26.1. Climate and the Biosphere (p. 444)
A. Global Air and Water Circulations
1. Both global climate and local weather create living conditions for organisms.
2. Biomes are major communities characterized by a certain climate and dominated by particular types of plants.
3. Biomes are dependent upon four major factors: a spherical earth causes variation in received solar radiation; the tilt of the earth's axis as it rotates about the sun causes seasonal change; land masses and oceans are distributed unevenly; and topography features, including mountain ranges, affect local climate.
B. Air Circulation
1. Since the earth is a sphere, the sun's rays are more direct near the equator and more spread out near the poles.
2. Tropics are therefore warmer than temperate areas. (Fig. 26.1a)
3. Tilt of earth's axis as it rotates about the sun causes one pole to be more directly exposed to sunlight.
4. Cold air is heavy and sinks; hot air is lighter and rises.
a. If the earth were standing still, equatorial air would rise and move toward the poles.
b. This would replace heavy polar air that sinks and flows toward the equator.
c. This would produce high altitude winds moving toward poles, and surface winds moving toward equator.
5. Water Cycle
a. Warm moist air near equator rises and cools as it ascends, causing much rainfall near the equator.
b. As the air moves toward the poles, at about 30o north and south, it sinks and reheats.
c. The sinking reheated air absorbs moisture, creating a zone of decreased rainfall and desert zones.
d. At about 60o north and south, the air rises and cools, producing additional zones of high rainfall.
e. This moisture supports the great forests of the temperate zone.
6. Earth's Rotation Has an Effect
a. The spinning of the earth shifts winds from directly north-south toward east or west.
b. In the zone from the equator to 30o north and south, the winds blow from the east-southeast in the Southern Hemisphere and from the east-northeast in the Northern Hemisphere.
c. Between 30o and 60o north and south, strong winds called the westerlies blow from west to east.
d. The west coasts of continents in these latitudes are wet, as is the Pacific Northwest.
e. Weaker polar easterlies blow from east to west between 60o north or south and the respective poles.
7. Seasonal Fronts
a. In January, local winds flow from cold continental masses toward warm maritime regions of the equator.
b. In July, continental masses of Asia and North America are warmer than equitorial oceans, so local airflow is reversed.
C. Ocean Currents (Fig. 26.3) [transp. 139]
1. Moisture that evaporates into the air carries the heat of evaporation.
2. Water is warm at the equator and cold at the poles due to the distribution of the sun's rays. (Fig. 26.3) [transp. 138]
3. Air takes on the temperature of the water below and warm air moves from the equator to poles.
4. Therefore, the oceans help make winds blow as well as hold heat or remain cool longer than land masses.
5. Winds generate ocean currents due to friction at the ocean surface.
6. Since ocean currents are bounded by land, they move in a circular path, counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.
7. Ocean currents take warm water from the equator to the polar regions.
a. Gulf Stream brings tropical Caribbean water to east coast of North America and upper western Europe.
b. A major Atlantic Ocean current warms the eastern coast of South America.
c. The Humboldt Current in the Pacific flows toward the equator off the west coast of South America.
8. Upwellings occur when cold nutrient-rich waters rise to supplant warm nutrient-poor waters.
a. Humboldt Current usually brings rich nutrients north.
b. This supports rich marine life and the fisheries of Peru and northern Chile.
c. El Niño is a reversal of narmal conditions, resulting in stagnation, poor fishing, and global climate pattern changes.
D. Effects of Topography
1. Topography is the physical features or "lay" of the land.
2. Mountains cause rain and rain shadows
a. As air blows up over a mountain, it rises and cools; windward side of the mountain receives more rainfall.
b. The leeward side of the mountain range receives dry air; it is in a rain shadow. (Fig. 26.4)
3. Coastal breezes
a. Since land heats up and cools down faster than oceans, it causes a daily pattern.
b. In the day, land heats up and warm air rises; cool sea breezes then blow inland to replace the rising air.
c. At night, the land cools first and cold air sinks and blows out to sea. (Fig. 26.5)
4. Monsoon climates
a. India and south Asia climate generates wet ocean winds for almost half the year.
b. The land heats more rapidly than the waters of the Indian Ocean during spring.
c. The difference in temperature causes a gigantic circulation of air with warm air rising and cooler air continuously coming in off the ocean to replace it.
d. As the warm air rises, it loses its moisture and the monsoon season begins.
e. The pattern reverses in the fall with dry continental air flowing continuously.
f. The main crop is rice, which is dependent on monsoon rains; failure of the monsoons means starvation.
