BIOL450 Lecture Notes - Intertropical Convergence Zone, Alpine Tundra, Cool Air
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Chapter 52: Ecology and the Distribution of Life
52.1: What is Ecology?
•Ecology: scientific study of the rich and varied interactions between
organisms and their environment.
•Communities: embracing all the organisms living together in the same area
•Ecosystems: embracing all organisms in an area plus their physical
•Biosphere: system that embraces all regions of the planet where organisms
•Environment: encompasses both abiotic and biotic factors
52.2: How are Climates Distributed on Earth?
•Climate of a region is the average of the atmospheric conditions found over a
•Weather is the short-term state of those conditions.
•Climates vary greatly because different places receive different amounts of
Solar energy drives global climates
•Every place on Earth receives the same total number of hours of sunlight but
not the same amount of solar energy; this depends primarily on the angle of
•Higher latitudes experience greater variation in both day length and the
angle or arriving solar energy over the course of a year = greater seasonal
variation in temperature.
•Air temperature decreases with elevation: when air rises, it expands, its
pressure and temperature drop, and it releases moisture; when a parcel of air
descends, it is compressed, its pressure rises, its temperature increases, and
it takes up moisture.
•Global air circulation patterns result from the global variation in solar energy
input and from the spinning of Earth on its axis.
•Air rises when it is heated by the sun and is replaced by air that flows in
toward the equator from the north and south produces the intertropical
•Cool air cannot hold as much moisture as warm air, so heavy rains fall in the
intertropical convergence zone.
•Air that moves into the intertropical convergence zone to replace the rising
air is replaced by air from aloft that descends at roughly 30N and 30S. It noẘ ̊
descends, warms, and takes up moisture. (Earth’s deserts such as the Sahara
and Australian deserts are located here).
•At about 60N and 60S, air rises again and moves either toward or away from̊ ̊
•At the poles, air descends.
•Spinning of Earth on its axis influences surface winds. As air mass moves
toward equator, it encounters an increasingly faster spin, and its rotational
movement is slower than that of the Earth beneath it. As an air mass moves
poleward, it confronts an increasingly slower spin, and speeds up relative to
the Earth beneath it.
•Air masses moving latitudinally are deflected to the right in the N.
Hemisphere and to the left in the S. Hemisphere.
•Air masses moving toward the equator from the north and south veer to
become northeast and southeast trade winds.
•Air masses moving away from the equator veer and become westerly winds
that prevail at mid-latitudes.
•When prevailing winds bring air masses into contact with a mountain range,
the air rises to pass over the mountains, cooling as it does. Clouds form on
the windward side and release moisture as rain or snow. On the leeward side,
dry air descends, warms and picks up moisture resulting in a rain shadow
on the leeward side.
Global oceanic circulation is driven by wind patterns
•Global air circulation drives the circulation patterns of surface ocean waters,
•Trade winds converge at the equator and move westward until it encounters
a continental land mass; then the water splits along the continental shores.
This movement of water which has been heated at the tropics transfer large
amounts of heat to the high latitudes.
•As currents move towards poles, the water, driven by the winds, veers right
in the N. Hemisphere and left in the S. Hemisphere.
•Water flowing towards poles turn eastward, encounters another continent
and is deflected laterally along its shores.
•In both hemispheres, water flows toward the equator along the western sides
of continents until it meets at the equator and flows westward again.
Organisms must adapt to changes in their environment
•Few individuals die exactly where they were born; most move or are moved
to a new place dispersal.
•If repeated seasonal changes alter an environment in predictable ways,
organisms may evolve life cycles that appear to anticipate those changes
migration and hibernation.