Mechanisms of Thermoregulation and Water Balance in Desert Ungulates

Abstract

Desert ungulates must contend with high solar radiation, high ambient temperatures, a lack of water and cover, unpredictable food resources, and the challenges these factors present for thermoregulation and water balance. To deal with the conflicting challenges of maintaining body temperature within acceptable limits and minimizing water loss, desert ungulates use a variety of physiological, morphological, and behavioral mechanisms. The mechanisms involved in thermoregulation and water balance have been studied in many domestic and wild African and Middle Eastern ungulates; studies involving ungulates inhabiting North American deserts are limited in comparison. Our objectives were to review available scientific literature on thermoregulation, water balance, and the effects of dehydration in desert ungulates. We discuss the physiological, morphological, and behavioral mechanisms used by ungulates to maintain temperature and water balance in arid environments, and the implications for research and management of desert ungulates in western North America.

Towards a mechanistic understanding of the responses of large terrestrial mammals to heat and aridity associated with climate change

“…Shade-seeking, another method to reduce radiative heat gain, is available to even the largest of mammals [47,89]. In the very hot desert environment of Saudi Arabia, Arabian oryx (Oryx leucoryx) sought shade as early as 06:30 in the morning (within an hour after sunrise), and were observed to be in shade for more than nine hours of the day, moving away from trees only when air temperature was lower than body core temperature, and heat therefore could be dissipated by non-evaporative means [90].…”

“…In the face of high diurnal heat loads, another option available to large mammals is to transfer activity to the night [89,91]. The timing of an animal's behaviour is determined by the interaction of outputs from its internal circadian clock, with that of masking, the direct stimulation or inhibition of behaviours by environmental factors [100].…”

“…For mammals that can switch to nocturnal activity, nighttime feeding offers the potential benefit of foraging on wet vegetation [89] or plants with higher water content [101]. However, a switch away from diurnal activity also may compromise energy acquisition if it results in a reduction in the animal's total 24 h activity, and therefore foraging time.…”

Adaptive thermoregulation during summer in two populations of an arid‐zone passerine

“…Many endotherms are thought to reduce this cost by storing heat (facultative hyperthermia) during periods of heat stress, thereby reducing the need for evaporative cooling at high T air (mammals, reviewed by Mitchell et al [2002], Cain et al [2006]; birds, reviewed by Tieleman and Williams [1999]). …”

Ruminants as Part of the Global Food System: How Evolutionary Adaptations and Diversity of the Digestive System Brought them to the Future

“…Under desert and tropical environments where feed resources are restricted in quantity and quality, ruminants present differences in the digestive tract [51][52][53]. Upon these harsh circumstances ruminants show adjustment of energy requirements for maintenance and ability to reduce metabolism, regulation of water usage in drought conditions [48,51,[54][55][56], competence to economize nitrogen, and thermoregulation by keratinized tissues [56,57]. Small ruminants like goats are skilled grazers with a great ability to select food, they have an efficient digestive system that allows retain a great amount of food and also to efficiently utilize the most of the food during feed shortage conditions [48,53].…”