an opinion by Ron Thomson
Wild animal numbers fluctuate for a number of reasons. Our cyclic rainfall patterns are one of them. Every 7 to 10 years in south-central Africa, the weather produces continuous periods of 3 to 5 years of below normal rainfall, followed by 3 to 5 years of above average rainfall.
This has a marked effect on the numerical strengths of a number of animal species populations when those populations have saturated their habitats. The population numbers of those animal species whose living conditions are favoured by the dry phase of the cycle, increase; and those that are disfavoured by it, decline. The reverse applies during the wet period of the cycle.
The fact that population fluctuations happen in KNP suggests that the habitats of most of the park's ungulate species have been saturated for many years. Saturation means, in simple terms, that all available home ranges and all available territories in the habitat of a particular species population are filled to capacity.
This up-and-down rain-regulated pattern does not fit all species. It also does not apply to species populations that are well below the sustainable carrying capacity of their habitats because cyclic rainfall patterns do not then, all other things being equal, cause serious shortages of habitat resources.
It also does not fit elephant populations even when they have grossly exceeded the sustainable carrying capacities of their habitats.
Elephants are preferential grazers. This means they prefer to eat grass. During the rains, therefore, when grass is at its most nutritious and most palatable, the elephants of Kruger compete seriously with the park's grazing animals.
During the dry season the elephants eat woody vegetation almost exclusively. They then compete seriously with the park's browsers. The effect that Kruger's currently excessive elephant population has on the population strengths of the so-called plains-game animals of Kruger must, consequently, be significant.
If one excludes the effect that animals have on Kruger's plants - the producers of food the general growth of plants varies, annually, only according to the rainfall. The long term average annual production of plant food, however, would remain constant.
Whatever the bulk annual production of food is in Kruger it has to be divided amongst all the animals present. This is further complicated by the fact that the plants, together with their physical environment, create the habitats that are home to the park's many animal species.
When a robust animal species - such as the elephant exceeds the carrying capacity of its habitat, and eats more than its own share of the available food, this MUST have an impact on all other animal species present. This happens in a number of different ways besides the obvious competition for food.
Excessive herbivore populations, for example - perforce over-utilise their habitats causing the habitats to change in character. And if the responsible population is not reduced in number, by management, sensitive plant species soon become locally extinct.
The resulting chain reaction results in the less robust animal species being extirpated too. These are all factors that must be considered when one thinks about elephant numbers in Kruger.Kruger's elephants first exceeded 6000 in the early 1960s. They were then doubling their numbers every 10 or 11 years. When elephant culling started in the park in 1967 the population was restricted to 7000 animals. This number was maintained until 1994 when elephant culling was stopped. Since 1994 a small number of live elephants have been removed from the park for a number of reasons but this did not stop the population from increasing rapidly.
Indeed, over the years, nobody seems to have given Kruger's sustainable elephant carrying capacity very much thought. Everyone seems to have assumed that 7000 represented the sustainable number. In my estimation 7000 elephants has always been infinitely too high a number for the game reserve's habitats to sustainably support.
This conclusion is, admittedly, a gut feeling. It is also, however, based upon one study of top canopy trees conducted near Satara in 1944 when there were no elephants in the ecosystem. Other than this one piece of research information there is precious little written-up data that quantifies the climaxstate of the Kruger habitats prior to the time when elephants began to seriously modify them - which was about 1960.
The Satara study revealed that in 1944 there were 13 top-canopy trees per hectare in the study area. I believe this number reflected the true climax-state of that Satara woodland at that time. The climax-state of a woodland is the ultimate state of maturity that the woodland can possibly attain.
The first pilot elephant bulls were recorded in the Satara woodland study area in the late 1950s. A small breeding unit had taken up residence by 1960 - more soon followed. By 1965 the top canopy trees at Satara had been reduced to 9 trees per hectare.
Elephant culling began in 1967 - after which time the elephant population in the park as a whole was stabilised at 7000. Despite the culling, by 1974 the number of top canopy trees at Satara had been reduced to 3 per hectare; and by 1981 it had been further reduced to1,5.
