Chapter 6: Biogeography

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Chapter 6 Biogeography

• Climate, Biomes, and Terrestrial Biodiversity

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6.1 Weather and Climate Brief Introduction

• Weather is a short-term atmospheric conditions in
  an area.
• Temperature
• Humidity
• Precipitation
• Sunshine
• Cloud cover

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6.1 cont.

• Due to the uneven heating of the earths surface,
  masses of air that are (1) warm or cold, (2) wet
  or dry, and (3) contain air at high or low
  pressure are constantly moving across the land
  and sea.
• Weather is most dramatic along the boundaries
  between these air masses - fronts

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6.1 cont.

• Warm front boundary between a warm mass of air
  and the cooler air it replaces. Often results in
  cloudy, rainy days
• Cold front advancing mass of cold air that
  stays close to the ground. It is often
  associated with thunderstorms and high winds.
• Jet streams near the top of the troposphere and
  circle the Earth. Have strong influence on
  weather patterns.

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6.1 cont.

• Changes in atmospheric pressure also affect
  weather.
• Atmospheric pressure is greater near the earths
  surface.
• High-pressure air mass contains cool, dense air
  that warms as it descends fair
• weather
• Low-pressure air mass produces cloudy, stormy
  weather. Can result in rain

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6.1 cont.

• Tornadoes and tropical cyclones are extremes of
  weather that cause much damage. Tornadoes form
  over land, and tropical cyclones form over warm
  ocean waters. Tornadoes are most prevalent in
  the U.S. and Australia.

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6.1 cont.

• Tropical cyclones are formed by low-pressure
  cells of air moving over tropical warm seas.
• Atlantic Hurricanes
• Pacific Typhoons
• Hurricanes can flush out excess nutrients from
  land runoff, dead sea grasses, and rotting
  vegetation from coastal bays and marshes. This
  can increase productivity of shellfish and fish
  and reduce algal growth.

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6.1 cont.

• Climate is a regions general pattern of
  atmospheric or weather conditions over a long
  period of time.
• Two major factors
• Average temperature
• Average precipitation

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6.1 cont.

• Climate is ultimately determined by the amount of
  incoming solar energy per unit area of land, air
  circulation over surface of the earth, and water
  circulation.

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6.1 cont.

• Four major factors determine global air
  circulation patterns
• Uneven heating of the earths surface. Equator
  is heated more than the poles due to the angle of
  the suns rays on different parts of the Earth
• Seasonal changes in temperature and precipitation
  due to the tilt of the Earth

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6.1 cont.

• 3. Rotation of the Earth on its axis results in
  the Earth moving faster beneath air masses at the
  equator and slower at the poles. This creates
  belts of prevailing winds. Coriolis effect

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6.1 cont

• 4. Properties of air, water, and land. Heat
  from the sun evaporates ocean water and transfers
  heat from the oceans to the atmosphere creating
  cyclical convection cells that transport heat and
  water. This leads to different climates and
  patterns of vegetation.

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6.1 cont.

• Ocean currents and winds influence climate by
  redistributing heat received from the sun from
  one place to another.
• Differences in water density and heat create
  ocean currents that are warm or cold
• Currents redistribute absorbed solar heat from
  one place to another and influence vegetation and
  climate near coastal regions

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6.1 cont.

• Currents also help mix ocean waters to distribute
  nutrients and dissolved oxygen needed for aquatic
  organisms
• Winds moving away from coastal regions result in
  upwelling of cold, nutrient-rich bottom waters as
  surface water moves offshore. These nutrients
  support large populations of phytoplankton,
  zooplankton, fish, and fish-eating sea birds.

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6.1 cont.

• El Niño and La Niña are changes in climate
  patterns that can trigger mild to extreme weather
  changes over at least ? of the globe.
• El Niño/Southern Oscillation (ENSO) results from
  a change in direction of tropical winds. Trade
  winds blowing west are weakened or reversed.

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6.1 cont.

• Surface water warms along the North and South
  American coasts, and upwelling of nutrients is
  suppressed, which reduces primary productivity
  that results in sharp decline of fish population.
  
• Jet stream above North America is also distorted,
  changing weather patterns.

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6.1 cont.

• La Niña cools some coastal surface waters and
  brings back coastal upwelling. This results in
  warmer, drier winters in the southeastern and
  southwestern U.S., wetter winters in the
  Northwest.
• Typically a La Niña causes more destruction in
  the U.S. because there are more Atlantic coast
  hurricanes and tornadoes.

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6.1 cont.

• Gases such as water vapor, carbon dioxide,
  methane, and nitrous oxide play key roles in
  determining the earths average temperatures and
  climates.
• Greenhouse gases
• The alteration of these gases by humans could
  lead to the alteration of precipitation patterns,
  sea levels, and crop growing areas

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6.1 cont.

• The ozone layer is created 11-16 miles above the
  earths surface due to reactions initiated by UV
  radiation that convert oxygen(O2) to ozone(O3)
  and back to oxygen. This thin layer of ozone
  blocks out 95 of the suns harmful UV radiation

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6.1 cont.

• Various topographic features can create local and
  regional climates different from the general
  climate of a region - microclimate
• Rain shadow effect
• Cities often have warmer temperature and less
  winds than the surrounding countryside.

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6.2 Biomes Climate and Life on Land

• Different climates lead to different communities
  of organisms, especially vegetation.
• Scientists divide the world into 12 major biomes.
  Based on
• Average annual precipitation, temperature, and
  soil type
• Biological communities unique to each biome
• Latitude and altitude

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6.2 cont.

• Why do Plant Sizes, Shapes, and Survival
  Strategies Differ?
• Succulent Plants
• Broadleaf Evergreen Plants
• Broadleaf Deciduous Plants
• Coniferous Evergreen Plants

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6.3 Desert Biomes

• A desert is an area where potential evaporation
  exceeds precipitation. (lt10 inches)
• Sparse, widely spread drought-resistant
  vegetation
• Found in all regions but mainly situated in
  tropical and subtropical regions
• Found in the interior of continents or from rain
  shadow effect

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6.3 cont.

• Three classes of deserts
• Tropical desert temperatures usually high
  year-round and little rain. Ex. Sahara
• Temperate desert Daytime temperatures high in
  summer and low in winter, more precipitation than
  tropical desert. Ex. Mojave
• Cold desert Winters are cold and summers are
  warm or hot. Ex. Gobi

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6.3 cont.

• Semi-deserts are intermediate between desert and
  grassland and dominated with thorn trees and
  shrubs adapted to long dry spells, with brief
  periods of sometime heavy rain.