Effect of human induced surface water scarcity on herbivore distribution during the dry season in Ruaha National Park, Tanzania

Abstract

In Africa, burgeoning human populations promote agricultural expansion and the associated demand for water. Water abstraction for agriculture from perennial rivers can be detrimental for wildlife, particularly when it reduces water availability in protected areas. Ruaha National Park (Ruaha NP) in southern Tanzania, one of the largest parks in Africa, contains important wildlife populations, including rare and endangered species. The Great Ruaha River (GRR) is the main dry season water source for wildlife in the Park. Water offtake from this river for large-scale irrigation and livestock production up-stream of the Park has caused large expanses of this formerly perennial river within the Park to dry out during the dry season. The dry season distribution of a species in relation to surface water is considered an indicator of its dependence on water and ability to cope with the loss of surface water. We investigated how diminishing surface water availability during three dry seasons (2011–2013) affected herbivores' distance to water in Ruaha NP. The distance held by herbivores to water is shaped by a range of factors including dietary category. We determined changes in the locations of available surface water throughout the dry season using standardized ground transects, close to and leading away from the GRR, to map the locations of nine herbivore species. Functional responses of herbivores, i.e. their change in distance to water between early and late dry season, indicated that distance to water was 1) shortest in buffalo and waterbuck (grazers), 2) similar for plains zebra (grazer), elephant and impala (mixed feeders), 3) larger in giraffe and greater kudu (browsers) and 4) largest in generalist feeders (warthog, common duiker). The substantial species' differences in surface water dependence broadly fit predicted species differences in their ability to cope with anthropogenic reduction in surface water in Ruaha NP.