Figure 6: Roan distribution in relation to annual rainfall
Figure 7: Sable distribution in relation to annual rainfall
Figure 8: Tsessebe distribution in relation to annual rainfall
The data (ASG 1998a) on distribution of roan (Figure
6), sable (Figure
7) and tsessebe (Figure
8) in southern Africa in relation to average annual rainfall
Mills, Biggs and Whyte (1995) concluded that rainfall was the principal
determinant of numbers of common ungulates in southern African
savannas. This fundamental constraint appears to receive too
little emphasis in the plethora of proposed research studies
and management measures designed to address the declines in
roan, sable and tsessebe in parts of southern Africa (e.g. Grant
and van der Walt 2000, Grant et al 2002, Harrington 1995, Harrington
et al 1999, RARE 2002 and numerous other references). Dunham
and Robertson (2001) demonstrate very clearly that rainfall
accounts for the observed declines in tsessebe populations in
Kruger National Park yet there appears to be a reluctance to
accept this too-simple finding or apply it to other 'rare species'
- There are no 'naturally' occurring populations of roan, sable
or tsessebe below the 400mm rainfall isohyet;
- Apart from a very few minor introduced populations of sable
and tsessebe elsewhere in the region, Namibia is the only southern
African country attempting to maintain populations of roan, sable
and tsessebe in areas where the average rainfall is below 400mm.
Introduced populations of sable and tsessebe below the 400mm
rainfall isohyet, occur on private land in the vicinity of the
Limpopo River in the northern province of South Africa and in
the Beit Bridge area of Zimbabwe, and there is an introduced
population of tsessebe in the Vaalbos National Park near Kimberley
in South Africa.
The African Antelope Specialist Group (ASG 1998) remark that
the populations of roan, sable and tsessebe in Namibia are outside
of the species' 'natural range'.
- Many of the 'crashes' in roan, sable and tsessebe populations
have occurred in areas where the average annual rainfall is close
to the lower limit.