Jen Guyton

Tyler Coverdale

Edu Jung

JERRYE & ROY KLOTZ MD

They look a little like crop circles and a little like artistic earthworks. Around the world, they have many names: in the Namib Desert of Africa, they're called "fairy circles;" in Brazil they're dubbed "murundus," and in North America they're known as "Mima mounds." In a recent paper for Nature, Princeton ecologist Corina E. Tarnita and her colleagues call them "landscapes of overdispersed (evenly spaced) elements." All are regions where plants grow into such perfectly symmetrical, large-scale patterns that they seem unnatural.

Debates rage among ecologists about whether these patterned environments have a common cause and what it might be. Two of the leading hypotheses involve plant cooperation and insect rivalries. In areas where water resources are scarce or irregular, plants are known to engage in "scale-dependent feedbacks," where plants over a wide area grow into clusters rather than spreading out over a big area. The plant clumps limit their sizes to make the best use of water, and this strategy leads to reproductive success. It also might explain why we see patterns of plant growth that are characteristic of fairy circles and Mima mounds.

But some scientists who have studied the pattern say that more is going on. They argue that water resources in these areas are being divvied up by warring groups of termites who suctioned water out of the dry areas and relocated it to their mounds. Given that successful termite colonies tend to have territory sizes that are roughly comparable, this would explain why so many of these odd regions contain mounds as well as dry patches.

Tarnita and her colleagues' paper in Nature suggests that we're probably seeing an unusual interaction between plants and termites, both attempting to maintain access to water in dry areas. Using a computer model that accounted for both plant and insect life cycles, the researchers were able to reproduce the exact patterns we see in fairy circles. Speaking to the Washington Post's Sarah Kaplan, Tarnita marveled, "It's an amazing thing that you can get such clean, beautiful geometric patterns. Such tiny creatures doing their thing very locally every day end up producing these unbelievable large-scale patterns... To me, it's mind-boggling that nature can do that." Kaplan added that Princeton chemist Salvatore Torquato identified the fairy circle patterns as "hyperuniform," a state often seen in substances whose semi-organized atomic structure puts them halfway between a crystal and a liquid.

Though we may not yet know for certain what kinds of interactions cause these eerily regular landscapes, Tarnita and her colleagues' model brings us one step closer. They argue that we are just at the dawn of understanding ecological self-organization, partly because satellite imagery makes it easier to see features like fairy circles. But we're only beginning to understand the way communities of lifeforms interact to produce such oddly partitioned environments. Concluding their paper, the scientists issued a call to "focus theoretical and empirical effort on the ways in which multiple mechanisms interact across scales to structure ecosystems." Nothing in nature is ever as simple as it seems.

Nature, 2017. DOI: 10.1038/nature20801

Listing image by Tyler Coverdale