Chapter 35: The Biosphere
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Climate and the Biosphere
Climate refers to the prevailing weather
conditions in an area as dictated by
temperature, rainfall, and these factors:
1) Variations in solar radiation due to a
spherical earth;
2) The tilt of the earth’s axis as it rotates
about the sun;
3) Distribution of land masses and
oceans; and
4) Topography (landscape) features.
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Air Circulation
The earth is a sphere, and thus the sun’s
rays are more direct at the equator and
more spread out at polar regions.
The tilt of the earth as it orbits the sun
causes one pole or the other to be
closer to the sun, and this accounts for
the occurrence of seasons everywhere
on earth except at the equator.
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Distribution of solar energy
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Seasons
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Atmospheric heat passes from warm
areas to colder areas.
Warm, equatorial air rises and moves
toward the poles, creating a zone of
lower pressure that is filled by cold air
moving toward the equator.
Rotation of the earth modifies air
circulation into three large circulation
cells in each hemisphere.
As a result, the great deserts occur
where air descends, warms, and
becomes very dry.
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Global wind circulation
35-7
Effects of Topography
Topography means the physical features
of the land.
Mountains effect climate; as air blows up
over a mountain range, it rises and
cools, so the windward side receives
more rainfall than the leeward side.
The leeward side of mountains is in a
rain shadow and receives considerably
less moisture.
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Formation of a rain shadow
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Atmospheric circulations between the
oceans or other large bodies of water
and the landmasses influence regional
climate conditions.
Oceans are slower to change
temperature than landmasses, thus
coastal weather is unique.
India has a monsoon climate in which
wet winds blow onshore for half the
year.
In the United States, the Great Lakes
produce lake effect snows.
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Biomes of the World
A biome is a large biogeographical unit
of the biosphere that has a particular
mix of plants and animals that are
adapted to living under certain
environmental conditions.
Biomes gradually change from one type
to the other, although their distribution
can be predicted by temperature and
rainfall.
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Pattern of biome distribution
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The distribution of biomes, and thus the
pattern of life on earth, is determined
principally by climate.
The effect of temperature is seen not only
when we consider latitude but also
when we consider altitude.
The same sequence of biomes that
appears from equator to the North Pole
is evident when ascending a mountain.
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Climate and biomes
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Terrestrial Biomes
Tundra
The Arctic Tundra encircles the earth just
south of ice-covered seas in the
Northern Hemisphere, covering 20% of
the earth’s land surface.
The Arctic Tundra is cold and dark much
of the year; a layer of permafrost is
present in the poorly-drained soil.
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The tundra
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Trees cannot grow in tundra because of
the short growing season, lack of
moisture, and permafrost.
Tundra plants include short grasses and
sedges, along with lichens, mosses,
and short woody shrubs.
Few animals exist in the tundra yearround, although the lemming,
ptarmigan, and musk ox are present.
Many migrating animals, including
caribou and reindeer, and migratory
birds use the tundra during summer.
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35-19
Coniferous Forests
Coniferous forests are found in three
locations:
1) In taiga, which extends around the
world in the northern part of North
America and Eurasia;
2) Near mountain tops as montane
coniferous forests; and
3) Along the Pacific coast of North
America as temperate rain forest.
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The taiga
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The taiga typifies the coniferous forest
with its cone-bearing spruce, fir, and
pine trees that are well-adapted to cold.
Birds, bears, deer, moose, and muskrat
live around lakes and streams.
The temperate rain forest along the west
coast of Canada and the United States
receives plentiful rainfall and is host to
the coastal redwoods.
As an old-growth forest, it’s resources
are valuable for both conservation and
logging.
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Temperate Deciduous Forests
Temperate deciduous forests are found
south of taiga in eastern North America,
eastern Asia, and much of Europe.
Climate is moderate with relatively high
rainfall, well-defined seasons, and a
growing season of 140 to 300 days.
Deciduous trees, such as oak, beech, and
maple, lose their leaves in autumn.
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Temperate deciduous forest
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Tallest trees form an upper canopy of leaves, yet
enough sunlight filters through to understory
trees, a shrub layer, and plant growth on the
forest floor.
