Altitudinal species turnover in southern Tanzania shown by anurans: Some zoogeographical considerations

Abstract

A transect was used to investigate the pattern of altitudinal species turnover shown by the rich fauna of frogs and toads in southeastern Tanzania, and to compare the pattern with those shown by transects taken further south. The transect, taken from the Udzungwa range to the southeastern coast, was divided into 50 m intervals. As with the southern transects, there appears to be a major grouping into lowland and highland sets, with opposing and overlapping subtraction margins that form a replacement‐transition zone. A distributionally complex assemblage of species occurs in this zone. When a similarity value (the Dice‐Sørensen index, expressed as a percentage) taken between the montane ridge and lowland faunas was compared with those of the southern transects, a markedly higher species turnover (low similarity value) is shown in Tanzania. Both lowland and highland faunas have more species than equivalent faunas to the south; the highland fauna is particularly rich in genera not known to occur further south. Yet overall, the pattern of altitudinal turnover shown in the Tanzanian transect is in agreement with the pattern shown in the southern transects. The transects discussed in this paper, combined with other evidence, suggest a need for re‐evaluating the common practice of including all sub‐Saharan Africa in a single so‐called Afrotropical Region.