Modeling black rhinoceros (Diceros bicornis) population performance in East Africa: the case of Lake Nakuru National Park, Kenya

Abstract

The black rhinoceros have declined across Africa both in numbers and range distribution, making long-term population persistence of this iconic species uncertain. We conducted simulation models to predict population performance of black rhinoceros in Lake Nakuru National Park under different scenarios of environmental variation and translocation regimes. A decade-long (1987-1997) demographic data were used to construct stochastic simulation models using VORTEX computer program. In addition, we assessed extinction risks and patterns of heterozygosity among the modelled populations (reported every five years) to characterize the dynamics of this population over a hundred years. The population of black rhinoceros showed varying patterns of fluctuations under different scenarios. The best-case scenario showed a considerable increase in the modelled population with the population attaining the highest growth (population growth (λ)= 1.04) after 40 years. The mean final population size for the successful cases was 70.85±2.0 animals, which was relatively close to the carrying capacity used in the simulation. The expected heterozygosity was 0.912±0.02 suggesting that the remaining population may be genetically viable. Further, environmental variation of 1-2% magnitude across the various age categories, and without translocation, had no significant effect on the deterministic growth rate of the population. Maintaining the translocation of 2 males and 2 females on yearly basis would significantly boost and sustain the population of black rhinoceros in the study area.