There are a variety of ways that animals have adapted to cope with life in desert environments. Describe five adaptations, giving examples if appropriate, that animals might use to cope with high heat and low water availability

Question

What will be an ideal response?

Answer 1

Answer: In Box 10.1, coping mechanisms can be broadly divided into two categories: (1) animals that resist dehydration (e.g., better at finding water) and (2) animals that tolerate dehydration. For example, desert beetles harvest water from air in the early morning, when the temperatures are low and the water condenses on the exoskeleton. Preformed water is also trapped in solid food, such as succulent cactus, which can be eaten. Water is also produced during the metabolic breakdown of dietary macromolecules. Other animals are better at storing preformed water. Some desert insects can swell in the rainy season, increasing water content dramatically. Over the course of the dry season, the insect can use this stored water for metabolic functions, until the animal is almost completely dried up.
Most desert vertebrates cannot tolerate severe dehydration, but the camel is one exception. Camels can drink excessively when water is available, up to 100 kg in 10 minutes! Also, camels gorge when food is available, and store "metabolic water" stores as fat in the hump. When food and water are scarce, the camel can draw on water stores and degrade fat in the hump to produce metabolic water.
Many animals have behavioral adaptations to help conserve water. Many animals spend the hot daylight hours underground in the cool soil or in shade to avoid evaporation of precious water stores. Additionally, staying under rocks or in burrows allows the animal to create its own microclimate. Water loss through respiration can be trapped in the burrow, providing a humid space away from the arid air.
Some animals have evolved physiological adaptations to prevent water loss across the external surface. For example, desert amphibians and reptiles have skin with a thicker stratum corneum than do those that live in wetter habitats. Birds and mammals face the risk of dehydration through cutaneous water loss. While cutaneous water loss leads to body cooling, which is important, it also can lead to dehydration. To conserve more water, evaporative cooling is minimized by allowing the internal body temperature to rise. Stored heat can be released at night when it is cooler.
Other physiological processes, such as ventilation and excretion, also lead to water loss. It is no surprise that desert animals have modified these processes to minimize water loss. For example, some desert animals reduce respiratory water loss by passing expired air over a region of the nose equipped with a countercurrent heat exchanger. Moisture condenses out of the expired air before it escapes. The kangaroo rat is able to extract most of the water from its urine and feces prior to excretion. The camel blocks urination completely by storing urea within the tissues until water becomes available.
The above examples describe how animals resist dehydration. However, there are many animals that cope with dehydration. For example, some animals enter a state known as anhydrobiosis, in which the animal loses much of its water, and sometimes ALL free water. The animal will revive when water returns.