Distributional niche of relatively rare sable antelope in a South African savanna: habitat versus biotic relationships

Abstract

The geographic distribution of a species is governed by climatic conditions, topography, resources and habitat structure determining the fundamental niche, while the local distribution expressed via home range occupation may be compressed by biotic interactions with competitors and predators, restricting the realised niche. Biotic influences could be especially important for relatively rare species. We investigated how rainfall, geology, land type and abundance of other ungulate species serving as competitors or prey for predators contributed to the patchy distribution of sable antelope herds within Kruger National Park. Data were provided by annual aerial surveys of ungulate populations conducted between 1978 and 1988. Sable herds were more commonly present on granitic and sandstone substrates than on more fertile basalt. They occurred both in the moist south‐west and dry north of the park. They were most abundant in sour bushveld and mopane savanna woodland, and mostly absent from knob thorn‐marula parkland. The presence of sable was negatively associated with high concentrations of impala and wildebeest, less consistently related to the abundance of zebra, and positively associated with the occurrence of buffalo herds. Best supported models included the separate effects of the most abundant grazers along with land type. Interspecific relationships seemed more consistent with vulnerability to predation as the underlying mechanism restricting the distribution of sable herds than with competitive displacement. Sable favoured land types distinct from those where wildebeest, the most preferred prey of lions, and impala, numerically the most important resident prey species, were most abundant. Hence the risk of predation, associated with habitat conditions where abundant prey species are most concentrated, can exert an overriding influence on the distribution of rarer species in terms of their home range occupation.

Mechanisms of coexistence in diverse herbivore–carnivore assemblages: demographic, temporal and spatial heterogeneities affecting prey vulnerability

“…There are also consequences for the broader‐scale distribution of prey species. Four of the rarer antelope species in KNP have their local distributions concentrated in regions where the principal prey species of lions are less abundant, meaning a lowered presence of lions (Chirima et al ). When the expanded distribution of artificial water points drew more zebra into the northern region favoured by the rare antelope, populations of the latter went into decline (Harrington et al , Owen‐Smith and Mills ).…”

Are relatively rare antelope narrowly selective feeders? A sable antelope and zebra comparison

“…These features allow sable herds to occupy regions with generally infertile soils where similar‐sized grazers are present in low abundance or absent. These findings lend credence to studies indicating that the main constraint on the local occurrence of sable antelope is their susceptibility to predation, restricting their presence in regions with fertile soils and a correspondingly high abundance of other grazers, especially wildebeest and impala Aepyceros melampus (Chirima et al ., ). In the Serengeti, topi Damaliscus lunatus and hartebeest Alcelaphus buselaphus occurred primarily in areas with adequate grass biomass that were relatively safe from predation (Hopcraft et al ., ).…”

“…Our study design entailed a comparison of grass species selection and resultant diet composition between sable antelope and zebra herds co‐inhabiting in one region of KNP, and between sable antelope herds in two regions that differed in rainfall, soils and hence grass species composition. The chosen regions had supported the highest local densities of sable in KNP, before the population decline (Chirima, Owen‐Smith & Erasmus, ). Being hindgut fermenters and somewhat larger than sable (310 kg vs. 220 kg in adult body mass), zebra were expected to accept a wider range of grass species, including those comparatively fibrous when mature, than sable.…”

Spatially nested niche partitioning between syntopic grazers at foraging arena scale within overlapping home ranges

“…Sable herds dynamically avoided close proximity to buffalo herds, but not zebra herds, but possibly due to avoidance of a shared predator rather than competitive displacement for resources (Macandza et al 2012b). Moreover, the regional distribution of sable antelope (Hippotragus niger) herds within KNP appears to be governed primarily by how the abundance of wildebeest and impala affects the risk of predation (Chirima et al 2013).…”