Chapt 35

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717

BiosphereChapter Concepts

35.1 Climate and the Biosphere Solar radiation provides the energy that drives

climate differences in the biosphere. 718 Global air circulation patterns and physical

features produce the various patterns oftemperature and rainfall about the globe. 719

35.2 Biomes of the World Communities can be divided into a few major

classes of terrestrial and aquatic biomes. 721

35.3 Terrestrial Biomes

The earths major terrestrial biomes are forests(broadleaf and coniferous), shrublands,grasslands (tropical savanna and temperategrasslands), tundra, and deserts. 722

35.4 Aquatic Biomes The earths major aquatic biomes are of two

types: freshwater and saltwater (usuallymarine). 731

Ocean currents also affect the climate and the

weather over the continents. 736

Coral reefs located in shallow tropical waters are among the mostproductive of the biological communities. Some fish feed on plank-ton brought by the tides, but photosynthesizing algae also produce

food (organic nutrients) for themselves and other members of thereef.

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35.1 Climate and the BiosphereThe distribution of biomes in the biosphere is dependent

upon (1) variations in reception of solar radiation due to aspherical earth, (2) the tilt of the earths axis as it rotatesabout the sun, (3) distribution of land masses and oceans,and (4) topography (landscape) features. Due to these fac-tors, climate is particularly dictated by temperature andrainfall differences throughout the biosphere.

Air CirculationBecause the earth is a sphere, the suns rays are more direct

at the equator and more spread out at polar regions. There-fore, the tropics are warmer than temperate regions (Fig.35.1a). The tilt of the earth as it orbits around the sun causesone pole or the other to be closer to the sun (except at thespring and fall equinoxes), and this accounts for the sea-sonal changes in climate in all parts of the earth except theequator (Fig. 35.1b). When the Northern Hemisphere is hav-ing winter, the Southern Hemisphere is having summer andvice versa.

718 Part 7 Behavior and Ecology 35-2

As the space shuttle orbits the earth, astronauts inside

train a variety of cameras and other survey instru-

ments on the planet below them. The first target is the

frigid land near the North Pole. Having little rainfall and de-void of light most of the year, this Arctic tundra only teems

with life in summer, when animals such as caribou migrate to

the region. The shuttle scientists next concentrate their at-

tention on a tropical rain forest in South America, home to a

tremendous diversity of animal and plant speciesmany

still undocumented. The astronauts then direct their devices

toward the Sahara, the massive desert that spans Northern

Africa. As dry as the Arctic tundra, but considerably warmer,

the desert is nevertheless home to an impressive variety of

hardy plants and animals. Finally, the shuttle passes abovethe waters of the south Pacific, where the scientists try to

determine if the weather phenomenon called El Nio will

strike again. In its brief time in orbit, the shuttle has studied

strikingly different parts of the earths biosphere, the thin

layer of water, land, and air inhabited by living organisms.

Figure 35.1 Distribution of solar energy.a. Since the earth is a sphere, beams of solar energy striking the earth near one of the poles is spread over a wider area than similar beams

striking the earth at the equator. b. 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.

equatorequator

autumnal equinox(sun aims directlyat equator)

summer solstice(Northern Hemisphere tiltstoward the sun)

60

equator

30

30

60

equator

30

30

60

equator

30

30

23

60

30

30

vernal equinox(sun aims directlyat equator) winter solstice

(Northern Hemisphere

tilts away from sun)

Sun

b.

NorthPole

SouthPole

equator

a.

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In the atmosphere, heat always passes from warm areasto colder areas. If the earth were standing still, and were asolid, uniform ball, all air movementswhich we callwindswould be in two directions. Warm equatorial airwould rise and move directly to the poles, creating a zone oflower pressure that would be filled by cold polar air movingequatorward.

Because the earth rotates, and because its surface con-sists of continents and oceans, the flows of warm and coldair are modified into three large circulation cells in eachhemisphere (Fig. 35.2). At the equator, the sun heats the airand evaporates water. The warm moist air rises, cools, andloses most of its moisture as rain. The greatest amounts of

rainfall on earth are near the equator. The rising air flows to-ward the poles, but at about 30 north and south latitude itsinks toward the earths surface and reheats. As the air de-scends and warms, it becomes very dry, creating zones oflow rainfall. The great deserts of Africa, Australia, and theAmericas occur at these latitudes. At the earths surface, theair flows both poleward and equatorward. At about 60north and south latitude, the air rises and cools, producinganother zone of high rainfall. This moisture supports thegreat forests of the Temperate Zone. Part of this rising airflows equatorward, and part continues poleward, descend-ing near the poles, which are zones of low precipitation.

