Elephant Management in Kruger National Park (4)
In Blog 3 on this subject, I said that I would explain the rationale about managing excessive elephant populations and the justification for reducing such populations, in the initial stages, by 50 percent. To do that, I am going to have to put you through a short explanatory course in population dynamics.
Figure 2, below, is a graph (from one of my books) depicting the theoretical growth of an elephant population under natural conditions (i.e. without the influence of man).
The left hand (vertical axis) of the graph indicates the population size as a percentage of the sustainable elephant carrying capacity of the habitat (which is attained at the 100 percent level). This can also be expressed as the habitat’s SAFE saturation level.
NB: The sustainable elephant carrying capacity of any habitat is the maximum number of elephants the habitat can carry without them causing irreparable habitat damage.
The bottom – lateral axis – indicates the passage of time (left to right) each demarcated segment representing one decade (10 years).
The population begins at zero. During the first decade, however, immigration occurs when small numbers of animals invade the habitat. Most early immigrants will be bulls. Cows arrive over time whereafter breeding begins. During the first and second decades the population grows very slowly. Gradually more and more births occur. Elephant cows are capable of breeding at about 10 years old – but they are normally a little older. Thereafter they have a calf every three to four years.
At the end of the 2nd decade the population “settles”. Habitat resources – food, water, shelter and lebensraum – are not limiting, so the population growth rate rockets. During the 3rd, 4th and 5th decades, the population doubles in size every 10 years!
After the 5th decade, due to population congestion (reduced lebensraum) and diminishing food supplies, young adults disperse in search of greater space and greener pastures; and there is a greater death rate of small calves and aging adults. All these factors slow down the rate of population increase. Population growth has stopped altogether by the 9th decade – when immigration and births equal emigration and deaths.
This kind of growth rate happens with many species of wild animals and it is presumed to be the natural way that their populations grow and regulate their numbers. Is this the way that elephant populations – before the advent of man – regulated their numbers? Nobody knows. A more correct answer is “probably”.
All over Africa, elephant populations were seriously reduced in number by commercial ivory hunters during the 19th century; and by 1900 elephant population numbers were very low throughout their range in southern Africa. I understand this was the case elsewhere in Africa, too. But in this series of blogs I will only be dealing with elephant populations south of Zambezi and Cunene Rivers (i.e. in southern Africa).
Many wildlife sanctuaries and national parks were created in southern Africa during the latter decades of the 19th Century; and during the first three decades of the 20th Century. These provided remnant elephant populations in the region with sanctuaries all over southern Africa; and they began to breed.
By the mid-1950s, all these elephant populations seem to have reached their SAFE saturation levels. Certainly, the elephant populations of northern Botswana; Hwange, the Gonarezhou, Chizarira, Matusadona and the lower Zambezi Valley in Rhodesia (now Zimbabwe); and Kruger National Park in South Africa, all showed signs of permanent habitat damage by 1960. THIS is the factor that tells us a population has become “excessive” (too many elephants for the habitat to sustainably carry). Once a population becomes “excessive” it starts a spiral of habitat degradation; loss of species diversity (plant and animal species become locally extinct); and the end result is the creation of a desert.
We will advance this discussion in the next blog (No.5.).
Ron Thomson. CEO. The TRUE GREEN ALLIANCE