Fairy circles: Circular truth

Fairy circles – regularly spaced, round patches of bare soil surrounded by grass – are one of nature’s greatest enigmas and most visually stunning phenomena.

Now, an international research team has collected detailed data to show that a model proposed in 1952 by mathematician and theoretical biologist Alan Turing explains the striking vegetation patterns of the Australian fairy circles, which are found only in a small area east of the outback mining town of Newman, WA.

The researchers also show that the grasses that make up these patterns act as “eco-engineers” to modify their own hostile and arid environment and keep the ecosystem functioning. The results have been published in the Journal of Ecology.

The systematic and detailed fieldwork done by the joint German/Australian/Israeli research team enabled, for the first time in such an ecosystem, a comprehensive test of the “Turing pattern” theory.

Turing’s concept was that in certain systems, due to random disturbances and a “reaction-diffusion” mechanism, interaction between just two diffusible substances was enough to allow strongly patterned structures to spontaneously emerge. Physicists have used this model to explain the striking skin patterns in zebrafish or leopards, for instance.

Earlier modelling had suggested this theory might apply to these intriguing vegetation patterns and now there is robust data from multiple scales that confirms that Turing’s model applies to Australian fairy circles.

The emergence of Turing-like patterned vegetation seems to be nature’s way of managing an ancient deficit of permanent water shortage.

The scientists found evidence that the grasses, with their cooperative growth dynamics, redistribute the water resources, modulate the physical environment, and thus function as “ecosystem engineers” to modify their own environment and better cope with the arid conditions.

“The intriguing thing is that the grasses are actively engineering their own environment by forming symmetrically spaced gap patterns,” says Stephan Getzin, from the University of Göttingen, Germany. “The vegetation benefits from the additional runoff water provided by the large fairy circles, and so keeps the arid ecosystem functional even in very harsh, dry conditions.”

This contrasts with the uniform vegetation cover seen in less water-stressed environments.

“Without the self-organisation of the grasses, this area would likely become desert, dominated by bare soil,” Getzin adds.