Habitat and resource partitioning between abundant and relatively rare grazing ungulates

Abstract

Species assemblages commonly include species persisting at low density alongside more abundant species, raising questions about the mechanisms enabling this coexistence. Relatively rare species may persist through (1) specializing on a narrow range of resource types that are sparsely but widely available or (2) precisely selecting patches where their favoured resources are concentrated that are only lightly exploited by more abundant species. Our study compared the habitat and resource use across a range of scales of relatively uncommon sable antelope with those of more abundant buffalo and zebra sharing a common preference for relatively tall grass. Buffalo occupied a wide range of habitat types, but shifted towards lowlands during the late dry season when water became limiting. Sable and zebra foraged year-round in upland regions, undertaking journeys to water. Zebra occupied mainly the prevalent habitat type on basaltic substrates. Sable more narrowly exploited habitats on quartzitic sandstone where green leaves persisted in grasslands through the dry season, and favoured the grass species that retained green leaves. Buffalo and zebra were tolerant of grass that was mostly brown. Hence, the coexistence of sable was enabled by their precise selection for the green foliage remaining in between the depletion zones generated by the more abundant grazers. Nevertheless, the local sable distribution had contracted following an influx of zebra, suggesting that resource use distinctions were insufficient to prevent the competitive displacement of sable from a wider region by zebra. Hence, niche breadth and resource availability concepts both have relevance.