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

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)

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:

Posted on June 02, 2023 07:08 PM by milewski milewski

Comments

The following is probably the best of its kind, on the Web:

https://traveltoeat.com/big-termite-mounds-in-botswana-with-facts-and-photos/

Posted by milewski about 1 year ago

Viljoen P J (1982) The distribution and population status of the larger mammals in Kaokoland, South West Africa/Namibia. Cimbebasia Series A, vol. 7, no. 2, pp. 5-33.

The following species occur in Kaokoland:

Smutsia temminckii (https://www.inaturalist.org/taxa/75083-Smutsia-temminckii) present, but not where mean annual precipitation is less than 100 mm

Otocyon megalotis (https://www.inaturalist.org/taxa/42095-Otocyon-megalotis) present even in the Namib, and favoured by overgrazing

Proteles cristatus (https://www.inaturalist.org/taxa/1306005-Proteles-cristatus) present even in the Namib, and favoured by overgrazing

Orycteropus afer (https://www.inaturalist.org/taxa/47062-Orycteropus-afer) present in eastern Kaokoland, and penetrates the mountainous edge of the Namib along drainage lines

Hystrix africaeaustralis (https://www.inaturalist.org/taxa/44173-Hystrix-africaeaustralis)

My commentary:

The presence of Smutsia temminckii in Kaokoland is not represented in the distribution map of this species, featured in iNaturalist.

It is remarkable that P. cristatus penetrates both the Namib and the mediterranean-type climate in South Africa, yet is absent from North and West Africa. Its distribution correlates best with Hodotermitidae, particularly Hodotermes and Microhodotermes, although these are not necessarily its main diet.

Posted by milewski about 1 year ago

@tonyrebelo

The six spp. of Macrotermes occurring in southern Africa are

falciger: avoids sandy soils but is nevertheless present in the miombo biome; builds massive mounds of variable shape; workers can forage in the open, without mud-runnels, 'harvesting' plant matter

michaelseni: tolerant of semi-arid conditions, but not occurring at high latitudes

natalensis: tolerant of high latitudes and low temperatures; this seems to be the species recorded as having burrowed down to 84 m deep in Namibia

subhyalinus: tolerant of aridity but restricted to low latitudes

ukuzii: restricted to southern Africa; builds only small mounds; associated with black alluvial soils

vitrialatus: disjunct distribution, tending to be mutually exclusive with falciger; workers can forage in the open, 'harvesting'

I do not know how Macrotermes swaziae fits into this.

Posted by milewski about 1 year ago

Although termites are usually assumed to be detritivores, Macrotermes is capable of cutting down living plants (both herbaceous and woody), to the extent of being a horticultural and sylvicultural pest.

Lee and Wood (1971), on page 169, point out that seedlings/saplings of Eucalyptus seem to be particularly susceptible to attack by termites in plantations in Africa (Macrotermes) and Brazil (Syntermes, https://www.inaturalist.org/observations?place_id=any&taxon_id=548075&view=species).

Odontotermes redemanni is a pest in plantations of sugarcane, tea, and coconut in the Indian subcontinent (https://en.wikipedia.org/wiki/Odontotermes_redemanni#:~:text=Odontotermes%20redemanni%2C%20is%20a%20species,of%20sugarcane%2C%20tea%20and%20coconut).

Posted by milewski about 1 year ago

Macrotermes operates at a different order of magnitude, in productivity and ecological importance, from non fungus-culturing termites that simply digest dead plant matter in their guts.

This is because it
a) utilises a fungus culture that aerobically breaks down lignin, greatly hastening decomposition,
b) benefits from economies of scale in its colonies, nests, and fungus chambers,
c) breaks down its food completely, making faeces redundant,
d) feeds the faeces of proboscideans and ungulates into its fungus-culturing system,
e) gathers plant matter in not only dead, but also living form (the latter being more nutritious), and
d) mines catalytic nutrients deep in the earth (particularly those leached to the groundwater).

In addition, there is a little-known fact emphasising how different Macrotermes is from simple, slow-metabolising consumers of plant fibre.

