Bats of Southern and Central Africa. Ara Monadjem
22. The rugged landscape of the extensive granitic shield extends from the Tete Province of Mozambique south across eastern and southern Zimbabwe to the Matobo Hills into southeastern Botswana. The most spectacular examples of inselbergs dominate the catchments of the Ruenya and Mazowe rivers in northeast Zimbabwe (here in the Mudzi district). The vegetation is diverse across the rocky slopes, especially where it is protected from fires. Miombo woodland dominates, although it has been largely destroyed by agriculture and settlement on arable lands. These large trees, granite kopjes and inselbergs (dwalas) provide abundant roosts for many species of bats. Here in northeastern Zimbabwe (70 km north of Mutoko), the rarely encountered molossids Tadarida fulminans and T. lobata are locally common (Cotterill 2001b) (© F. P. D. Cotterill).
The ecological importance of granites is demonstrated in roost selection by the large molossid bats Tadarida fulminans, T. lobata, and T. ventralis. The distributions of these species are closely associated with crevice roosts in granite precipices, and to a lesser extent in Karoo sandstones and basalts (Cotterill and Fergusson 1993, Cotterill 2001b).
Sedimentary rocks
Many formations of sedimentary rocks exercise significant controls over bats in southern Africa today. The oldest formed as long ago as 3.8 billion years. The oldest of these – the rocks of the Dominion Group (over 3 billion years old) – represent the earliest accumulation of sediments on the basement provided by the Kaapvaal Craton, and are preserved in the North West Province of South Africa. In northern KwaZulu-Natal and Eswatini similar formations developed and include the Nsuze Group (3,000 Ma). The slightly younger sedimentary formations of the Transvaal Supergroup (2,600–2,100 Ma) and the extensive Waterberg and Soutpansberg groups (1,800 Ma) formed after renewed rifting and the eventual subsidence of extensive areas to below sea level. Cyanobacteria thrived in this shallow sea and caused the precipitation of a deep layer (up to 1 km deep) of calcium carbonate across most of the Kaapvaal Craton; this calcium carbonate was later converted to dolomite (calcium magnesium carbonate). Today the dolomites form karstic outcrops in the Northern Cape, North West, Gauteng and Mpumalanga in South Africa and in southern Botswana (the Ghaap and Chuniespoort groups). The Transvaal Supergroup also contains thick quartzites, which represent highly recrystallised sandstones.
Later, the hard sandstones in these sediments were weathered and eroded into ridges and mountain ranges, and their regular horizontal bedding led to the formation of crevices. Many species of molossid and vespertilionid bats now exploit these crevices for shelters.
Although deep caves are the exception in these sandstones, caves and sinkholes characterise the surface weathering of the slightly soluble dolomites. The large cave systems that formed in these rocks, for example at the Cradle of Humankind in Gauteng and Gcwihaba (Drotskys') Caves in northwestern Botswana, are significant to several species of bats. The extensive caves in Gauteng, which many of us more readily associate with hominin ancestors, provide critically important roosting resources for the breeding and seasonal roosts of several species, notably the Natal long-fingered bat, Miniopterus natalensis. It is remarkable to realise that ancient marine bacteria formed these Gauteng dolomites between 2,600 and 2,400 Ma.
Precambrian dolomites in central Zimbabwe (the Lomagundi Formation) and in central Zambia and southern Katanga in the DRC are equally important and a high density of cave systems characterises these regions, for example, the Mpongwe and Chipongwe caves in Zambia (Kaiser et al. 1998), and the Chinoyi and Mabura caves in central Zimbabwe. These calcareous formations scattered across the southern Congo basin and northern Zambia are associated with metamorphosed sediments of the Lufilian Arc (∼700 Ma), represented in the heavily mineralised Copperbelt of northern Zambia and neighbouring Katanga (Kaiser et al. 1998, Porada and Berhorst 2000, Wendorff 2005). The caves formed in these calcareous formations across Katanga support a diverse bat fauna (Hayman et al. 1966, Whitaker and Black 1976, Anciaux de Faveaux 1978). In addition, some localised deposits of limestones in banded ironstones, and also the ancient greenstones, have weathered into cave systems, and also constitute important bat roosts; examples that have escaped mining occur in the vicinity of Redcliff in Zimbabwe (F. P. D. Cotterill, unpublished data).
