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

Abstract

Animals that are relatively rare in local species assemblages are commonly assumed to be narrowly selective in their habitat or dietary requirements, with the latter generally assessed in terms of the range of food types consumed. We investigated whether a narrow dietary range might help explain the restricted distribution and low local densities attained by sable antelope Hippotragus niger compared with other grazing ungulates. Selection by sable antelope for grass species, its relation to species availability and the resulting evenness of the diet were compared with these measures for zebra Equus quagga, which are assumed to be generalist feeders owing to their hindgut fermentation system, under dry season conditions when food was most limiting. Both grazers exhibited a clear distinction between highly favoured and infrequently accepted or rejected grass species in the same region, and both favoured mostly the same common grass species, but sable showed greater acceptance of several less common grass species than did zebra. Distinctions were evident among individual sable herds in favoured grass species, dependent on local availability. Dietary evenness was similar for sable and zebra herds overall, although seasonal trends differed depending on whether animals concentrated their diet more narrowly on a few grass species or broadened it during more extremely dry conditions. Hence, although sable were more narrowly selective for green leaf content than zebra, the dietary acceptance range of these two grazers at grass species level did not differ fundamentally. In particular, sable readily consumed tall grass species rated as having low to moderate forage value. This dietary tolerance enables sable antelope to occupy savannah woodlands associated with relatively infertile soils where the risk of predation is reduced due to the relatively low abundance of other prey. Accordingly, the causes of local rarity may lie in the restricted availability of food in the places to which these species are restricted by other factors.

Grass greenness and grass height promote the resource partitioning among reintroduced Burchell's zebra and blue wildebeest in southern Mozambique

“…In response, herbivores should broaden their diets to include grass species not exploited at other times of the year (Owen‐Smith et al . ).…”

“…The tolerance of grasses, with many stems, has been recorded in other African herbivores, such sable antelope, Hippotragus niger (Parrini ; Macandza ; Owen‐Smith et al . ) and buffalo, S. caffer (Macandza ).…”

Habitat differences do not explain population declines of sable antelope in an African savanna

“…Overall, our results do not support the contention that locally deteriorating habitat conditions (habitat becoming less favorable for sables), as a result of the low rainfall conditions between 1982 and 1995, and changing fire management policies, have led to declines in the Pretoriuskop sable population. Furthermore, while the habitat assessments provided by the remotely sensed imagery available to us represented only the woody component of the vegetation structure, other studies indicate that the grass species favored by sables remain available (Owen‐Smith et al ., ). Our findings leave heightened predation as the only tenable causal mechanism of the sable population decline (Owen‐Smith & Mills, ; Owen‐Smith et al ., ).…”

“…There are several reasons to suspect that changes in vegetation characteristics could drive sable declines. Sable habitat selection is based, at least partly, on vegetation structure, with them generally favoring wooded savanna landscapes (Estes & Estes, ; Wilson & Hirst, ; Grobler, ; Skinner & Chimimba, ; Macandza, Owen‐Smith & Cain, ), probably because of a preference for Panicum grass, which grows in the shade of tree canopies, as well as other grasses that remain relatively green throughout the dry season (Owen‐Smith, Le Roux & Macandza, ). These vegetation features are characteristic of the relatively moist savanna on granitic soils typical of the Pretoriuskop region (mean annual precipitation = 650–750 mm per year), which is characterized by Terminalia sericea / Dichrostachys cinera / Combretum spp.…”

Resource use and the nutritional status of sable antelope in the Okavango Delta region of northern Botswana

“…In the Kruger National Park, sable antelope consume a wide range of grass species, but select strongly for greener grass during dry season months (Macandza, Owen‐Smith & Cain, ; Owen‐Smith, le Roux & Macandza, ). Elsewhere, sable depends on grassy valleys termed ‘dambos’ to provide green forage through the dry season, especially following burning (Estes & Estes, ; Grobler, ; Magome et al ., ; Parrini & Owen‐Smith, ).…”