Post on 23-Feb-2016
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Desert and Tundra Biomes
Chapter 7
7.1 Deserts
ObjectivesDescribe the characteristics of a desertExplain how desert organisms adapt to live in their environment
Deserts are different, but they all receive very little rain.
Deserts continued
Desert soil–Rich in minerals–Poor in organic materials–Very little leaching
Leaching a process where rainwater moving through soil carries minerals deeper into the soil– Little rain -> little leaching -> upper desert soil rich
in minerals
Deserts continued
Lack of rainfall makes deserts dry–Prevents many plants from living there–Slows decay of organic material–Not much topsoil–Soil easily blown away
• Exposing the Pavement
Pavement
The lower layer of the desert soilIt is the desert floorMade mostly of –Hard-baked sand–Bare rock particles–Or both
Types of Deserts in the US
Cool Deserts - Sagebrush–On eastern side of the mountains in western US
Hot Deserts - Cactus– In the southwest:
• Arizona, • New Mexico and • western Texas
Desert Climate
Lack of precipitation is the limiting factorLess than 25 cm per year, most less than 10 cm–Determines the types of plants
• Determines the types of animals
Most rain during a few short stormsMost water runs off due to compacted pavement
Desert Temperature
Varies GreatlyMoisture helps to stabilize temperature– Acts like a blanket– Absorbs heat in day– Holds in warmth at night
Without this moisture, desert temperature rise and fall dramatically within 24 hour periods
Desert Biome Video
Desert Organisms
Must be adapted to survive with– Lack of water– Extreme temperatures
Despite these challenges, deserts are actually species-rich complex ecosystems
Desert Plants
They Must– Be able to absorb scarce water from ground– Prevent water loss form tissues
• Cactus spines (leaves) reduce water loss by reducing surface area
Succulents – have thick water filled tissue (cacti, aloe vera)– An attractive source of food and water for desert animals– Spines also help protect from being eaten by animals
Desert Plants continued
Another adaptation is the rootsSome shallow but covering a wide areaOthers grow very deepBoth help to maximize the amount of water they can get
Desert Animals
Many typesMost get water from their foodMost have adaptations to help reduce water lossAlso adaptations to survive the heat– Many are nocturnal – active at night, sleeping during
the heat of the day
7.2 Formation of Deserts
ObjectiveIllustrate the processes that cause deserts to form.
Natural Desert Formation
Two broad belts of deserts– Northern one near Tropic of Cancer– Southern near Tropic of Capricorn
Around the equator (tropics) very moist airAfter moisture has fallen as rain air becomes dryThen flows towards poles becoming cooler and heavierSinks back to earth as dry winds forming deserts
Rainshadow Effect
Exact locations are determined by local geographic features such as mountainsIn U.S.– Winds move from west to east– Forces warm moist air over mountains– Drops moisture on mountains– Cool dry air reaches eastern side– Picks up moisture from soil– Soil becomes very dry forming desert
Life in the Desert Video
Desertification
Deserts often bordered by semiarid regions with grasses and shrubsHuman activity (raising livestock) has caused these semiarid regions to become desertsThe process of changing semiarid land into desert as a result of human activity is called desertification
Human Impact on the Desert
7.3 Tundra
ObjectivesDescribe why the characteristics of the tundra make it a fragile ecosystemCompare the characteristics of tundra organisms with those of their relatives in warmer climates
The tundra is a cold , windy, dry region.
Tundra Facts
In northern hemisphere just south of polar ice caps in Alaska, Canada, Greenland, Iceland, Norway and AsiaA large biome –10% of Earth’s surfaceFewer types of organisms than any other biomeLack of diversity makes them fragile and unstable
Tundra Video
Tundra Climate
Like a desert little precipitation– Less than 25cm per year
A cold climate–Usually below 10 degrees Celsius
Most precipitation falls as ice or snowTemperature is the limiting factor
Permafrost
Only the top layer, or active zone, of soil thaws in summerThe active zone may be as thin as 8 cmThe frozen soil beneath the active zone is called permafrostA dense mat of mosses, grasses, and other plant life keeps the ground insulated and prevents the permafrost from meltingAny disruption of this mat affects the permafrost
Tundra Climate continued
Tundra vegetation does not recover from disruption as quickly as in other biomesRain in summer cannot penetrate the permafrostWater collects forming bogs,, marshes, ponds, and streamsCreates a great breeding ground for mosquitoes and black flies (an important link in the food web)Permafrost is therefore important to the stability of a tundra ecosystem
Tundra OrganismsPlants–Short growing season–Small and close to ground–Ground warmed by radiant energy–Roots close to surface–Small trees (less than 1 meter)–Lichens are very important producers
Tundra AnimalsSeasonal visitors (migrate south for winter)Safe place for breeding due to less predatorsBirds feed on mosquitoes and fliesPredators feed on birdsCaribou- large migratory mammal– Thick coat big hooves– Feed on lichen
Fox, Bears, Wolverines don’t migrate
The End