In semi-arid rangelands, the foraging range of free-ranging large mammalian herbivores is constrained by the distribution of drinking water during dry seasons. Animal impacts become concentrated around these watering sites according to the geometrical relationship between the available foraging area and the distance from water; the spatial distribution of animal impacts becomes organised along a utilisation gradient termed a "piosphere". This is the first mechanistic study of two aspects of animal spatial foraging behaviour arising as a direct consequence of animals' need to drink water: the development and maintenance of piospheres, and the subsequent animal response. Core to this investigation is the response of animals to the heterogeneity of their resources so that aspects of spatial foraging are widely commented on, whilst explaining the consequences of piosphere phenomena for individual animal intake, population dynamics, feeding strategies, livestock and wildlife management, and herbivore evolution. This book on piospheres is the first to entirely focus on the pivotal landscape feature in the work of rangeland managers, conservationists and scientists.