Deserts are characterized by environmental stresses of low and unpredictable precipitation, low relative humidity, dessicating winds, and high summer temperatures. These factors, combined with low nutrient availability, severely limit plant growth. However, desert communities often contain a surprising amount of plant biomass and diversity despite the relatively harsh environmental stresses (Rundel and Gibson 1996). Most organisms in desert ecosystems evolved in response to 2 main factors: high and fluctuating temperatures and extremely low water availability. A xerophyte is a general term that describes desert adapted plants (Armstrong 1997).

Here's a list of some common adaptations seen in desert plants:

1. Enhanced cuticle, a waxy covering, which prevents water loss.

2. Long vertical roots enabling a plant to reach water sources beneath the soil.

3. Shallow, radial roots, those which extend horizontally, which maximize water absorption at the surface.

4. Tricombs, hair-like projections, that create a thick boundary layer which will deflect heat as well as IR wavelengths.

5. Spines and hairs which discourage herbivores and increase boundary layer effects.

6. Increased vacuoles (see diagram below) in both size and number which allow for the accumulation of C4 acids (see Crassulacean Acid Metabolism).

7. Small and narrow leaves which decreases heating from the sun.

8. Rotating leaves which enable the plant to orient its leaves away from maximum exposure to the sun.

9. Crassulacean Acid Metabolism.

10. Ephemeral life history strategies in which plant activity is limited to periods that are optimal for growth and development, i.e. after a heavy rain (see diagram below).

11. Recessed and reduced stomates which decreases water loss.

12. Succulent leaves (see diagram below) which reduce the surface-to-volume ratio and favor water conservation.

13. Leaf polymorphism in which broad leaves are formed when soil moisture is high and narrow leaves follow as that water is used up.

14. Increased surface area which increases the rate of heat dissipation.
 

Animalia
 

Extreme temperature fluctuations and water shortage are the primary forces that animals experience on a daily basis in the desert. However, animals have the ability to alter their internal environment and possess a plethora of possible behavioral and physiological adaptive strategies.

Here's a list of some common behavioral/physiological and morphological adaptations seen in animals of the desert.
 

Behavioral/physiological
 

1. The use of burrows (see diagram below) is very common to many different mammals, insects, and birds in the desert. The advantages of utilizing a burrow is that the organisms are exposed to little or no sunlight. Therefore cooling strategies that use water such as sweating, panting, etc. need not be employed, and water is thus conserved. Also, some species of rodents purposely pant inside the burrows in order to make the water available for a second round of consumption (Rundel and Gibson 1996).

2. Use of shady micro-habitats is similar in function to burrows in that they enable an organism to reduce overall exposure to high light and temperature levels.

3. Excretion on the feet or legs which evaporates and then cools the organism as the excretion evaporates, known as urohydrolysis.  This is a common adaptation in birds such as turkey vultures.

4. Nocturnal activity reduces the amount of exposure to light and heat extremes.

5. Migration to other areas, i.e. where water is more abundant or temperatures are cooler.

6. Gular/tongue fluttering; a cooling method.

7. Body "acrobatics" in which body positions are altered in order to reduce surface contacting the hot surface or to increase surface area where moisture may be collected from morning fogs common to many desert mornings.  This beetle is collecting moisture falling from a thorny branch in the Namib Desert.

8. Toleration of temperature changes where the organism's internal temperature rises and falls along with outside temperatures is another adaptation to extreme environmental changes. This conserves water that would be lost with sweating or panting.

9. Efficient kidneys which shunt water from waste products, resulting in water conservation.

10. Hibernation/estivation during the hotter and/or cooler times of the seasons.

Morphological

1. Coloration is thought to be an important factor in the reduction of heat absorption. That is, a lighter colored coat will reflect more light relative to a darker coat which will absorb more light. The result is reduced body temperatures and more water conservation.

2. Enlarged appendages in order to increase surface area and hence promote heat loss. This is commonly referred to as Allen's Rule (see figure below).

3. Insulation in the form of feathers, hair, or even body fat which protects tissues beneath by insulation.