5. The "lake effect"
a. Arctic winds blowing across the Great Lakes become warm and moisture laden.
b. When these winds rise and lose their moisture, snow falls.
c. Icy winds from the former Soviet Union blow over the eastern coast of England with same effect.
26.2. Biomes of the World (p. 449)
A. The biosphere is divided into large biogeographic units called biomes.
1. A biome has a characteristic mix of plants and animals adapted to living under certain environmental conditions.
2. Average temperature and rainfall influence where the different biomes are found on the surface of the earth. (Fig. 26.6a) [transp. 140]
3. Climate is a principle determinant of the distribution of biomes. (Fig. 26.6b)
4. The latitude temperature gradients are also seen when we consider altitude; the rain forest-deciduous forest-coniferous forest-tundra sequences are also seen when ascending a mountain. (Fig. 26.7)
a. The mountain coniferous forest is a montane coniferous forest.
b. The tundra near the peak is an alpine tundra.
B. Soil Types
1. Soil is the uppermost layer of the lithosphere.
2. Soil originates with weathering of bedrock and reorganization of this material by water, plants, and animals.
3. Humus is the decomposed component of soil.
4. Topsoil takes thousands and even millions of years to form; soil erosion is a serious loss of resources.
5. Soil particle sizes and properties
a. Sand is a large particle that forms large pores for fast water drainage.
b. Silt is intermediate in particle size and in pore properties.
c. Clay is small, drains slowly, and leaves no pore spaces for roots to get air to carry on cellular respiration.
d. Loam is a mixture of sand, silt, and clay and when mixed with humus, has the best properties.
6. Soil horizons
a. The A horizon is uppermost topsoil; it contains litter and humus but soluble chemicals have been leached out.
b. The B horizon has little or no organic matter but contains the inorganic nutrients leached from A horizon.
c. The C horizon is weathered or shattered rock.
7. Soils formed in grasslands have a deep A horizon built up from decaying grasses over many years with little leaching into the B horizon.
8. Forest soil has enough inorganic nutrients in the A and B horizons to allow root growth.
9. In tropical rain forests, the A horizon is very shallow and the B horizon is deeper due to more leaching; since the topsoil lacks nutrients, it can only support crops for a few years.
26.3. Terrestrial Biomes (p. 451)
A. Tundra (Fig. 26.9)
1. The Arctic tundra encircles the earth just south of the ice-covered polar seas in the Northern Hemisphere.
2. Arctic tundra covers about 20 percent of the earth's land surface.
3. It is cold and dark much of the year.
4. Tundra receives about 20 cm of rainfall annually; melting snow makes water plentiful during summer.
5. Only the topmost layer of earth thaws; the permafrost beneath this layer is always frozen.
6. Trees are not found in the tundra because the growing season is too short, their roots cannot penetrate the permafrost, and they cannot become anchored in the boggy soil of summer.
7. In the summer, the ground is nearly completely covered with sedges and short grasses, but there are also numerous patches of lichens and mosses.
8. Dwarf woody shrubs flower and seed quickly while there is plentiful sun for photosynthesis.
9. A few animals that are highly adapted to cold live in the tundra year-round (e.g., lemming, ptarmigan).
10. During the summer the tundra contains numerous insects and migratory animals.
11. The alpine tundra is a similar community that occurs above the timberline on mountain ranges.
B. Coniferous Forests (Fig. 26.10)
1. Taiga is a coniferous forest extending in a broad belt across northern Eurasia and North America.
2. Near mountain tops, it is called a montane coniferous forest.
3. Along the Pacific Coast down to California, it is called a temperate rain forest.
4. Contains great stands of spruce, fir, hemlock, and pine; these trees have thick protective leaves and bark.
5. The needlelike leaves can withstand the heavy weight of snow.
6. There is a limited understory of plants; floor is covered by low-lying mosses and lichens beneath needles.
7. Birds harvest seeds of conifers; bears, deer, moose, beaver and muskrat live around cool lakes and streams.
8. Major carnivores include wolves, wolverines, and mountain lions.
9. The temperate rain forest along the Pacific Coast has the largest trees in existence, some as old as 800 years.
C. Temperate Deciduous Forests (Fig. 26.11)
1. These are found south of the taiga in eastern North America, eastern Asia, and much of Europe.
2. The climate is moderate, with a relatively high annual rainfall (75-150 cm).
3. Seasons are well-defined with a growing season that ranges between 140 and 300 days.
4. Trees of a deciduous forest have broad leaves, which they lose in the fall and grow again in the spring.
5. In temperate deciduous forest, enough sunlight penetrates the canopy to support a well-developed understory composed of shrubs, a layer of herbaceous plants, and then often a ground cover of mosses and ferns.
