Science proves Alan Turing’s ‘fairy circle’ theory
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5 months ago
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Dr Stephan Getzin from the University of Goettingen flying a Microdrone md4-1000 quadcopter, mounted with a multispectral camera. The multispectral camera was used to map the distribution of grass vitality across the landscape.
Fairy circles are one of nature’s greatest enigmas and most visually
stunning phenomena. An international research team led by the University
of Göttingen has now, for the first time, collected detailed data to
show that Alan Turing’s model explains the striking vegetation patterns
of the Australian fairy circles. In addition, the researchers showed
that the grasses that make up these patterns act as “eco-engineers” to
modify their own hostile and arid environment, thus keeping the
ecosystem functioning. The results were published in the Journal of Ecology.
Researchers
from Germany, Australia and Israel undertook an in-depth fieldwork
study in the remote Outback of Western Australia. They used drone
technology, spatial statistics, quadrat-based field mapping, and
continuous data-recording from a field-weather station. With the drone
and a multispectral camera, the researchers mapped the “vitality status”
of the Triodia grasses (how strong and how well they grew) in five
one-hectare plots and classified them into high- and low-vitality.
Drone image of the Australian fairy circles, taken at a flying altitude of 40 m above ground. The gaps have average diameters of 4 m and the spatially periodic pattern results from approximately equal distances between the centers of nearest-neighbouring gaps. This study plot burnt in 2014 and the recovering spinifex grasses were two years and eight months old.
The
systematic and detailed fieldwork 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
which confirms that Alan Turing’s model applies to Australian fairy
circles.
The data show that the unique gap pattern of the
Australian fairy circles, which occur only in a small area east of the
town of Newman, emerges from ecohydrological biomass-water feedbacks
from the grasses. In fact, the fairy circles – with their large
diameters of 4m, clay crusts from weathering and resultant water run-off
– are a critical extra source of water for the dryland vegetation.
Clumps of grasses increased shading and water infiltration around the
nearby roots. With increasing years after fire, they merged more and
more at the periphery of the vegetation gaps to form a barrier so that
they could maximize their water uptake from the fairy circle’s runoff.
The protective plant cover of grasses could reduce soil-surface
temperatures by about 25°C at the hottest time of the day, which
facilitates the germination and growth of new grasses. In summary, the
scientists found evidence both at the scale of the landscape and at much
smaller scales 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.
Dr
Stephan Getzin, Department of Ecosystem Modelling at the University of
Göttingen, explains, “The intriguing thing is that the grasses are
actively engineering their own environment by forming symmetrically
spaced gap patterns. 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-organization of the grasses, this area
would likely become desert, dominated by bare soil,” he adds. The
emergence of Turing-like patterned vegetation seems to be nature’s way
of managing an ancient deficit of permanent water shortage.
In 1952 when the British mathematician, Alan Turing, published his ground-breaking theoretical paper on pattern formation, he had most likely never heard of the fairy circles before. But with his theory he laid the foundation for generations of physicists to explain highly symmetrical patterns like sand ripples in dunes, cloud stripes in the sky or spots on an animal’s coat with the reaction-diffusion mechanism. Now, ecologists have provided an empirical study to extend this principle from physics to dryland ecosystems with fairy circles.