Resource partitioning between low-density and high-density grazers : sable antelope, zebra and buffalo

摘要

The issue of how the spatial scale and other aspects of food resources and habitatudconditions may enable several species of grazing herbivores to coexist while using theudsame grass resources in the same region is of fundamental importance in ecology andudmanagement of herbivore communities. With this project I aimed at improving theudunderstanding of the ecology of the tall-grass grazers assemblage, particularly how theudspatial scale of resource use influenced resource partitioning between grazers that attainuddifferent regional density in the same region. Based on theories of patterns of speciesudabundance, body size, feeding specialization and competition, I predicted that at alludspatial scales the low density, smaller, resource specialist sable would be more narrowlyudselective for resources than the high density and generalist grazers buffalo and zebra,udwhich I expected to be more broadly tolerant to resources at different spatial scales. Iudfound that the grass species most preferred by sable were also preferred by the abundantudspecies, but buffalo and zebra grazed a wider range of grass species than sable. Sableudwere narrowly selective for green grass whereas buffalo and zebra grazed grass within audwider range of phenological stages, including completely brown grass. The three grazersudoverlapped in habitat features prevailing in foraging areas and, contradictingudexpectations, the breadth of habitat features in areas used did not differ among grazers.udThe low density sable used resources that occurred in restricted areas of the landscapeudduring periods of food abundance, but the resources required became sparser as the dryudseason progressed prompting sable to move notably more widely during the late dryudseason. Buffalo and zebra used space more evenly suggesting that resources supporting these high density grazers were abundant and widely distributed in the landscape yearround.udThe sections of the landscape supporting the low density sable were distinct fromudareas frequently used by high density grazers. Overall, results showed that resourceudpartitioning occurred through spatial separation of core grazing areas, despite overlaps atudlower spatial levels of resource use. The narrow tolerance of resources by sable at theudgrass species and grass features level suggests that the dry season is a more stressfuludperiod to sable than to more common grazers due to a progressive decrease in theudavailability of resources favoured by sable. This could contribute to explaining why sableudoccur in low density as well as the decline and the lack of recovery by the population.