biomes and the physical environment temperature and precipitation determine ranges of species and...
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Biomes and the Physical Environment
•Temperature and precipitation determine ranges of species and biomes•Atmospheric circulation patterns determine climatic zonation•Whittaker and Walter plots summarize climatic data•Zonation in freshwater and marine environments
Plant geographers noticed areas with similar climates had similar looking plants, though often from unrelated families
A tree-forming cactus from Mexico (Cactaceae)
An East African spurge (Euphorbiaceae)
Leafless, thick, fleshy branches with spines have evolved to minimize water loss in unrelated plants—convergence. Cactus spines are leaf petioles and euphorb spines are stem spurs.
Climate is the major determinant of plant distribution
The distribution of sugar maple—this area has the temperature and precipitation regime that the species needs
Other maple species have different ecological tolerances and their ranges differ somewhat
Heinrich Walter’s biome classification was based on climate zones
Whittaker plotted temperature and precipitation data for each biome
At high temperatures, precipitation varies greatly
Variation in precipitation decreases as temperature decreases
Warm moist air rises in the tropics—constant rain
Hadley cells—a circulation pattern resulting from differential heating
Convergence zone—constant downwelling of cool dry air
Earth’s rotation deflects the surface flows in the Hadley cells because of the Coreolis force—rotational speed of the earth is highest at the equator
Air flowing toward the equator will be deflected west—it will be spinning more slowly than the earth and lag behind
poleward flow will be deflected east—it will be spining faster than the earth and surge forward
Clockwise circulation
Counter-clockwise circulation
Direction of spin40,000 km/d
35,000 km/d
20,000 km/d
Hadley cell pattern establishes the major deserts and rain forest zones of the world
Walter Climate diagramsAt higher temperatures plants require more water
Generally plants need about 20 mm of monthly ppt for every 10Cso the Precipitation scale interval is twice the temperature scale
When the blue line is above the orange line, precipitation is plentiful and temperature is the main determinant of plant growth
Walter plots allow meaningful comparisons among sites
Tropical rain forestBlue always above orange
DesertBlue always below orange
Tropical seasonal forestBlue below orange during dry season
Global distribution of the world’s biomes
The lake environment is structured around light and temperature
Light reaches the bottom—rooted plants
Phytoplankton are the major primary producers
little light—few rooted plants
Little wave disturbanceSediments accumulate
Climate doesn’t work nearly as well for classifying aquatic environments
The dimictic mixing pattern of temperate zone lakes
In the summer termperate lakes are stratified
Epilimnion—warm mixed layer,
Hypolimnion—cold lower layer
In the winter the lake is inversely stratified
The spring and fall are mixing periods, water column 4oC
Thermal stratification allows both warm and cold water species to coexist
Ecological zones in the ocean
Light, the continental shelf, and tides contribute to marine zonation
The intertidal zone is exposed to air regularly when the tide recedes
Coral reef are found in shallow well lit seas—highly productivesystems
The major ocean currents are driven by winds and the earth’s rotation
Upwelling zones occur mainly on the western sides of continentsSurface waters are drawn towards the equator and away from the continent by the coreolis force—this draws deep nutrient-rich water upward
The major ocean currents “gyres” generate zonation in temperature and productivity
A satellite image showing the gulf stream, a clockwise current in the North Atlantic
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