Tau.Neutrino said:
Termites vs. plants: Mystery of desert “fairy circles” solved
The grasslands of the Namib Desert in Africa are pock-marked with patches where vegetation just won’t grow. Dubbed “fairy circles,” these strange structures have sparked debate for years about how they form, with theories ranging from plants competing for limited water, to termite colonies clearing their territories. Now, scientists at Princeton have put forward a new explanation: it’s actually both of those ideas, working in unison.
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According to David Attenborough, these circles are a mystery. So this article is particularly interesting. First, let’s check Wikipedia.
https://en.wikipedia.org/wiki/Fairy_circle_
“Fairy circles are circular patches of land barren of plants, varying between 2 and 15 metres (7 and 49 ft) in diameter, often encircled by a ring of stimulated growth of grass. Until 2014, the phenomenon was only known to occur in the arid grasslands of the Namib desert in the western South African region, being particularly common in Namibia. In that year, ecologists were alerted to similar rings of vegetation outside of Africa, in a part of the Pilbara in Western Australia.”
“Like the heuweltjies and Mima mounds, the cause of fairy circles has long been a puzzle and the investigation has proved challenging. One favoured theory is that the distinct vegetation patterns are a population-level consequence of competition for scarce water, as the plants “organise” themselves to maximise access to scarce resources. The circular barren patches capture water which then flows to the outer edges of the ring. More water available increases biomass and roots which leads to the soil becoming looser. The less dense soil allows more water to penetrate and feed the vegetation, creating a feedback loop supporting the plants at the edge of the circle”.
The wikipedia explanation sounds like hogwash to me – it’s claiming that arid plants are fleeing away from where the water is captured, which is sheer lunacy.
The explanation that Wikipedia doesn’t like is “The sand termite, Psammotermes allocerus is responsible, but the range of the phenomena is much wider than that of the termite species”.
Now let’s turn to the paper.
“Starting from satellite images of social-insect nests taken from four continents, the researchers ran computer simulations to determine why those nests took on such uniform arrangements, which look like honeycomb patterns from above. Those models told an interesting story: a colony of insects, like termites, will expand its territory outward in the search for food and water until it encounters another colony. Being fiercely territorial creatures, the two will battle it out and the smaller colony will usually be wiped out. Eventually, all that’s left in an area are the stronger, larger colonies, and when their territories bump up against each other, it’s a stalemate. Borders become clearly defined, and the honeycomb pattern of nests emerges.”
So far so good, but this requires battles between termites, and the fairy rings in the Namib are all well separated. OK, the article then goes on to claim that the termites are doing all they can to avoid battles. That makes sense.
“As a result of scarce water, plants tend to organize themselves into clumps, where they end up helping out their immediate neighbors by shading each other and concentrating soil moisture directly beneath them.”
I don’t see it that way, but the paper may be right. The plants nearest the rings are tallest because there’s more water there, but they can’t move in because foraging termites would eat all their seeds.
It still; doesn’t explain why rings exist where termites don’t, but it’s a good hypothesis that needs testing. Like by making a cast of a termite nest.