Comparing small mammal assemblages between communal and commercial rangelands within a region of the Succulent Karoo, South Africa

[摘要] The widespread ecological impacts of overgrazing by livestock within the SucculentKaroo have received considerable attention. Literature shows communal andcommercial rangelands have been thoroughly studied, and vegetation responses havebeen investigated in an attempt to understand the effects of overgrazing. Regardinganimal species, literature is in short supply. In a one-year study of small mammalassemblages, the effect of the rangelands, and subsequently vegetation, on smallmammal assemblages was examined, as well as the effects on number of occupied,unoccupied and collapsed burrows.This study shows that vegetation composition differs between rangelands, with agreater perennial shrub cover on the communal rangelands and a greater perennialsucculent cover on commercial rangelands, consequently creating different habitatsfor animal assemblages. This study supports the notion of small mammalcomposition relating to vegetation structure, with certain species being impacted byheavy grazing. Four small mammal species were found in greater abundances oncommercial rangelands, with one being exclusive, while communal rangelands wereexclusively occupied by three nocturnal species. Diet and habitat requirements are themost important factors regarding species occurrence. With small mammal speciescomposition differing between rangelands, and species richness not being affected byrangeland type, this study illustrates that the disappearance of certain species mayarise without these different rangelands. This could result in reduced species richness,and thus diversity being lost.Regarding species present on both rangelands, no differences were observed in bodymass, body size or body condition. Despite no differences found in body condition,calculating a body condition index is a good method for investigating how a species iscoping within an environment. The proportion and number of occupied and collapsedburrows can be seen as a measure of trampling effect. It was expected for grazingintensity, as well as vegetation changes, to affect the occurrence of such burrows.This study showed differences between the communal and commercial rangelands asnegligible. As expected, numbers of burrowing small mammal species werenegatively correlated with numbers of collapsed burrows. However, a lack ofconsistency deemed this result unimportant.Results show that the effects of overgrazing on small mammal populations arecomplex and require more attention if to be fully explained. This study providesinsights into the effects of land use on small mammals and burrow numbers, whichhave implications for the conservation of these species within arid regions.

[发布机构] Stellenbosch University