Ecology of South African large herbivores in a managed arid savanna: body mass, local distribution, and parasites.

Abstract

Large herbivores are an important natural resource for humans, but a high proportion of these species are classified as globally endangered. Current declines of these species are mainly caused by unsustainable harvesting and land use loss or conversion. These processes frequently increase herbivore mortality rates, and alter a species' behaviour and local distributions. Because of their importance, humans frequently attempt to manage large herbivores to assure their sustainable use and effective protection. Nevertheless, these actions usually focus on managing and monitoring target species, neglecting possible side effect on other species or components of the environment. In this thesis, I focus on studying both environmental and anthropogenic effects on a large herbivore community that inhabits a seasonal, human-modified arid savanna. Firstly, I propose a method to automate monitoring body mass variation of large herbivores over time and use this to explore seasonal mass changes. The method permitted continual body mass monitor of three species over an 18-month period. Animals lost weight during the dry season and gained weight during the wet season, though interesting sex-specific variation in mass change phenology occurred. Frequency of precipitation was the main predictor of annual mass variation. Such work has the potential to inform on the potential impacts of changing future climatic regimes on large herbivores. Secondly, I map the spatial abundance of 16 species using Distance Sampling and Density Surface Models. My results suggest that this highly diverse community of large herbivores can coexist in African savannas because they spatially differentiate their vegetation and water preferences within and between seasons. I found that both target and non-target hunted species avoided human activities at my study site, suggesting that management activities in the area are perceived as a threat, and that hunting has impacts beyond target species. Finally, I use Structural Equation Modelling to assess the simultaneous effects of prescribed fire on tick abundance, grass volume and large herbivore abundance. My results show that ticks decline in number during the first 12 months after burning, but then rapidly return to previous densities. Burning vegetation has a longer-lasting effect on grasslands, and grass volume only returned to pre-burn levels after three to four years. My findings highlight the need for conservation managers to monitor the effects of target actions to assess impacts on both focal and non-focal organisms as well as on the health of the wider ecosystem. Here I have presented a tool to monitor the day-to-day condition of the larger wild ungulates of African savanna systems, which could inform management activities (such as relocating animals, provision of additional resource etc) based on realtime, empirical data. I have demonstrated that relatively inexpensive ground surveys can provide consistent, regular indices of the abundance of ungulate species. The role of human activities in altering herbivore use of the landscape indicates how reducing such activity might actually increase savanna ungulate carrying capacity. These findings, along with the more detailed understanding of the role of fires on the vegetation-grazer-parasite system that I present, should aid conservation managers and researchers in conserving such species, under both current and future scenarios.