The performance and spatial ecology of the critically endangered black rhinoceros, diceros bicornis l., population in iThala game reserve, KwaZulu Natal, South Africa.

Abstract

Ensuring the persistence of populations of endangered species requires an understanding of, and response to, the causes of population declines. Species occurring in small populations are vulnerable to stochastic problems that are environmental, demographic, or genetic in nature, and can reduce survival as much as the threats of habitat degradation. Critically endangered black rhinoceros, Diceros bicornis, populations have declined throughout Africa since 1960, but, more recently, numbers are increasing at a continental level, but remain lower than three generations ago. The south-central black rhinoceros, Diceros bicornis minor is considered critically endangered and are found primarily in protected areas. To ensure the persistence of the species, management efforts have focussed on live-harvesting and translocation of individuals from certain sub-populations to populate additional reserves, whilst monitoring involved collecting demographic data (births, deaths, density, and sex and age structure) that could be used to improve conservation management of this species. This study was initiated to determine population estimates, growth rate, and fecundity over time, as well as sex and age structure and age-specific probabilities of survival, using 18 years (1990–2008) of long-term sightings data from Ithala Game Reserve, KwaZulu-Natal, South Africa. I also wanted to determine if mortality occurrences were associated with social or environmental factors, or as a result of management interventions. There was no significant difference in the sex ratios at birth, although the proportion of females in the population was 0.58. There was strong evidence for density-dependent regulation, with density in conception year a key driver of population ii performance (birth rate). The population does not appear to be at ecological carrying capacity; however, social effects are delaying conception. The model analyses showed that social interactions carried more weight than environmental factors on mortality, with a strong association between mortality and intensity of use, as well as mortality and management removals from the population. The mechanism of density dependence in Ithala Game Reserve is through mortality that is associated with increased social interactions, rather than from resource limitations. To mitigate density-dependent social effects, my study recommends an adaptive management strategy of pre-selecting individuals with known information on their social behaviour and context, before removal from the reserve, so as to maintain stability in the social organization of the population. In the absence of restoring linkages between populations of black rhinoceros, the translocation of black rhinoceros is a primary tool to mimic how meta-population dynamics would play out across the landscape. However, careful monitoring to enhance understanding of social factors, particularly black rhinoceros male behaviour, should be intensified to allow strategic translocation of individuals in such a way that negative density dependent effects are mitigated.