The earth is not standing still; it is rotating on its axisdaily. The spinning of the earth affects the winds, so that themajor global circulation systems flow toward the east or westrather than directly north or south (Fig. 35.2). Between about30 north latitude and 30 south latitude, the winds blowfrom the southeast to the west in the Southern Hemisphere

and from the northeast to the west in the Northern Hemi-sphere (the east coasts of continents at these latitudes arewet). These are called trade winds because sailors dependedupon them to fill the sails of their trading ships. Between 30and 60 north and south latitude, strong winds, called theprevailing westerlies, blow from west to east. The west coastsof the continents at these latitudes are wet, as is the PacificNorthwest where a massive evergreen forest is located.Weaker winds, called the polar easterlies, blow from east towest at still higher latitudes of their respective hemispheres.

Topography means the physical features or the lay ofthe land. One topographical feature that affects climate isthe presence of mountains. As air blows up and over a

mountain range, it rises and cools. This side of the moun-tain, called the windward side, receives more rainfall thanthe other side, called the leeward side. On the leeward side,the air descends, picks up moisture and produces clearweather (Fig. 35.3). The difference between the windwardside and the leeward side can be quite dramatic. In theHawaiian Islands, for example, the windward side of themountains receives more than 750 cm of rain a year, whilethe leeward side, which is in a rain shadow, gets on the av-erage only 50 cm of rain and is generally sunny. In theUnited States, the western side of the Sierra Nevada Moun-tains is lush, while the eastern side is a semidesert.

The distribution of solar energy and the rotation and

path of the earth about the sun affect how the winds

blow and the amount of rainfall that regions of the

biosphere receive. Topography also affects rainfall.

Chapter 35 Biosphere 71935-3

westerlies

westerlies

60S

30S

30N

60N

0

northeast trades

southeast trades

equatorial doldrums

equatorial doldrums

ascendingmoist aircools andloses moisture

descendingdry air warmsand retainsmoisture

moist air

condensation

dry air

Figure 35.2 Global wind circulation.At the equator, warm air rises and loses its moisture. At 30, dry air

descends; therefore, deserts occur at 30 latitude around the world.Because the earth is rotating on its axis, the trade winds move from

the northeast to west in the Northern Hemisphere, and from the

southeast to the west in the Southern Hemisphere. The westerlies

move toward the east.

Figure 35.3 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 mountains receives

relatively little rain and is therefore said to lie in a rain shadow.

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35.2 Biomes of the WorldA biomeis the largest biogeographical unit of the biosphere.

Although the term arose with reference only to terrestrialcommunities, we will be using it for both terrestrial andaquatic communities. A biome has a particular mix of plantsand animals that are adapted to living under certain envi-ronmental conditions, of which climate has an overriding in-fluence. For example, when terrestrial biomes are plottedaccording to their mean annual temperature and mean an-nual rainfall, a particular pattern results (Fig. 35.4a). The dis-tribution of biomes is shown in Figure 35.4b. Even thoughFigure 35.4 shows definite demarcations, the biomes gradu-

ally change from one type to the other. Also, although wewill be discussing each type of biome separately, we shouldremember that each biome has inputs from and outputs toall the other terrestrial and aquatic biomes of the biosphere.

The pattern of life on earth is determined principally byclimate, which is influenced also by topographical features.

The effect of a temperature gradient can be seen not onlywhen we consider latitude but also when we consider alti-tude. If you travel from the equator to the North Pole, it ispossible to observe first a tropical rain forest, followed by atemperate deciduous forest, a coniferous forest, and tundra,in that order, and this sequence is also seen when ascendinga mountain (Fig. 35.5). The coniferous forest of a mountain iscalled a montane coniferous forest, and the tundra near thepeak of a mountain is called an alpine tundra. When goingfrom the equator to the South Pole, you would not reach aregion corresponding to a coniferous forest and tundra ofthe Northern Hemisphere. Why not? Look at the distribu-tion of the land massesthey are shifted toward the north.

The distribution of biomes is determined by

physical factors such as climate (principally

temperature and rainfall), which varies according

to latitude and altitude.


IncreasingAltitude

ice

alpinetundra

montaneconiferousforest

coniferousforest

deciduousforest

temperatedeciduousforest

tropicalforest

tundra ice

Increasing Latitude

Figure 35.5 Climate and biomes.Biomes change with altitude just as they do with latitude because vegetation is partly determined by temperature. Rainfall also plays a significant

role, which is one reason why grasslands, instead of tropical or deciduous forests, are sometimes found at the base of mountains.

