AMPHIBIAN DIVERSITY AND SPECIES TURNOVER IN SOUTHERN AFRICA: INVESTIGATION BY MEANS OF A BLOEMFONTEIN-DURBAN TRANSECT

Abstract

A transect from Bloemfontein to Durban, partitioned into quarter-degree intervals, is analysed to examine the performance of a quarter-degree grid in biogeographical pattern analysis, and to evaluate the quantity of available data. Only 5 out of 21 intervals show an estimated 100% intensity (or success) of collecting, which makes the determination of species boundaries uncertain, and shows the distribution and quantity of data to be unsuitable for mechanical analysis. The data are nevertheless sufficient to show that the total species/subspecies diversity at the western end of the transect is only 42% that of the eastern end. A pattern is shown of overlapping diversity gradients from the coastal lowland (21 forms) and from the interior plateau (6 forms). A complex of 21 other forms is localized within the transect zone, and 5 forms appear to cover the length of the zone. The turnover from one end of the zone to the other is substantial (27% similarity). The zone has a smaller interior plateau Comp.nent and a larger plateau slopes complex than a Zimbabwe—Mozambique transect. Crowe's recently published map of amphibian biogeographical and species richness zones, based on a coarser grid (+ two degree), does not receive close corroboration, primariily on account of difference in grid size.