TERMITE ABUNDANCE – QUO VADIS?

People are asking me why has termite mound abundance, especially in the Phalaborwa region, dissipated in recent years. It was a concern of mine, too, doing a cursory survey of the area in 1998/99. However, it was only later that I realized that because of unusual high rainfall commencing just after the mid nineties, and the relative lack of clay in the granitic landscapes, that mound resistance to augmented rain was inadequate.

The Natal fungus grower (Macrotermes natalensis) constructs mounds with sand particles mended/cemented together with clay (hardened when lime occurs, e.g. landscapes 23 and 26, although this termite does not occur in the former and are low in abundance in the latter) using saliva. A similar case of termite inactivity was recently (2000) noticed in the rhyolitic Lebombo Mountains after a thorough aerial survey for termite hotspots in the area (1999). Roughly fifty mounds occurring along a belt have for instance gone inactive. The problems arising when termites repair damaged mounds due to torrential rain is obvious: vulnerability and unusual exposure to predators, especially ants gaining entry to mounds; the fact that fresh mound repairs cannot dry quick enough and as such are frequently washed away.

Societal organisms are known to occur with increasing aridity. However, using 1995 data it was shown that a poor but positive relationship existed between termite mound abundance and annual rainfall. It was later suggested that because these termites consume litter, increased plant biomass is needed in order to produce raised litter levels in drier years. Just as termites are adversely affected by severe and prolonged drought in the arid/mesic Kruger National Park (esp. up north), I suspect that the same is the case during extreme wet cycles for savanna-woodland (non-forest) species.

The last severe drought in the KNP was during 1991/92, seemingly recurring every decade. Dry or wet cycles reappear every 9–19 years, and it is therefore very difficult to predict whether a further decline in termite numbers is likely, as weather patterns due to the effects of El Niño and La Niña have become more difficult to predict.

It does seem that the decline of termites is due to natural consequences of wet and dry periods, and that their numbers will increase during the course of the latter. Alternatively, air pollution over the Lowveld may cause termite decline as detrimental gases diffuse through mound walls (capping uniquely porous according to species). Acid rain accelerates mound erosion. It cannot be stressed enough that monitoring the distribution and density of termites, especially the most abundant M. natalensis, may be vital for their and other fauna and flora’s survival. Certainly to understand the cyclic intricacies of termite population dynamics and hence the degree of nutrient cycling during certain periods, future monitoring is warranted.
 

Further Reading

BENNETT, N.C. 1988. The trend towards sociality in three species of southern African mole-rats (Bathyergidae) – causes and consequences. PhD thesis, University of Cape Town.
BRAACK, L.E.O. 1995. Seasonal activity of savanna termites during and after severe drought. Koedoe 38: 73–82.
GERTENBACH, W.P.D. 1983. Landscapes of the Kruger National Park. Koedoe 26: 9–121.
HOLT, J.A. 1987. Carbon mineralization in semi-arid northeastern Australia: the role of termites. Journal of Tropical Ecology 3: 255–263.
LEE, K.E. & WOOD, T.G. 1971. Termites and Soils. Academic Press, London.
MEYER, V.W. 1997. Distribution and density of mound-building termites in the northern Kruger National Park. MTech thesis, Technikon Pretoria.
MEYER, V.W., BRAACK, L.E.O. & BIGGS, H.C. 2000. Distribution and density of Cubitermes Wasmann (Isoptera: Termitidae) mounds in the northern Kruger National Park. Koedoe 43: 57–65.
MEYER, V.W., BRAACK, L.E.O., BIGGS, H.C. & EBERSOHN, C. 1999. Distribution and density of termite mounds in the northern Kruger National Park, with specific reference to those constructed by Macrotermes Holmgren (Isoptera: Termitidae). African Entomology 7: 123–130.
ZAMBATIS, N. & BIGGS, H.C. 1995. Rainfall and temperatures during the 1991/92 drought in the Kruger National Park. Koedoe 38: 1–16.
 

Suggestions are welcome

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