Physiology and the future of animals in shifting-sand deserts: respiration, energetics and water balance.

The many invertebrates and reptiles of the shifting-sand deserts, and their rare mammals, live in and on the sand. Their conservation requires a thorough understanding of the physiological mechanisms that not only enable them to function, but that may buffer them against future change. The almost-spherical shape of the aeolian sand grains of shifting-sand deserts enables gas diffusion from the surface to maintain a normoxic environment deep in the sand, with sufficient volume to sustain sand-swimming animals, even the mammals. In the resource-poor desert landscapes, cellulose is the dominant source of metabolic energy for herbivores, much of it contained in detritus that can originate hundreds of kilometres from the desert. Carnivores and omnivores consume mainly detritivores, with termites often contributing substantially to their diets. Many animals of shifting-sand deserts manage their body water by the acquisition of metabolic and preformed water, balanced against limited loss of body water via integument, excreta and respiration. Those that do drink usually use droplets from fog or dew. Some small invertebrates extract water vapour from unsaturated air. The animals have evolved mechanisms to counteract osmotic shock when they consume pure water that can constitute more than 40% of body mass in a single drink. In a companion review, we discuss how the animals move and how they cope with potentially lethal desert heat and cold in and on the sand. We need to conserve their fortresses in the sand, and, anomalously, it is food, not water, that requires attention.