Selection of Vegetation Greenness by Nyala Antelopes on a Resource Productivity Gradient

Geographic gradients in plant productivity can present foraging large herbivores with varying resource levels across the range of a population, to which individuals can demonstrate varying intensity of selection. To investigate individually-specific responses of nyala antelopes (Tragelaphus angasii ) to vegetation greenness, we monitored the landscape use of eight telemetry-collared adult females, half at the wetter end and half at the drier end of Hluhluwe–iMfolozi Park, South Africa. We used remotely-sensed greenness as an index for plant productivity and data on canopy structure, and we compared the strength of selection for greenness between animals having different greenness averages within their home ranges. We found a decreasing pattern between home-range average greenness and strength of selection, which depended on season and presence of tree canopies. Animals in low-greenness home ranges tended to have stronger positive selection in closed-canopy vegetation in the dry season; those in high-greenness home ranges tended to have the stronger negative selection in open-canopy vegetation in the wet season. Our study emphasizes the possibility that a spatial resource gradient on a landscape might provide a valuable model of temporal change in a resource and an indication of potential for foraging animals to adapt to those changes.