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Freie Universität Berlin (2016)

The ecological effects of changes in surface water availability on larger mammals in the Ruaha National Park, Tanzania

Stommel, Claudia

Titre : The ecological effects of changes in surface water availability on larger mammals in the Ruaha National Park, Tanzania

Die ökologischen Effekte einer veränderten Verfügbarkeit von Oberflächenwasser auf größere Säugetiere im Ruaha Nationalpark, Tansania

Auteur : Stommel, Claudia

Université de soutenance : Freie Universität Berlin

Grade : Doctor rerum naturalium (Dr. rer. nat.) 2016

Résumé
Large-scale crop irrigation is thought to be responsible for a substantial reduction in the dry season flow of the Great Ruaha River (GRR), the main dry season water source for wildlife in Ruaha National Park (NP), Tanzania. In the early 1990s the GRR was perennial, whereas currently a substantial reduction in dry-season flow has resulted in large sections of the GRR drying out. This thesis aimed to investigate the impact of reduced flow in the GRR on the quantity and quality of water available in the GRR and alternative water sources to assess the effect of these parameters on the distribution of mammal species inside Ruaha NP during three dry seasons. The results revealed a deterioration of water quality (increased salinity and total aerobic bacterial load) when water flow stopped. I document that several mammal species actively dug for water or drank from animal dug waterholes, and did so even when surface water was present. Statistical analyses revealed that digging was more likely when the total aerobic bacterial load in surface water was high but independent of salinity. These finding indicate that digging accesses less contaminated sub-surface water, thereby providing better quality water with fewer harmful pathogens (Chapter 2). I examined the consequence to the common hippopotamus (Hippopotamus amphibius) of reduced water availability along a 104 km stretch of the GRR during two dry seasons. Hippos are highly dependent on aquatic day resting sites to prevent skin damage by solar radiation and overheating. My findings revealed substantial changes in hippo distribution as the dry season progresses. Hippo numbers at monitored locations increased with the expanse of surface water present and was independent of water quality. As downstream resting sites dried out, hippos accumulated in large numbers at a few upstream locations – an extensive loss of dry season habitat in terms of resting sites and night foraging areas. The GRR provided the most important day resting sites for hippos within the study area (Chapter 3). I also examined the effect of water availability on the spatio-temporal distribution of nine species along a total network of 200 km ground transects and modelled the distance each species maintained to the nearest surface. This showed (i) grazers (African buffalo [Syncerus caffer], waterbuck [Kobus ellipsiprymnus] and plains zebra [Equus quagga]) maintained the shortest distance throughout the dry season to surface water, (ii) species that both grazed and browsed (impala [Aepyceros melampus], African savanna elephant [Loxodonta africana]) and those that were predominantly browsers (Masai giraffe [Giraffa tippelskirchi], greater kudu [Strepsiceros zambesiensis]) maintained intermediate distances to water, and, (iii) omnivores (warthog [Phacochoerus africanus], common duiker [Sylvicapra grimmia]) tolerated the largest distances to surface water. Species distribution data revealed upstream movements of buffalo and elephant at the end of the dry season (Chapter 4). My thesis demonstrates the profound importance of the GRR for the viability of populations of larger mammals within Ruaha NP and the urgent need to restore dry season flow.

Mots clés  : Mammals herbivores Great Ruaha River water scarcity behavioural adaptation spatio-temporal distribution

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