Omnivores and browsers are more resilient than mixed feeders and grazers to human induced surface water scarcity 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 in southern Tanzania, one of the largest parks in Africa, contains important wildlife populations, including rare and endangered species. The Great Ruaha River 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 up during the dry season. We investigated how available surface water during the dry season affected the distribution of ungulate species. During three dry seasons (2011-2013), we determined locations of surface water and collected spatial data for nine ungulate species by driving standardized ground transects, including a 104 km section of the Great Ruaha River. The dietary niche hypothesis predicts a functional relationship between mammalian herbivore diets and their dependence on surface water, and thus the distance maintained to surface water during the dry season. Distance maintained to water should increase from grazers (buffalo, waterbuck, plains zebra) to mixed feeders (elephant, impala), to browsers (giraffe, greater kudu) to omnivores (warthog, common duiker). Functional responses of herbivores, as analysed by a generalised linear mixed effects model, demonstrated that during the dry season, distance to water was (i) shortest in buffalo and waterbuck (grazers), (ii) similar for plains zebra (grazer), elephant and impala (mixed feeders), (iii) larger in giraffe and greater kudu (browsers) and (iv) largest in omnivores (warthog, common duiker). These findings demonstrate substantial species differences in surface water dependence that are broadly in line with predicted species resilience to anthropogenic reduction in surface water in Ruaha National Park.

Impacts of Constructed Water Pans on Mammal Distribution and Abundance. A Case of Mt. Kenya Wildlife Conservancy, Kenya

“…The extent of water dependence in mammals is determined by factors such as feeding guilds, digestive physiology, thermoregulatory mechanism, body size and the loss of water through feaces and urine [32,33,34]. Differences in water requirements cause animals to be distributed differently around water points and the distance mammal species if found from water source during dry season shows their water dependence level (Schmied et al, 2023. The water-dependent species are usually observed mostly around the water source while the waterindependent species are usually found away from the water source during the dry season.…”