Many of Africa’s conservation areas (CAs) are experiencing large declines in the size and diversity of their ungulate populations (Whyte & Joubert, 1988; Ben-Shahar, 1993; Williamson, 2002; Owen-Smith & Mills, 2006; Caro & Scholte, 2007; Bolger et al., 2008; Newmark, 2008; Harris et al., 2009; Ogutu et al., 2009; Western, Russell & Cuthill, 2009). We provide evidence from a wide range of African CAs showing that the major reason for these declines appears to be because many of Africa’s CAs do not
encompass the full range of functional resource gradients, migratory corridors and seasonal habitats critical for the maintenance of a diverse array of productive ungulate populations.
Forage quantity and quality in the savannas of Africa are highly variable both spatially and temporally (Vesey-Fitzgerald, 1960; Breman & De Wit, 1983; Ellis & Swift, 1988; Illius & O’Connor, 2000; Fryxell et al., 2005; Owen-Smith, 2007). The stability and productivity of ungulate populations is dependent upon them being able to pursue an optimal energy-maximizing foraging strategy by tracking this spatial and temporal variability in forage quantity and quality (Albon & Langvatn, 1992; Rettie & Messier, 2000; Owen-Smith, 2002, 2004; Fryxell et al., 2005; Holdo, Holt & Fryxell, 2009; Parker, Barboza & Gillingham, 2009; Hopcraft, Olff & Sinclair, 2010).
Forage quality is generally at its highest in lower productivity regions such as on shallow, upland soils and in low-rainfall regions because minerals, protein and energy become more diluted and digestibility decreases as grass biomass increases (Jarrell & Beverly, 1981; Breman & De Wit, 1983; McNaughton & Banyikwa, 1995; Murray, 1995). Thus, except for a few species such as sable antelope (Hippotragus niger) and topi (Damaliscus korrigum), which have mouth parts adapted to selecting green leaves
on taller grasses (Murray & Illius, 2000), the predominance of short grasses in these less productive areas results in greater rates of nutrient and energy intake by most ungulate species (Wilmshurst, Fryxell & Bergman, 2000; Owen-Smith, 2002). Low productivity areas are, therefore, critical for supplying sufficient protein, energy and minerals in forage during the period of lactation and for building up body stores before the dry season (McNaughton & Banyikwa, 1995; Parker, Barboza & Gillingham,
2009; Hopcraft, Olff & Sinclair, 2010). By contrast, more productive, high-rainfall regions or floodplains, although supporting grasses generally lower in quality during the wet season than grasses in less productive regions, often provide some form of green forage in the late dry season (Vesey-Fitzgerald, 1960; McNaughton, 1985; Fryxell, 1987; Fryxell & Sinclair, 1988a), when forage quality is severely limiting (Ellis & Swift, 1988; Mduma, Sinclair & Hilborn, 1999; Illius & O’Connor, 2000).
In addition to the advantages of better adaptive foraging capability for migratory populations, migration also allows ungulate populations to break free from predation limitation (Fryxell, Greever & Sinclair, 1988; Mills & Schenk, 1992; Heard, Williams & Melton, 1996; Rettie & Messier, 2000; Fryxell et al., 2007), which limits the size of nonmigratory ungulate populations well
below the ecological carrying capacity (Smuts, 1978; Gasaway, Gasaway & Berry, 1996; Hopcraft, Olff & Sinclair, 2010). In addition, as human population densities adjacent to CAs increase (e.g. Newmark, 2008; Ogutu et al., 2009), ungulates having to migrate to seasonal grazing grounds outside of CAs often experience greatly elevated levels of poaching and human interference
in these unprotected areas (Whyte & Joubert, 1988; Williamson, Williamson & Ngwamotsoko, 1988; Newmark, 2008; Ogutu et al., 2009).