Implications of potential biome boundary shifts for small mammal assemblages in the arid zone of South Africa

Abstract

Desertification deteriorates the landscape functionality of rangelands, affecting the resilience of biome boundaries and this has a cascading effect on vegetation and animal communities. This study aimed to assess landscape functionality along the biome boundary of two arid biomes and its relationship to small mammal assemblages. The study further aimed to provide a landscape perspective of the current desertification process and projected expansion of the Desert biome in South Africa. Three Desert biome, ecotone and Succulent Karoo biome sites were selected to assess landscape functionality and small mammal assemblages over a oneyear period. The difference in landscape functionality between the three areas was assessed to determine the resilience of the biome boundary to desertification. Our results showed that the vegetation of the ecotone had higher desert-like affinities while the soils seemed resilient and remained closely related to the Succulent Karoo biome. High livestock grazing pressure, as evident in the pastoral rangeland, may further deteriorate vegetation parameters and expose the soil to erosion, thereby advancing desertification. During both winter and summer, small mammal surveys using live Sherman traps were conducted and over the total 3204 trapping nights, 119 small mammal captures were recorded from three species. Desmodillus auricularis, Elephantulus rupestris and Gerbillurus paeba all had significantly higher densities in the Succulent Karoo biome. Our study supports the view that G. paeba would be the only species able to thrive in the less diverse Desert biome. This might have implications for the ecosystem services provided by the other two small mammal species in the landscape. As the trajectory for projected desertification appears to be on track, concerted efforts in improving rangeland management are required to maintain landscape functionality and stabilise small mammal assemblages.