6. This stratification beneath the canopy provides a variety of habitats for insects and birds.
7. The deciduous forest also contains many rodents, which provide food for bobcats, wolves, foxes.
8. The deciduous forest also contains deer and black bears.
9. In contrast to the taiga, the winters are not so cold, allowing many amphibian and reptiles to survive.
D. Tropical Forests
1. Tropical rain forests are found in regions near equator.
2. The climate is always warm (20°- 25° C) and the rainfall plentiful (with a minimum of 190 cm per year).
3. This is probably the richest biome, both in diversity and in total biomass.
4. The tropical rain forest has a complex structure, with many levels of life. (Fig. 26.12)
5. Although there is animal life on the ground (e.g., pacas, agoutis, peccaries, armadillos, and coatis), most animals live in the trees and many spend their entire life in the canopy.
6. Insects are so abundant in tropical rain forests that the majority have not been identified yet.
7. Termites are critical in the decomposition of wood.
8. The various birds tend to be brightly colored.
9. Amphibians and reptiles are well represented by many species of frogs, snakes, and lizards.
10. Lemurs, sloths, and monkeys feed on fruits in tropical rain forests.
11. The largest carnivores are the cats (e.g., jaguars in South America and leopards in Africa and Asia).
12. Epiphytes are air plants that grow on other plants; they have roots of their own to absorb moisture and minerals leached from the canopy.
13. Some tropical forests in India, Southeast Asia, West Africa, Central and South American are seasonal and have deciduous trees that shed leaves in dry season.
14. The warm, moist climate that supports high productivity also promotes rapid decomposition of detritus.
15. Combined with a year-long growing season, tropical forests have a rapid cycling of nutrients.
16. Soil is relatively poor, because nutrients are tied up in the biomass, and they are poor agricultural soils.
E. Shrubland
1. Shrubland is dominated by shrubs with small but thick evergreen leaves that are often coated with a thick, waxy cuticle, and with thick underground stems that survive the dry summers and frequent fires.
2. Shrubland is found in parts of South America, western Australia, central Chile, around the Mediterranean Sea.
3. Dense shrubland in California, where the summers are hot and very dry, is chaparral. (Fig. 26.14)
a. This Mediterranean-type shrubland lacks an understory and ground litter, and is highly flammable.
b. The seeds of many species require the heat and scarring action of fire to induce germination.
4. West of the Rocky Mountains is a cold desert region dominated by sagebrush and birds dependent on it.
F. Grasslands
1. Grasslands occur where rainfall is greater than 25 cm but is generally insufficient to support trees. (Fig. 26.15)
2. Natural grasslands once covered over 40 percent of the earth's land surface.
3. In temperate areas where rainfall is between 10 and 30 inches a year, grassland is the climax community because it is too wet for desert and too dry for forests.
4. Most grasslands have now been utilized to grow crops, especially wheat and corn.
5. Grasses are the dominant plant form; grazing and burrowing species are the dominant forms of animal life.
6. The extensive root systems of grasses allows them to recover quickly from grazing, flooding, drought, and sometimes fire.
7. Temperate grasslands include the Russian steppes, the South American pampas, and North American prairies.
8. A tall-grass prairie occurs where moisture is not quite sufficient to support trees.
9. A short-grass-prairie survives on less moisture and is between a tall-grass prairie and desert.
10. Animal life includes mice, prairie dogs, and rabbits, and animals that feed on them (e.g., hawks, snakes, etc.).
11. Prairies once contained large herds of buffalo and pronghorn antelope.
12. Savanna is tropical grassland that contains some trees.
a. Savanna contains the greatest variety and numbers of herbivores (e.g., antelopes, zebras, wildebeests, etc.).
b. This supports a large population of carnivores (e.g., lions, cheetahs, hyenas, and leopards). (Fig. 26.16)
c. Any plant litter not consumed by grazers is attacked by termites and other decomposers.
