Ecologists confirm Alan Turing's theory forAustralian fairy circles22 September 2020

Drone image of the Australian fairy circles, taken at aflying altitude of 40 m above ground. The gaps haveaverage diameters of 4 m and the spatially periodicpattern results from approximately equal distancesbetween the centers of nearest-neighboring gaps. Thisstudy plot burnt in 2014 and the recovering spinifexgrasses were two years and eight months old. Credit: SGetzin, University of Göttingen

Fairy circles are one of nature's greatest enigmasand most visually stunning phenomena. Aninternational research team led by the University ofGöttingen has now, for the first time, collecteddetailed data to show that Alan Turing's modelexplains the striking vegetation patterns of theAustralian fairy circles. In addition, the researchersshowed that the grasses that make up thesepatterns act as "eco-engineers" to modify their ownhostile and arid environment, thus keeping theecosystem functioning. The results were publishedin the Journal of Ecology.

Researchers from Germany, Australia and Israelundertook an in-depth fieldwork study in theremote Outback of Western Australia. They useddrone technology, spatial statistics, quadrat-basedfield mapping, and continuous data-recording from

a field-weather station. With the drone and amultispectral camera, the researchers mapped the"vitality status" of the Triodia grasses (how strongand how well they grew) in five one-hectare plotsand classified them into high- and low-vitality.

The systematic and detailed fieldwork enabled, forthe first time in such an ecosystem, acomprehensive test of the 'Turing pattern' theory.Turing's concept was that in certain systems, due torandom disturbances and a 'reaction-diffusion'mechanism, interaction between just two diffusiblesubstances was enough to allow strongly patternedstructures to spontaneously emerge. Physicistshave used this model to explain the striking skinpatterns in zebrafish or leopards for instance.Earlier modeling had suggested this theory mightapply to these intriguing vegetation patterns andnow there is robust data from multiple scales whichconfirms that Alan Turing's model applies toAustralian fairy circles.

The active formation of nearly circular grassland gaps(fairy circles), as seen from a helicopter. At this transitionfrom Eucalypt and Acacia trees to a Triodia grassland,the hummock grasses arrange themselves to form roundbare-soil gaps. This "ecoystem-engineering" results inthe most green and vital grasses growing next to the fairycircle while grey and less vital grasses further away

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cannot benefit from this extra source of water in the sameway. Credit: S Getzin, University of Göttingen

The data show that the unique gap pattern of theAustralian fairy circles, which occur only in a smallarea east of the town of Newman, emerges fromecohydrological biomass-water feedbacks from thegrasses. In fact, the fairy circles—with their largediameters of 4m, clay crusts from weathering andresultant water run-off—are a critical extra source ofwater for the dryland vegetation. Clumps of grassesincreased shading and water infiltration around thenearby roots. With increasing years after fire, theymerged more and more at the periphery of thevegetation gaps to form a barrier so that they couldmaximize their water uptake from the fairy circle'srunoff. The protective plant cover of grasses couldreduce soil-surface temperatures by about 25°C atthe hottest time of the day, which facilitates thegermination and growth of new grasses. Insummary, the scientists found evidence both at thescale of the landscape and at much smaller scalesthat the grasses, with their cooperative growthdynamics, redistribute the water resources,modulate the physical environment, and thusfunction as "ecosystem engineers" to modify theirown environment and better cope with the aridconditions.

Dr Stephan Getzin from the University of Goettingenflying a Microdrone md4-1000 quadcopter, mounted witha multispectral camera. The multispectral camera wasused to map the distribution of grass vitality across the

landscape. Credit: Dr Hezi Yizhaq

Dr. Stephan Getzin, Department of EcosystemModeling at the University of Göttingen, explains,"The intriguing thing is that the grasses are activelyengineering their own environment by formingsymmetrically spaced gap patterns. The vegetationbenefits from the additional runoff water providedby the large fairy circles, and so keeps the aridecosystem functional even in very harsh, dryconditions." This contrasts with the uniformvegetation cover seen in less water-stressedenvironments. "Without the self-organization of thegrasses, this area would likely become desert,dominated by bare soil," he adds. The emergenceof Turing-like patterned vegetation seems to benature's way of managing an ancient deficit ofpermanent water shortage.

In 1952 when the British mathematician, AlanTuring, published his ground-breaking theoreticalpaper on pattern formation, he had most likelynever heard of the fairy circles before. But with histheory he laid the foundation for generations ofphysicists to explain highly symmetrical patternslike sand ripples in dunes, cloud stripes in the skyor spots on an animal's coat with the reaction-diffusion mechanism. Now, ecologists haveprovided an empirical study to extend this principlefrom physics to dryland ecosystems with fairycircles.

More information: Stephan Getzin et al, Bridgingecology and physics: Australian fairy circlesregenerate following model assumptions onecohydrological feedbacks, Journal of Ecology(2020). DOI: 10.1111/1365-2745.13493

Provided by University of Göttingen

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APA citation: Ecologists confirm Alan Turing's theory for Australian fairy circles (2020, September 22)retrieved 4 June 2022 from https://phys.org/news/2020-09-ecologists-alan-turing-theory-australian.html

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