To identify factors that drive plant species richness in South-African savanna and explore their relative importance, we sampled plant communities across habitats differing in water availability, disturbance, and bedrock, using the Kruger National Park as a model system. We made plant inventories in 60 plots of 50 × 50 m, located in three distinct habitats: (i) at perennial rivers, (ii) at seasonal rivers with water available only during the rainy season, and (iii) on crests, at least ~ 5 km away from any water source. We predicted that large herbivores would utilise seasonal rivers' habitats less intensely than those along perennial rivers where water is available throughout the year, including dry periods. Plots on granite harboured more herbaceous and shrub species than plots on basalt. The dry crests were poorer in herb species than both seasonal and perennial rivers. Seasonal rivers harboured the highest numbers of shrub species, in accordance with the prediction of the highest species richness at relatively low levels of disturbance and low stress from the lack of water. The crests, exposed to relatively low pressure from grazing but stressed by the lack of water, are important from the conservation perspective because they harbour typical, sometimes rare savanna species, and so are seasonal rivers whose shrub richness is stimulated and maintained by the combination of moderate disturbance imposed by herbivores and position in the middle of the water availability gradient. To capture the complexity of determinants of species richness in KNP, we complemented the analysis of the above local factors by exploring large-scale factors related to climate, vegetation productivity, the character of dominant vegetation, and landscape features. The strongest factor was temperature; areas with the highest temperatures reveal lower species richness. Our results also suggest that Colophospermum mopane, a dominant woody species in the north of KNP is not the ultimate cause of the lower plant diversity in this part of the park.

Biology Centre Institute of Entomology Czech Academy of Sciences Branišovská 31 37005 České Budějovice Czech Republic

Center for Theoretical Study Charles University Prague Czech Republic

Centre for Invasion Biology Department of Botany and Zoology Stellenbosch University Stellenbosch South Africa

Department of Ecology Faculty of Science Charles University Viničná 7 12844 Prague Czech Republic

Department of Mathematical Sciences Stellenbosch University Stellenbosch South Africa

Institute of Botany Department of Invasion Ecology Czech Academy of Sciences 25243 Průhonice Czech Republic

Scientific Services South African National Parks Private Bag X402 Skukuza 1350 South Africa

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Habitat modifies the relationship between grass and herbivore species richness in a South African savanna

Moth Diversity Increases along a Continent-Wide Gradient of Environmental Productivity in South African Savannahs

Thirteen moth species (Lepidoptera, Erebidae, Noctuidae) newly recorded in South Africa, with comments on their distribution