Culling and the dynamics of the Kruger National Park African elephant population

Abstract

South Africa's National Parks Board has opted to control African elephants (Loxodonta africana) through culling in the Kruger National Park (KNP). Killing elephants is highly controversial. The Board must balance this controversy against the probable destruction of vegetation and the consequent depletion of biological diversity that high elephant densities cause. Annual aerial counts provided the population estimates on which the culling quotas were based. For management purposes, the elephant population of the Park is divided into four sub-populations. From 1984 to 1994, the annual quota was usually taken from only one of these sub-populations during a given year. This resulted in 3 to 5 years elapsing between culls in each sub-population. We investigated the year-toyear changes in densities after culling. These changes were density dependent. Density dependence implies that immediate culls following estimated high densities may be premature. If left alone, the densities would decline naturally. Indeed, culling becomes self-reinforcing as it moves population densities towards the level where reproduction is greatest. Data confirm this intuition: at densities greater than 0.37 elephants/km 2 elephant numbers generally declined without culling. Many culls were unnecessary. Culling, as implemented in the past, may have had consequences for elephants and their habitat that were different to those expected from a mere reduction in their numbers. Densities in the year immediately after a cull tended to decline -not increase as would be expected from density dependence alone. Undoubtedly, this unexpected decline was the consequence of disturbance and subsequent emigration. In following years, the densities rose as animals moved back into the sub-population. A management programme where culling will be instituted only when densities exceed 0.37 elephants/km 2 in selected regions in the park for at least 1 year, may be more acceptable than the programme used up to 1995. However, we do not know if the vegetation of KNP can withstand the resulting episodic high densities. With densities presently exceeding the cut-off values calculated for both the south and the northern management regions vegetation changes there need to be monitored.

Metabolic rate links density to demography in Tetrahymena pyriformis

“…As a population grows, a feedback loop is generated that reduces the per-capita growth rate (PGR) of the population, resulting in density-dependent population regulation (Pearl, 1927;Turchin, 1999;Berryman et al, 2002;Sibly et al, 2005). The mechanism of regulation operates at the individual level; densitydependent regulation occurs when increasing population size increases mortality, decreases natality or alters migration patterns of individuals in the population (Hixon and Carr, 1997;Turchin, 1999;van Aarde et al, 1999;Ohman and Hirche, 2001;Lambers et al, 2002).…”

Examining Human Perception of Elephants and Large Trees for Insights Into Conservation of an African Savanna Ecosystem

“…Culling an elephant population actually counteracts its own purpose as it decreases population densities to a level of optimal reproduction. When reaching the upper tier population density levels that make culling seem rational, populations would naturally decline just as effectively (van Aarde, Whyte, and Pimm, 1999). Due to perceptual implications and the logistics of tree impact control effectiveness, environmental manipulation should be a primary management option.…”

A Welfare State for Elephants? A Case Study of Compassionate Stewardship

“…The alternative to fertility control is witnessing one's calf slowly starve to death in a degraded habitat, or the brutal practice of "culling" (i.e. massacring whole elephant families) to prevent ecological devastation (Aarde, Whyte, and Pimm 1999). Nevertheless, even if it were the case that elephants did experience some loss of freedom due to human intervention, the suffering they would otherwise endure is far worse.…”