1. Chapter 35: The Biosphere

2. Climate and the Biosphere
Climate refers to the prevailing weather conditions in an area as dictated by temperature, rainfall, and these factors:
Variations in solar radiation due to a spherical earth;
The tilt of the earth’s axis as it rotates about the sun;
Distribution of land masses and oceans; and
Topography (landscape) features.

3. 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.
The spherical earth and the uneven distribution of the sun’s rays means that the tropics are warmer than temperate regions.
When the Northern Hemisphere is having one season (i.e., winter), the Southern Hemisphere is having the opposite season (i.e., summer), and vise versa, except at the spring and fall equinoxes.

4. Distribution of solar energy
Since the earth is a sphere, beams of solar energy striking the earth near one of the poles are spread over a wider area than similar beams striking the earth at the equator.

5. Seasons
The seasons of the Northern and Southern Hemispheres are due to the tilt of the earth on its axis as it rotates about the sun.

6. 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.

7. Global wind circulation
At the equator, warm air rises, cools, and loses its moisture. The equator receives the greatest amount of rainfall on earth. At 30o, dry air descends and warms; therefore, deserts occur at 30o latitude around the world. At the earth’s surface, the air flows both poleward and equatorward. At about 60o north and south latitude, the air rises and cools, producing additional zones of high rainfall. This moisture supports the great forests of the temperate zone. Part of this rising air flows equatorward, and art continues poleward, descending near the poles, which are zones of low precipitation.
Because the earth is rotating on its axis, the trade winds move from northeast to the west in the Northern Hemisphere, and from the southeast to the west in the Southern Hemisphere. Between 30o and 60o north and south latitude, strong winds, called westerlies move toward the east. The west coasts of the continents at these latitudes are wet, as is the Pacific Northwest where a massive evergreen forest is located.

8. 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.

9. Formation of a rain shadow
When winds from the sea cross a coastal mountain range, they rise and release their moisture as they cool this side of a mountain, which is called the windward side. The leeward side of a mountain receives relatively little rain and is therefore said to lie in a “rain shadow”.

10. In the United States, the Great Lakes produce lake effect snows.
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.
During the day, the land warms more quickly than the ocean, and the air above the land rises. Then a cool sea breeze blows in from the ocean. At night, the reverse happens; the breeze blows from land to sea.

11. 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.

12. Pattern of biome distribution
This graph shows the pattern of world biomes in relation to temperature and moisture. The dashed line encloses a wide range of environments in which either grasses or woody plants can dominate the area, depending on the soil type.

13. The same type of biome can occur in different regions of the world, as shown on this global map.

14. 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.
The coniferous forest of a mountain is called montane coniferous forest, and the tundra near the peak of a mountain is called an alpine tundra.

15. Climate and biomes
Biomes change with altitude just as they do with latitude because type of vegetation is partly determined by temperature. Rainfall also plays a significant role, which is one reason grasslands, instead of tropical or deciduous forests, are sometimes at the base of mountains.

16. 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.
Only the top layer of the soil thaws each summer. Beneath that layer is a layer called permafrost that never thaws. Thus water does not drain off and tundra soils tend to be boggy.

17. The tundra
In this biome, which is nearest the polar regions, the vegetation consists mostly of lichens, mosses, grasses, and low-growing shrubs.

18. 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.
Wolves follow the migratory herds of animals; insects are present in abundance during the short summers.

19. Pools of water that do not evaporate or drain into the permanently frozen ground attract many birds that feed on the plentiful insects in the summer. Caribou, more plentiful in the summer than in the winter, feed on lichens, grasses, and shrubs.

20. Coniferous Forests Coniferous forests are found in three locations:
In taiga, which extends around the world in the northern part of North America and Eurasia;
Near mountain tops as montane coniferous forests; and
Along the Pacific coast of North America as temperate rain forest.

21. The taiga
The taiga, which means swampland, spans northern Europe, Asia, and North America. The appellation “spruce-moose” refers to the dominant presence of spruce trees and moose, which frequent the ponds.

22. Birds, bears, deer, moose, and muskrat live around lakes and streams.
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.
The old-growth forest of the Pacific northwest is currently in the news. Whether the limited portion that remains should be preserved from logging has been quite controversial. Unfortunately, the controversy has centered around the northern spotted owl, which is endemic to this area, rather than around the larger issue, the conservation of this particular ecosystem.

23. 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.

24. Temperate deciduous forest
A temperate deciduous forest is home to many varied plants and animals. Millipedes can be found among leaf litter, chipmunks feed on acorns, and bobcats prey on these and other small mammals.

25. 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.

26. 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.
Epiphytes are plants that grow on other plants but usually have roots of their own that absorb moisture and minerals leached from the canopy. The most common epiphytes are related to pineapples, orchids, and ferns.

27. Tropical rain forest location

28. Levels of life in a tropical rain forest
The primary levels in a tropical rain forest are the canopy, the understory, and the forest floor. But the canopy (solid layer of leaves) contains levels as well, and some organisms spend their entire life in one particular level. Long lianas (hanging vines) climb into the canopy, where they produce leaves. Epiphytes are air plants that grow on the trees but do not parasitize them.

29. 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.
Slash-and-burn agriculture has been successful but destructive in the tropics. Trees are felled and burned, and their ashes provide enough nutrients for several harvests. Thereafter, the forest must be allowed to regrow and a new section must be burned and cut.
In humid tropical forests, iron and aluminum oxides occur at the surface, causing a reddish residue known as laterite. When the trees are cleared, laterite bakes in the hot sun to a bricklike consistency that will not support crops.

