A comparison and conservation assessment of the high-altitude grassland and forest-millipede (Diplopoda) fauna of the South African Drakensberg

Abstract

The Drakensberg mountains, classified as part of the Afromontane region, form the division between the more low lying coastal plain and the high-lying interior of South Africa, and comprise a relatively homogenous and continuous grassland matrix, with small, isolated forest patches. The millipede fauna of the region, particularly in grassland, was previously neglected, and existing data provided no basis for making conservation decisions in this global hotspot of biodiversity. We carried out a quantified survey of the region in order to identify the millipede fauna and its distribution in forest and grassland. We measured levels of endemism and beta diversity, and then made recommendations for conservation. We collected 1184 specimens representing 51 species. The 28 species recorded in the forest were predominantly Polydesmida, mainly Dalodesmidae, and also from two orders unique to forest, the Siphonophorida and Nematozoniida. The 23 grassland species were dominated by Spirostreptida, but some Polydesmida were also recorded. No orders, families or genera were unique to grassland. The Sphaerotheriidae were represented in both habitats, but by different species. Only four species were recorded from both biomes. Each biome was characterised by a distinct fauna, of almost equal richness, but with a different composition (βsim value for grassland and forest = 0.8). Overall, 85 % of species sampled have only been recorded from the Drakensberg region, with a similar level of endemism in both grassland (78 %) and forest (79 %), although the forests had more site endemics (64 %), i.e. restricted to one region. This high level of narrow endemism resulted in high levels of beta diversity especially in grassland (βsim for most pairs of regions = 1) but also in forest (βsim between 0 and 0.7). Adjacent forest regions were not always the most similar. These trends may be attributed to past climate change and the distribution of forest, but the data must be accepted as being incomplete. The conservation implications of the study are that the millipede fauna has high conservation value, and that a large proportion of the Drakensberg area, for both grassland and forest, will need to be protected in order to conserve the millipede fauna.