Elephant Population Management
Dr. Fred de Boer
In and around Kruger National Park (KNP), the issue of elephant management is highly debated, as some scientists argue that there are too many elephants.
Fact is that elephant populations have increased considerably over the last decades, and we know that elephants have a large effect on tree cover.
Scientists have so far not been able to understand completely what limits elephant populations. Surface water availability seems to be an important factor, and a study carried out in Zimbabwe recently showed that changes in elephant population numbers strongly correspond to changes in rainfall, indicating that water availability and consequently vegetation growth are limiting elephant numbers.
Most scientists believe that population of elephants (or other large herbivores) are regulated by the availability of the resources (water and forage). At low resource levels population growth is almost exponential, but as the population increases a threshold will be reached at which consumption and production of the vegetation is equal and the population will not increase further. This threshold is called the carrying capacity.
Kruger National Park Elephants
However, the elephant population at KNP does not seem to follow these classical models of decreasing population growth at increasing population sizes, leading to a stable density of elephants. Are these models just wrong? Or maybe the time frame of our analysis is not sufficiently large to understand the population dynamics of the elephant population? Maybe populations of elephants crash over 10-20 years when their resources have been exhausted? Or maybe the so-called "carrying capacity" is far higher than people thought it was?
Hence, a lot of ecological research is focussing on the factors that drive elephant population growth, their spatial distribution, and their impact on the vegetation. At the same time projects are underway to study possibilities decrease elephant population growth, such as through immunocontraception. One way of decreasing the pressure of elephants on a certain area is to increase your area size, as a doubling of your area with elephants could lead to a considerable reduction of elephant impact in that area.
However, unfortunately elephants do not distribute themselves evenly over an area, so that localised high elephant impact zones will remain, even if the area available to elephants is increased. The area available to elephants and the elephant density has changed rapidly over the last decades and centuries.
The proclamation of the KNP, the creation of the Greater Kruger Park with free movements of wildlife between the KNP and the private conservation areas in the east, and the initiatives for establishing an even larger Transfrontier Conservation Area, linking conservation areas in Mozambique, South Africa and Zimbabwe, have all led to larger areas that became available to elephants and an improved conservation status of the elephants.
More land, more Elephants?
However, nobody has really addressed the impact of this continuously increasing area for elephants on elephant population dynamics. The Tembo programme (a co-operation between scientists from Wageningen University, the Netherlands, the UKZN, and scientists from KNP, together with other institutes) have now modelled this effect in a small project carried out by a Dutch MSc student, Marjolein Sterck.
This modelling is a abstract way of trying to figure out what will happen over time, using mathematical equations that mimic the effect of elephant population growth, mortality and dispersion, in relation to changes in forage resources. Forage resources are not distributed evenly in space and time, and differ largely from one spot to another and from one year to the next. This is partly influenced by the erratic rainfall pattern in the area. The Tembo scientists used the existing rainfall data and studied the spatial and temporal variation in rainfall.
Using this variation they were able to model the differences in forage availability, the amount of grass and browse resources available to elephants. After having achieved this they could model the elephant population changes over time, dependent on the amount of forage that is available. The next step was to increase or decrease the area size that is available to elephants. And indeed, they found an effect of area size on elephant population changes.
For instance, if an area is too small (or if the elephant population is restricted to a small, fenced area within a larger conservation areas), the chances that this elephant population will not survive over several decades is larger than when the area is larger. This is due to the spatial heterogeneity of the rainfall. Being restricted to a smaller area will also restrict the choices an elephant population has to find alternative forage resources if the rainfall is insufficient.
When larger areas are made available in the computer, the elephants have the ability to look for alternative resources, if rainfall is locally poor and insufficient to support the entire population. The main result of the computer study is that an increase in area will lead to an increase in the elephant density. This is an interesting conclusion, especially in the light of the recent changes, the creation of the Greater Kruger and the creation of corridors between KNP and bordering conservation areas in Zimbabwe and Mozambique.
Hence, the creation of larger conservation areas, sometimes in an effort to release the pressure of elephant on the vegetation in KNP, could ultimately and in the long-term lead to an even larger pressure of elephant in the entire area. Is this not opening up a worse case scenario in the areas?
Predicting Elephant Changes
I think that we should be careful in predicting elephant changes over time. First of all, we do not fully understand the factors that influence elephant population growth. Secondly, we should also bear in mind that this was just a computer model, and we need data to validate the model. These data are not (yet) available. However, I think that the basic assumptions hold: under spatial heterogeneity larger areas can hold a larger density of elephants than smaller areas.
Hence, if your only aim is to reduce the elephant pressure on a certain area, the long term viable strategy seems to be to fragment your area into smaller concessions between which no exchange of elephants can occur and let nature take its course..... This is certainly a bold statement, and we need to understand better how elephant populations are regulated. It is only then that we can make better, informed decisions about alternative management actions.