Ecological relationships between the armadillo lizard, Cordylus cataphractus, and the southern harvester termite, Microhodotermes viator
Thesis (MSc (Botany and Zoology))--University of Stellenbosch, 2006.
The role of the southern harvester termite, Microhodotermes viator, and several climatic parameters in the distribution of the group-living lizard, Cordylus cataphractus, was investigated. Microhodotermes viator is considered the most important prey item of C. cataphractus and termitophagy as the causative agent in the evolution of group-living in this species. One would therefore expect a high degree of correspondence in the ranges of C. cataphractus and M. viator. As climate will also play a role in the distribution of any species, various climatic variables were investigated to determine their influence on the distribution of C. cataphractus. Species distributions were visualized using the minimum polygon technique and the degree of overlap was determined using standard geographic information systems (GIS) techniques. A total of 53 C. cataphractus localities were investigated for the presence of termites. The climatic limits of the geographical distribution of C. cataphractus were investigated by means of three models, namely Classification Trees, General Discriminant Analysis and Logistic Regression. The range of C. cataphractus was completely included within the range of M. viator Microhodotermes viator was included in the diet of C. cataphractus at 73 % of the localities sampled within the lizard’s range. The current geographical range of C. cataphractus is mainly correlated with two climatic factors, namely the low summer rainfall and high monthly solar radiation. The restricting role of both these factors can be directly linked to the group-living nature of C. cataphractus. If termitophagy were the overarching cause of group-living in C. cataphractus, then one would expect a close relationship between termite density and lizard density and termite density and lizard group size. I investigated these relationships at both a local and regional scale. For the local scale study, 25 quadrats of 25 × 25 m were plotted at a selected site, and for the regional scale study, ten 35 × 35 m quadrats at sites throughout the lizard’s range were used. In each quadrat, a range of variables were recorded, the most important of which were lizard density, lizard group sizes, termite foraging port density, distance to nearest termite foraging ports, vegetation height and vegetation cover. I found that the density of termite foraging ports determines C. cataphractus density. Vegetation height and cover affects crevice selection by C. cataphractus groups, probably because an unobstructed view is necessary to locate termite activity at foraging ports. I also investigated possible differences in the use of termites by different sized groups of C. cataphractus during different times of the year. Faecal samples, collected once a month at Eland’s Bay from small, medium and large groups from January 2005 to December 2005, were analysed for the presence of termite head material. I found that large groups fed on termites to a greater extent than small groups during certain times of the year and there was a general tendency for this phenomenon throughout the year. The results collected in this study indicate that the southern harvester termite, M. viator, plays a central role in the ecology of the group-living lizard, C. cataphractus.