Xerocole

Xerocole are animals adapted to live in a desert. Under the scorching rays of sun, the arid and baked sands of deserts may appear to be devoid of animal life. But surprisingly a large number of animal species may thrive there. The animals are either drought evaders or drought resistors. Drought evaders make their appearance only when rain sets in, remaining dormant in the interim. All sorts of specialized animals, ranging from insects to mammals are found in a desert. Such animals are well adapted to desert life.

The Thar Desert near Jaisalmer, India

1. Surface grazer animals make use of water available from desert water holes and conserve it for long periods of time.
2. Desert rabbits, tortoises, and wood rats (Neotoma) eat succulent plants for their water needs and do not drink water even if it becomes available.
3. Jerboas, Kangaroo Rats (Dipodomys), pocket mice (Perognathus) and other desert rodents depend entirely on metabolic water produced in their body during oxidation of dry seeds and vegetation.
4. Carnivorous animals get required water from the bodies of their prey.
5. The skin of certain animals like sand lizards or Moloch horridus is hygroscopic and absorbs water like blotting paper.

Water Conservation

Xerocoles have developed numerous water conservation adaptations.

• To avoid water evaporation:
  • The number of sweat glands are reduced or absent.

    

    E. mingrelicus

  • Scorpions and reptiles have developed almost impermeable outer coverings.
  • Scales and spines are developed on the exposed surfaces of animals like sand lizards (such as Moloch horridus) and horned lizards.
  • The carapaces of desert insects are waxy to prevent water from escaping.
  • Camels can tolerate high temperature and can control loss of water through sweating. Water lost from their body is not from blood but from other tissues. They can lose 30% of their body weight without showing sign of distress.
• To avoid loss of moisture during evaporation:
  • Many desert animals cool exhaled air in their noses before it is expelled out through nostrils. As a result moisture condenses in the nose and is not lost as water vapor.
• To avoid loss of water during excretion:
  • This is brought about by excreting concentrated urine or urine in semisolid state. Desert rats and kangaroo rats excrete urine that contain 24% urea. The reptiles, insects, and birds excrete body waste in the form of uric acid and no water is lost.

Other methods of conserving water

• Burrowing animals come out of their burrow in late night or early morning when moisture content in their burrow and outside atmosphere is almost equal. Some animals plug the mouth of their burrow during the day.
• Some desert animals, known as drought evaders, are active only for a brief period of the year when water and food is available. The period of inactivity is called aestivation.

Protection against scorching sun

• Xerocole animals possess a thick hide or protection armor of scales, spines, or dermal scutes.
• Long legs of desert animals lift their body above the ground to avoid direct contact of the body with burning sands.
• Burrowing habits of the animals help to protect them from the scorching rays of the sun for a considerable period of time.
• Some desert animals have acclimatized to the high temperature of the desert. Beetles and lizards in general can tolerate temperatures much higher than can be tolerated by human beings.

Protection against sand storms

A camel's thick coat is one of many adaptations that aid them in desert-like conditions.

• Nostrils are either reduced to small pin holes or they are protected with complicated valves.
• In camels, nostrils can be closed in the same way as eyes are closed by eye lids.
• In sandswimming lizards, the nostrils are directed upward; this may provide a protection from clogging by wind blown sands.
• In the lizard Mabuya, an enlarged transparent lower eyelid, or nictitating membrane, can cover the eyes thereby protecting them from sand without obstructing vision. In the lizard Ablepharus, the lower eyelid permanently covers the eyes and is fused with the lower margin of the eyelid. In camels the eyes are high on the head and are protected by long thick eyelashes.
• The ear openings of desert animals, if they exist, are either small, protected by fringes, scales or hairs.

Speed

Since desert animals have to move far and wide in search of food and water, the majority of them have great speed. The limbs are specialized and adapted to walk on sand.

1. Limbs are often long.
2. Desert cats have wide soles thickly covered with fur which enables them to walk comfortably even on hot sand.
3. Legs of ostriches are padded with hair, muscular and developed.
4. Camels have extra padding on the undersurface of their feet.
5. Some lizards like Crotaphytus and Callisaurus have longer hind limb for fast running on the sandy surface.