Desert Ecology: Fascinating Facts

Deserts may be dry and even desolate but they are certainly not barren. These biologically rich biomes possess life-forms and ecosystems beyond your wildest imaginations! Here are 10 fascinating facts about our deserts:

1. The Yucca Plant and the Yucca Moth: A Specialized Relationship

Specific relationships between species can directly determine their very existence. Relationships between plants and their pollinators are sometimes extremely exclusive in which a plant relies solely on one other species to carry out pollination. The relationship between the yucca plant and the yucca moth (Tegeticula) is a remarkable example of such a specialized relationship.  Yucca moths depend on yucca flowers to lay their eggs. After hatching, larvae feed partially on yucca seeds causing many seeds to drop to the ground. The moth not only lays her eggs in the flowers but also gathers pollen, which she rolls into a ball and carries to other yucca flower stigmas where pollination occurs. Without this mutual relationship neither the moth nor the yucca plant could survive.

2. Desert Sandy Soils Are Extremely Complex

Without biological constituents, sandy desert soils would simply be blown away by the wind and although there are deserts with shifting sandy dunes, some deserts rely on soil crusts to remain intact. Most soil types rely on an abundance of microorganisms for their formation. Desert soils are no different. Millions of cyanobacteria, also known as blue-green algae along with other microorganisms form structures that produce microphytic crusts. Cyanobacteria, fungi and lichen act as binding material creating relatively strong web-like soil networks which retain not only its physical form but important nutrients as well. These soil crusts are an important contribution to many desert plant and animal life.

3. Desert Plants “Play” Dead

Walking through a desert you may wonder how plants can possibly exist in such a dry and desolate environment. You may even notice several plants that appear to be dead or dying. However, desert plants have evolved many ways to tolerate and even avoid extremely hot and dry conditions. Drought tolerant plants tend to have very small leaves and stems which decrease surface area and often produce waxy or resinous coatings which prevent excessive water-loss. The candelilla (Euphorbia antisyphilitica) is an example of a plant that produces waxy stems. Plants also have developed ways to avoid drought by dropping their leaves when conditions are less favorable. Some plant species can withstand long periods of desiccation and remain in a state of dormancy for many years. This state of dormancy allows the plant to significantly slow its metabolic activity. The resurrection plant (Selaginella lepidophylla), a fern-like moss, is a wonderful example of this amazing adaptation. It can re-hydrate and resume full metabolic activity just within a few hours of receiving rain, going from a seemingly dead brown cluster to a fully expanded and bright green plant. So next time you take a walk in a desert landscape, be sure to watch your step, the dead-looking plants just beneath your feet may simply be sleeping.

4. Fairies Live in the Desert

Not only can plants withstand long periods of desiccation but some animals can as well. One tiny creature, the fairy shrimp measuring around less than an inch, can remain as encased embryos called cysts, totally dehydrated and inactive for many years and in some cases decades in dry lake beds. These cysts require water to hatch but not just any rain will do. The reanimation of these embryos requires near freezing temperatures accompanied by rain or snowmelt. Only then will fairy shrimp be shaken from dormancy. The lifespan of fairy shrimp is very brief and they can take as little as 18 days to develop depending on the species. Almost immediately after mating, cysts begin to develop within the female brood pouch. When fully formed, the cysts will settle to the bottom the pool where they will await in suspended dormancy, until next year’s rains.

These temporary or “ephemeral” pools are often located in very remote areas, far from any other permanent water body sources. Migratory birds will occasionally land in desert lakes carrying with them cysts of fairy shrimp on their feet from surrounding water bodies. Dispersal of fairy shrimp is not always possible due to the remoteness of desert pools. Interestingly, studies have shown entirely isolated genetic pools from one small body of water to another which indicates fairy shrimp cyst dispersal is not common.

5. An All-Female Lizard Species

Of the many adaptations desert animals possess, none may be as unique as the all-female whiptail species. Whiptails are a lizard species belonging to the Aspidoscelis genus. The Checkered Whiptail (Aspidoscelis tesselata) is an example of a whiptail species comprised of only females. These whiptails can reproduce successfully without the assistance of male fertilization reproducing by a process called parthenogenesis. Parthenogenesis results in essentially twinned or clonal offspring. Clonal reproduction usually results in reduced genetic richness. However, checkered whiptails can produce offspring without genetic weaknesses and can maintain genetic richness. In most cases genetically similar offspring would make a species vulnerable to mutation and disease. Female-only whiptails avoid this by beginning the process of reproduction with double the amount of chromosomes. This allows for greater variability in the genes of their offspring.