Such stratification provides a variety of habitat
for birds, insects and ground life.
Amphibians and reptiles find a home in
deciduous forest where winters are moderate.
Autumn fruits, nuts, and berries provide food for
winter, and leaves turn brilliant colors.
Deciduous forest soils are rich with humus and
minerals.
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Tropical Forests
In the tropical rain forests near the
equator, the weather is always warm
and rainfall is plentiful.
This may be the most diverse biome,
both in terms of numbers of species
and their abundance.
A tropical rain forest has a complex
structure with many layers of life,
including tall trees and their epiphytes.
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Tropical rain forest location
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Levels of life in a tropical rain
forest
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Most animals live in the trees of the
tropical rain forest.
Insect life is so abundant that most
species have yet to be identified.
Termites and ants have an important role
in decomposition.
Bird and amphibian life is very diverse.
Primates feed on fruit in the trees.
Soils are poor and nutrient-depleted;
nutrients are rapidly recycled among
plants.
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Animals of the tropical rain
forest
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Shrublands
Shrubs are shorter than trees with a
woody persistent stem and no central
trunk.
Shrubs have small but thick evergreen
leaves, with a protective waxy coating.
Shrubs are adapted to drought and fire
and often require fire for seed
germination.
Dense shrubland in California is
chaparral; it lacks an understory and is
highly flammable.
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Shrubland
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Grasslands
Grasslands occur where rainfall is
greater than 25 cm but insufficient to
support trees.
Natural grasslands once covered 40% of
the land surface but most of this area
has been converted to agriculture.
Grasses tolerate a high degree of
grazing, flooding, drought, and fire.
Large herds of bison once roamed the
prairie.
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The prairie
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Savannas, which are grasslands that
contain some trees, occur where a
relatively cool dry season is followed
by a hot, rainy one.
The African savanna supports the
greatest variety and number of large
herbivores of all the biomes, including
elephants, giraffes, antelopes, zebras,
wildebeests, water buffalo, and
rhinoceroses.
Termites build towering nests and tend
their fungal gardens.
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The savanna
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Deserts
Deserts are found at 30o north and south
latitudes and are characterized by low
precipitation (under 25 cm annually).
Some deserts, such as the Sahara, have
no plants, but others, such as the North
American desert, have succulent
plants, such as cacti, adapted to water
conservation.
Reptiles and insects, along with running
birds and rodents, are desert residents.
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The desert
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Aquatic Communities
Aquatic communities can be classified as
freshwater or saltwater.
The two sets of communities interact and
are joined by the water cycle.
Gravity eventually returns all fresh water
to the sea, but meanwhile, it is
contained as standing water in lakes
and ponds, or as flowing water within
streams and rivers.
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Freshwater and saltwater
communities
35-40
When rain falls, some of the water
percolates into the ground; the top of
the saturation zone is called the
groundwater table.
Sometimes groundwater is also located
in underground aquifers.
Humans have altered aquatic habitats
and drained wetlands.
These activities degrade ecosystems and
contribute to seasonal flooding.
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Lakes
Lakes are bodies of freshwater often
classified by their nutrient status.
Oligotrophic lakes are nutrient-poor and
have low productivity.
Eutrophic lakes are nutrient-rich and
have high productivity.
Through the activities of both nature and
humans, oligotrophic lakes become
eutrophic through large inputs of
nutrients; this is called eutrophication.
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Types of lakes
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In the temperate zone, lakes are stratified
in the summer and winter.
In summer, the upper layer, or epilimnion,
is warm from the sun; the middle
thermocline experiences a sharp drop in
temperature; and the lowest layer, or
hypolimnion, is cold.
In the fall, the whole lake cools and mixes,
resulting in fall overturn; nutrients are
redistributed throughout the lake.
Vertical stratification also exists in winter;
spring overturn follows spring warming.
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Lake stratification
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Life Zones
Microscopic floating organisms in lakes
are called plankton; phytoplankton are
photosynthesizing algae, and
zooplankton are the tiny animals that eat
them.