G. Deserts
1. Deserts are found in regions where annual rainfall is less than 25 cm and at latitudes about 30o north or south where winds pick up moisture and ascend. (Fig. 26.17)
2. Because of a lack of cloud cover, the days are hot and the nights are cold.
3. The Sahara and a few other deserts are nearly devoid of vegetation.
4. However, most have a variety of plants, all adapted to heat and scarcity of water (e.g., succulents).
5. Animal life includes arthropods (e.g., insects and arachnids), reptiles (e.g., lizards and snakes), running birds, rodents (e.g., the kangaroo rat), and a few larger birds and mammals (e.g., hawks and coyote).
26.4. Aquatic Biomes (p. 459)
A. Classifications
1. Aquatic biomes are classified as freshwater or saltwater.
2. Wetlands that lie near the sea have mixed fresh and salt water and are brackish.
3. Aquatic biomes share nutrients and biogeochemical cycles.
4. Evaporated water precipitates and flows through lakes and ponds, streams and rivers, and/or groundwater.
5. Human activities
a. Wandering streams are often channeled into straight channels, eliminating storage for flood control.
b. Elimination of wetlands removes unique habitat for fish, waterfowl, and other wildlife.
c. Wetlands also filter toxic wastes.
6. Freshwater communities are found in lakes, rivers, and streams.
B. Lakes
1. Lakes are freshwater bodies often classified by their nutrient status.
a. Oligotrophic (nutrient-poor) lakes have low organic matter and low productivity.
b. Eutrophic (nutrient-rich) lakes are highly productive from natural or agricultural nutrients.
c. Eutrophication occurs when added nutrients change an oligotrophic lake to eutrophic.
2. In the temperate zone, deep lakes are stratified in the summer and winter. (Fig. 26.20) [transp. 141]
a. The epilimnion is the surface layer warmed from solar radiation; it is nutrient-poor but has high O2 levels.
b. At the thermocline, there is an abrupt drop in temperature.
c. The hypolimnion is the lower cold region; it soon becomes depleted in oxygen but is nutrient rich.
d. The less dense epilimnion floats on the heavier cold hypolimnion; this prevents mixing.
3. Fall and spring overturns (Fig. 26.20) [transp. 140]
a. In the fall, the upper epilimnion waters become cooler than the hypolimnion.
b. This causes the surface water to sink and deep water to rise.
c. The fall overturn continues until the temperature is uniform.
d. In winter, ice forms on the top because the ice is lighter; this provides an insulating cover.
e. In spring, the ice melts and the cooler water on top sinks below the warmer water on the bottom.
f. After the spring overturn, the water returns to a more uniform temperature.
g. Fish and other aquatic life are adapted to the strata and seasonal changes.
C. Life Zones (Fig. 26.21)
1. Plankton includes freshwater and marine microscopic organisms that freely drift in fresh or salt water.
2. Phytoplankton are the photosynthetic plankton, including algae.
3. Zooplankton are animals that feed on the phytoplankton.
4. The littoral zone is shallow and closest to the shore; plants root in this zone and harbor some animals.
5. The limnetic zone is open sunlit layer of the body of a lake; it contains plankton, a few insect larvae, and fish.
6. The profundal zone is that portion of a lake below any significant sunlight penetration; contains zooplankton and fishes that feed on debris that falls from above.
7. The benthic zone is the soil-water interface with bottom-dwelling organisms, including worms, mollusks, etc.
D. Coastal Communities
1. At mouth of rivers, a salt marsh (temperate zone) and a mangrove swamp (tropical zone) are likely to develop.
2. The silt carried by rivers also forms mudflats.
3. An estuary is a body of water at the end of a river where freshwater and seawater mix.
a. Fewer organisms are tolerant of the mix of fresh river water and salty tidal water.
b. For organisms suited to rapid changes in salinity, estuaries provide abundant nutrients.
c. It is a nutrient trap since nutrients are delivered by river or brought in from the sea by tides.
(Fig. 26.22)
d. This serves as a nursery for spawning and rearing of over half of marine fishes, mollusks and crustaceans.
