Comparing small mammal assemblages between communal and commercial rangelands within a region of the Succulent Karoo, South Africa
Thesis (MScConsEcol (Conservation Ecology and Entomology))--Stellenbosch University, 2008.
The widespread ecological impacts of overgrazing by livestock within the Succulent Karoo have received considerable attention. Literature shows communal and commercial rangelands have been thoroughly studied, and vegetation responses have been investigated in an attempt to understand the effects of overgrazing. Regarding animal species, literature is in short supply. In a one-year study of small mammal assemblages, the effect of the rangelands, and subsequently vegetation, on small mammal 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 a greater perennial shrub cover on the communal rangelands and a greater perennial succulent cover on commercial rangelands, consequently creating different habitats for animal assemblages. This study supports the notion of small mammal composition relating to vegetation structure, with certain species being impacted by heavy grazing. Four small mammal species were found in greater abundances on commercial rangelands, with one being exclusive, while communal rangelands were exclusively occupied by three nocturnal species. Diet and habitat requirements are the most important factors regarding species occurrence. With small mammal species composition differing between rangelands, and species richness not being affected by rangeland type, this study illustrates that the disappearance of certain species may arise 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 body mass, 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 is coping within an environment. The proportion and number of occupied and collapsed burrows can be seen as a measure of trampling effect. It was expected for grazing intensity, as well as vegetation changes, to affect the occurrence of such burrows. This study showed differences between the communal and commercial rangelands as negligible. As expected, numbers of burrowing small mammal species were negatively correlated with numbers of collapsed burrows. However, a lack of consistency deemed this result unimportant. Results show that the effects of overgrazing on small mammal populations are complex and require more attention if to be fully explained. This study provides insights into the effects of land use on small mammals and burrow numbers, which have implications for the conservation of these species within arid regions.