The Competition for Resources
This story illustrates vividly the consequences of mankind's competition for resources, the fragility of the ecosystem, and also the impact of well-intentioned efforts to intervene on our part.
Roan, sable and tsessebe antelope are all found at the southern extremities of their natural range in the northern corners of South Africa. Their eastern range approximates the lowland valleys of the Limpopo catchment between 400 and 900m where savannah vegetation is abundant. Roan and tsessebe historically ranged further south to the confluence of the Orange and Vaal rivers as well. These species share certain niche habitats and are sensitive to ecological disruption. The size and condition of their populations acts as a proxy for the health of the ecosystem as a whole- technically they are indicator if not keystone species demonstrating the health or otherwise of the ecosystem.
Illustration by John Millais from 1892 showing the abundance of Roan and Sable antelope on the Nuanetsi plains
All three antelope are edge species found within the mixed sub-tropical conditions where grassland adjoins dry bush savannahs. All three are selective grazers preferring medium to tall grass and each is dependent on the availability of fresh water. They are highly vulnerable to habitat changes and competition - all are poor competitors where rangeland is heavily utilised. These species cope poorly when the veld is damaged. Typical causes of this are persistent overstocking leading to overgrazing of the bush. Fences inhibit natural migrations and can leave the land insufficient time to recover from grazing by animals unable to move on elsewhere. Encroachment of the bush can transform areas into dense thickets, often caused by modern humanity’s suppression of the natural cycle of man- and lightning-induced fires and clearing of the land. More obviously the presence or otherwise of the antelope is a good indicator of whether levels of hunting (by man or animal) are sustainable.
A comparison of the former natural distribution of these antelope and present natural occurrence in South Africa reveals a catastrophic decline in numbers corresponding to a radical transformation of their preferred habitat. Local extinction has now occurred in over 90% of the former ranges of all three species.
Former Ranges of Roan, Sable, Tsessebe in K2C (Click to enlarge)
Their preferred habitat was excised from the Sabi Game Reserve (the progenitor of the Kruger) in 1923: the area to the west of the present Kruger boundary and south of the Olifants river. This was estimated at the time to be around 928,000 hectares in extent. It included the areas of Numbi, Mkhuhlu, Thulamahashe, Acornhoek and extended further north along the Klaserie river. These areas were critically important habitats not only for these rare ungulates in the western sectors but part of the ranges of wildebeest and zebra in the western part of the Park. Herds of up to 200 sable at a time were seen in these and neighbouring districts. In 1958, a group of sixty were seen on the slopes of the Drakensberg escarpment at a height of 700 meters. Sable were once so plentiful that they were shot for rations by the land companies and stock farmers competing for grazing in the early 1920s. Records for roan distribution reveal that they also preferred these western districts of the Lowveld, particularly the open plains at slightly higher altitudes in the vicinity of the escarpment slopes. The numerous perennial rivers of the lower Olifants Basin (the Klaserie, Blyde, Makutswi, Selati and Letaba) fulfilled their need for water and the ecotone mix of woodland and plains that was their preferred habitat.
|Historic Range||Present Natural /
|%||% Loss of Habitat|
|Tsessebe||180,000 sq km||15,000 sq km||8%||92%|
|Roan||180,000 sq km||15,000 sq km||8%||92%|
|Sable||110,000 sq km||22,000 sq km||20%||80%|
Former Ranges in South Africa of Tsessebe, Roan and Sable
Source: John Williams, Extrapolation from anecdotal records
In the case of Tsessebe it was estimated that there were 280 scattered outside the Kruger Park in their former range in 1980, with 1163 in the park. In the 1930s, Sandenberg estimates their numbers to have been 4,000 in the Lowveld as a whole.
Since the expropriation of the land from the Game Reserve in 1923, approximately 450,000 hectares have been returned to protected area status under both private and provincial ownership.
However, the impact of the intervening years on their ranges has been dramatic. Initial research efforts to understand the reason for the decline in roan, the most threatened species, indicated that the supply of artificial water in previously dry areas made new habitats available to water dependent species such as zebra. This led to a migration of zebra into previously exclusive roan areas, thus competing with roan at a point when resources were severely limited due to the drought.
In 1994 it was decided to close the windmills pumping water into the waterholes in the prime roan habitat to encourage zebra to move away. However, in spite of a significant decline of the zebra in the area and an improvement in the veld condition, the roan has not been able to recover, although the population has stabilised. This could be due to the very low numbers (27 on northern plains) that the roan population had to build up from again or it could be the result of predator pressure that has increased on the roan and other rare game with the movement of zebra from the plains.
Historic Pumped Waterhole Distribution in the Kruger National Park
Source: Kruger National Park Management