Land snail biogeography and endemism in south-eastern Africa: Implications for the Maputaland-Pondoland-Albany biodiversity hotspot

regionalisations also suggest further investigations on the limits of a Knysna transition zone between the greater CFR and the greater MPA region. Concerning land snails, the proposed regionalisation permits further refinement when a more complete data set is available at a finer scale equal-area geographical unit, for more genera, to support a much more rigorous analysis, while the data becoming newly available supports the patterns identified here (e.g. [92, 93]). Land snail endemism in south-eastern Africa Quantitative measures mapped for land snail species richness and endemism reveal similar patterns (Fig 5), with higher values along the south-eastern coastal belt and on the south-east- ern escarpment, especially its eastern aspects towards the coastal belt, similar to those for milli- pedes [94, 95], vertebrates [24], bryophytes [96] and higher plants [20]. The Highveld and Bushveld provinces are generally species- as well as endemic-poor, although the Bushveld sup- ports more land snail endemics compared to the Highveld (Fig 5E), which could possibly be attributed to the comparatively higher habitat heterogeneity in the Bushveld that provide shel- tering microhabitats into which snails can retreat, supported by the higher spatial area covered by Bushveld, and again to the supposedly stable and milder climate in the Bushveld (see the role of forests discussed above) compared to that of the Highveld characterized by drought, frost, waterlogging and wildfire causing its treelessness [97]. The northern Mpumalanga escarpment, northern Middleveld, southern Maputaland,

Ngoye, Natal coastal belt, Natal Midlands, Drakensberg-KwaZulu-Natal escarpment, Pondo- land, southern Transkei coastal belt, Amatola-Winterberg, Albany coastal belt and Knysna OGUs (from North to South) are established as strongholds of both species richness and ende- mism of land snails (Fig 5A and 5B), while narrow endemism is concentrated within the extended Pondoland and Natal districts (Fig 5C). Measures of weighted endemism (Fig 5D) further emphasize the importance of the land snail districts of Soutpansberg-Wolkberg, north- ern Middleveld, southern Maputaland, Drakensberg-KwaZulu-Natal escarpment, Natal, extended Pondoland, and Albany-Knysna (from North to South) for malacofaunal conserva- tion, strongly supporting the concept of a greater MPA region of land snail endemism. The corrected weighted endemism (Fig 5E) further highlights the Drakensberg plateau and the lower Karoo as important for land snail conservation in addition to the above districts. Recov- ery of similar endemism peaks from both the UPGMA and PAE clustering as well as the BEA re-confirms the importance of the greater MPA region for restricted-range land snail radiations. Pondoland, a prominent centre of plant endemism, is well recovered here for land snails, even though it showed a comparatively lower endemicity for vertebrates [24]. Nevertheless, the Natal centre, well established for vertebrates, was also found to be an important centre for land snails, even though it is not widely acknowledged for plants. In contrast to the western

limits of the Albany COE for flora [20], land snail endemism in this area extends westward recovering a single Albany-Knysna COE. The overlap of the distribution of forest and Albany thicket biomes with COEs for land-snails (Fig 4D) is noteworthy for further investigation, par- ticularly at a finer scale, while the present study confirms a congruence of endemism between plants and land snails. The data revisited The species selected comprise a representative sample of endemic land snail lineages of SEA and their distributions collectively span much of the study area. More importantly, the land snail genera selected for the study are some of the best collected throughout the study area and PLOS ONE Land snail endemism in the Maputaland-Pondoland-Albany biodiversity hotspot PLOS ONE | https://doi.org/10.1371/journal.pone.0248040 March 4, 2021 17 / 26