Ecophysiological characteristics of large herbivorous mammals in arid Africa and the Middle East

Abstract

This paper attempts to focus our knowledge and our understanding of the ecophysiological capacities of wild and domesticated ungulates in arid zones of north Africa and the Middle East. Sheep and goats are kept over a wider range of climatic conditions than cattle, and are blamed as the major destructive agent on semi-arid rangelands. The timing of births and the ability of female ungulates to conceive while lactating are not species-specific characteristics but simply a matter of short-term adaptation to changing environmental conditions. Behavioural adaptation can supplement physiological adaptation. Wild ungulates reduce heat loads by being active at night while remaining in shade during the day. In addition they forage during the night, when air humidity is high and plant material more hydrated. Various species can minimize evaporative water loss by using an adaptive heterothermy, they store heat by day and lose it passively at night. Evaporation from the respiratory tract is reduced by a counter-current heat exchange in the respiratory passage which lowers the temperature, and therefore the saturation of the expired air allowing the brain to remain cooler than the rest of the body. Wild ungulates usually require less water than domesticated species. The daily water turnover rates (WTR) in their natural habitat varies between 6% of the animal's body mass (camel, dorcas gazelle) and 14% (bedouin goat). They can concentrate their urine, thereby reducing urine volume by as much as 50% and desiccate the faeces. When nutritional conditions deteriorate, infrequent drinking helps certain species to maintain their energy balance by improving the digestion of low quality feed more efficiently than in non-desert breeds. During summer, after 3–4 days of water deprivation, goats like camels, lose 30% of their body mass, but they continue to graze the dry roughage while the dorcas gazelles stop eating altogether and become moribund. When they have access to water, goats and camels gulp down volumes that may exceed 40% of the body mass while gazelles consume only 15%. Lactation doubles WTR in the bedouin goat while the total body water is increased by 35%. The capacity of bedouin goat and Awassi sheep to store water does not seem to be shared by camels and wild ruminants. There is no increase in urine flow in the rehydrated goats, the kidneys help to conserve water and solutes. The water is gradually released into the other body fluid compartments. In gazelles the water obtained in this way exceeds their WTR and may remove the need to drink. The camel's WTR (82 ml) and metabolic rate (210 kJ kg−1 day−1) are about half those of a cow living in a similar arid area. The camel and the bedouin goat have the capability of converting poor quality arid rangeland forage into milk and meat, even in dry season. Wild ungulates, but also some domestic species do not respond significantly to the changing climatic conditions. They are relatively independent of water and hence of overgrazed areas. It is now necessary to evaluate the capacities of the water economy of a range of ungulate species in relation to their energy metabolism in the field.