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35.3 Terrestrial BiomesThere are many major terrestrial biomes, and we will con-sider these: tundra, coniferous forests (taiga, temperate rainforest), temperate deciduous forest, tropical rain forest, sa-vanna, temperate grasslands, shrubland, and desert.

TundraThe Arctic tundrabiome, which encircles the earth just southof ice-covered polar seas in the Northern Hemisphere, coversabout 20% of the earths land surface (Fig. 35.6).(A similar community, called the alpine tundra, occurs above

the timberline on mountain ranges.) The Arctic tundra is coldand dark much of the year. Because rainfall amounts to onlyabout 20 cm a year, the tundra could possibly be considered adesert, but melting snow creates a landscape of pools andmires in the summer, especially because so little evaporates.Only the topmost layer of earth thaws; the permafrostbeneaththis layer is always frozen, and, therefore, drainage is minimal.

Trees are not found in the tundra because the growingseason is too short, their roots cannot penetrate the per-

mafrost, and they cannot become anchored in the boggy soilof summer. In the summer, the ground is covered with shortgrasses and sedges, but there also are numerous patches oflichens and mosses. Dwarf woody shrubs, such as dwarf

birch, flower and seed quickly while there is plentiful sunfor photosynthesis.

A few animals live in the tundra year-round. For exam-ple, the mouselike lemming stays beneath the snow; theptarmigan, a grouse, burrows in the snow during storms;and the musk ox conserves heat because of its thick coat and

short, squat body. In the summer, the tundra is alive withnumerous insects and birds, particularly shorebirds and wa-terfowl that migrate inland. Caribou and reindeer also mi-grate to and from the tundra, as do the wolves that preyupon them. Polar bears are common near the coast.


Figure 35.6 The tundra.a. In this biome, which is nearest the polar regions, the vegetation

consists principally of lichens, mosses, grasses, and low-growingshrubs. b. Pools of water that do not evaporate nor drain into the

permanently frozen ground attract many birds that feed on the

plentiful insects in the summer. c. Caribou, more plentiful in the

summer than the winter, feed on lichens, grasses, and shrubs. c.

a.

b.

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Coniferous ForestsConiferous forests are found in three loca-tions: in the taiga, which extends around

the world in the northern part of NorthAmerica and Eurasia; near mountaintops (where it is called a montane conif-erous forest), and also along the Pacificcoast of North America, as far south asnorthern California.

The taiga (Fig. 35.7a, b) typifies theconiferous forest with its cone-bearingtrees, such as spruce, fir, and pine. These

trees are well adapted to the cold be-cause both the leaves and bark havethick coverings. Also, the needlelikeleaves can withstand the weight ofheavy snow. There is a limited under-story of plants, but the floor is covered

by low-lying mosses and lichens beneaththe layer of needles. Birds harvest theseeds of the conifers, and bears, deer,moose, beaver, and muskrat live around

the cool lakes and along the streams.Wolves prey on these larger mammals. Amontane coniferous forest also harborsthe wolverine and mountain lion.

The coniferous forest that runs alongthe west coast of Canada and the UnitedStates is sometimes called a temperaterain forest. The prevailing winds mov-ing in off the Pacific Ocean lose their

moisture when they meet the coastalmountain range. The plentiful rainfallalong with a rich soil have producedsome of the tallest conifer trees ever inexistence, including the coastal red-woods. This forest is also called an old-growth forest because some trees are asold as 800 years. It truly is an evergreenforest because all trees are covered withmosses, ferns, and other plants that grow

on their trunks. Whether the limited por-tion remaining should be preservedfrom logging has been quite a contro-versy. Unfortunately, the controversyhas centered around the northern spot-ted owl, which is endemic to this area.The actual concern is conservation ofthis particular ecosystem.


Figure 35.7 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.

bull moose,Alces americanus

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Temperate Deciduous Forests

Temperate deciduous forests are found south of the taiga ineastern North America (Fig. 35.8), eastern Asia, and much of

Europe. The climate in these areas is moderate, with rela-tively high rainfall (75150 cm per year). The seasons arewell defined, and the growing season ranges between 140and 300 days. The trees, such as oak, beech, and maple, have

broad leaves and are termed deciduous trees; they lose theirleaves in the fall and grow them in the spring.

