The ecology of large herbivores native to the coastal lowlands of the fynbos biome in the Western Cape, South Africa

[摘要] The south-western Cape is a unique region of southern Africa with regards to generally lowsoil nutrient status, winter rainfall and unusually species-rich temperate vegetation. Thisregion supported a diverse large herbivore (> 20 kg) assemblage at the time of permanentEuropean settlement (1652). The lowlands to the west and east of the Kogelberg supportedpopulations of African elephant, black rhino, hippopotamus, eland, Cape mountain and plainzebra, ostrich, red hartebeest, and grey rhebuck. The eastern lowlands also supported threeadditional ruminant grazer species - the African buffalo, bontebok, and blue antelope. Thefate of these herbivores changed rapidly after European settlement. Today the few remainingspecies 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 thereintroduction of wild animals into endangered and fragmented lowland areas. Thesereintroductions, together with the realisation that we have limited knowledge of thefunctional role of native large herbivores in the fynbos ecosystem, provided the rationale forthis study. Questions on large herbivore ecology were addressed at three different spatialscales.At the biome level, the reason for the absence of three ruminant grazers from the westernlowlands was investigated. It was hypothesised that the absence of adequate high qualityfodder in the form of C4-grass during the hot and dry summers made it impossible forbuffalo, blue antelope, and bontebok to survive on the western lowlands. The results fromcarbon isotope analysis of late prehistoric, historic and contemporary large herbivore remainswere 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 coastallowlands) can survive with very little (< 15%) C4 grass in their diet. In contrast, bontebokutilized 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-poorsandstone, sand, and limestone fynbos shrublands in favour of the more nutrient-rich shalerenosterveld habitats. Support for this Renosterveld Preference Hypothesis was found bymeans of dung count surveys, which showed that both eland and bontebok readily utilizerenosterveld, but avoid sandstone and limestone fynbos. In the latter they only utilize grassymicrohabitats such as karstic sinkhole depressions. The same hypothesis was addressed in anovel way by using strontium isotope analysis and concluded that the technique needs morerefinement for it to produce reliable results.At a landscape level, interactions between fire and grazing by native large herbivores inrelation to renosterveld vegetation dynamics were addressed. I conclude that thedisappearance of the native herbivores probably had little bearing on the putative structuralchanges in renosterveld (grassland-shrubland dynamics). Support was found for the notionthat a high fire frequency followed by intense grazing by livestock could have convertedoriginal renosterveld grasslands to unpalatable shrublands. Herbivory by nativegrazers/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 herbivoretolerantplant communities. However, in combination with fire, the presence or absence oflarge herbivores can change the trajectory of the system among the alternative structuralstates.

[发布机构] Stellenbosch University