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Chapter 35: The Biosphere

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Climate and the BiosphereClimate 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

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Effects of TopographyTopography 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

TundraThe 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 year-round, 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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Coniferous ForestsConiferous 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 ForestsTemperate 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 ForestsIn 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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ShrublandsShrubs 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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GrasslandsGrasslands 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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DesertsDeserts 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

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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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LakesLakes 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 ZonesMicroscopic 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 CommunitiesNear 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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EstuariesAn 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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SeashoresThe 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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OceansClimate 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 phosphorus-rich 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 DivisionThe 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.