Species turnover, community boundaries and biogeographical composition of dung beetle assemblages across an altitudinal gradient in South Africa

Aim: To identify biogeographical boundaries which are obscured by faunal ov erlap and habitat modification. Location: KwaZulu-Natal in south-east, South Africa beyond the southern tip of the Mocambique Coastal Plain. Methods: Species abundance data for dung beetles (Scarabaeidae: Scarabacina e) were collected at six levels from the coastal escarpment (30 degrees 16' S - 500 m) to the top of the nearby Drakensberg (29 degrees 35'S - 2850 m). Cross-altitudinal boundaries were identified using clustering techniques, beta-diversity indices, and range edge analysis. Biogeographical data for t he species were drawn from an extensive reference collection and used to cl assify the biogeographical affinities of the assemblages. Results: Three discrete communities are defined (<10% similarity) from spec ies abundance distributions. These communities occur in coastal forest (500 m), coastal to highveld grassland (500-1500 m), and montane grassland (190 0-2850 m). Two of these communities are biogeographically homogeneous compr ising >89% east coast endemics (coastal forest) or >84% South African monta ne endemics (montane grassland) in terms of abundance. The third community in coastal to highveld grassland is biogeographically more heterogeneous. P redominant biota of this community comprise both South African highveld end emics and elements with distributions extending into the tropics. At highve ld levels (1500 m), there are proportionately more highveld endemics wherea s at lowland levels (500 m), there are proportionately more tropical elemen ts. At 1000 m, there was a change in the balance between these two groups a cross an anthropogenic gradient due to a decline in the proportion of endem ics in favour of temperate/tropical generalists. This gradient from a natur al grassland fragment to improved pastures of Kikuyu grass also parallels a decline in species richness and abundance. Species turnover analyses showe d three different cross-altitudinal patterns. Range-edge analysis showed a trimodal pattern of species turnover (peaks in forest and the Drakensberg f oothills as in the community analysis but also at (1000 m). Five beta-diver sity indices showed either a bimodal pattern of turnover (forest/grassland and foothills/middle Drakensberg slopes) or a trimodal turnover pattern (fo rest/grassland, highveld Drakensberg foothills, Drakensberg peaks). Main conclusions: Clear altitudinal zonation is revealed by community and b iogeographical analysis but one natural biogeographical boundary may be obs cured by the process of habitat modification. This boundary at 1000 m is re vealed by range-edge analysis and is supported by findings for plant commun ities. Beta-diversity, species turnover patterns diverged slightly from tho se suggested by the community and range-edge analyses.