Epsilon Archive for Student Projects

Abstract

The population of white rhinoceros (Ceratotherium simum simum) is now declining in the Kruger National Park (KNP) in South Africa due to the intense poaching crisis ongoing since the early 2000s. The need for an efficient conservation effort has never been greater and requires a better understanding of white rhinoceros distribution in the landscape. As the white rhinoceros is highly water dependent, I suspected that water availability would be an important driver of its distribution. Additionally, national parks and game reserves have been changing their water management plan in the recent years towards more natural ecological processes leading to less artificial sources. Thus, there is likely discrepancies between water provisioning over the study area, encompassing a small portion of the central-western KNP and adjacent nature reserves, the Associated Private Nature Reserves (APNR).
I investigated the influence of distance to the closest waterhole and river on the mean density of white rhinoceros in the study region. I calculated the distance from cells centre to rhinoceros observations, using a 1x1 km grid cell covering the entire study area. I also researched the effect of cumulative rainfall of the 2 previous months, used as a single predictor and interacting with distance to waterholes and rivers. I had 2 datasets, one originating from a standardised game count made by aerial transect sampling and occurring once a year in September, late dry season, for 4 years. The other dataset was a count originating from aerial transects samplings and targeted towards megaherbivores species. Megaherbivores reach or exceed 1 000 kg when attaining adulthood, and this very large body size set them apart from other smaller terrestrial herbivores. They act as ecosystem engineers by promoting more nutrient-rich vegetation and a higher diversity of habitat, which is benefitting smaller species of herbivores. The white rhinoceros acts as such by creating and maintaining grazing lawns.
I analysed both datasets using zero inflated generalised linear mixed models. Distance to waterhole in correlation with rainfall was the strongest predictor of variability in mean rhinoceros density overall in the study area. In the model focusing on the dry season, white rhinoceros mean density was higher close to water sources when previous rainfall supposedly allowed for vegetation regrowth. In the same model, white rhinoceros mean density increased with distance away from water sources when there had been little to no rain. In the year-round study model, white rhinoceros density increased with distance to waterhole regardless of the season. The increase in white rhinoceros density was stronger with longer distance to water and under higher rainfall. This result implied that white rhinoceros kept away from permanent water likely due to habitat preferences, food depletion, and perhaps other pressures observed at waterholes. This study suggests that water provisioning in the study area probably alleviated the need for white rhinoceros to find water sources during the dry season, making food resources the first limiting factor and main driver of rhinoceros mean density and distribution even during the dry season.