Poaching is directly and indirectly driving the decline of South Africa's large population of white rhinos

Abstract

AbstractLarge herbivores, particularly in water limited systems, are vulnerable to the impacts of poaching (illegal hunting) and human‐induced climate changes. However, we have little understanding of how these processes can reshape their populations. With some rapidly declining populations there is a need to understand the effects of these stressors on populations of vulnerable large herbivores like the white rhino (Ceratotherium simum simum). We developed age‐structured models for the rhino population in Kruger National Park, home to 49% of South Africa’s rhinos. We wanted to determine the relative influence of poaching and climate on the current and future population size and demographics, examine the potential of a dependency effect (the loss of calves from poached females) and quantify the compound effect (loss of future young). Our results indicated that population declines were largely driven by poaching and included a dependency effect. Rainfall had a measurable but smaller influence on rhino populations and had an additive effect; reduced rainfall exacerbated poaching losses. Current poaching levels have resulted in a reduction to the lifetime reproductive output per cow from approximately 6 to 0.7 calves: a compound effect of 5.3 future offspring. Under current levels of poaching, we project a 35% decline in the Kruger rhino population in the next 10 years. However, if poaching intensity is cut in half, we project a doubling of the current population over the same time frame. Overall, our models showed little sensitivity to demographic and environmental parameters, except for adult survival. Our results suggest that maintaining and improving the lifetime reproductive output of rhino cows should thus be the highest management priority and that new management targets should consider both the dependency and compound effects associated with poaching on rhino cows.