10.2.3.3. Migratory Species
10.2.3.3.1. Large-mammal migratory systems
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.
10.2.3.3.2. Bird migrations
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.
10.2.3.3.3. Locust migrations
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.
10.2.3.3.4. Human migratory systems
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.
|