The Comparative Population Dynamics of Browsing and Grazing Ungulates

Abstract

Among African ruminants a clear dietary distinction exists between grazers, feeding predominantly on grasses and sedges (graminoids) year-round, and browsers consuming mostly the leaves and shoots of woody plants as well as herbaceous dicots (or forbs) and fruits (Owen-Smith 1992, 1997). Even so-called mixed feeders can be divided between a subset obtaining the greater proportion of their diet from grasses year-round (mainly grazers, e.g., Thomson’s gazelle (Gazella thomsoni), and mainly browsers dependent largely on woody and herbaceous dicots, especially during the dry season (e.g., Grant’s gazelle Gazella granti). Just two species seem firmly intermediate, switching between consuming mostly grass in the wet season, and a predominance of browse during the dry season: impala (Aepyceros melampus) and nyala (Tragelaphus angasi). The grazerbrowser distinction is replicated among the African rhinos, with the white rhino (Ceratotherium simum) being exclusively a grazer and the black rhino (Diceros bicornis) almost entirely a browser (Owen-Smith 1988). All extant zebras (Equus spp.) are exclusively grazers.