Ecologically relevant aspects of the biogeography of fungus-culturing termites in southern Africa

In iNaturalist, the coverage of termites is poor.

This is unfortunate, because these insects are ecologically important.

In this Post, I compensate somewhat for this deficiency by reviewing the literature on the biogeography of certain termites in southern Africa, in an interpretive way.

The references are

• Coaton and Sheasby (1972, https://books.google.com.au/books/about/Preliminary_Report_on_a_Survey_of_the_Te.html?id=2DhDAAAAYAAJ&redir_esc=y),
• Ruelle et al. (1975, https://pascal-francis.inist.fr/vibad/index.php?action=getRecordDetail&idt=PASCAL7536010953),
• Marais and Irish (1989, https://scholar.google.com.au/scholar?hl=en&as_sdt=0%2C5&q=Marais+and+Irish+1989&btnG=),
• Turner (2000, https://scholar.google.com.au/scholar?hl=en&as_sdt=0%2C5&q=Turner+2000+macrotermes&btnG=), and
• Tinley (1985, https://researchspace.csir.co.za/dspace/handle/10204/2353 and https://books.google.com.au/books/about/Coastal_Dunes_of_South_Africa.html?id=WuUHAQAAIAAJ&redir_esc=y and https://www.si.edu/object/siris_sil_312931 and https://www.abebooks.com/first-edition/Coastal-Dunes-South-Africa-Tinley-K/16862566834/bd).

Let us begin with the astonishing fact that termites (presumably Macrotermes) have been recorded burrowing as deep as 84 m. This has important implications ecologically, particularly for the retrieval of leached nutrients and the boosting of productivity in whole ecosystems.

Marais and Irish (1989) state "we have observed active termite tunnels at the following depths in South West African caves: 25 m (Pofaddergat), 27 m (Ghaub Cave), 47 m (Dante's Cave), 84 m (Arnhemgrot)"

The following provides information in the location of these caves: https://en.wikipedia.org/wiki/Caves_of_Namibia.

Ghaub Cave https://africantourer.com/attraction/ghaub-cave and https://www.booknamibia.com/listings/ghaub-cave-ghaub-nature-reserve-farm

Dante Cave https://www.ncei.noaa.gov/access/metadata/landing-page/bin/iso?id=noaa-cave-14268

Arnhem Cave: 85 km east-southeast of Windhoek https://www.namibweb.com/arnhemcave.htm and https://www.arnhemcaves.com/

I infer that the species penetrating underground to a depth of 84 m is Macrotermes natalensis.

The subfamily Macrotermitinae of the family Termitidae consists of fungus-culturing termites. This means that they function more like large herbivores than like mere invertebrate agents of decomposition.

Macrotermes is an extremely important genus of termites. However, few naturalists have a grasp of it, even at the generic level - partly owing to confusion with Odontotermes. One of the reasons why the biogeography of Macrotermes remains so obscure is that the size and shape of the mounds varies greatly among, and within, species.

For example:
The mounds of Macrotermes natalensis (https://www.inaturalist.org/taxa/431392-Macrotermes-natalensis)

• vary from low and conical to massive and domed, with diameter up to 30 m,
• tend to be relatively low at high altitudes, and
• tend to be open at the top in Uganda (https://en.wikipedia.org/wiki/Uganda), but sealed at the top in Ivory Coast (https://en.wikipedia.org/wiki/Ivory_Coast).

Macrotermes natalensis

• is the only species in its genus to penetrate south of 28 degrees South,
• reaches part of the Highveld (https://en.wikipedia.org/wiki/Highveld), as far south as 29 degrees South in Free State province in South Africa, - marginally penetrates the Nama Karoo (https://en.wikipedia.org/wiki/Nama_Karoo), and
• reaches nearly as far south as 33 degrees South in Eastern Cape province of South Africa.

Tinley (1985) refers to the occurrence of large mounds of Macrotermes natalensis in the Eastern Cape, at the southerly limit of the genus. The large mounds occur in a strip, hugging the coast from Transkei (https://en.wikipedia.org/wiki/Transkei) to near East London (https://en.wikipedia.org/wiki/East_London,_South_Africa). The soils in these landforms are red loams with clay subsoil.

