A polka dot pattern on patches of bare ground in the Namibian grasslands – termed fairy circles – have intrigued people for thousands of years. Ancient local legends speak of gods walking the earth, or dragons poisoning it with their breath. More recently, scientists have started to question what could be causing the fairy circles.
Since the 1920s, two main theories have evolved. However, until recently, scientists found it impossible to agree on which of the two theories caused the arid grass formations. Competition and self-organisation between the grass plants in a harsh, dry environment? Or the influence of subterranean termite colonies, competing against each other and living off the superficial grass roots?
Now, a study conducted by researchers at Princeton University has provided a new take on the problem by combining the two previously leading theories.
Ecologists from Princeton worked together with mathematicians from the University of Strathclyde to create a computer model where both competing grasses and termite colonies occurred and, indeed, the computer model replicated the fairy circle patterns found in the Namib deserts. In fact, the models also showed small-scale patterns in the grass between the fairy circle bald spots.
Whilst modelling either just the grass’s self-organisation or just the competing termite colonies also replicated the fairy circles, only the combination of the two factors yielded the smaller scale patterns.
Upon in-person investigation of the fairy circles at several locations in Namibia, the ecologists found the small-scale patterns in the formations of grass in between the fairy circles. These patterns abided by the same mathematics as the patterns found in the computer simulations. Since only the combination of both factors produces the patterns on both the larger and smaller scale, it’s likely that an interaction between the termite colonies and the grass’ competition for resources is what causes the fairy circles in Namibia.
The Namibian fairy circles are not the only ecological phenomenon which is likely caused by different factors of flora, fauna, and environment interacting with each other.
The surales mounds covering a big part of the Colombian and Venezuelan wetlands were previously thought to be built by a long-dead civilisation. Recently, however, scientists have theorised that the mounds are in fact formed as a result of temporary flooding in combination with the presence of large earthworms. As the flooding recedes, the mounds – mainly consisting of earthworm excrement – stay behind and are over time covered by vegetation.
These kinds of discoveries prove how important it is to consider the interactions of multiple factors when investigating ecological phenomena. The more we learn about nature, the more we seem to find that humans are not the only ones having a great impact on our surroundings. Other species interact and cause lasting changes to the landscape around them, sometimes forming unusual or even mathematically intricate patterns.
Image: Luca Galuzzi