Two important sandstone formations had their origins during Gondwana times. The first is the Cape Supergroup (∼500–460 Ma), which ultimately formed the Cape Fold Belt mountains that fringe Africa’s southern margin. The second important formation was forged during the Mesozoic, in Karoo times, when vast sediments built up across the interior of Gondwana and formed the Karoo Supergroup (∼350–200 Ma). Ultimately, the more recent of these sediments, the Molteno and Ecca formations, came to form extensive sandstone formations in southern Africa, while wind-borne sand deposition resulted in the Cave Sandstones (Clarens Formation), characteristic of parts of the Drakensberg mountains. These Karoo sandstones, especially where exposed along valley margins, provide important roosts to bat assemblages, notably in the Limpopo, Luangwa and Zambezi drainage basins.
Rift valleys
Major zones of uplift and faulting across southern Africa created the Luangwa, Gwembe and Kamalondo rift valleys. Precursors of these graben first formed during Karoo times (350–180 Ma). This tectonic activity is associated with the rifting that continues across Africa today in the East African Rift System, which started to propagate into southern Africa about 20 Ma. The East African Rift is a narrow zone in which the African Plate is in the process of splitting into two new tectonic plates. The dramatic scarps and graben that characterise the East African Rift System are very young when considered against the deep antiquity of the continent’s geological history; nevertheless, they are of key importance in controlling biotic evolution (see Geomorphology below). The chain of rift valleys propagates south across East Africa from Afar, Ethiopia, diverging into two discrete forks across southern Africa. One is expressed southward, through Malawi into the Urema Trough of Mozambique; the second extends southwest into the Okavango graben in northeastern Botswana from Katanga (DRC) and Zambia.
GEOMORPHOLOGY
The greater portion of southern Africa lies at an average elevation of 1,000 m above sea level. Aptly termed the Kalahari Plateau, this hinterland extends north far across the Congo basin, with its northeastern boundaries abutting the East African Rift System along Lake Tanganyika. This anomalous topography is geologically ancient, dating from before the final break up of Gondwana in the Mesozoic (∼127 Ma) and is likely even older. The characteristically subtle changes in drainage and landforms across the Kalahari Plateau (de Wit 2007) have exercised marked control over biogeographical processes over the past 30 million years (Cotterill 2003, 2005, 2006).
Escarpments
The margins of the Kalahari Plateau are edged with steep escarpments, comprising a single horseshoe arc. In the south, the high relief of the Cape Fold Belt forms a partial arc against these greater escarpments flanking southern Africa that extend west and east. The eastern escarpment is dominated by the rim of the Drakensberg Massif, continuing north in the Lebombo and Mpumalanga mountains, and farther northeast into East Africa. In Zimbabwe, the Eastern Highlands dominate the topography, especially in contrast to the Mozambique coastal plain. The Livingstone Mountains, bounding the eastern edge of the Nyasa (Malawi) graben (Smithers and Lobão Tello 1976), form the northern margin of the plateau (albeit recently modified by the Malawi rift). On the Atlantic coast, the western margin of the Kalahari Plateau is formed by the mountainous flanks of the Bokkeveld and Namaqua plateaux, and extends northwest through Namibia. It reappears north of the Kunene River’s incision in the high mountain land of western Angola.
The topography of southern Africa has been influenced by past tectonic events, which have expressed both subtle and dramatic effects across the subcontinent. The most dramatic evidence lies in the East African Rift System, exemplified in the deep graben occupied by lakes Tanganyika and Malawi. A southwestern extension of the East African Rift accounts for the remarkably varied topography of Katanga in the DRC, especially the Kundulungu and Kibara plateaux, which at over 1,800 m above sea level dominate the adjacent Kamalondo and Lufira depressions (whose lowest elevations lie below 600 m above sea