Bats of Southern and Central Africa. Ara Monadjem

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СКАЧАТЬ 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bat roosts; examples that have escaped mining occur in the vicinity of Redcliff in Zimbabwe (F. P. D. Cotterill, unpublished data).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 level) (Broadley and Cotterill 2004, Cotterill 2005). There are steep escarpments in this region, most notably Zambia’s Muchinga Escarpment, which bounds the western edge of the Luangwa valley. The significance of the Muchinga Escarpment as a biogeographical boundary was originally emphasised by Neave (1907, 1910a, b) and Ansell (1978). The enhancement of the Muchinga Escarpment by the East African Rift created a prominent eastern bound to the Kalahari Plateau; this rugged scarp extends south, bordering the Gwembe trough, markedly eroded by the Middle Zambezi (today artificially impounded in Lake Kariba at Kariba Gorge).

      Equally impressive escarpments form the steep flanks of the Middle Zambezi valley in Zambia and Zimbabwe (Cotterill 2003, Moore et al. 2009, 2020) (Figure 28). These escarpments bound formerly extensive landscapes, and have witnessed a prolonged history of uplift and erosion that has persistently lifted and warped the Kalahari Plateau, faulting its margins in parts (de Wit 2007).

Drainage systems

      The modern hydrology of southern Africa is dominated by several major drainage basins, with the Congo and Cuanza basins in the extreme north, the Zambezi and Limpopo rivers, which drain eastwards into the Indian Ocean, and the Kunene and Orange–Vaal systems that drain west into the Atlantic (Figure 24). River topology strongly influences the distributions of bat species that depend on riparian habitats for food and daylight roosts. This can be seen very clearly in the Namib Desert, where the Kuiseb River supports populations of tree-roosting bats.

      The drainage systems that characterise southern Africa today are very different from their precursors. Repeated uplift and erosion of the Kalahari Plateau and the propagation of the East African Rift System into southern Africa caused radical rearrangements of the region’s drainage systems.

      Following the final stages in the break up of Gondwana (∼127 Ma), the Palaeo-Limpopo River drained a large part of the interior of central southern Africa, with most of the rivers of today’s lower DRC, Angola, Botswana and Zimbabwe flowing into it. About 80 Ma, epeirogenic uplift created vast depressions across the Kalahari Plateau Basin in the interior of southern Africa. What are today the headwaters of the Kunene, Orange, Limpopo and Zambezi rivers originally flowed into the Kalahari Basin (Moore et al. 2009). These endorheic rivers maintained vast lakes in the interior, notably in the Etosha basin and northeastern Botswana; one of the largest of these lakes was Palaeo-Lake Makgadikgadi, which had an area of ∼67,000 km² (Cotterill 2006, Moore et al. 2012).

      Figure СКАЧАТЬ