Near East London, the mounds of M. natalensis have diameters of about 10 m and heights up to 2.5 m. They are covered in bush-clumps of Phoenix reclinata (https://www.inaturalist.org/taxa/166729-Phoenix-reclinata) and Phyllanthus reticulatus (https://www.inaturalist.org/taxa/340305-Phyllanthus-reticulatus), exempt from wildfire.

Richard Knight told me, in 2001, that the (aggregated?) mounds of M. natalensis in Transkei (https://en.wikipedia.org/wiki/Transkei) actually reach 200-300 m in diameter and 5 m in height; these are usually on duplex, not seasonally waterlogged soils. He emphasised the prominence of these mounds in the landscape, with soils and vegetation extremely different from the surroundings. Richard Knight claimed that the mounds were more or less covered in forests, in which e.g. Mimusops reached bole diameters exceeding 50 cm.

(I have yet to reconcile any differences in the accounts given by Ken Tinley vs Richard Knight.)

Macrotermes penetrates rainforest in tropical Africa, but not in southern Africa.

Macrotermes subhyalinus (https://www.inaturalist.org/observations?taxon_id=673979) builds mounds at least 6 m high in Angola and northeastern Africa, but no higher than 4.2 m in Kaokoland (https://en.wikipedia.org/wiki/Kaokoland), where it penetrates the pro-Namib.

Macrotermes bellicosus (https://www.inaturalist.org/taxa/346641-Macrotermes-bellicosus) in Uganda transports earth into its mounds at rates of 0.4-0.9 cubic metres per hectare per year. This produces mounds averaging 4-8 cubic metres per hectare.

Some spp. of Macrotermes (e.g. vitrialatus and falciger) harvest plant matter, including living plants which they cut down, in the open. In this way they resemble the hodotermitids Hodotermes (https://www.inaturalist.org/taxa/558313-Hodotermes) and Microhodotermes (https://www.inaturalist.org/taxa/568761-Microhodotermes-viator). Adding to this similarity is the fact that M. vitrialatus - like the ecologically powerful Hodotermes mossambicus (https://www.inaturalist.org/taxa/558312-Hodotermes-mossambicus) - does not build mounds.

Other spp. of Macrotermes forage on the ground surface (mainly for litter and faeces, including those of Bos and Loxodonta) under the cover of mud-runnels. They construct these temporary shelters ad-hoc, as they go along. Examples are M. natalensis, M. michaelseni, and M. subhyalinus.

Let us focus on Namibia, where the relationship of large-bodied, fungus-culturing termites to aridity and temperature is relatively easy to describe.

The biogeography of Macrotermes and Odontotermes in Namibia, proceeding from north to south, is as follows:

• Macrotermes is widespread (together with Odontotermes) north of Windhoek, except for the arid western regions,
• Macrotermes reaches the pro-Namib only in the northernmost area (Kaokoland), where M. subhyalinus builds structures up to 4.2 m high,
• Macrotermes michaelseni is widespread in the north of the country (north of 22 degrees South), building spires rather than mounds; these spires are tallest in the extreme north, where they reach up to 6 m high;
• Macrotermes vitrialatus occurs in places in northern Namibia;
• Macrotermes natalensis (which is particularly widespread in Africa) is the main species on the sandy substrates of the east-central part of the country, where it co-occurs with Odontotermes (https://www.inaturalist.org/observations?place_id=113055&taxon_id=492047&view=species),
• Macrotermes is absent from the area west and south of Windhoek, and the southwestern Kalahari, where Odontotermes remains present by virtue of its greater latitudinal tolerance, and
• this leaves about 40% of Namibia, in the west and particularly the south, devoid of fungus-culturing termites; here, the ecologically most powerful termites - none of which builds above-ground structures comparable with those of Macrotermes and Odontotermes - are Psammotermes (https://www.inaturalist.org/observations?place_id=any&taxon_id=643360&view=species), Hodotermes, Microhodotermes, and Trinervitermes (please see https://www.inaturalist.org/journal/milewski/80318-scarcity-of-termitaria-of-the-grass-harvesting-termite-trinervitermes-in-namibia-and-implications-for-the-aardwolf-proteles-cristatus#).

Posted on 02 June, 2023 19:08 by milewski