature because nature is the planet and we live on the planet; it keeps us alive.

Below are some more articles on interspecies relationships.