Desert Environments

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Desert Environments
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What is a desert?

• Water - predominant controlling factor of
  biological processes.
• Precipitation is highly variable
• Variation in precipitation has a large
  unpredictable component.
• Where precipitation 1/2 the potential
  evaporation.

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Causes of deserts

• Dry air dropping at 30º latitude
• Cool coastal deserts (Baja, Atacoma of Chile
  Peru, Namib) add the cool coastal water.
• Rain shadow effects

30º
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Physical factors insolation

• Dry air and low, sparse vegetation - high of
  suns rays hit the ground directly.

• Ground reradiates energy
• Color of soil
• Night radiation continues
• Large fluctuations in temperature.

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Subtropical deserts

• Mediterranean climate
• Cooler winter temperature
• Typically at 300 - includes the Sahara, Arabian,
  Sonoran in the northern Hemisphere and the
  Australian, Kalahari (So. Africa) in the southern.

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Subtropical deserts

• Poleward boundaries of subtropical boundaries
  begin to blend with high deserts.
• Polar air masses
• Winter precipitation - summer drought
• In No. Hemisphere, polar air masses may drop
  temperatures below freezing.

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Continental Interior

• Away from maritime influence. May be influenced
  by rain shadow.
• Winter - high pressure region
• Winter precipitation often as snow - from fronts.
  
• Summer precipitation spotty and low.

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Cool, Coastal Deserts
Atacoma

• Similar locations to those of subtropical deserts
• Often due to upwellings (15-18ºC).
• Thin layer of air is affected by water
  (temperature inversion).
• No rain since low volume and inversions prevents
  convectional rise.
• Fog develops in 3 situations
• At coast when temperature drops
• 16-40 mi. inland nocturnally
• Seaward Mtn. slopes

Atacoma
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Heat transfer
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Water Gain and Loss

• Sources of water
• Oxidation water
• Food
• Drinking Water
• Loss of water
• Evaporation from lungs
• Evaporation from skin
• Water in feces
• Water in urine

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Adaptations to Desert Environments

• We will consider adaptations made by plants and
  animals to desert conditions such as
• High light
• High temperatures
• Fluctuating temperatures (day/night)
• Dry air - with somewhat random rain events
• Dry soil
• Lack of cover for protection from predators

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Plant Adaptations

• Three Major strategies
• escape drought

High variability rainfall - annuals 96 of
flora Low variability rainfall - 1 of flora
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Adaptations (cont)

• evade drought

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Adaptations (cont)

• tolerate drought

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Animal Adaptations

• Escape heat drought
• Aestivation
• Diapause
• Migration
• Retreat

Fairy shrimp
Phainopepla
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