Evolution at the arid extreme: the influence of climate on sand termite colonies and fairy circles of the Namib Desert

Abstract

In the hyperarid Namib Desert, the sand termite Psammotermes allocerus Silvestri, 1908 (Isoptera: Rhinotermitidae) establishes colonies that create conspicuous, barren patches known as ‘fairy circles' on permeable, sandy soils. The central bare areas of fairy circles serve the key function of storing moisture received from sparse rainfall. The sandy soil texture allows rapid infiltration and percolation of precipitation, while localized herbivory by the termites creates the bare patch, thereby reducing the rapid loss of soil moisture by the uptake and transpiration of water by plants. The resulting storage of rain water even during prolonged periods of drought enables perennial life in hyperarid desert environments and forms a globally unique example of ecosystem engineering by social insects. During the past decade, most publications primarily debated the origin of fairy circles. Here, we contribute to the special issue with a focus on the functional and evolutionary dimension of the structure of the Psammotermes colony with two differing nest types and two spatially separated key resources, as a successful adaptation to extreme desert environment. The paper is primarily a review and a synthesis of previous work, with the inclusion of new, relevant findings. This article is part of the theme issue ‘The evolutionary ecology of nests: a cross-taxon approach’.

Aeolian Sand Sorting and Soil Moisture in Arid Namibian Fairy Circles

“…The soil water diffusion coefficient, W D , is also larger for the coarser grains. A numerical simulation of a model for the Namibian FC showed that the FC size increases with W D [13], in agreement with our new finding.…”

“…These vegetation patterns can survive drier conditions than the uniform vegetation and they are very important for the ecological system in these harsh environments [4]. A recent work, based on remote sensing analysis [7], claimed that FC-like patterns are globally distributed, and discovered 263 new sites of vegetation gaps, but more detailed field work is needed to understand the formative mechanisms (physical Land 2024, 13,197 2 of 14 and ecological) at these new sites and to distinguish between FC-like patterns (vegetation gaps) to proper FCs [8].…”

“…Two main theories have been proposed to explain fairy circle development. According to the termite hypothesis, the termites eat the grass' roots in the Namibian fairy circles (NFCs), whereas the hard pavement created by the termites prevent grass growth in the Australian fairy circles (AFCs; [11][12][13][14]). The self-organizing theory views the fairy circles as one of the various vegetation patterns that form in water-limited systems due to competition between plants for water [15,16].…”

“…(NFCs), whereas the hard pavement created by the termites prevent grass growth in the Australian fairy circles (AFCs; [11][12][13][14]). The self-organizing theory views the fairy circles as one of the various vegetation patterns that form in water-limited systems due to competition between plants for water [15,16].…”

The evolutionary ecology of nests: a cross-taxon approach

“…Juergens et al . [ 63 ] now further show that the largest termite nests are located underneath the bare patches within the fairy circles, whilst smaller nests are located outside of fairy circles and thus have direct access to grass tussocks as food [ 63 ].…”