I Thought some mites might find this as interesting as I did
Its some of the research the School of Animal plant and environmental sciences at WITS has done on the subject and how the scientists went about trying to figure out the problem.
Sable and Roan antelope are both members of the Bovidae Family and the Hippotragini tribe. They are also members of the same genus Hippotragus; where sable in SA are H.niger niger
and roan are H. equinus.
The problem: During the late 1980's and particularly after 1991 there was a sharp decline in the population of both antelope in KNP. In general there is a list of causes that are generally responsible for the decline in a species:
1:Climatic extremes such as drought
3:Competition from other species
6:changing ecosystem context
So is the decline in kruger caused by an external factor like climatic and habitat change or due to internal management plans? The scientists decided that the best way to try and understand the problem within KNP was to study the dynamics of how a successful breeding population of sable functions and to do this they looked at the herds within a reserve in the Waterberg where there are also no predators. The initial objectives where to look at the time of year that they are the most vulnerable as well as the resources they rely on to support them during these critical periods.
1: large scale- Habitat usage
2: small scale- species of plants foraged
3: behavioural ecology
4: The faeces were also examined (nitrogen and phosphorous as an indicator of quality)
Females from each herd were collared as they form the herds while adult males of about 2-3 years form bachelor herds.
Some of the basic observations:
1: behaviour of each animal within the herd taken at ten minute intervals
2: proportion of daily time spent foraging
3:bites, steps and time in between
4: quadrats ( usually 1x1m squares placed over the surface as a representative measure) to determine grass species and length of the grass eaten.
The study was running during periods where the reserve was burnt and all the herds would feed extensively in these burnt areas on the new green shoots which contradicts with what was previously known about the animals. So after a few years the results of the study suggest that sable are able to adapt their behaviour in terms of consuming much shorter grass when food quality is low as well as feeding for more lengthy periods at a time. During dry periods when all that remained was dry unburned dry grass the crude protein levels which are essential for normal functioning were found to be just above maintenance levels. During periods where crude protein levels are low the antelope are severely susceptible to stress and cold snaps and during this time a sever col snap resulted in the death of all the calves and a large proportion of the adult population.
THEN:Applying it to Kruger
From this study, by looking at a healthy population and making use of data collected from the KNP whose sable and similarly roan population (the antelope are extraordinarily similar) are declining and failing to recover
they could start to examine the possible reason for this problem.
Data shows that major droughts occurred in Kruger during 1984/85 and again in 1990/91 although this corresponds fairly well with the initial decline in the population it is most likely not the primary cause as droughts have a delayed effect on population numbers particularly when the animals in poor condition fail to breed. During those time periods Kruger also experienced a decrease in the length off their wet seasons.
On comparing population data it seems to suggest that the antelope decline when the population of zebra increases. But further analysis shows that although the two seem to correlate that this cannot be the cause as if their is competition for food between animals there will be a decline in calf survival before a decline in adult survival is seen and this was not the case. Also it has been shown that roan and sable utilize a very wide variety of grass species, even tall unpalatable "stemmy" plants. so competition is thus not the cause.
The lion population started to increase in 1985 quite dramatically so could predation be the cause?
Management of water points:
By the late 1970's the water points in kruger had increased 5 fold to a point at which the maximum distance to water from any one point was as little as ten kilometres in some places. Historically the north was always much drier than the south so the installation caused water dependent animals such as zebra and wildebeest to migrate northwards and with them they brought about an increase in the lion population This phenomenon where another herbivore appears to compete with another, in this case increasing the lion population is called apparent competition. The water points were later systematically closed and still there has been no recovery, so what is the problem? why can the population not recover. The one big factor is that not only is the northern population decreasing but so is the pretoriuskop population so water points are not solely to blame.
The herd size as well as their distribution (the area they move in) has substantially decreased in both the punda and pretoriuskop populations. They are left with a patchy distribution. Seasonal movement patterns show that sable avoid areas with high concentrations of buffalo and zebra as these animals tend to bring about an increased threat from lion. Distribution also shows that sable appear to inhabit areas with low prey densities and this is clearly visible if the two maps are superimposed.
The remaining groups are generally small and the loss of a few individuals could result in a collapse. The antelope are also insecure against predation and this may contribute to increased stress levels. These factors coupled with poor feeding conditions and the susceptibility of these antelope to these influences when their condition is poor (poor crude protein levels) may account for their decline and inability to recover. So basically it is a suite of interacting characteristics that together cause the problem which makes solving the issue incredibly difficult.
Ok im done, i thought it was quite interesting and I hope i explained it well enough