The littoral zone of a lake is closest to the
shore, the limnetic zone is the sunlit
open area, the profundal zone is below
the level of light penetration, and the
benthic zone is at the soil-water
interface.
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Zones of a lake
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Coastal Communities
Near the mouth of a river, a salt marsh in
the temperate zone or a mangrove
swamp in the subtropical and tropical
zones is likely to develop.
The silt carried by the river may form
mudflats.
Seacoasts, mudflats, salt marshes, and
mangrove swamps all belong to one
ecological system.
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Estuaries
An estuary is a partially enclosed body of
water where fresh water and salt water
mix.
Organisms living there must be able to
tolerate changing salinity.
Estuaries trap nutrients delivered by
rivers and act as nurseries for larval
fish.
Estuaries are the feeding grounds for
man birds, fish, and shellfish.
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Estuary structure and function
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Types of estuaries
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Seashores
The littoral zone of the seashore lies
between the high and low water marks
of the tide.
The littoral zone of a rocky beach is
divided into subzones, each of which
has characteristic attached algae and
animals.
Invertebrates living on sandy shores
must burrow underground.
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Seacoasts
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Oceans
Climate is driven by the sun, but the
oceans play a major role in
redistributing heat in the biosphere.
When the wind blows strongly and
steadily across a great expanse of
ocean, the moving air drags water
along with it, creating ocean currents.
Major ocean currents, such as the Gulf
Stream, move heat from the equator to
cooler parts of the biosphere.
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Ocean currents
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In the Southern Hemisphere, the
Humboldt Current carries phosphorusrich cold water northward along the
west coast of South America.
During upwelling along this coast, cold
offshore winds cause nutrient-rich
waters to rise, enabling an abundance
of marine life to thrive there.
Sometimes the Humboldt Current is not
as cool as usual, fisheries fail, and
climate patterns change; this is the El
Niño – Southern Oscillation.
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Pelagic Division
An ocean is divided into the pelagic and
the benthic division.
The pelagic division includes the neritic
province (overlying the continental
shelf) and the oceanic province (open
ocean).
The oceanic province lacks the inorganic
nutrients of the neritic province but
still supports an abundance of
plankton and fish.
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Marine environment
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The epipelagic zone of the oceanic
province is sunlit and supports
phytoplankton that in turn become food
for zooplankton, which then feed fish.
Animals in the mesopelagic zone are
carnivores adapted to dim light;
translucent or luminescent organisms
exist there.
The bathypelagic zone is in complete
darkness; carnivores and scavengers
are found in this zone.
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Coral reefs are areas of biological
abundance found in shallow, warm
tropical waters.
Their chief constituents are stony corals
with a limestone exoskeleton, and
calcareous red and green algae.
A coral reef is densely populated with a
great diversity of sponges, sea squirts,
crabs, and exotic fish.
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Benthic Division
The benthic division includes organisms
living on or in the soil of the continental
shelf (sublittoral zone), the continental
slope (bathyal zone), and the abyssal
plain (abyssal zone).
Organisms of the benthic division depend
on the debris that floats down from
above.
Unique food chains are based on
chemosythesis at hydrothermal vents
on the ocean bottom.
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Ocean inhabitants
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Chapter Summary
The spherical earth causes different
amounts of sunlight to be received at
different latitudes, resulting in
differences in temperature from the
equator to the poles.
The tilt and rotation of the earth cause the
four seasons.
Rising and falling air currents trigger moist
or dry areas across the globe.
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Topography also influences rainfall
patterns.
Terrestrial biomes are distributed
according to climate; moisture and
temperature determine major types of
vegetation.
Terrestrial biomes include tundra,
coniferous forest (taiga), temperate
deciduous forest, tropical rain forest,
shrublands, grasslands, savanna, and
deserts.
Each biome has characteristic organisms.
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Streams, rivers, lakes, ponds, and
wetlands are different freshwater
communities.
Lakes in temperate zones undergo
seasonal stratification and overturn.
Lakes and ponds have life zones.
Estuaries and coral reefs are highly
diverse saltwater communities.
An ocean has a pelagic and a benthic
division.
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