Elephant Management in Kruger National Park (5)
In Blog 3 on this subject, I said that I would explain the rationale about managing excessive elephant populations and the justification for reducing them by at least 50 percent, repeatedly, until the population size is correct. To do that, I started putting you through a short explanatory course in population dynamics.
Without this understanding, you will never fully grasp the principles and practices of elephant management; and you will never understand why Kruger National Park’s biological diversity is in such serious trouble. You will also not be able to understand, accept and support the solution that I propose to resolve this problem.
In Blog 4, I presented you with a graph (Figure 2) which depicted the theoretical growth of an elephant population under natural conditions (i.e. without the influence of man). Now we take you one step further along the road to understanding. In Figure 3 (below) you will recognise the sigmoid curve of Figure 2 – which depicts the exact same information that I explained in Figure 2. Now we are going to have a different look at that information and transcribe it into an explanation about an elephant population’s productivity.
In Figure 3, the vertical dark green columns reflect the time periods: 2nd; 5th; and 9th decades. Now, from the points where the vertical lines that depict the beginnings and the ends of each of these decades, intercept with the blue population growth curve, we have drawn horizontal lines to the left – towards and up against the perpendicular axis of the graph. The spaces between each of these parallel sets of twin horizontal lines are demarcated (where possible) by the colour pale-green. This is not possible in the 9th decade because the growth curve is flat. The different percentages – marked by the bottom and the top levels of each of these pale-green blocks – reflect the percentage of population growth during each decade. This number is easily determined – simply by subtracting the bottom percentage from the top one.
Thus, in the second decade, the numerical level of the population is very low at both the beginning and the end of that 10 year period.
Furthermore, these figures (in the second decade) are highly variable because of the addition of just two or three extra calves, or the subtraction of as many elephant deaths makes population growth trends impossible to predict. And the bull-to-cow sex ratio – in such a small population – can vary greatly, too. Nevertheless, the pale-green colouration still depicts the population’s theoretical productivity (otherwise known as its incremental rate) during the second decade.
In decades 3, 4 & 5, the population growth is consistently high. This is because, during that (what we call) surge phase of the population’s growth pattern, food, water, shelter and lebensraum is not limiting. This is when (on this graph) the population doubles in number every 10 years. This is most noticeable in decade 5 when the population increases from 40 percent (of the habitat carrying capacity) to 80 percent. The more elephants there are in the population, the more impressive does the numerical annual increment become.
After decade 5, however – as the population increases ever more rapidly every year – food, water, shelter and lebensraum become progressively more scarce. This induces young adults (which are subjected to more and more social pressure – from bigger, stronger and older adults) to disperse into distant regions. They leave the parental home range, therefore, and seek new places to live where there are fewer elephants; and where there are better food, water, shelter and lebensraum resources available.
During the 6th, 7th and 8th decades, therefore, more and more elephants disperse from the parental home range; food resources become ever more taxing at home; and the numbers of deaths amongst yearling calves and older adults, increases annually. Finally, emigration and mortality equal the number of surviving births and immigration. Theoretically, this is how stability happened within wild animal populations of all kinds before the advent of man.
By the 9th decade (theoretically) the population stabilises. Growth stops. And annual productivity is zero.
Now, in the 6th blog in this series, we can explain very easily, and justify, why “SAFE” elephant populations can be reduced in number quite safely by 50 percent; and why excessive populations MUST be so drastically reduced – to save the national park’s biological diversity.
Ron Thomson. CEO. The TRUE GREEN ALLIANCE