Roan (Hippotragus equinus) population decline in Kruger National Park, South Africa: influence of a wetland boundary

Abstract

Effective management of grazers requires understanding of the mechanisms influencing population declines. Roan antelope, a specialist grazer, has declined in population numbers within Kruger National Park, South Africa. The most widely accepted hypothesis is that habitat deterioration throughout the entire northern plains landscape is responsible for declines in this species. Observations suggest, however, that on the northern plains of Kruger National Park, roan antelope grazes at the boundary between ephemeral wetland and the savanna matrix. The boundary is characterized by nutrient-rich soil and forage, and thus attracts grazing from both generalist and specialist species. We hypothesize that competition for resources at this ecotone, and not at other places in the landscape, is responsible for the observed declines in roan antelope. Changing management strategies to be more cognizant of patchiness and savanna heterogeneity, i.e. more spatially informed, will improve the likelihood that management will result in increasing roan population numbers.

Habitat heterogeneity as the key determinant of the abundance and habitat preference of prey species of tiger in the Chitwan National Park, Nepal

“…Promoting high spatial heterogeneity is therefore a major component of nature conservation. It is especially important in isolated and protected areas like the CNP (Smith et al 1998), which supports a high herbivore species richness and abundance (Kroger and Rogers 2005), which, in turn, affects long-term viability of their predators-tigers (Panthera tigris ;Gurung 1983;Smith et al 1987;Dinerstein and Wikramanayake 1993;Smith et al 1998).…”

Habitat heterogeneity as a driver of ungulate diversity and distribution patterns: interaction of body mass and digestive strategy

“…A clear showcase of the increasing emphasis on spatial heterogeneity in biodiversity conservation has been the adoption of the so‐called ‘heterogeneity paradigm’ in the management of grazing systems (Du Toit & Cumming, 1999; Fuhlendorf & Engle, 2001; Du Toit et al ., 2003; Kroger & Rogers, 2005). This paradigm implies that managers should promote high spatial heterogeneity in savanna systems to maintain high herbivore species richness and abundance; especially in relatively small, fenced savanna reserves (Owen‐Smith, 2004).…”

Tasmanian lentic wetland lawns are maintained by grazing rather than inundation

“…Herbivore grazing has been shown to increase at times of high lawn productivity (McNaughton 1985;Kröger & Rogers 2005). In Tasmania, summer as a whole is likely to be the time of peak productivity, as day lengths are long, temperatures are high and soils are moist but not inundated.…”

“…Thus, one key to understanding processes of lawn maintenance lies in the causes of exclusion of potentially taller plants. Apart from grazing pressure and its possible interactions with fire (Archibald et al 2005;Kirkpatrick 2007), causes of exclusion of taller species could include seasonal inundation (Bell 1971;Milchunas & Lauenroth 1989;Johnson & Rogers 2003;Kröger & Rogers 2005), root competition (Fensham & Kirkpatrick 1992) and abrasion by wind, water or ice (Costin 1954). Apart from grazing pressure and its possible interactions with fire (Archibald et al 2005;Kirkpatrick 2007), causes of exclusion of taller species could include seasonal inundation (Bell 1971;Milchunas & Lauenroth 1989;Johnson & Rogers 2003;Kröger & Rogers 2005), root competition (Fensham & Kirkpatrick 1992) and abrasion by wind, water or ice (Costin 1954).…”