The biosphere can be divided into large
regions called biomes.
Biomes are massive areas that are classified
mostly on the basis of their climates and
plant life. Because of the different climates
and terrains on the earth, the distribution of
living organisms varies.
Summary of Major Biomes
Tundra
Regions—northernmost regions
Plant life—few, if any, trees; primarily grasses and wildflowers
Characteristics—contains permafrost (a layer of permanently frozen
soil); has a short growing season
Animal life—includes lemmings, arctic foxes, snowy owls, caribou, and
reindeer
Taiga
Region—northern forests
Plant life—wind-blown conifers (evergreens), stunted in growth,
possess modified spikes for leaves
Characteristics—very cold, long winters
Animal life—includes caribou, wolves, moose, bear, rabbits, and lynx
Temperate Deciduous Forest
Regions—northeast and middle eastern United States, western Europe
Plant life—deciduous trees that drop their leaves in winter
Characteristics—moderate precipitation; warm summers, cold winters
Animal life—includes deer, wolves, bear, small mammals, birds
Grasslands
Regions—American Midwest, Eurasia, Africa, South America
Plant life—grasses
Characteristics—hot summers, cold winters; unpredictable rainfall
Animal life—includes prairie dogs, bison, foxes, ferrets, grouse, snakes, and
lizards
Deserts
Regions—western United States
Plant life—sparse, includes cacti, drought-resistant plants Characteristics—
arid, low rainfall; extreme diurnal temperature shifts Animal lift—includes
jackrabbits (in North America), owls, kangaroo rats,
lizards, snakes, tortoises
Tropical Rain Forests
Regions—South America
Plant life—high biomass; diverse types
Characteristics—high rainfall and temperatures; impoverished soil
Animal life—includes sloths, snakes, monkeys, birds, leopards, and insects
COMMUNITY
A community refers to a group of interacting plants and animals that show some degree of
interdependence. All organisms within a community fill one of the following roles:
Producers, or autotrophs, have all of the raw building blocks to make their own food. From
water and the gases that abound in the atmosphere, and with the aid of the sun's energy
autotrophs convert light energy to chemical energy. They accomplish this through
photosynthesis.
Consumers, or heterotrophs, are forced to find their energy sources in the outside world.
Basically, heterotrophs digest the carbohydrates of their prey into carbon, hydrogen, and
oxygen, and use these molecules to make organic substances.
The bottom line is: Heterotrophs, or consumers, get their energy from the things they
consume.
Decomposers
All organisms at some point must finally yield to decomposers. Decomposers are the organisms
that break down organic matter into simple products. Generally, fungi and bacteria are the
decomposers. They serve as the "garbage collectors" in our environment.
Niche
• An organism position
or function in a
community.
• Because every species
occupies a niche, it's
going to have an effect
on all the other
organisms.
• These connections are
shown in the food
chain.
A food chain describes the way different organisms depend on one another
for food. There are basically four levels to the food chain: producers,
primary consumers, secondary consumers, and tertiary consumers.
Autotrophs produce all of the available food. They make up the first trophic (feeding)
level. They possess the highest biomass (the total weight of all the organisms in an
area) and the greatest numbers. Plants make up about 99 percent of the earth's total
biomass.
Primary consumers are organisms that directly feed on producers. A good example is
a cow. These organisms are also known as herbivores. They make up the second
trophic level.
The next level consists of organisms that feed on primary consumers. They are the
secondary consumers, and they make up the third trophic level. Above these are
tertiary consumers.
So now you have it. We've got our four complete levels of the food chain.
Producers make their own food.
Primary consumers (herbivores) eat producers.
Secondary consumers (carnivores and omnivores) eat producers and primary consumers.
Tertiary consumers eat all of the above.
The 10% Rule
• In a food chain, only about 10 percent of the energy is transferred from
one level to the next
•
The other 90 percent is used for things like respiration, digestion, running
away from predators—in other words, it's used to power the organism
doing the eating!
• The producers have the most energy in an ecosystem; the primary
consumers have less energy than producers; the secondary consumers
have less energy than the primary consumers; and the tertiary consumers
will have the least energy of all.
ECOLOGICAL SUCCESSION
• Communities of organisms don't just spring up on their own; they develop
gradually over time. Ecological succession refers to the predictable procession of
plant communities over a relatively short period of time (decades or centuries).
• Centuries may not seem like a short time to us, but if you consider the
enormous stretches of time over which evolution occurs, hundreds of
thousands or even millions of years, you'll see that it is pretty short.
• The process of ecological succession where no previous organisms have existed
is called primary succession.
• How does a new habitat full of bare rocks eventually
turn into a forest?
• The first stage of the job usually falls to a community
of lichens. Lichens are hardy organisms. They can
invade an area, land on bare rocks and erode the rock
surface, and over time turn it into soil. Lichens are
considered pioneer organisms.
• Once lichens have made an area more habitable,
they've set the stage for other organisms to settle in.
Communities establish themselves in an orderly
fashion. Lichens are replaced by mosses and ferns,
which in turn are replaced by tough grasses, then low
shrubs, then evergreen trees, and finally, a climax
community is reached.
HUMAN IMPACT ON THE ENVIRONMENT
Unfortunately, humans have disturbed the existing ecological balance, and the results
are far-reaching. Soils have been eroded and various forms of pollution have
increased. The potential consequences on the environment are summarized below:
•Ozone depletion—Pollution has also led to the depletion of the atmospheric ozone
layer by such chemicals as chlorofluorocarbons (CFCs), which are used in aerosol
cans. Ozone (0,), forms when UV radiation reacts with 02. Ozone protects the earth's
surface from excessive ultraviolet radiation. Its loss could have major genetic effects
and could increase the incidence of cancer.
•Desertification—When land is overgrazed by animals, it turns grasslands into deserts
and reduces the available habitats for organisms.
•Deforestation—When forests are cleared (especially by the slash and burn method),
erosion, floods, and changes in weather patterns can occur
•Greenhouse effect—The increasing
atmospheric concentrations of carbon
dioxide through the burning of fossil fuels
and forests have contributed to the warming of the earth. Higher temperatures may
cause the polar ice caps to melt and
flooding to occur. Other potential effects of
global warming include changes in
precipitation patterns, changes in plant and
animal populations, and detrimental
changes in agriculture.
•Acid rain—The burning of fossil fuels produces pollutants such as
sulfur dioxide and nitrogen dioxide. When these compounds react
with droplets of atmospheric water in clouds they form sulfuric and
nitric acids, respectively. The rain that falls from these clouds is
weakly acid and is called acid rain. Acid rain lowers the pH
of aquatic ecosystems and soil which damages water systems,
plants and soil. For example, the change in soil pH causes calcium
and other nutrients to leach out, which damages plant roots and
stunts their growth. Furthermore, useful microorganisms that release
nutrients from decaying organic matter into the soil are also killed,
resulting in less nutrients being available for the plants. Low pH also
kills fish, especially those that have just hatched.