A thesis submitted to the Faculty of Science, University
of the Witwatersrand, in fulfilment of the academic
requirements for the degree of Doctor of Philosophy.
August 2016, Johannesburg / Termites are widely distributed in tropical and subtropical savanna. They are recognised as major ecosystem engineers through their role in nutrient cycling, decomposition, hydrology and alteration of landscape topography with cascading effects manifesting in ecosystem heterogeneity and productivity up the food chains. In this thesis I addressed the effect of geology on termite species diversity, followed by questioning how the different geologies influence the size and spatial distribution of Macrotermes mounds. Furthermore, I explored the effect of termite mounds emanating from different geologies on herbaceous vegetation heterogeneity and finally the effect this heterogeneity has on grazing intensity. Although the diversity of termites has been explored across different environmental gradients such as rainfall, altitude and disturbance, little is known regarding variation in their diversity across landscapes of varying geology. In my quest to understand how varying geology influences the ecology of termites and their functional importance, I sampled granite and basalt for termite diversity using standard transects (100 m x 2 m). I predicted that termite diversity is higher on nutrient-rich geology following the productivity diversity hypothesis. However, both functional and taxonomic diversity were higher on nutrient-poor granite. Twelve species from three subfamilies representing two feeding groups were recorded on granite whereas on basalt only five species from two subfamilies consisting of one feeding group were recorded. Although the influence of Macrotermes mounds on ecosystem heterogeneity has been well studied, little is known on how the environment (geology) and other termite colonies influence size and distribution pattern, despite how these interactions could influence ecosystem functioning. Termite mounds were sampled in 1 km2 plots, four in each geology. Each mound location was recorded using a hand held GPS and structural variables (height and diameter) measured. The data were analysed for spatial distribution of termite mounds using the software Programita. The general distribution pattern of termite mounds (active and inactive mounds combined) was investigated using both the pair correlation function, g(r), and Ripley’s K(r) function. Termite mounds were larger and covered a significant proportion of the landscape on granite compared to basalt. Mounds were generally over-dispersed on granite and randomly distributed on basalt. Mounds covered ~ 6% of the landscape on granite compared with only ~ 0.4% on basalt. These results show that the significance of termites varies across geologies, being more important on nutrient-poor geologies because of their size and a more productive spatial pattern displayed here. The majority of studies testing
mound effects on savanna vegetation spatial heterogeneity have been based on single site observations mostly comparing mounds and their paired savanna control plots. Furthermore studies did not consider the spatial effects of mounds with distance into the savanna matrix from mound edge, and this has rarely been tested across landscapes of varying geologies, as well as across mounds of different sizes. Therefore there was a need to explore this in order to broadly understand the functional importance of mounds. I sampled the herbaceous community on and off termite mounds and along distance transects from mounds on nutrient-rich and nutrient-poor geologies. Termite mounds as sources of spatial vegetation heterogeneity was more pronounced on nutrient-poor granite, with larger mounds having greater effect on vegetation composition and diversity than smaller ones. Mounds harboured compositionally different herbaceous plants compared with the savanna matrix on granite whereas there was no difference on basalt. In acknowledging the effect erosion from mounds may have on vegetation heterogeneity, termite mound effect on composition expressed at landscape level based on mound densities recorded in this study was estimated to be 19% of the landscape on granite whereas on basalt, the mounds influenced ~ 0.4% of the landscape. The choice of foraging sites by large herbivores in the landscape is influenced by food quantity, quality, inter and intra-specific competition and predation risk. Termite mounds harbour highly nutritious herbaceous plants compared to the savanna matrix, which makes them preferred foraging sites. Due to very small differences in soil nutrient content between mounds and savanna on basalt, mounds were expected to have little effect on grazing. In line with the set hypothesis termite mounds largely influenced grazing on the nutrient-poor granite and when viewed at landscape scale, based on mound densities and extent of erosion recorded, mounds influenced ~ 28% on granite and only ~ 0.8% on basalt. Overall my study has demonstrated that the significance of termites as ecosystem engineers varies across landscapes of varying geology, being more important on nutrient-poor compared with nutrient-rich geologies. / MT2017
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/22729 |
| Date | January 2017 |
| Creators | Muvengwi, Justice |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | Online resource (ix, 151 leaves), application/pdf |
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