Influences of resource availability on African ungulates

Although what drives the abundance and habitat selection of ungulates is a long-standing question, coherent datasets investigating the influences of rainfall, competition and fire on ungulates are unusual. Over 4 years I carried out extensive monthly road transects in Ithala Game Reserve, South Africa, to determine the demographics and habitat occupancy of the region’s prevalent grazer (wildebeest) and mixed-feeder (impala). Habitat occupancy was determined using a GIS-based approach. I obtained 8,742 sighting records, encompassing 8,400 wildebeest and 10,071 impala.

Annual rainfall did not significantly correlate with population sizes of either species. Fecundity of wildebeest, but not of impala, showed a significant positive relationship with rainfall specifically over the perinatal period (November– December), whilst no significant relationships were found for either species between fecundity and rainfall over the previous year, 2 years, rut (February–April) or height of the dry season (June–August). Impala unexpectedly favoured browse habitats to grassland year round, probably consequent on competition for grass with wildebeest. Dry-season grass flushes attracted both wildebeest and impala. The study emphasized how rainfall, competition and fire regimes may affect differently grazers compared with mixed-feeders.

Project Publications

O’KANE, C.A.J., PAGE, B. & MACDONALD, D.W. 2014. Differing influences of resource availability on the demographics and habitat selection of wildebeest compared to impala. Journal of Tropical Ecology 30:189-198.