Elephant population responses to increased density in Kruger National Park

Albertus S Louw,Sandra Macfadyen,Sam Ferreira,Cang Hui

doi:10.4102/koedoe.v63i1.1660

Abstract

The elephant population in the Kruger National Park (KNP) has been increasing since the cessation of culling in the mid-1990s. This contrasts with recent trends in elephant populations in many parts of Africa where poaching continues to decrease numbers. Logistic growth theory predicts that increased competition for vital resources when densities increase should serve to constrain population growth, implying a negative density-growth correlation. We tested this prediction using 28 years of elephant census data to investigate how the growth of the KNP’s elephant population responds to increasing elephant density from the period 1985 to 2012. We expected a spatially variable population growth pattern in response to the distribution of elephant densities in the park and thus classified the park into zones with low, medium or high long-term (28 years) average, dry-season elephant density. Zones were named ‘peripheral’, ‘semi-peripheral’ and ‘core’ zones, respectively, and represent proxies of resource availability to elephant herds. Using a Stochastic Ricker growth model, we tested for the presence of negative density-dependence in population growth in the core versus peripheral zones. In response, we only detected density-dependent growth in the core zone. Overall the population grew at 4.1% per year, coupled with local recruitment rates that increased over time, particularly in the peripheral zones. These density-dependent trends support previous observations of homogenisation of elephant distribution and density across the KNP landscapes.Conservation implications: Density-dependent changes to elephant growth rates are scale-dependent (local vs. park level). Only core areas with long-term high density show signs of density-dependent growth. Overall, the distributions of elephants are homogenising in the KNP. Conservation authorities should monitor the impact of such homogenisation to landscape heterogeneity. The spatial variation of the negative density-growth correlation, especially between the core and peripheral zones, can be considered when developing effective strategies to manage the KNP elephant population.

Highlights

Despite threats of poaching and habitat loss, trends in the numbers of African elephants (Loxodonta africana) in southern Africa contrast with their declining numbers in the rest of the continent (Chase et al 2016)
Changes in conservation philosophy led to the subsequent cessation of elephant culling in 1995, in favour of allowing density-dependent processes to guide population dynamics over the longer term (Whyte et al 1999)
In the period after 1995, growth can be described by an exponential model with per capita annual growth rate of 4.1% (Figure 2; Appendix 1 Table 1-A1; R2 = 0.95, F(1,15) = 278.4, r = 0.041, p < 0.001)

Summary

Introduction

Despite threats of poaching and habitat loss, trends in the numbers of African elephants (Loxodonta africana) in southern Africa contrast with their declining numbers in the rest of the continent (Chase et al 2016). South Africa epitomises these trends with populations increasing in trans-frontier (Selier et al 2016) and fence protected areas (Pretorius, Garaï & Bates 2019). The influence of elephants on ecosystems has stimulated much debate (Van Aarde, Whyte & Pimm 1999; Van Wyk & Fairall 1969). The Kruger National Park (KNP) in South Africa is a large, protected area where elephant numbers increased from an estimated 10 animals in the early 1900s to over 17 000 elephants in 2015 (Ferreira, Greaver & Simms 2017). Authorities linked increasing elephant population size to vegetation impact, resulting in action being taken to control elephant numbers through culling (Van Aarde, Whyte & Pimm 1999). In the same period (1997), the systematic removal of many artificial water points in the park was implemented to regulate game distributions by returning surface water availability to a more natural state (Pienaar et al 1997)

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Discussion

Conclusion