Though mating is not required for these lizards to reproduce, female parthenogenetic whiptails may still mount other females, a behavior believed to bring about ovulation. Scientists believe female-only whiptails were not always without males which may also account for the mounting behavior; but since evolving a greater number of chromosomes males were no longer needed for the species to thrive and eventually died off.

6. Millipedes are harmless, but they secret cyanide…

The Desert Millipede (Orthoporus ornatus) is a large, docile millipede species found throughout North America. Depending on the species, the color of millipedes can range from a dark gray, brown or tan. Millipedes have cylindrical, segmented bodies with two pairs of legs per segment. They can grow as long as 6 inches in length.

While millipedes are extremely docile creatures they possess a very unpleasant defense weapon. When threatened they may simply roll themselves into a tight coil, but if provoked further they can secret a liquid containing cyanide which can be extremely irritating for predators.

7. Not All Deserts Are Cold

Desert biomes are classified by the amount of rain they receive. An ecosystem that receives less than 10 inches (25 cm) of rainfall per year and in which the rate of evaporation exceeds precipitation is considered a desert.

While deserts are usually perceived as hot environments, there are deserts that remain cold year round. The Gobi desert, located in Asia, is an example of a cold desert. Another cold desert is Greenland, an Arctic desert that receives as little as 25 mm of precipitation each year. Most people are taught the largest desert is the Saharan desert when in fact Antarctica, a cold desert, is the largest desert in the world.

8. Nurse Plants

A nurse plant is a plant with an established canopy under which other plant species may germinate and become established. Nurse plants provide suitable micro-environments for seedlings by providing shade, moisture and even nutrients. This form of ecological facilitation is important for the survival of many plant species. The nurse plant association can occur in many types of ecosystems with vegetation though it is a commonly associated with desert biomes. A very important desert nurse plant is the Creosote Bush (Larrea tridentata), without it many Cholla Cacti (Cylindropuntia sp.) would not survive. While some succulents can only be found in microhabitats at the base of nurse plants, some young plants may continue to grow so large that they begin to compete with the very nurse plant that fostered it. This competition for natural resources often results in the nurse plant’s death.

9. Atacama Desert

The Atacama Desert in Chile may be the driest place on earth. This mountainous region situated next to the Pacific Ocean extends high into the Andes Mountains. The Atacama Desert receives an average of less than .004 inches (.01 cm) of rainfall each year. And in some parts of the Atacama rain has not been recorded in 400 years! However, in higher elevations the area does receive snow which can remain for long periods of time because it rarely gets warm enough to melt. Despite its lack of rainfall, the Atacama does have groundwater and since the region is volcanically active, eruptions can cause geysers in certain areas. Fog and dew also exists in the area which local residents can collect water from as it condensates. For creatures living in the Atacama Desert the moisture from fog and dew may be all the moisture they will ever use to survive. On March 25, 2015 however, the Atacama Desert received an unusual 14 years worth of rain in just one day as a result of the effects of El Niño.

Ancient Chinchorro people of the Atacama Desert began mummifying their dead 2,000 years before Egypt. And though they followed certain preparations for mummification and burial, bodies would began to mummify naturally after death due to the lack of moisture in the region.

10. The Oldest Living Organism on Earth

Creosote Bush (Larrea tridentata) is one of the most common plants in the North American deserts. The Creosote bush has a remarkable ability to withstand drought by producing resinous leaves and super-efficient root systems. These fibrous roots are masters at intercepting water both at the surface and deep within the ground. The Creosote bush can also produce clonal colonies. New shoots grow from beneath the ground at the edges of root crowns, gradually extending away from the parent plant. This can result in a ring of Creosote Bushes. While these plants may be separated from one another they all share the same genetic makeup.

Creosote bush in general can live for hundreds of years. A large clonal colony of Creosote bushes was discovered in the Mojave Desert of Arizona in the 1970’s. Curious scientists analyzed the ring of creosotes and discovered each plant shared the exact same genetic makeup. With further investigation, carbon-dating revealed the individual to be around 11,700 years old, making it the oldest known living organism on Earth. Biologists named the ancient creosote “King Clone” in honor of its extraordinary feat of nature.

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