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Population recovery of black rhinoceros in north-west Namibia following poaching

Authors


  • Editor: Matthew Gompper

  • Associate Editor: Carmen Bessa-Gomes

Correspondence
Jedediah F. Brodie, David H. Smith Conservation Research Fellow, Wildlife Biology Program, University of Montana, Missoula, MT 59812, USA. Tel: +1 (406) 274 0505
Email: jedediah.brodie@gmail.com

Abstract

Curtailing overharvest, whether illegal or legal, is often a critical conservation objective. Yet even if overexploitation can be stopped, subsequent rates of population recovery can be highly variable due to Allee effects, alterations to age and sex structure and disruptions of animal social systems. Moreover, understanding the influence of density dependence can be difficult but important for long-term management. Here, we investigate the dynamics of black rhinoceros Diceros bicornis in the Kunene region of Namibia as they recover from illegal hunting. We use multi-strata mark–recapture models to examine survival and stage-transition rates from 1992 to 2005. Survivorship estimates ranged from 0.793 for calves to 0.910 for adult males and 0.944 for adult females. The annual reproductive rate in adult females was estimated at 0.315. Model selection showed that these vital rates were time invariant, suggesting that Allee effects and transient dynamics did not have an important effect upon population dynamics, even in the early stages of recovery. Relative population density increased significantly from 1992 to 2005 once illegal hunting had ceased in Kunene. However, the best-fit models did not include relative density in the estimation of survival or stage-transition rates. We then used the vital rates generated from our mark–recapture analysis to build matrix projection models that assessed overall population dynamics. The female-only model gave a population growth rate estimate of λ=1.011. Two-sex models suggest that the growth rate of the population could range from 0.990 to 1.012. The relatively slow growth rate of this population, even without hunting or density dependence, could stem from the low productivity of the region. Adult females had the highest reproductive value and their survival had the highest elasticity among vital rates. Translocating adult females would lead to the fastest initial population growth rate in founder populations but would have the most impact on the source population.

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