Bats of Southern and Central Africa. Ara Monadjem

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Figure 34. (a) Interior of dense gallery forest that includes Guinean–Congolian plant species, at the source of the Zambezi River, Ikelenge Pedicle, Mwinilunga District, northwestern Zambia; (b) dense riparian forest (East African Coastal Mosaic) with emergent palms, Zambezi Delta, Mozambique.

Savanna

      The savanna biome is characterised by widely spaced trees that form an open canopy, allowing sufficient light to reach the ground to support an unbroken herbaceous layer consisting primarily of grasses. This biome originated in the early Neogene (de la Estrella et al. 2017) and expanded in the Late Miocene (∼7 Ma) (Bouchenak-Khelladi and Hodkinson 2011). Much of the southern African region is covered by such savanna woodlands, which support the greatest species richness of bats (Gelderblom et al. 1995, Schoeman et al. 2013). Second only to rodents, bats are also one of the most species-rich groups of mammals occurring in the southern savanna biome (Grubb 1999).

      Miombo woodlands – the world’s most extensive dry forests – cover a large portion of southern Africa north and east of the 600 m annual rainfall isohyet.

      Miombo occurs from Angola in the west across Katanga (DRC), Zambia and Malawi to Tanzania, most of Mozambique, and much of Zimbabwe (Frost 1996). The southern limit of miombo just reaches South Africa near the Luvuvhu River and on the Soutpansberg massif. Bat species encountered in mesic miombo include the molossid Mops niveiventer and the vespers Mimetillus thomasi and Scotoecus hindei/albigula. The southernmost limits of many Congo basin vertebrate species are associated with gallery forests that penetrate mesic miombo woodlands (Cotterill 2002a, b). These include the fruit bats Myonycteris angolensis and M. torquata.

      There are also extensive miombo woodlands on deep Kalahari sands in the western regions of Zambia, eastern Angola and the southern DRC. Although much of the southern portion of this belt receives rainfall characteristic of semi-arid savannas, these tall woodlands depend on groundwater in deep Kalahari sediments. This edaphic control on the vegetation is exemplified in the Cryptosepalum evergreen forests (Mavunda) on Kalahari sediments in western Zambia and eastern Angola (White 1983), and equally in the hardwood Zambezi teak forests dominated by Baikiaea plurijuga, with their distribution centred on the Four Corners Region (Huckaby 1986, Frost 1996).

      Mopane woodlands, dominated by the emergent Colophospermum mopane, are associated with particular soil formations, largely on alluvium at lower altitudes throughout the middle and lowveld of Zimbabwe, and also in large parts of southern Zambia, central and southern Mozambique, northern South Africa, northern and eastern Botswana, as well as northern Namibia and southwestern Angola (Cole 1986). Mopane woodlands are of singular significance to bat biogeography, because the hollows in mature trees, the aptly named cathedral mopane, offer plentiful roosting sites for bats. Woodland degradation, whether by elephants or humans (e.g. wholesale clearing for cotton plantations in northwestern Zimbabwe), destroys the larger trees and has highly negative effects on the abundance and species richness of bat assemblages (Fenton et al. 1998a, McCleery et al. 2018) (Figure 32).

      Thorny acacia (genera Vachellia and Senegalia) savannas dominate large parts of southern Zimbabwe, northern South Africa, Botswana and Namibia, extending into the Kalahari. Cavities in these large trees, and cavities under bark, support tree-roosting bats.

      The community structure of savanna bat assemblages arises from abiotic and biotic processes operating at local and regional scales (Schoeman and Monadjem 2018). At a regional scale, speciation mediated by historic geomorphic and climatic events has shaped the bat diversity of the regional species pool. The high taxonomic and phylogenetic bat diversity in the savanna biome is maintained by the stable wet and warm climate and high habitat heterogeneity. Processes at the mesoscale probably play a minor role because the high mobility of bats enables them to select habitat patches even in human-dominated urban and agricultural landscapes. Multiple biotic processes, including competition and prey defences, operate at a local scale, but non-random patterns are not ubiquitous within and across ecomorphological variables (Schoeman and Jacobs 2008, 2011).

Forest

      The northernmost reaches of the region covered in this book interface, in complex, historically derived patterns, with the southern margin of the main belt of moist tropical forests, which extend from the Congo basin into West Africa. This transition zone comprises a forest–savanna mosaic, whose southern limits are represented by the gallery forests that fringe drainage lines in northern Angola, Katanga and northern Zambia (Figures 27, 28, 34). Locally termed mushitu in Zambia or mihulu in Katanga, these gallery forests constitute important habitats for forest-adapted species, including bats. Alongside several species of fruit bats, at least one endemic bat, Rhinolophus sakejiensis, occurs here (Cotterill 2002a, b, 2005, 2006).

      Coastal forest mosaic associations extend along the eastern seaboard from Tanzania into the Eastern Cape and KwaZulu-Natal in South Africa.

      High-altitude Afromontane forest occurs as ‘islands’ in the Eastern Cape and Drakensberg mountains, the Chimanimani-Nyanga in Zimbabwe, and Gorongosa in Mozambique, and the highlands of Malawi. Relatively few endemic mammals are associated with these forests in southern Africa: a recently described crocidurine shrew (Taylor et al. 2013d) and a golden mole (Carpitalpa arendsi) are endemic to Zimbabwe’s Eastern Highlands.

      In addition, riparian forest plays an important role in bat distributions. Riparian fringes along the Limpopo and Zambezi rivers and their major tributaries extend the ranges of several species deep into the semi-arid savanna of southern and northern Zimbabwe. This factor can be invoked to explain outlying records of several species, including Epomophorus dobsonii and Myotis bocagii, and especially Pipistrellus rueppellii. Available data on the diversity of bat communities reveal that bat communities in high tropical forests are richer in species (e.g. at least 59 species in a Liberian study area) (Monadjem et al. 2013b) compared to the richest bat assemblages recorded in the savanna woodlands of southern and Central Africa. In savanna, total species richness ranges from 40 to 45 species at three intensive study sites: Pafuri, Kruger National Park (Aldridge and Rautenbach 1987), Soutpansberg Mountains (Monadjem et al. 2018b) and Sengwa Wildlife Research Area, Zimbabwe (Fenton 1975, 1985). These differences represent the greater diversity of clutter foragers and also frugivorous species in rainforests (Monadjem et al. 2018b).

ECHOLOCATION

      The majority of vertebrates rely on vision to perceive their environment. Even nocturnal predators such as owls and lions principally use their eyes to navigate and hunt. In contrast, most bats find food and avoid obstacles at night with great ease using an alternative sensory mechanism, called echolocation. Although usually associated with bats, other animals such as toothed whales, porpoises, some species of shrews and tenrecs, oilbirds, and several species of swiftlets also use echolocation.

      Echolocating bats emit sound pulses and analyse the returning echoes to detect, characterise, and localise objects that reflect the impinging pulse as an echo (Fenton 1990, Schnitzler and Kalko 2001, Fenton et al. 2016) (Figure 35). Sound pulses are generated in the larynx (except in Rousettus species, which produce echolocation pulses by repeatedly clicking their tongue against the palate), and emitted through the mouth (e.g. Vespertilionidae, Miniopteridae, Cistugidae, Emballonuridae, and Molossidae) or nose (e.g. СКАЧАТЬ