unveiled a new explanation, competition between plants:
In the harsh desert environment, plants compete for resources below ground, and some don’t survive. When weaker grass dies, its absence facilitates growth of neighboring plants. The vegetation gap expands until it reaches a size that limits competition between grasses.But if the explanation is something so general as competition among plants, then these circles ought to be found in all dry grasslands, right?
went looking for them in Australia, and lo and behold they found plenty of them (above). As the theory predicts, they are limited to areas with the right amount of rainfall, and they wax and wane according to how much rain falls in a given year. This doesn't quite nail down the explanation, but it is very strong evidence, especially since the insect species that feature in some African explanations don't exist in Australia.