Elephant population responses to increased density in Kruger National Park

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.