Presentation on theme: "Desert. General definition deserts are areas that receive less than 25 cm of precipitation in one year and have little or no vegetation."— Presentation transcript:
General definition deserts are areas that receive less than 25 cm of precipitation in one year and have little or no vegetation.
Location 30° latitude
Though some receive a fair amount of rainfall, it is not evenly distributed throughout the year. Flash floods are common in some desert areas. The resulting water runs off, and doesn’t soak into the ground.
Water in deserts is also lost through evaporation. Many deserts have little cloud cover, so that 90% of the sun’s rays reach the Earth, resulting in extremely hot temperatures. When it is that hot rain will often evaporate before it hits the ground.
While it is hot during the day, the lack of cloud cover has the reverse effect at night, where the temperatures will be much colder (up to 50 degrees difference).
This hot/cold affect in the deserts also creates a lot of wind. Movement of hot, dry wind increases evaporation.
There are hot deserts, like the Arizona’s Sonoran or the Sahara in Africa. These are closer to the equator. Main form of precipitation is rain (10 inches or less)
There are also cold deserts like the Gobi in China and the Great Basin of the western United States. Main precipitation is snow!
All deserts share the following characteristics: 1.Seasonally hot temperatures 2.Spotty precipitation 3.High rate of evaporation 4.Strong winds
Deserts occupy approximately 20% of the Earth’s land area. Of this, only 10% are sand dunes.
There are four types of deserts, based on the conditions that created them
Subtropical: these are located at 23 N latitude and 23 S latitude. An example is the Sahara desert, which is about the size of the United States
Coastal: in these areas humidity may be high, but there is little or no rainfall. Examples are the Atacama of Chile and the Namib in southern Africa.
Interior: these are located far inland from ocean winds, and have very dry air. The Gobi desert in Asia is an example
Rain shadow: these are formed when you have a mountain range next to a moist, coastal area. The mountains block movement of moisture-filled clouds, which limits precipitation. This is called the rain shadow effect
9. Label the diagram
In the United States the Mojave desert is a rain shadow desert. One national park located in this desert is Death Valley National Park. It has the lowest point in the United States, 282 feet below sea level. The highest maximum temperature measured here was 134 F
Vegetation in the Mojave desert is predominantly low, widely spaced shrubs. 25% of the plants are endemic, or native to that area. One of the most striking in appearance is the Joshua tree. A dominant species is the creosote bush, which is often associated with bur sage plants Plants
Worldwide deserts are growing at an alarming rate. This process is called desertification, when land that used to support life is transformed into desert with little or no life
Deserts of N. America
Plant Adapations Thick, fleshy stems and leaves that store water Waxy coating - prevents water loss Sharp spines - protection Shallow, spread root systems
Some well-adapted desert animals include the Gila monster and rattlesnakes. Their thick and scaly skin prevents water loss
One great adaptation is that of the spadefoot toad. They survive the hot summers by estivating, or burying themselves in the ground and waiting for cooler conditions
Without trees to nest in, birds may build their nests in cactuses to avoid predators
Insect adaptations include body armor to retain water
The most common adaptation for survival in the desert is avoidance. Most desert animals are nocturnal, or only active at night. That keeps them out of the day’s heat.
THINK ABOUT THESE……
They may stay in burrows or, like the case of the pack rat, build elaborate dens from desert litter that may be up to 3 feet high and 8 feet across. Inside the pile is a series of tunnels and a nest lined with soft plant fiber
Some animals create their own shade, such as the white-tailed antelope squirrel. These rodents look for seeds, fruits and insects during the day and use their bushy tail like a parasol over their backs
Larger mammals cannot hide in burrows but will seek out shady spots during the day. They have the advantage of large body size. A large body will heat up more slowly than a small one (think of how long it takes to boil a large pot of water versus a small pot)
Birds have a higher body temperature than mammals, and can release heat through their legs. This same ‘radiator’ technique, dilating blood vessels near surfaces, is found with the long ears of a jackrabbit
The primary method for cooling down a bird or mammal is evaporative cooling
Coyote Panting -, air moves quickly through the nose and mouth where it removes excess heat
Owl Gular fluttering - A cooling behavior in which birds rapidly flap membranes in the throat to increase evaporation
Vulture Urinates on it’s legs
Sheep and other mammals Evaporative cooling of the nasal passages, which cools blood vessels to the brain
Kangaroo Rat - has both physical and behavioral adaptations Hairy soles on their feet - aid in jumping in loose sand Short fore feet with sharp claws Get their water from the seeds that they eat Specialized kidneys