30. Animals of the tropical rain forest

31. 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.
Shrublands tend to occur along coasts that have dry summers and receive most of their rainfall in the winter. Shrublands are found along the cape of South Africa, the western coast of North America, and the southwestern and southern shores of Australia, as well as around the Mediterranean Sea, and in central Chile. There is also a northern shrub area that lies west of the Rocky Mountains. This area is sometimes classified as a cold desert, but the region is dominated by sagebrush and other hardy plants.

32. Shrubland
Shrublands, such as chaparral in California, are subject to raging fires, but the shrubs are adapted to quickly regrow.

33. 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.

34. The prairie
Tall-grass prairies are seas of grasses dotted by pines and junipers. Bison, once abundant, are now being introduced into certain areas.
Temperate grasslands include the Russian steppes, the South American pampas, and the North American prairies. Tall-grass prairie requires more water than short-grass prairie. Small mammals, such as mice, prairie dogs, and rabbits are abundant.

35. Termites build towering nests and tend their fungal gardens.
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.
The herbivores support a large population of carnivores. Lions and hyenas hunt in packs, cheetahs hunt singly by day, and leopards hunt singly by night.

36. The savanna
The African savanna varies from grassland to widely spaced shrubs and trees because the soil is low in moisture and nutrients. This biome supports a large and varied assemblage of grazers (e.g., zebras and wildebeests) and browsers (e.g., giraffes). Cheetahs and lions prey on these herbivores.

37. 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.

38. The desert
Plants and animals that live in a desert are adapted to arid conditions. The plants are either succulents that retain moisture or shrubs with woody stems and small leaves that lose little moisture. The kangaroo rat feeds on seeds and other vegetation; the roadrunner preys on insects, lizards, and snakes.

39. 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.

40. Freshwater and saltwater communities

41. Sometimes groundwater is also located in underground aquifers.
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.
Wetlands are wet for at least part of the year and provide food and habitat for fish, waterfowl, and other wildlife. They also purify waters by filtering them and by diluting and breaking down toxic wastes and excess nutrients. Wetlands directly absorb storm waters and also absorb overflows from lakes and rivers. In this way, wetlands protect farms, cities, and towns from the devastating effects of floods.

42. 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.

43. Types of lakes
Lakes can be classified according to whether they are (a) oligotrophic (nutrient-poor) or (b) eutrophic (nutrient-rich). Eutrophic lakes tend to have large populations of algae and rooted plants, resulting in a large population of decomposers that use up much of the oxygen, leaving little oxygen for fishes.

44. 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.
In productive lakes, stratification often leads to oxygen depletion in lower levels, with the possibility of fish kills. During spring and fall overturn, oxygen and nutrients are redistributed throughout the lake.

45. Lake stratification
Temperature profiles of a large oligotrophic lake in a temperate region vary with the season. During spring and fall overturn, the deep waters receive oxygen from surface waters, and surface waters receive inorganic nutrients from deep waters.

46. 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.
Each life zone has characteristic organisms inhabiting there.

47. Zones of a lake
Rooted plants and clinging organisms live in the littoral zone. Phytoplankton, zooplankton, and fishes are in the sunlit limnetic zone. Water striders stand on the surface film of water with water-repellant feet. Crayfishes and molluscs are in the profundal zone as well as the littoral zone. Pike are top carnivores prized by fishermen.

48. 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.

49. 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.

50. Estuary structure and function
Since an estuary is located where a river flows into the ocean, it receives nutrients from the land. Estuaries serve as a nursery for the spawning and rearing of the young of many species of fish, shrimp and other crustaceans, and molluscs.

51. Types of estuaries
Some of the many types of regions that qualify as estuaries include the salt marsh depicted in the previous slide, mudfats (top photo), which are frequented by migrant birds, and mangrove swamps (bottom) skirting the coastlines of tropical and subtropical lands. The tangled roots of mangrove trees trap sediments and nutrients that sustain many immature forms of sea life.

52. 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.

53. Seacoasts
The littoral zone of a rocky coast, where the tide comes in and out, has different types of shelled and algal organisms at its upper, middle, and lower portions.

54. Some organisms of a rocky coast live in tidal pools
Some organisms of a rocky coast live in tidal pools. A sandy shore looks devoid of life except for the birds that feed there. However, a number of invertebrate species (clams, sand dollars, ghost crabs, sandworms, and sand shrimp) burrow in the sand.

55. 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.

56. Ocean currents
The arrows on this map indicate the locations and directions of the major ocean currents set in motion by global wind circulation. By carrying warm water to cool latitudes (e.g., the Gulf Stream) and cool water to warm latitudes (e.g., the Humboldt Current), these currents have a major effect on the world’s climates.

57. 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.

58. 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.

59. Marine environment
Organisms reside in the pelagic division (blue), where waters are divided as indicated. Organisms also reside in the benthic division (brown) in the surfaces and zones indicated.

60. 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.

61. 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.
Limestone is calcium carbonate.

62. 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.
At hydrothermal vents, seawater percolates through cracks and is heated to 350oC, causing sulfate to react with water and form hydrogen sulfide (H2S). Chemosynthetic bacteria that obtain energy from oxidizing hydrogen sulfide exist freely or mutualistically within the tissues of organisms. They are the start of food chains for a community that supports huge tube worms and clams. Chemosynthesis does not require light energy.

63. Ocean inhabitants
Different organisms are characteristic of the epipelagic, mesopelagic, and bathypelagic zones of the pelagic division compared to the abyssal zone of the benthic division.

64. 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.

65. 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.

66. 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.