Density of Microhodotermes viator (Hodotermitidae) mounds in southern Africa in relation to rainfall and vegetative productivity gradients

Abstract

Giant earth mounds (heuweltjies) formed by the southern harvester termite Microhodotermes viator occupy a large proportion of the land surface of the Succulent karoo, Nama-karoo and Fynbos biomes. Microhodotermes viator is associated with specific vegetation types and low winter rainfall, prompting the hypothesis that rainfall and vegetative productivity govern the distribution and population densities of M. viator. Using an analysis of aerial photographs, the density of termite mounds at 34 sites in 10 vegetation types was determined across the full range of their distribution. The number of mounds ranged from 143 to 704 km À2 with a mean of 297. When all sites were considered together, mound density was not related to temperature, altitude, rainfall and vegetative productivity [as measured by the normalized difference vegetation index (NDVI)]. However, if the single Fynbos and five Coastal Renosterveld sites (with rainfall 4350 mm year À1 ) were excluded from the analysis, then mound density was significantly related to both rainfall and NDVI values. A separate analysis of the relationship between mound density, rainfall and soil fertility was undertaken. There was a significant relationship between rainfall and mound density for sites occurring on soils of high-fertility status but not for sites occurring on soils of lowfertility status. These results suggest that soil fertility and vegetation composition are parameters that influence the effect of rainfall and vegetative productivity on termite mound distribution and density. Finally, the positive relationship between rainfall and mound density in areas with o350 mm year À1 suggests that M. viator populations are in equilibrium with climatic conditions. This provides further evidence that heuweltjies are constructed by their current occupants, M. viator, and are not the product of an extinct termite species as has been suggested previously.

Deciphering earth mound origins in central Brazil

“…This landscape type, with tree-covered mounds in a matrix of floodtolerant grasses, occurs extensively throughout the cerrado ( Fig. 1; Oliveira-Filho and Furley 1990), but there are analogous formations elsewhere in the Neotropics (Cox et al 1989;Ellery et al 1998;McCarthy et al 1998;Brossard et al 2007) in Africa and Australia (Picker et al 2007;Midgley et al 2002;Rahlao et al 2008) and also in north America, where mound fields (prairie mounds) occur from Saskatchewan to Minnesota and south through Iowa and Missouri to Arkansas, eastern Oklahoma, and the coastal plain of Louisiana and Texas (Ross et al 1968;Mollard 1982).…”

Ecophysiology, Vigour, Berry and wine Quality of Grapevines Growing on and off Heuweltjies

“…Heuweltjies are prominent landscape features in the southwestern parts of South Africa. They occupy roughly 14% to 25% of the land surface (Lovegrove & Siegfried, 1986;Picker et al, 2007), averaging 17 m in diameter and 1.45 m in height (Moore & Picker, 1991). In some areas, heuweltjies can even occupy up to 60% of the surface area in vineyards (Shange et al, 2006) and can modify the landscape considerably.…”

“…They can also be found in diverse environments, ranging from the succulent Karoo to the coastal Renosterveld and Fynbos (Picker et al, 2007). The soil and vegetation cover that generally occurs on and between heuweltjies differs significantly.…”

“…The water infiltration and absorption rates on heuweltjies can be impaired and are related to the formation of algal crusts or salinity (Palmer et al, 1999). Considering the above-mentioned, it is evident that on-mound vegetation under natural conditions is distinctly different from that occurring off-mound (Knight et al, 1989;Midgley & Musil, 1990;Picker et al, 2007). Heuweltjies in all stages of development, ranging from loose soil and frass over young termite colonies to large mounds up to 32 m in diameter, can be distinguished in the landscape (Lovegrove & Siegfried, 1989).…”

“…Heuweltjies are virtually absent on base-poor parent material, such as sandstone. They also contain higher concentrations of nutrients than the soils surrounding them (Midgley & Musil, 1990;Picker et al, 2007). On-mound soils are also more aerated, with increased water availability as well as higher levels of both macro-and micro-elements.…”