Thesis (DSc (Botany and Zoology))—-Stellenbosch University, 2008. / The south-western Cape is a unique region of southern Africa with regards to generally low
soil nutrient status, winter rainfall and unusually species-rich temperate vegetation. This
region supported a diverse large herbivore (> 20 kg) assemblage at the time of permanent
European settlement (1652). The lowlands to the west and east of the Kogelberg supported
populations of African elephant, black rhino, hippopotamus, eland, Cape mountain and plain
zebra, ostrich, red hartebeest, and grey rhebuck. The eastern lowlands also supported three
additional ruminant grazer species - the African buffalo, bontebok, and blue antelope. The
fate of these herbivores changed rapidly after European settlement. Today the few remaining
species are restricted to a few reserves scattered across the lowlands. This is, however,
changing with a rapid growth in the wildlife industry that is accompanied by the
reintroduction of wild animals into endangered and fragmented lowland areas. These
reintroductions, together with the realisation that we have limited knowledge of the
functional role of native large herbivores in the fynbos ecosystem, provided the rationale for
this study. Questions on large herbivore ecology were addressed at three different spatial
scales.
At the biome level, the reason for the absence of three ruminant grazers from the western
lowlands was investigated. It was hypothesised that the absence of adequate high quality
fodder in the form of C4-grass during the hot and dry summers made it impossible for
buffalo, blue antelope, and bontebok to survive on the western lowlands. The results from
carbon isotope analysis of late prehistoric, historic and contemporary large herbivore remains
were consistent to this Summer Nutritional Stress Hypothesis. I found that eland, elephant,
grey rhebuck, ostrich, and red hartebeest (all species that historically occurred in both coastal
lowlands) can survive with very little (< 15%) C4 grass in their diet. In contrast, bontebok
utilized at least 43% C4 grass biomass in what was considered their natural habitats.
At a regional level, I tested the hypothesis that the large herbivores avoid nutrient-poor
sandstone, sand, and limestone fynbos shrublands in favour of the more nutrient-rich shale
renosterveld habitats. Support for this Renosterveld Preference Hypothesis was found by
means of dung count surveys, which showed that both eland and bontebok readily utilize
renosterveld, but avoid sandstone and limestone fynbos. In the latter they only utilize grassy
microhabitats such as karstic sinkhole depressions. The same hypothesis was addressed in a
novel way by using strontium isotope analysis and concluded that the technique needs more
refinement for it to produce reliable results.
At a landscape level, interactions between fire and grazing by native large herbivores in
relation to renosterveld vegetation dynamics were addressed. I conclude that the
disappearance of the native herbivores probably had little bearing on the putative structural
changes in renosterveld (grassland-shrubland dynamics). Support was found for the notion
that a high fire frequency followed by intense grazing by livestock could have converted
original renosterveld grasslands to unpalatable shrublands. Herbivory by native
grazers/browsers, or the release from it, cannot by itself bring about the vegetation-state
(structural) changes in renosterveld patches which had already been altered to herbivoretolerant
plant communities. However, in combination with fire, the presence or absence of
large herbivores can change the trajectory of the system among the alternative structural
states.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/1178 |
| Date | 12 1900 |
| Creators | Radloff, Frans Gustav Theodor |
| Contributors | Mucina, L., Bond, W. J., Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | Stellenbosch University |
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