Animals living in deserts

Reasons for rejecting idea that camels store water: No realistic sites for water storage found in the body “Water sacs” contain mainly food “Juices” they contain are isotonic with blood Capacity of 4.5dm3 is insignificant as a water store

Oxidation of fat in hump is physiologically uneconomical… …since breathing to obtain oxygen loses more water from lung surface than is obtained from respiring fat The assumption was that camels drink water in anticipation of their needs They don’t, in fact, drink in excess of their requirements

Even long-established explanations should not be accepted without evidence from adequate research Other possibilities for water economy are physiological adaptations such as: Specialised kidney function concentrated urine Reduced sweating Method of conserving water when breathing

In the camel water leaves the body fluids & enters blood plasma Greater percentage of water loss from: Body fluids (camel) Blood plasma (Man) In the camel water leaves the body fluids & enters blood plasma Physical effect on blood is to make it more viscous (thick)… …so reduced blood flow less heat distribution so core temperature rises 6oC Tolerating a temperature rise or “storing” heat reduces the temperature gradient between body & environment so less heat gained At night the camel loses heat by conduction, convection & radiation… …none of which require water for heat loss

…delays sweating & investment of water in maintaining body temperature The advantage of allowing body temperature to fall at night: Takes longer next morning to reach equilibrium… …so sweating delayed In summary: Allowing body temperature to fall overnight, & tolerating rise in body temperature during day… …delays sweating & investment of water in maintaining body temperature

Water intake = 53.7g 6.2g deficit Water loss = 59.9g Source of intake is “metabolic water” from food oxidation Water deficit is reduced by increased humidity… …which increases water intake (more water absorbed by seeds)… …& less water is lost (in faeces, urine & by evaporation) Water balance is on the intersection of water intake & water output

Temperature is lowest at the tip of the nose This conserves water as vapour condenses on nasal membranes before air is breathed out In summary: Water vapour conserved from expired air Dry faeces Concentrated urine Lives in burrows Nocturnal Sweat glands only on soles of feet