Largest on earth: Discovery of a new type of fairy circle in Angola supports a termite origin

Abstract

1. Circular bare patches occur in high numbers among the vegetation of the Namib Desert margin. There is an ongoing scientific debate on the origin of these so-called "fairy circles" (FCs). One of the most frequently discussed hypotheses regards the bare patches to be the result of localised herbivory by sand termites of the genus Psammotermes (family Rhinotermitidae).2. In all earlier publications, the fairy circles of the Namib Desert region within their entire range from Angola through Namibia to South Africa were, in principle, regarded to be of one type, albeit increasing in size towards the north. Here we present evidence that at −16.23 ∘ latitude there is an abrupt discontinuity which separates the FCs on either side from each other.3. South of this discontinuity all studied FCs share the properties of the previously described fairy circles in Namibia and South Africa, especially the presence of Psammotermes termites.4. In contrast, north of −16.23 ∘ S the FCs are much larger and are caused by a different and undescribed termite species, most closely related to the harvester termite genus Microhodotermes (family Hodotermitidae). The two sets of fairy circles differ in a specific set of morphological features, associated termites, and soil parameters.5. The observed juxtaposition of the newly discovered large structures caused by a hodotermitid termite and the Psammotermes FCs caused by a rhinotermitid species is interpreted as an interesting example of convergent evolution resulting in similar ecological structures.

Definition of “fairy circles” and how they differ from other common vegetation gaps and plant rings

“…Likewise, Pogonomyrmex harvester ants in North America clear circular areas in grasslands around the nest structure in the center of the gap (Dibner et al, 2015; Nicolai et al, 2010). Similar circles with a central termite‐nest structure have been recently found in southern Angola by Juergens et al (2021). As the authors state, these are not “classic FCs” and the large circular gaps with an elevated termite nest in the center near Baba in Angola are caused by an undescribed Hodotermitidae termite species.…”

“…Likewise, Pogonomyrmex harvester ants in North America clear circular areas in grasslands around the nest structure in the center of the gap (Dibner et al, 2015;Nicolai et al, 2010). Similar circles with a central termite-nest structure have been recently found in southern Angola by Juergens et al (2021). As the authors state, these are…”

“…Likewise, a recent meta‐analysis of 25 spatial patterns has demonstrated that there is no example known from the world's arid lands, including the same Australian FC landscape, where termites or ants have spatially periodic nest distributions (Getzin et al, 2019a). Such termite and ant nest patterns merely attain less‐ordered regular distributions, as for example the Macrotermes termite mounds in Namibia (Figure 3c,d) and the Hodotermitidae termites at Baba in Angola (Juergens et al, 2021). These typical and globally common termite gap patterns cannot be called FCs because they violate two fundamental characteristics that jointly define genuine FCs.…”

“…For example, abiotic gas leakage as proposed by Naude et al ( 2011) cannot result in such a high degree of regularity because there is no such regularity in the underlying geology (Getzin et al, 2015a;Tschinkel, 2012). The (mis)use of the term "fairy circle" for a completely dif- and the Hodotermitidae termites at Baba in Angola (Juergens et al, 2021). These typical and globally common termite gap patterns cannot be called FCs because they violate two fundamental characteristics that jointly define genuine FCs.…”

Barren ground depressions, natural H2 and orogenic gold deposits: Spatial link and geochemical model

“…Small mean nearest-neighbor distance may be a key factor allowing for self-organization in such structures by reducing the probability for the occurrence of heterogeneities at the surface or in the underlying basin/regolith. Jürgens et al (2021) noted the same relationship in their point pattern analysis of fairy circles in Angola with small g max values for large mean nearest-neighbor distance. Comet-shaped and elliptical depressions are also described on the seafloor (Chen et al, 2015(Chen et al, , 2020 and formed by a combination of gas venting generating pockmarks and surface properties such as bottom current direction or slope leading to the comet shape (Berton and Vesely, 2018).…”