I. Characteristics of Deserts Cover 30% of Earth’s surface Found on every continent except Antarctica Most lie between desert belts on either side of the equator –Northern belt deserts are near the Tropic of Cancer (23 degrees N) –Southern belt deserts are near the Tropic of Capricorn (23 degrees S) Not all deserts are alike. All have very little rainfall annually. Very few organisms can survive there due to lack of rainfall and extreme temperature

Two types of Deserts: resulting from variations in elevation and latitude affecting their summer and winter climates. –Hot Deserts- located in the southwest (Arizona, New Mexico and western Texas) –Cool Deserts- located eastern side of Sierra Nevada and the Rocky Mountains

II. Desert Soils Rich in minerals due to lack of leaching –Leaching- when rainwater moves through soil carrying minerals deeper into the soil Lack of leaching due to lack of rainfall Poor in organic matter Due to lack of precipitation which slows the decaying process of organic material Also due to lack of rainfall there is a limited amount of organisms living in the desert Not much topsoil Because decaying organic material is important in the makeup of topsoil

Very thin top layer of soil Easily blown away because it’s dry and loose exposing the desert floor –Pavement- the exposed desert floor after the upper loose layer of soil has been blown away Mostly made-up of hard baked sand, bare rock particles or both

III. Desert Climates Rarely receive more than 25 cm of precipitation annually Precipitation is Limiting Factor –Determines plant organisms which in turn determines animal organisms Most deserts receive less than 10 cm of rain per year –Most rainfall occurs during a few short thunderstorms –Followed then by a long dry period –Rainfall that does fall tends to runoff rather than be absorbed due to dry compacted pavement

Lack of moisture affects temperatures –Moisture in atmosphere has stabilizing affect on temperature Acts as blanket, absorbing heat during the day and holding in heat during the night –Because so little moisture, deserts have extreme temperatures Very hot days and very cool nights

IV. Desert Organisms Must be adapted to survive two challenges: lack of water and extreme temperatures Despite great challenges, deserts are species-rich, complex ecosystems

A. Desert Plants Must be able to absorb water from the ground Must prevent loss of water from their tissues –Spines: leaves of plants Familiar adaptation reducing water loss by reducing surface area from which water can evaporate Protect plants from organisms that would harm their tissues Most common type of plants are cacti –Succulents: plants like cacti having thick, water-filled tissues Allows them to live longer off stored water Makes them an attractive source of food and water for desert animals –Cacti are only native to American continents but deserts in other parts of the world still have succulents Aloe Vera: succulent native to Africa

Shallow root systems show adaptations to dryness –They grow over wide area absorbing rainfall as it runs off Other plants have root systems very deep –Absorbing water from 20 m deep

B. Desert Animals Home to many types of animals –Insects, reptiles, birds and mammals –No amphibians Most get their water from their food Face challenge of reducing water loss –Most insects and reptiles have coating (shells and scales) to reduce water loss –Covering helps them survive dry, hot climate Face challenge of surviving heat –Adaptation to this challenge is burrowing where they spend their days in underground burrows –Most are Nocturnal Sleep during the day and are

V. Formation of Deserts Natural Desert Formation: –Result of cool, dry winds moving toward the poles from the tropics Tropics- wet region between the Tropic of Cancer and the Tropic of Capricorn –In the United States most winds move from west to east Semiarid- region that is dry but not as dry as a desert able to support small grasses and shrubs Rainshadow effect- drying of the eastern side of the mountains Desertification: –Transformation of semiarid land into desert Can begin with too many animals grazing on too little land. They eat all the vegetation and compact the soil

VI. Characteristics of Tundra Cold Dry Windy One of the largest biomes Makes up almost 10% of Earth’s surface Fewer types of organisms live in the tundra than any other biome –Lack of biodiversity –Very fragile and unstable ecosystem if disturbed Summer growing season last only about 60 days Located in Northern hemisphere…just south of the polar ice caps in Alaska, Greenland, Iceland, Scandinavia and Russia In the Southern hemisphere…what would be the tundra is covered by oceans

VII. Tundra Climate Receives very little precipitation like deserts –Less than 25 cm annually Difference between tundra and deserts is temperature –Air temperature rarely reaches above 10 degrees Celsius (even in summer months) –Due to below freezing temperatures most precipitation falls as ice or snow –Temperature is Limiting Factor in the Tundra

VIII. Tundra Soil Due to temperatures only the top layer, or active zone, of soil thaws during the summer. –May be as thin as 8 cm –Poor in Nutrients Beneath the active zone is soil that never thaws –Permafrost- frozen soil below the active zone Insulated by dense mat of mosses, grasses and other plant life growing in the active zone Keeps it from melting Rain that falls during the summer months cannot drain through the permafrost so it collects at the surface forming bogs, marshes ponds and small streams –Breeding grounds for insects such as mosquitoes and black flies

VIIII. Tundra Organisms Plants: –Most common are mosses, shrubs, grasses, and small colorful wildflowers –Root systems grow very close to the surface because they cannot penetrate the permafrost –Trees that grow there are usually less than I m tall and more like shrubs –Dwarfed by short growing season, limited space for root growth and strong polar winds

Animals: –Many are seasonal visitors Migration- seasonal travel from one area to another –Fewer predators –Migratory birds flock here during their breeding season and feed on the abundance of insects –Birds are in turn prey for few migratory predators such as artic fox Which hunts them during the summer buries them in permafrost and then eats them during long winter –No reptiles or amphibians –Small herbivores are common such as –Large migratory herbivores are common as well like the caribou a close relative to the reindeer which feed on lichen –Mammals of the tundra have thick coats filled with air acting as a insulator and wide hooves –Permanent members of the tundra: musk oxen, coastal polar bears and wolverines