A population dynamics model for the management of Buffon’s kob ( Kobus kob kob) in the Bénoué National Park Complex, Cameroon

Abstract

A computer simulation model was developed to compare six alternative management strategies with respect to their economic performance and impact on population size and structure of Buffon’s kob ( Kobus kob kob). The model allows for both controlled and illegal harvesting depending on the level of protection enforcement. Additional features include age–sex structure, density dependence, and environmental stochasticity. The compared strategies combine two enforcement levels and three harvest rates in both sexes. Under low enforcement regime, the population size either remained stable or decreased with legal harvesting. By contrast, an increased protection resulted in a population growth that was either logistic or dampened by legal off-take. Within the tested range of parameters, it appeared that a sustainable harvest could be achieved by taking up to 7% of the kob population. The sex ratio was slightly biased towards females under illegal but random shooting or when male harvesting was high. Both recruitment and yearling-to-cow ratios tend to be low in undisturbed, lightly hunted populations and relatively higher in depressed populations. A substantial reduction in the percentage of illegal harvest was achieved by raising the minimum anti-poaching effort from 0.15 to 0.3 (in arbitrary monetary units). Allowing a simultaneous controlled harvesting increased the amount of captured benefits (meat, trophies and their total value) and hence the household shares in the neighbouring community. At lower discount rates (10% or less), ecological and economic goals are better balanced by combining an increased protection with a high harvest rate. A sensitivity analysis revealed that small increments of the harvest quota return larger increase in revenues, especially for quota levels below 5%. Further, the rate of illegal harvest showed low sensitivity (i.e., hardly changed) when the model assumed that illegal off-take was a quadratic rather than a linear function of anti-poaching effort. In practical terms, the reduction in illegal off-take can be expected to decline linearly with the enforcement budget. Based on the obtained results, a number of suggestions are made with respect to the interpretation of survey results and the harvesting of kob populations.