The distribution patterns of African elephant (Loxodonta africana) and white rhinoceros (Ceratotherium simum simum) in relation to waterhole availability in a South African savanna

Abstract

Anthropogenic activities, including the illegal poaching trade, have been threatening the global populations of elephants and rhinoceros for decades. Rigorous studies into the ecology of these megaherbivores are imperative for conservation strategies. I studied the relationship between water availability, and the African elephant and the southern white rhinoceros. Water resources are crucial environmental determinants of animal distribution within semi-arid habitats, particularly during the dry season when water is relatively scarce. I hypothesised that elephant and rhino would spend more time in water-present areas during the dry season and high temperatures. During the dry season, I predicted that elephant and rhino would prefer permanent sources of waterholes that were mostly artificial. I also expected that the herbivores would select for waterholes large enough for full-submergence, and lastly, I hypothesised that elephants (mixed-feeders) would spend more time around waterholes with high shrub and grass cover, and rhinos (grazer) with more grass cover. In Kempiana, an area within Greater Kruger, South Africa, waterhole occurrence was identified using satellite imagery and ground-truthing by foot and aeroplane. Waterhole characteristics were also classified using satellite imagery, and animal density data was provided from Southern African Wildlife College in the form of aerial counts between 2016 and 2018. Generalised linear mixed-effect models were used to deduce the best-fit models for animal presence and density. Elephant presence was significantly found to increase in areas of water occurrence as temperatures rose. In water-present areas, both elephant and rhino utilised medium- and small-sized waterholes more during the dry season, with elephants utilising medium and rhinos preferring small. Elephants also associated more with permanent waterholes but less with temporary waterholes during the dry season, and rhino density around waterholes of neutral permanence was higher during the dry season. Shrub cover positively predicted elephant and rhino density during the wet season, whilst grass cover negatively predicted elephant density. Rhinos preferred natural waterholes for both seasons, and elephant density was significantly higher at artificial waterholes during the dry season (and the opposite trend for the wet season). These results suggest differences in thermoregulation strategies of elephant and rhino, with elephant depending more on water. It also supports the notion that elephants utilise artificial waterholes considerably more during the dry season, which may propagate their distribution and population numbers. Lastly, species-specific preferences for waterhole characteristics may also indicate that displacement between rhino and elephant has led to waterhole niche partitioning.