4. Seashores are constantly bombarded by tidal seas.
a. The littoral zone is covered and uncovered daily by tides.
b. The upper littoral zone is covered by barnacles.
c. The mid littoral zone harbors brown algae that may overlie barnacles.
d. The lower littoral zone has oysters and mussels attached to rock and various snails.
e. Below the littoral zone, seaweeds are main photosynthesizers anchored to rocks by holdfasts.
f. Sandy beaches have no anchor holds; therefore, beach organisms are burrowing or tube-living.
E. Oceans
1. The pelagic division includes the neritic and oceanic provinces. (Figs. 26.25 and 26.26) [transp. 142 and 143]
a. Neritic province lies over the continental shelf.
b. This contains a greater concentration of organisms than in the oceanic province.
c. It is a more productive part of the ocean because of the concentration of sunlight and nutrients.
d. It provides the base of the food web leading to commercially valuable fishes (e.g., herring, cod, and flounder).
2. The oceanic province lies over the continental slope and abyssal plain.
a. The epipelagic zone extends from the surface to the maximum depth at which photosynthesis significantly occurs.
1) It does not have a high concentration of phytoplankton because it lacks nutrients.
2) However, the numbers of these producers that do occur in this zone still support a large assembly of zooplankton, which support large numbers of other marine organisms, when the entire ocean is considered.
3) Epipelagic animals include mackerels, tunas, and sharks.
b. The mesopelagic zone extends below the maximum depth at which photosynthesis significantly occurs, to the maximum depth at which light still penetrates.
1) It is dominated by luminescent animals that are carnivores adapted to the absence of light.
c. The bathypelagic zone is a zone of absolute darkness except for an occasional flash of bioluminescent light.
1) Animals are carnivores and scavengers.
2) This level supports a variety of strange carnivores (e.g., viperfish and angler fish).
3. Benthic Division
a. The benthic division includes organisms that live on or in the soil of the ocean floor, including the continental shelf, continental slope and abyssal plain. (Fig. 26.6)
b. The sublittoral zone is located on the continental shelf up to the low tide mark on the coast.
1) It supports a mixed food web with seaweeds and filter-feeding organisms as the first trophic level.
2) The seaweeds comprise the first trophic level for a grazing food web; the detritivores (e.g., clams and worms) comprise the first trophic level for a detrital food web.
3) Starfishes, lobsters, crabs, brittle stars, and some bottom-dwelling fish occupy the upper trophic levels.
c. Bathyal zone is located on continental slope and extends through mesopelagic and bathypelagic depths.
1) It contains a detrital food web with detritivores (e.g., clams and worms) as the first trophic level.
2) Again, starfishes, crabs, brittle stars, and some bottom-dwelling fish occupy the upper trophic levels.
d. The abyssal zone is located on and immediately above the abyssal plane.
1) This is a region of extreme cold and intense pressure.
2) It contains a detrital food web in which the detritivores (e.g., sponges, worms, tubeworms, sea cucumbers, sea lilies, and sea urchins) comprise the first trophic level.
3) Starfishes, crabs, brittle stars, and some bottom-dwelling fish occupy the upper trophic levels.
e. Hydrothermal vents are areas where seawater percolates through cracks.
1) The water is heated to about 350o C.
2) This causes sulfate to react with water to form hydrogen sulfide (H2S).
3) Chemosynthetic bacteria obtain energy by oxidizing hydrogen sulfide.
4) These communities, not based on light energy support huge tube worms and clams.
F. Coral Reefs
1. Coral reefs are a formation composed of the calcium carbonate skeletal remains of stony corals and calcareous red and green algae, covered by a living coralline organisms.
2. It is densely populated with diverse animal life. (Fig. 26.27)
3. A coral reef community consists of colonies formed by budding.
4. Zooxanthellae are microscopic algae housed in the coral.
5. The corals feed at night and the photosynthetic algae feed at day in a mutualistic relationship.
6. Closely related sea anemones are important coral inhabitants.
7. Numerous crevices and caves provide shelter for filter feeders (e.g., sponges) and for scavengers.
8. Barracuda, moray eel, and sharks are top predators. (Fig. 26.27b)
9. Coral reefs are affected by overfishing and pollution.
10. The Great Barrier Reef of Australia is threatened by an overabundance of crown-of-thorns starfish that is normally controlled by the giant triton, which is recently diminishing.