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Restricted habitat use by an African savanna herbivore through the seasonal cycle: key resources concept expanded



Areas within regional landscapes that make a disproportionate contribution to supporting large herbivore populations have been interpreted as key resource areas, hotspots, buffers, stepping stones or serving other functional roles. We investigated the role that the restricted extent of habitat types exploited at different stages of the seasonal cycle might play in limiting the abundance of a blue wildebeest subpopulation in the Kruger National Park, South Africa. GPS collars enabled the space use patterns of the animals to be related to available habitat types, and faecal nutrient concentrations to be related to the habitats exploited at that time. Wildebeest herds occupied primarily grazing lawn grasslands associated with gabbro uplands or sodic lowlands through the wet season into the early dry season. During the late dry season, they switched to seep-zone grasslands in mid slope regions of granitic landscapes. Use of recently burned areas enhanced forage quality at the beginning of the wet season. The seasonal habitat shifts enabled wildebeest to obtain adequate nitrogen, phosphorus and sodium throughout the year. Lawn and seep-zone grasslands combined constituted 10% of the available area. Grazing lawns, which encompassed only ˜ 3% of the study area, appeared to be the primary limitation on the abundance of wildebeest. However, the greater security from predation provided by the open vegetation cover in the grazing lawns is not easily disentangled from the resource benefits that they yield. Nevertheless, findings indicate how local abundance can be restricted by the extent of portions of the landscape providing crucial benefits during particular phases of the seasonal cycle. Hence the key resources concept needs to be expanded to accommodate the functionally distinct contributions made by different habitats towards supporting local herbivore populations.