Interpretive notes on the termite family Hodotermitidae in Africa, part 2: Microhodotermes (Coaton and Sheasby, 1974)

...continued from https://www.inaturalist.org/journal/milewski/80715-interpretive-notes-on-the-termite-family-hodotermitidae-in-africa-part-1-coaton-and-sheasby-1972-1975#

The body mass of Hodotermes mossambicus is recorded as 7.66 mg.

My commentary:
Is this the fully-grown worker? Is this as large as the largest-bodied termite in Australia? (see https://www.termigold.com/australias-giant-northern-termite/#:~:text=Anatomy%20Of%20Mastotermes%20Darwiniensis&text=The%20giant%20northern%20termite%20soldier,antennae%20of%2020%2D26%20segments.)

Hodotermes mossambicus

• is effectively a grazer (more so than confamilial Anacanthotermes)
• digs extremely deeply
• corresponds biogeographically to the distinctive fauna of large mammals in southern and East Africa
• corresponds biogeographically to the largest termitophage on Earth
• has no counterpart in the Sahel or North Africa
• is excluded by leaching climates and winter rainfall
• has no ecological counterpart on any other continent (although Anacanthotermes in India deserves further investigation)
• builds no mounds, yet greatly affects soils and fire-regimes.

The size of the colonies of Hodotermes mossambicus is approximately constant. Hence, during dry periods, it clears all the grass from an expanding area. I note that this happens instead of the colony allowing its size to be reduced by drought. So, H. mossambicus seems to operate with the same inertia as large herbivores. The result is freedom from combustion and its associated wastage.

Seely M K and Mitchell D (1986) Termite casts in Tsondab sandstone. pp. 109-112 in: Palaeoecology of Africa and the surrounding islands, ed. by E M van Zinderen Bakker, J A Coetzee and L Scott, vol. 17. A A Balkema, Rotterdam.

Hodotermes mossambicus occurs even in the 'sand sea' of the Namib. Its surface burrows have diameter about 1.15 cm. One nest serves an area of 1,900 square metres, with 16 soil dumps and 125 foraging entrances/exits, with mean density 0.3 holes per square metre.

Hodotermes mossambicus on the dunes of the Namib becomes active after unusual rainfall, which occurs at a frequency less than once per decade.

Hodotermes mossambicus burrows down to the water table. Whenever the supply of grass suffices, it makes saliva-cemented 'pedotubules'.

My commentary:
It is remarkable that a grazing termite survives even in the Namib desert. The fact that H. mossambicus penetrates the Namib, but remains absent from Transkei-Pondoland-southern Natal, and the vicinity of Barberton (https://en.wikipedia.org/wiki/Barberton,_South_Africa), indicates that freedom from leaching is biogeographically important to this termite.

Hewitt P H, van der Westhuizen M C, van der Linde T C de K, and Mitchell J (1990) The dry matter, energy and nitrogen budget of the harvester termite Hodotermes mossambicus (Hagen). S Afr J Sci 86: 30-34.

https://www.cabdirect.org/cabdirect/abstract/19941102325

580 individual termites (were these all fully-grown workers?) weighed 4442 mg (fresh mass) or 834 mg (dry mass).

Hodotermes mossambicus eats almost exclusively dry grass, with an efficiency of conversion of 4.8-6.4%.

The rate of consumption of air-dry plant matter is 7-1,500 kg per hectare per year.

Of the energy ingested, 67% goes to maintenance, 6% to growth, and 27% to faeces. Of the nitrogen ingested, 63% goes to growth, and 37% foes to faeces. There is no fixation of nitrogen in the gut.

The energy-conversion of H. mossambicus is inefficient for an insect. Nitrogen, however, is converted to biomass about as efficiently as in ruminants.

My commentary:
This strengthens the analogy with ungulate grazers. Hodotermitids differ from most other termites in producing faeces which are potentially valuable as fertilizer for herbaceous plants.

About 700 kg per hectare of soil is brought to the surface, per year. The soil dumps of H. mossambicus are about 5-fold richer in nitrogen than the surrounding soil.

"Approximately 14 times more dry grass was collected in the winter than green grass in the summer. Populations actually increase in dry times, rather than decreasing as they do in coexisting ungulates.

