BIOL 3130 Lecture Notes - Intertropical Convergence Zone, Alpine Tundra, Rain Shadow
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
Communities: embracing all the organisms living together in the same area
Ecosystems: embracing all organisms in an area plus their physical environment
Biosphere: system that embraces all regions of the planet where organisms live
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 long term.
Weather is the short-term state of those conditions.
Climates vary greatly because different places receive different amounts of solar energy.
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 sunlight.
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 convergence zone.
Cool air cannot hold as much moisture as warm air, so heavy rains fall in the intertropical
Air that moves into the intertropical convergence zone to replace the rising air is replaced by air
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-
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, currents.
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
If repeated seasonal changes alter an environment in predictable ways, organisms may evolve
life cycles that appear to anticipate those changes migration and hibernation.
52.3 What is a Biome?
Biome is a terrestrial environment defined by the growth forms of its plants.
Species richness the number of species present in its communities.
o Found in Arctic at high elevations in mountains at all latitudes
o Vegetation consists of low-growing perennial plants underlain by permafrost
o Little precipitation, lowland Arctic tundra is very wet (no drain source).
o Plants grow for only a few months each year
o Most Arctic tundra animals either migrate or remain dormant for most of the year.
o Tropical alpine tundra is not underlain by permafrost.
BOREAL FOREST AND TEMPERATE EVERGREEN FOREST
o Found toward the equator Arctic tundra and at lower elevations on temperate-zone
o Winters are long and very cold; summers are short (favours trees w/evergreen leaves).
o Boreal forests of the N. Hemisphere are dominated by evergreen coniferous
gymnosperms; in S. Hemisphere the dominant trees are southern beeches.
o Temperate evergreen forests also grow along the western coasts of continents at
middle to high latitudes in both hemispheres; winters are mild but very wet and
TEMPERATE DECIDUOUS FOREST
o Found in eastern N. America, E. Asia, and Europe.
o Temperatures fluctuate dramatically and precipitated is evenly distributed.
o Deciduous trees dominate these forests.
o More trees live here than in boreal forests.
o Centered on S.
o Receive most of their scarce rainfall in summer; also receive winter rains from storms
that form over the mid-latitude oceans.
o Driest large regions are in the center of Australia and the middle of the Sahara Desert.
o Except in driest regions, hot deserts have richer and structurally more diverse
vegetation than cold deserts.
o A rich fauna of rodents, termites, ants, lizards, and snakes.
o Found on the western sides of continents at mid-latitudes where cool ocean currents
o Winters are cool and wet; summers are warm and dry
o Dominant vegetation are low-growing shrubs and trees with tough, evergreen leaves.
o Annual plants are abundant; supports large populations of small rodents.
TROPICAL DECIDUOUS FOREST
o As length of the rainy seasons increases, tropical deciduous forest replaces thorn
o Have taller trees and fewer succulent plants than thorn forests; are much richer in plant
and animal species.
o Soils of the tropical deciduous forest biome are some of the best soils in the tropics for
52.4 What is a Biogeographic Region?
Biogeography: the study of the patterns of distribution of populations, species, and ecological
communities across Earth.
Biogeographic regions are based on the taxonomic composition of the organism living in them;
boundaries are set where species compositions change dramatically over short distances.
Species found only within a certain region is said to be endemic to that region. Remote islands
typically have distinctive endemic biotas b/c water barriers greatly restrict immigration.
Three scientific advances changed the field of biogeography
Three scientific advances changed biogeography into the field it is today: 1. Acceptance of the
theory of continental drift, 2. the development of phylogenetic taxonomy, 3. The development
of the theory of island biogeography.
CONTINENTAL DRIFT: Carolus Linnaeus believed that all organisms had been created in one
place from which they later dispersed.
PHYLOGENETIC TAXONOMY: method of reconstructing phylogenetic relationships among
ISLAND BIOGEOGRAPHY: a theory to explain why islands always have fewer species than a
mainland of equivalent size. Based on two processes: immigration of new species to an island
and the extinction of species already present on that island; the list of species on the mainland
that might possibly colonize the island constitutes the species pool. The first species to arrive
large and relatively close to the mainland.
A single barrier may split the ranges of many species
The appearance of a physical barrier that splits the range of a species is called a vicariant event.
It divides the population of a species into two or more discontinuous populations.
If members of a species cross an already existing barrier and establish a new population, the
Biotic interchange follows fusion of land masses
When formerly separated land masses fuse, two different biotas can merge.
Many species of both biotas are likely to disperse into the region they had not previously
inhabited biotic interchange.