What Causes Fairy Circles in the Namib Desert?

A fascinating new paper in Science on the so-called “fairy circles” in the inhospitable Namib Desert in southern Africa:

The sand termite Psammotermes allocerus generates local ecosystems, so-called fairy circles, through removal of short-lived vegetation that appears after rain, leaving circular barren patches. Because of rapid percolation and lack of evapotranspiration, water is retained within the circles. This process results in the formation of rings of perennial vegetation that facilitate termite survival and locally increase biodiversity. This termite-generated ecosystem persists through prolonged droughts lasting many decades.

Ars Technica summarizes:

But now, after a six-year study and more than 40 trips to the Namib Desert, Dr. Norbert Juergens believes he has come to understand the biological underpinnings of this strange phenomenon. According to Juergens, a single species of termites is responsible for creating and maintaining the circles. But the barren circles aren’t just a byproduct of these tiny insects living below the sandy desert surface; they are part of a carefully cultivated landscape that helps the termites—and many other organisms—thrive in an otherwise inhospitable climate.

Juergens hypothesized that if the fairy circles’ cause was biological, the organism would need to co-occur with the circles and would probably not be found elsewhere. Only one species fit the bill:Psammotermes allocerus, the sand termite. Not only was the sand termite the only insect species that lived across the entire range of the fairy circles, but these termites were found to be living beneath nearly every circle sampled. And the harder the termites worked – foraging, burrowing, and dumping their refuse – the more grass died, leading Juergens to conclude that the termites keep the circles barren by burrowing underground and foraging on the roots of germinating grasses.

In summary: the termites are cultivating their own constant sources of water and food by creating and maintaining these circles. It’s a phenomenon known as ecosystem engineering.

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