Most soil-dumping occurs in late summer-autumn. The nitrogen-richness of dumped soil indicates faecal content. The concentration of nitrogen in faeces is about 1.16%. This suggests a role resembling that of earthworms, rather than other termites.

Hodotermes mossambicus does use faeces to construct its hives. However, most of the faeces are dumped back on to the ground surface, serving as fertiliser for grass.

My commentary:
This is a good reference for the fertilisation effect of Hodotermes on the topsoil.

For every 100 kg (dry matter) of grass ingested, about 5 kg of this species of termite is produced.

Reproduction may amount to 3 million individuals per hectare per year.

MICROHODOTERMES

My third main reference is Coaton W G H and Sheasby J L (1974) National survey of the Isoptera of southern Africa. 6. Microhodotermes Sjoestedt (Hodotermitidae). Cimbebasia Series A, vol. 3, no. 6, pp. 47-59.

My commentary:
Please note that these authors do not mention any relationship between H. viator and heuweltjies (https://en.wikipedia.org/wiki/Heuweltjie).

Like Hodotermes, this genus is approximately restricted to non-leaching climates (mean annual rainfall <750 mm). Whereas Hodotermes is associated with summer rainfall, Microhodotermes is associated with winter rainfall.

My commentary:
The threshold value of 750 mm of rainfall seems to correspond to Paarl Mountain, where I observed M. viator (https://www.inaturalist.org/posts/80176-thought-provoking-observations-from-a-brief-visit-to-the-karoo-desert-national-botanical-garden-and-paarl-mountain-botanic-garden-october-2001#).

The genus Microhodotermes occurs under winter rainfall not only in southern Africa, but also in North Africa, where Hodotermes is absent. The North African spp. are:

• Microhodotermes maroccanus (Morocco), and
• Microhodotermes wasmanni (Tunisia, Libya, and Egypt).

My commentary:
Note that this genus, and the whole family, is absent from the Sahel (https://en.wikipedia.org/wiki/Sahel). This parallels various ungulates and myrmecophages such as Equus, Alcelaphus, Connochaetes, Raphicerus campestris, and Sylvicapra grimmia, which are typical of semi-arid climates in southern Africa, but have no wild counterparts in the Sahel in West and west-central Africa.

Microhodotermes viator

• was not recorded by these authors from the Agulhas Plain,
• was recorded from what is now Addo National Park (https://en.wikipedia.org/wiki/Addo_Elephant_National_Park), marginally penetrating climates in which rainfall in summer exceeds that in winter,
• has an abrupt eastern border to its distribution indicating mutual exclusiveness with Macrotermes natalensis,
• occurs under a range in mean annual rainfall from <125 mm to 750 mm, and an altitudinal range from the coast to 1,700 m.

My commentary:
The upper limit of rainfall is similar to that for H. mossambicus. There seems to be exact geographical complementarity between this hodotermitid and the southernmost fungus-culturing termite, with both spp. ostensibly capable of building large mounds.

Microhodotermes viator

• collects faeces of ungulates to some extent, as food,
• inhabits a single hive per colony, in contrast to H. mossambicus,
• builds a low, broadly conical mound, up to 1.5 m diameter, above each hive, the latter being buried just below the general level of the ground and about 0.5 m below the apex of the mound,
• forages over a radius of up to 45 m around the (buried) hive, by emerging from small holes at various distances from the hive, and
• sometimes makes little piles of sticks and other litter at the entrance of these holes.

My commentary:
There are regions of winter rainfall (mediterranean-type climates) in Europe, California, Chile, Western Australia, and South Australia. However, none of these has any termite ecologically similar to Microhodotermes.

Microhodotermes viator does not extend to the 'karoid' vegetation (https://www.inaturalist.org/observations/33095087 and https://www.inaturalist.org/observations/112265311) of the southwest Kalahari (it does not extend north of the Orange River (https://en.wikipedia.org/wiki/Orange_River) at the longitudes of the Kalahari).

My commentary:
Microhodotermes viator penetrates the southwestern Namib.

(Please also see https://www.inaturalist.org/journal/milewski/59182-comparisons-of-termites-and-termite-eating-animals-in-africa-and-australia-part-1#.)

Publicado el junio 8, 2023 09:15 TARDE por milewski