The tallest trees form a canopy, an upper layer of leavesthat are the first to receive sunlight. Even so, enough sunlightpenetrates to provide energy for another layer of trees called

understory trees. Beneath these trees are shrubs that mayflower in the spring before the trees have put forth theirleaves. Still another layer of plant growthmosses, lichens,

and fernsresides beneath the shrub layer. This stratificationprovides a variety of habitats for insects and birds. Groundlife is also plentiful. Squirrels, cottontail rabbits, shrews,skunks, woodchucks, and chipmunks are small herbivores.

These and ground birds such as turkeys, pheasants, andgrouse are preyed on by red foxes. White-tail deer and black

bears have increased in number of late. In contrast to thetaiga, amphibians and reptiles occur in this biome because thewinters are not as cold. Frogs and turtles prefer an aquatic ex-istence, as do the beaver and muskrat, which are mammals.

Autumn fruits, nuts, and berries provide a supply of foodfor the winter, and the leaves, after turning brilliant colors andfalling to the ground, contribute to the rich layer of humus.

The minerals within the rich soil are washed far into theground by the spring rains, but the deep tree roots capturethese and bring them back up into the forest system again.


Figure 35.8 Temperate deciduous forest.A temperate deciduous forest is home to many and varied plants and animals. Millipedes can be found among leaf litter; chipmunks feed on

acorns; and bobcats prey on these and other small mammals.

eastern chipmunk

millipede

marsh marigolds

bobcat


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After DNA analysis, scientists were amazed to find that some60% of loggerheads drowning in the nets and hooks of fisheries

in the Mediterranean Sea were from U.S. Southeast beaches.

Since the unlucky creatures were a good representative sample

of the turtles in the area, that meant that more than half the

young turtles living in the Mediterranean Sea had hatched from

nests on beaches in Florida, Georgia, and South Carolina. Some

20,000 to 50,000 loggerheads die each year due to the Mediter-

ranean fisheries, which may partly explain the decline of log-

gerheads nesting on U.S. Southeast beaches observed for the last25 years. . . .

At the Institute of Arctic Biology at the University of Alaska,

Fairbanks, graduate student Sandra Talbot recently finished se-

quencing DNA by hand from Alaskan brown bears. Wildlife ge-

neticist Gerald Shields, who heads the program, and Talbot

have determined that there are two types of brown bears in

Alaska. One type resides only on southeastern Alaskas Admi-

ralty, Baranof, and Chichagof Islands, known as the ABC Is-

lands. . . .The other brown bear in Alaska is found throughout the rest

of the state, as well as in Siberia and western Asia. A third dis-

tinct type of brown bear, known as the Montana grizzly, resides

in other parts of North America. The three distinct types com-

prise all of the known brown bears in the New World.

The ABC bears uniqueness may be bad news for the timber

industry, which has expressed interest in logging parts of the

ABC Islands. Says Shields, Studies show that when roads are

built and the habitat is fragmented, the population of brown

bears declines. Our genetic observations suggest they are trulyunique, and we should consider their heritage. They could

never be replaced by transplants. . . .

In what will become a classic exam-

ple of how DNA analysis might be used

to protect endangered species from fu-

ture ruin, scientists from the United

States and New Zealand recently carried

out discreet experiments in a Japanese

hotel room on whale sushi bought in lo-cal markets. A staple of the Japanese

diet, sushi is a rice and meat concoction

wrapped in seaweed. Armed with a

miniature DNA sampling machine, the

scientists found that of the 16 pieces of

whale sushi they examined, many were

from whales that are endangered or pro-

tected under an international morato-

rium on whaling. Their findings

demonstrated the true power of DNA

studies, says David Woodruff, a conservation biologist at the

University of California, San Diego.

One sample was from an endangered humpback, four were

fin whale, one was from a northern minke, and another from a

beaked whale. Stephen Palumbi, of the University of Hawaii,

says the technique could be used for monitoring and verifying

catches. Until then, he says, no species of whale can be consid-

ered safe.

Meanwhile, Ken Goddard, director of the unique U.S. Fish

and Wildlife Service Forensics Laboratory in Ashland, Oregon,is already on the watch for wildlife crimes in the United States

and 122 other countries that send samples to him for analysis.

DNA is one of the most powerful tools weve got, says God-

dard, a former California police crime-lab director.

