Other reports in this collection
The vast herds of migratory ungulates in east and southern Africa remain a distinguishing ecological characteristic of the continent. A major migratory system is located in the Serengeti area of Tanzania and the Masai-Mara region of Kenya. Reduced large-mammal migratory systems persist in the Kalahari (Botswana, South Africa, and Namibia) and Etosha (Namibia) areas of southern Africa.
Migrations typically are regular, and between dry-season and wet-season grazing areas, and to that extent they are sensitive to climate change. There is currently no indication that the broad pattern of seasonality is likely to change in the Serengeti or the Kalahari, since they are controlled by gross features of the atmospheric circulation (the monsoon system and the position of the Hadley cells). The intensity of seasonality, and the absolute annual rainfall total could change, by about 15% in either direction (Hulme, 1996). This is well within the range of interannual variability. Thus the migratory systems are likely to persist if land-use pressures permit them to.
About one-fifth of southern African bird species migrate on a seasonal basis within Africa, and a further one-tenth migrate annually between Africa and the rest of the world (Hockey, 2000). A similar proportion can be assumed for Africa as a whole. One of the main intra-Africa migratory patterns involves waterfowl, which spend the austral summer in southern Africa and winter in central Africa. Palearctic migrants spend the austral summer in locations such as Langebaan lagoon, near Cape Town, and the boreal summer in the wetlands of Siberia. If climatic conditions or very specific habitat conditions at either terminus of these migratory routes change beyond the tolerance of the species involved, significant losses of biodiversity could result. Although the species involved have some capacity to alter their destinations, in an increasingly intensively used world the probability of finding sufficient areas of suitable habitat in the new areas is small. The current system of protected habitats under the Ramsar Convention is based on the present distribution of climate.
Aperiodic locust outbreaks characterize the desert/semi-arid fringe in southern Africa and the Sahelian region. The population biology of the outbreak phenomenon is strongly linked to climate, particularly the pattern of soil moisture and temperature (Hanrahan et al., 1992). Outbreaks typically occur when a dry period is followed by good rains—for instance, in southern Africa following an El Niño episode. Changes in El Niño frequency would impact the timing, location, and extent of locust outbreaks in ways that presently are unpredictable.
Semi-arid areas of the Sahel, the Kalahari, and the Karoo historically have supported nomadic societies that respond to intra-annual rainfall seasonality and large interannual variability through migration. Nomadic pastoral systems are intrinsically quite robust to fluctuating and extreme climates (because that is what they evolved to cope with), provided they have sufficient scope for movement and other necessary elements in the system remain in place. The prolonged drying trend in the Sahel since the 1970s has demonstrated the vulnerability of such groups to climate change when they cannot simply move their axis of migration because the wetter end already is densely occupied and permanent water points fail at the drier end. The result has been widespread loss of human life and livestock and substantial changes to the social system.
|
Other reports in this collection |
|