The ecology and potential factors limiting the success of Sable antelope in south eastern Zimbabwe : implications for conservation.

Thesis (MScConEcol) Stellenbosch University, 2012.

ENGLISH ABSTRACT: The decline of sable antelope through much of the lowveld region of Zimbabwe and South Africa has become an issue of concern for wildlife managers. On Malilangwe Wildlife Reserve (MWR) alone, sable numbers crashed from 237 animals in 1994 to only 62 by 2005. The purpose of this study was to determine the cause of the decline and the continued lack of success in the sable population. The study had three specific aims: 1) to assess the current viability of the sable population at MWR and understand the sensitivity of the population to environmental changes, 2) to gain an understanding of the space-use and habitat selection of sable at the landscape scale, and 3) to speculate on the possible causes of the decline in sable antelope numbers at MWR. GPS collars were fitted to four sable herds at MWR and a fifth herd was monitored opportunistically over the study period. From these, life history data were collected and fed into a VORTEX population viability model to assess the current viability of the sable population at MWR. Vital rates input into the model were then manipulated, simulating the effect of natural pressures placed on the population. A sensitivity analysis was used to determine the sensitivity of the population to these natural pressures, using the long term growth rate as a relative measure of overall fitness. The results suggest the current population will remain extant but that natural pressure placed on the adult female segment of the population could have a drastic impact on the success of the sable population. The evidence indicates that the decline in sable numbers at MWR must have been driven by an increase in mortality in the adult segment of the population. The GPS collars gave regular fixes enabling the development of a spatial pattern of home-range and habitat use over time. LoCoH was used to develop seasonal home ranges and utilization distributions for the sable herds at MWR. A multiscale approach was used to investigate habitat selection by sable over time at MWR, using a Bonferonni Z-statistic, time series graphs and Maximum Entropy modeling. Sable used much larger ranges during the early wet season than during any other season at MWR and were highly selective at the broad scale spending more than 92% of their time foraging on the nutrient rich basalt derived soils. At the finer scale sable generally chose for areas characterized by a well developed grass layer on shallow calcareous soils moving onto areas of deeper clay rich soils during the dry season and consistently made use of areas further than average from water. Data from the collars were then used to conduct bi-monthly tick drags along the sable foraging paths to assess the level of tick challenge faced by each herd over time and this was related back to the survival rate of calves within each herd using linear regressions. The effects of predation were assessed again using the GPS collar data and a novel method of determining predation risk using motion sensor camera traps. The level of predation risk was then related back to the survival rate of each age class in the sable population. The long term effects of predation on the sable population was investigated using historical data on sable carcasses discovered and the annual rate of population decline. These were regressed against lion population numbers to determine whether any relationship existed between lion population numbers and the rate of population decline. Tick challenge had no effect on the survival of sable calves and the overall tick challenge at MWR was extremely low during the study period. Predators however seemed to have an impact on the sable population in a number of ways. Hyaena’s seemed to have a major impact on the survival of sable calves, particularly during the first few weeks of life and lion numbers showed a strong relationship with the overall rate of population decline. Sable antelope are highly susceptible to predators and lions seem primarily to blame for driving the decline in the species at MWR. The relationship is however not entirely clear and evidence suggests that a number of variables including vegetation cover and water distribution play a role in determining the impact that predators have on sable populations.

Masters