The ecologically powerful genera of termites, Macrotermes and Nasutitermes, tend not to coexist in Zimbabwe

 (writing in progress)
 
The termite genus Nasutitermes occurs in Australasia, South America and Africa. The termite genus Macrotermes occurs in Africa and tropical Asia.

Both genera contain species that build extremely large structures, 6 m high or more. Both feature prominently in the diets of termite-eating animals.

However, there seems to be a kind of complementarity between these genera, despite their wide geographical overlap.

Nasutitermes is important in the diets of myrmecophages in South America, where Macrotermes is absent. It forms its largest termitaria in Australia, where Macrotermes is likewise absent.

In the main habitats of Macrotermes in Africa, Nasutitermes seems marginalised in the sense that it tends to occur mainly in vegetation unsuitable for Macrotermes.

In this Post, I test whether Nasutitermes coexists with Macrotermes in the tropical African country, Zimbabwe. My reference is Mitchell B L (1980) Report on a survey of the termites of Zimbabwe, Occasional Papers of the National Museums and Monuments Series B, Natural Sciences, vol. 6 part 5.
 
In Zimbabwe, there occur 6 spp. of Macrotermes and at least 13 spp. of Odontotermes, as well as at least 9 other species of macrotermitines.

In the case of nasutitermitines, there occur 2 spp. of Nasutitermes, 5 spp. of Trinervitermes, and 6 other spp. in the same subfamily.

So Nasutitermes and Macrotermes certainly are sympatric at the coarse scale of the country in general. But do they actually coexist anywhere?
 
Nasutitermes infuscatus occurs in Zimbabwe only in the eastern Highlands sensu stricto, close to the Mozambique border. All sites are at altitudes < 750 m a.s.l. and > 1200mm/year rainfall. The vegetation is evergreen forest of Newtonia and woodland of Brachystegia and Uapaca. The termitaria are arboreal, at heights 1->6m above ground (I infer that they are made of carton). Nasutitermes kempae has only one location in Melsetter district, in similar habitat to the above in one of the same areas (forest of Newtonia, Breonadia & Lovoa). In Tanzania the shelter of this species was described as a loose earthy mound among the roots of a tree. All the sites for Nasutitermes in Zimbabwe are too wet for Hodotermes, which is widespread in the country but cuts out in the wettest forms of miombo, and certainly does not occur in the eastern Highlands.
 
Species of Macrotermes occurring in the eastern Highlands sensu stricto, at the same locations as N. infuscatus, are falciger, michaelseni, natalensis, subhyalinus, and vitrialatus.

So yes, there is sympatry between the two genera in this small corner of Zimbabwe. But do they occur in the same vegetation types?
 
Macrotermes falciger occurs in various types of woodland and savanna in the wetter parts of Zimbabwe, typically miombo. So, it does seem to co-occur with Nasutitermes in the limited habitat of the latter genus in the eastern Highlands, at least in miombo. Macrotermes natalensis is similar (both falciger and natalensis prefer sandy soils over granite bedrock).
 
Macrotermes michaelseni is also widespread in Zimbabwe. However, it tends to occur in somewhat drier situations, and is unlikely to penetrate the vegetation in which Nasutitermes occurs (M. michaelseni has not been recorded in vegetation containing Uapaca or Newtonia/Breonadia/Lovoa). The situation in M. subhyalinus and M. vitrialatus is intermediate, in the sense that it remains unclear whether there is ecological overlap between these relatively scarce spp. and Nasutitermes, within the extremely restricted range of the latter genus.
 
Discussion:

Macrotermes is widespread in Zimbabwe (with several spp. coexisting over most of the country) but Nasutitermes is extremely restricted in occurrence, centred on evergreen forest in the valleys of the eastern Highlands.

Nasutitermes has penetrated the miombo vegetation adjacent to evergeen forest, but no farther afield. Macrotermes seems to be absent from the evergreen forest referred to. Although it is clear that it coexists with Nasutitermes in several study sites in miombo, the overlap in distribution between the two genera in this country is small.
 
So, Nasutitermes is indeed marginalised in a country that is a stronghold for Macrotermes.

This tendency towards mutual exclusion cannot be attributed to biogeographical accidents. Nasutitermes has probably existed in this area since Gondwana times; it fully belongs here as an ancient presence. The interesting thing is that this genus, so widespread in mesic Australia and the forests (and presumably woodlands and savannas) of South America, has been excluded from 99% of Zimbabwe.
 
It sounds as if Nasutitermes is basically restricted in Zimbabwe to fire-free situations (if I am right in my interpretation of forest with Newtonia, Breonadia, and Lovoa).

Mitchell (1980) does not mention recording any species of Macrotermes (a genus widespread in Zimbabwe) in evergreen forest of Newtonia, Breonadia and Lovoa, whereas this was one of the two habitats of Nasutitermes in the Zimbabwe.

Even in that forest, Nasutitermes builds nothing on the ground, and even in the trees probably builds exclusively from carton. If I am right in thinking that its main habitat is fire-free, we can say that the ecological separation between Nasutitermes and Macrotermes in Zimbabwe is complete even though they undoubtedly abut each other at a within-hectare scale.
 
What this means is that one cannot possibly invoke some sort of geographical barrier between these genera in Zimbabwe; what we find is an ecological barrier. This is significant in view of

• the cosmopolitan range of Nasutitermes on Earth in terms of continental presence,
• the vast area of potential overlap between these two genera in Africa and Asia,
• the wide range and abundance of Nasutitermes in Australia, and
• the extreme prominence of Nasutitermes in tropical Australia.

We cannot invoke any accidental geographical separation, and we can be sure that the pattern of mutual exclusion is ecological.

In summary:

Nasutitermes is extremely restricted ecologically in southern Africa. If there is any overlap on a hectare scale between it and Macrotermes, then that is because of the extreme ecological breadth of Macrotermes here.
 
It might be possible, with a particular search-image, to find a remote hectare in some valley of the eastern Highlands in which a colony of Nasutitermes can be found in the same hectare as a colony of Macrotermes (probably falciger or natalensis). However, there seems to be no chance that one will find both of these genera building earth shelters in that hectare. This is simply because no species of Nasutitermes in Zimbabwe (or the whole of Africa as far as I know) builds any structure on the ground, let alone of earth.

So, in that sense the spatial separation, and the separation in construction methods, is complete.
 
(writing in progress)

Posted on 16 de julho de 2022, 06:20 AM by milewski