My reference is Ruggiero R G and Fay J M (1994) Utilization of termitarium soils by elephants and its ecological implications. African Journal of Ecology 32: 222-232.

Referring to a study area in Central African Republic (https://en.wikipedia.org/wiki/Central_African_Republic), these authors state:
"Macrotermes spp. termites also often consume large quantities of skin and bone at elephant and other carcasses."

Posted by milewski about 1 year ago

Large mounds occur near Vryburg (https://en.wikipedia.org/wiki/Vryburg), in the Northern Cape province of South Africa.

My reference:
Cox G W, Lovegrove, B G and Siegfried W R (1987) The small stone content of mima-like mounds in the South African Cape region: implications for mound origin. Catena 14: 165-176.

My commentary:
This location is just within the distribution of Macrotermes natalensis.

Posted by milewski about 1 year ago

Boutton et al. (1983, https://pubmed.ncbi.nlm.nih.gov/25024140/ and https://www.researchgate.net/publication/225315273_Stable_isotope_analysis_of_termite_food_habits_in_East_African_grasslands and https://www.semanticscholar.org/paper/Stable-isotope-analysis-of-termite-food-habits-in-Boutton-Arshad/29cf794169c16f8c606240d82299ef3fdb5ead75 and https://agris.fao.org/agris-search/search.do?recordID=US201302617706 and https://www.jstor.org/stable/4217058)

These authors studied Macrotermes michaelseni in semi-arid savanna near Kajiado (https://en.wikipedia.org/wiki/Kajiado_County) and Ruiru (https://en.wikipedia.org/wiki/Ruiru) in Kenya. Another species of Macrotermes common in semi-arid Kenya is Macrotermes subhyalinus.

This is a good reference to the diet of Macrotermes being a flexible combination of herbaceous and woody material.

Kajiado (savanna of Vachellia tortilis and grasses, e.g. Themeda triandra, Cynodon dactylon, and Pennisetum mezianum): herbaceous 70% (mainly grass), woody 30%.

Ruiru: herbaceous 36%, woody 64%.

Both spp. resort to living plant matter and roots, if hungry enough.

In plantations of eucalypts: "Inspection of the litter at Ruiru site clearly indicated that termites were consuming both decaying and relatively fresh Eucalyptus leaves which had fallen to the ground recently".

Each colony consists of 2-3 million individuals. The queen is fed stomodeally, i.e. via liquid from the salivary glands of minor workers.

Macrotermes michaelseni alone can consume 1-1.5 tonnes per hectare per year of plant matter, which is about as much as that consumed by all the large mammals, collectively, in the same ecosystem.

Posted by milewski about 1 year ago

Pomeroy D E (1983, https://bsssjournals.onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2389.1983.tb01055.x)

The study area was near Kajiado, Kenya, under a non-leaching rainfall averaging 450-600 mm per year.

Structures occurred on various substrates, except blackish cracking clay.

'Mounds': 3-4 m diameter, 1-1.5 m high. "Much larger ('massive') mounds occur rarely in the Kajiado area, being confined to cooler, moister places, especially valleys at higher altitudes, where they reach diameters in excess of 12 m and heights up to 3 m".

The mounds are rich in calcium, potassium, and magnesium, derived partly from the foods consumed. However, the content of nitrogen and carbon was limited, and possibly restricted to the salivary cement used

In two studied mounds, the incorporated clay consisted mainly of montmorillonite. However, all clays contributed less than a third of the mass of the mound. In all structures consisting of more than a third clay, the clay was mainly kaolinitic. According to Pomeroy, these observations "suggest that the termites are able to build turrets and rims from a wide range of soils". Maximum content of clay was 60%.

Posted by milewski about 1 year ago

Lee and Wood (1971), page 70: Odontotermes latericius occurs in the Highveld in the vicinity of Bloemfontein (https://en.wikipedia.org/wiki/Bloemfontein), at a population density of one nest per hectare.

Posted by milewski about 1 year ago

Add a Comment

Sign In or Sign Up to add comments