Herbivory by subterranean termite colonies and the development of fairy circles in SW Namibia

Abstract

1. The growth pattern of Namibian fairy circles was examined in relation to environmental, termite, and plant variables to provide support for the sand termite (Psammotermes allocerus Silvestri) hypothesis of circle origin.2. New and young circles were associated with the highest number of sand termites and their foraging grass sheetings which were both considerably lower in mature and senescent circles.3. Circles increased in size with age, and apart from the senescent stage had higher soil moisture levels than the matrix.4. In laboratory trials sand termites browsed seedling roots, negatively impacting root and leaf number.5. This provides a potential mechanism for circle formation through central‐based foraging by P. allocerus which eliminates Stipagrostis grass clumps around its nest system.6. The resulting bare disc is postulated to be maintained through a combination of a depleted seed bank, termite herbivory on seedlings, and excavations by pugnacious ants (Anoplolepis steingroeveri Forel).