Abstract
Long-term population performance trends of eight large herbivore species belonging to groups of disparate foraging styles were studied in the semi-arid savanna of the Kruger National Park, South Africa. Over the past century the number of bulk feeders (buffalo, waterbuck, blue wildebeest and plains zebra) had increased towards comparatively high population densities, whereas population numbers of selectively feeding antelope species (sable antelope, roan antelope, tsessebe and eland) declined progressively. Detailed analyses revealed that population numbers of buffalo and waterbuck fluctuated in association with food quantity determined by rainfall. Population performance ratings (1944–2003) of the species for which forage quality was important (blue wildebeest, zebra and selective grazers) were correlated negatively with minimum temperature and positively with dry-season rainfall.Interpretation according to a climate–vegetation response model suggested that acclimation of forage plants to increasing temperature had resulted in temperature-enhanced plant productivity, initially increasing food availability and supporting transient synchronous increases in population abundance of both blue wildebeest and zebra, and selective grazers. As acclimation of plants to concurrently rising minimum (nocturnal) temperature (Tmin) took effect, adjustments in metabolic functionality occurred involving accelerated growth activity at the cost of storage-based metabolism. Growth-linked nitrogen dilution and reduced carbon-nutrient quality of forage then resulted in phases of subsequently declining herbivore populations. Over the long term (1910–2010), progressive plant functionality shifts towards accelerated metabolic growth rather than storage priority occurred in response to Tmin rising faster than maximum temperature (Tmax), thereby cumulatively compromising the carbon-nutrient quality of forage, a key resource for selective grazers.The results of analyses thus revealed consistency between herbivore population trends and levels of forage quantity and quality congruent with expected plant metabolic responses to climate effects. Thus, according to the climate-vegetation response model, climate effects were implicated as the ultimate cause of large herbivore population performance in space and over time.Conservation implications: In its broadest sense, the objective of this study was to contribute towards the enhanced understanding of landscape-scale functioning of savanna systems with regard to the interplay between climate, vegetation and herbivore population dynamics.
Highlights
The abundance of herbivore communities in African savannas is determined principally by the availability of food resources of adequate quality (East 1984; Fritz & Duncan 1994; Sinclair, Dublin & Borner 1985)
Large herbivore population trends in the Kruger National Park (KNP) over the past century have been characterised by a notable dichotomy: a progressive increase of the three main bulk-feeding large herbivore species, namely blue wildebeest (Connochaetes taurinus), zebra (Equus burchelli) and buffalo (Syncerus caffer), stabilising at relatively high population densities, and the population decline of four selectively feeding species, namely sable antelope (Hippotragus niger), roan antelope (Hippotragus equinus), tsessebe (Damaliscus lunatus lunatus) and eland (Taurotragus oryx)
With the climate–vegetation response model being central to an explanatory framework, we proceeded to apply an approach of pattern/process matching where we explored the extent of consistency with which climate impacts on key nutritional resources could explain spatiotemporal correlations between climate and herbivore population trends
Summary
The abundance of herbivore communities in African savannas is determined principally by the availability of food resources of adequate quality (East 1984; Fritz & Duncan 1994; Sinclair, Dublin & Borner 1985). The influence of rainfall, especially during the dry season, on the availability of forage of adequate quality and large herbivore population performance has been recorded in numerous studies (inter alia De Bie 1991; Dunham, Robertson & Grant 2004; Mduma, Sinclair & Hilborn 1999; Mills, Biggs & Whyte 1995; Owen-Smith & Ogutu 2003). Initial population increases of bulk-feeding antelope and browsing species during the first half of the twentieth century were attributed largely to population recovery from decimation by hunting and epizootics (Joubert 2007a; Pienaar 1963). Impacts by boundary fencing of the park, culling operations and water provisioning further shaped population abundance and spatial distributions of some species http://www.koedoe.co.za doi:10.4102/koedoe.v54i1.1047
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