This meant that between 1960 and 1981 Satara's top canopy woodland climax had been reduced by 89.5 percent. I have neither heard of nor seen any figures reflecting what the comparative state of the Satara woodland is today - 24 years after 1981! It is not scientifically acceptable to extrapolate the results of such a small sample to explain what happened to the top canopy trees in the rest of Kruger National Park during this same period.
Nevertheless, after 45 years of living with elephants, seeing the damage elephants do to their habitats, and managing elephant populations in several of Zimbabwe's national parks in the 1960s, 1970s and 1980s I believe the probability is very great that exactly the same thing has happened to all the other elephant-occupied habitats in Kruger between 1960 and 2005.
Taking this idea one step further, thinking and intelligent people upon reading this small dissertation will (surely?) also understand that the 1967 culling-maintenance target of 7000 elephants represented far too many for even the originally healthy Kruger habitats to support.
And that today's still growing elephant population of 11 500 in Kruger, and the continuance of a no-culling policy in what is now a seriously degrading habitat, is totally unacceptable.
Note: The new Kruger elephant management plan is not designed to maintain a stable elephant population. It is based upon a different philosophy and has a different objective that is too involved to address here and now. "If 7000 elephants represents too high a number for the Kruger habitats to sustainably carry", you might ask, "what number of elephants should Kruger be carrying?" Nobody can answer that question.
To determine that number, the elephants of Kruger would have to be culled continuously until the habitats started to recover and, when that stage was reached, the lowered population numbers would have to be maintained until the vegetation had recovered to a near climax state.Only then should the elephant numbers be allowed to increase - but only to the stage where they begin to sustainably utilise their habitat. Only by juggling elephant numbers and by monitoring the habitat's response to those numbers over a long period of time, can a reasonably accurate sustainable number of elephants be determined. My guess is it would unlikely exceed 5000.
Elephants, like all other animals, begin to select and to occupy what is called a homerange immediately they become post-pubertal. A home range provides an animal with its living needs - air, water, food and shelter. In the case of young female elephants this normally means they attach themselves to their parental herd. In the case of young bulls, they attach themselves to the family bull herds that live nearby.
Once they are truly adult both bulls and cows become cemented to their home-ranges - to all intents and purposes for the rest of their lives. Just as happens with humans it is the young bulls that seek a different place to live - away from the older bulls - a place which they can call their own. And it is the younger cows that join them.
Natural dispersal amongst elephants, therefore, is a phenomenon that is associated with young adults - as it is with most wild animal spe cies. As it is in human societies too. But the young adults don't move too far away from their parental populations because the older animals represent their fall-back security.
All these factors affect the patterns of elephant dispersals. One thing that is certain, with regards the elephant recolonisation of Kruger, is the fact that the early dispersals occurred long before the localised populations had reached anywhere near the sustainable carrying capacities of their habitats.
This fact must be coupled with another observation: No animals elephants included ever vacate their established home ranges UNLESS those home ranges are NOT satisfying the animals' living needs.
The fact that the early elephant dispersals in Kruger occurred at very low population density levels tells us that elephants prefer to live under habitat conditions that are well below the sustainable carrying capacity level.
We must conclude from this, therefore, that elephants prefer to live under conditions of relatively low population density. This I call the optimum ecological carrying capacity of the habitats.Getting back to numbers, IF the sustainable elephant carrying capacity of the original and healthy Kruger habitats is no more than 5000, the optimum ecological carrying capacity of these same habitats must be somewhere in the region of only 3000. In conclusion might I add that it does not make good ecological sense to look at wild animals just in terms of their population numbers. This may be a tangible way for some folks to look at the status of wild animal populations but this is not a valid parameter for the wildlife manager.There are much more important ecological factors that need to be considered when trying to assess the health and vigour of wildlife in a national park. These will be discussed in future articles. ACKNOWLEDGEMENTS: Data on the Kruger elephant populations have been drawn from Dr. Ian Whyte's doctorate thesis, and from my private discussions with Dr Whyte. The interpretations, however, are my own.