Viability of a diminishing roan antelope population: predation is the threat.

The roan antelope (Hippotragus equinus) population inhabiting the Kruger National Park, South Africa, declined from 450 animals in 1986 to around 25 free-ranging animals subsequent to 1994. A computer simulation model was developed to: (1) evaluate likely contributions of low rainfall, habitat deterioration, population fragmentation and predation to the observed population decline; (2) project future likelihood of persistence of the population remnant, under various scenarios. Direct consequences of severe drought and habitat deterioration alone were inadequate to explain the observed decline, unless effects were more severe than assumed in the model. An increased predation loss to around 30% per year was needed. Persistence probability over 50 years was less than 0.5 if the predation loss remained above 20% per year. Models that take into account only stochastic uncertainty in demography and environmental variability are of limited reliability if potential changes in predation risk are not also accommodated. [ABSTRACT FROM AUTHOR]