2017-01-20 08:46:15
Trilobites: Fishing for Clues to Solve Namibia’s Fairy Circle Mystery

08:46, January 20 270 0

With its bone-dry grasslands and oppressive heat, the middle of the Namib Desert may seem like a strange place to go fishing. Yet there Jennifer Guyton and Tyler Coverdale were, standing in a sea of orange sand and brittle yellow grass with their 30-foot carp pole.

But the two Princeton graduate students weren’t trying to catch some sort of desert-dwelling dogfish or a literal “sand shark.” That would be absurd. Instead, they had swapped the hook with a camera so they could investigate the scenery around something much more scientifically sensible: fairy circles.

That is what scientists call the mysterious bald spots speckled across Namibia’s grasslands. The rings are six feet to 115 feet wide and are regularly spaced out in a hexagon or honeycomb pattern. As their ethereal name would imply, fairy circles have long bewildered researchers as to their origins. But a new study published on Wednesday in the journal Nature that Ms. Guyton and Mr. Coverdale were involved in seeks to offer some insights into how the enchanting landscapes may have formed.

Although the name fairy circles sounds sweet and peaceful, there is passionate scientific disagreement over how they arise, and the two prevailing hypotheses have become adversaries in the dispute.

One side suggests that termites, locked in never-ending competition with neighboring colonies, create the circles as they fight for dominance and resources. The other says that perpetually thirsty plants simultaneously assist and compete with their neighbors’ roots, causing the vegetation to “self-organize” into the patterns.

The new study suggests that termites and plants may be jointly responsible for forming fairy circle landscapes in Namibia. And it has received mixed reviews from scientists entrenched in the dispute.

“We thought both sides of the debate bring in compelling arguments for each of these mechanisms, so why should it be one or the other?” said Corina Tarnita, an ecologist from Princeton University and the study’s co-lead author.

Dr. Tarnita worked with Juan Bonachela, a mathematician from the University of Strathclyde in Scotland, to test the termite and plant explanations in a computer model. They found that either hypothesis could generate the fairy circle features. But when they tested both mechanisms together, the model revealed a second, smaller pattern hidden within the clumps of grass between the fairy circles.

“Everyone was focusing on the circles and not what was happening in between them,” said Robert M. Pringle, an ecologist at Princeton and another author on the paper.

The next step for the team was to confirm that this second vegetation pattern existed in nature. So they sent Ms. Guyton and Mr. Coverdale to Namibia in 2015 with their camera and fishing pole.

Ms. Guyton said that each of the grassy patterns was as different as fingerprints, but were mathematically similar. By comparing the photos with their model, the team verified that the second pattern did exist in the grass surrounding the Namibian fairy circles. That finding, they said, confirmed that their mathematics reflected reality and suggested that only by interacting together could insects and plants create the landscape that characterizes Namibian fairy circles.

Some fairy circle experts firmly placed in either team termite or team plant had strong doubts about the paper’s findings, while others welcomed it.

Norbert Juergens, a biologist from the University of Hamburg in Germany who published the study that said termites engineer fairy circles agreed with the overall findings and said that he hoped they would “be an eye-opener for all those who since 2013 questioned the termite hypothesis.”

Stephan Getzin, an ecologist at the Helmholtz Centre for Environmental Research in Leipzig, Germany, was not persuaded, saying in an email that the paper was unable to account for the presence of fairy circles where sand termites were completely absent, as in Australia.

“Logically, if there are fairy circles without the presence of termites, the termite theory cannot be considered as a strong explanation for the phenomenon,” he said.

Dr. Tarnita responded that their model showed that both termites and plants could make the fairy circles, but that the entire system, which includes the vegetation and the small-scale patterns seen in the Namibian fairy circles, needed both.

Walter R. Tschinkel, a retired entomologist from Florida State University who was not involved in the study, said in an email that the assumptions the team made about termites in their computer model were untested.

“There is no evidence that the real termite Psammotermes allocerus does what the computer ‘termite’ does,” he said.

But Max Rietkerk, an environmental scientist from Utrecht University in the Netherlands, said that the authors showed that the two hypotheses could have worked together in Namibia’s fairy circles. He also agreed, however, that the argument could use more empirical evidence.

Dr. Pringle defended the use of their model, pointing out that it drove the team to discover new empirical evidence that no one had found before, the small-scale grass patterns.

Despite the team’s attempt to solve the mystery, it seems the fairy circle scuffle flutters on.