The lab has blood samples, for example, for all of the wolves

being released into Yellowstone Parkfor the obvious reason

that we can match those samples to a crime scene, says God-

dard. The lab has many cases currently pending in court that he

cannot discuss. But he likes to tell the story of the labs first

DNA-matching case. Shortly after the lab opened in 1989, Cali-

fornia wildlife authorities contacted Goddard. They had seized

the carcass of a trophy-size deer from a hunter. They believed the

deer had been shot illegally on a 3,000-acre preserve owned by

actor Clint Eastwood. The agents found a gut pile on the prop-

erty but had no way to match it to the carcass. The hunter had

two witnesses to deny the deer had been shot on the preserve.

Goddards lab analysis made a perfect match between tissue

from the gut pile and tissue from the carcass. Says Goddard:

We now have a cardboard cutout of Clint Eastwood at the labsaying Go ahead: Make my DNA.

725

Wildlife Conservation and DNA

Figure 35A Brown bear diversity.These two brown bears appear to be similar, but DNA studies recently revealed that one type

known as an ABC bear resides only on southeastern Alaskas Admiralty, Baranof, and

Chichagof Islands.


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Tropical Forests

In the tropical rain forests of South America, Africa, and theIndo-Malayan region near the equator, the weather is al-

ways warm (between 20 and 25C), and rainfall is plentiful(with a minimum of 190 cm per year). This may be the rich-est biome, both in terms of number of different kinds ofspecies and their abundance.

A tropical rain forest has a complex structure, with manylevels of life (Fig. 35.9). Some of the broadleaf evergreen treesgrow from 15 to 50 meters or more. These tall trees often havetrunks buttressed at ground level to prevent their topplingover. Lianas, or woody vines, that encircle the tree as it grows,

also help to strengthen the trunk. The diversity of species isenormousa 10-km2 area of tropical rain forest may contain750 species of trees and 1,500 species of flowering plants.

Although there is animal life on the ground (e.g., pacas,agoutis, peccaries, and armadillos), most animals live in the

trees (Fig. 35.10). Insect life is so abundant that the majorityof species have not been identified yet. Termites play a vitalrole in the decomposition of woody plant material, and antsare found everywhere, particularly in the trees. The various

birds, such as hummingbirds, parakeets, parrots, and tou-cans, are often beautifully colored. Amphibians and reptilesare well represented by many types of frogs, snakes, andlizards. Lemurs, sloths, and monkeys are well-known pri-mates that feed on the fruits of the trees. The largest carni-vores are the big catsthe jaguars in South America and theleopards in Africa and Asia.

Many animals spend their entire life in the canopy, as dosome plants. Epiphytes are plants that grow on other plants

but usually have roots of their own that absorb moisture andminerals leached from the canopy; others catch rain and debrisin hollows produced by overlapping leaf bases. The most com-mon epiphytes are related to pineapples, orchids, and ferns.


lianas

epiphyte

understory

canopy

fore

stfloor

Figure 35.9 Tropical rain forest.Levels of life in a tropical rain forest. Even the canopy (solid layer of leaves) has levels, 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.

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While we usually think of tropical forests as being non-seasonal rain forests, there are tropical forests with wet anddry seasons in India, Southeast Asia, West Africa, South andCentral America, the West Indies, and northern Australia.

Here, there are deciduous trees, with many layers of growthbeneath the trees. In addition to the animals just mentioned,certain of these forests also contain elephants, tigers, andhippopotamuses.

Whereas the soil of a temperate deciduous forest biomeis rich enough for agricultural purposes, the soil of a tropicalrain forest biome is not. Nutrients are cycled directly fromthe litter to the plants again. Productivity is high because ofhigh temperatures, a yearlong growing season, and the rapid

recycling of nutrients from the litter. (In humid tropicalforests, iron and aluminum oxides occur at the surface, caus-ing a reddish residue known as laterite. When the trees arecleared, laterite bakes in the hot sun to a bricklike consistencythat will not support crops.) Swidden agriculture, oftencalled slash-and-burn agriculture, is a type of agriculture thathas been successful, but also destructive, in the tropics. Treesare felled and burned, and the ashes provide enough nutri-ents for several harvests. Thereafter, the forest must be al-lowed to regrow, and a new section must be cut and burned.

Figure 35.10 Animals of the tropical rain forest.

lemurPropithecus verreauxi

cone-headed katydid,Panacanthuscuspidatus

arboreal lizard,Calotes calotes

brush-footedbutterfly, Anartiaamalthea linnaeus

dart-poison frog,Dendrobates reticulatus

blue and gold macaw,Ara ararauna

ocelot,Felis pardalis


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ShrublandsIt is difficult to define a shrub, but in general shrubs areshorter than trees (4.56 m) with a woody persistent stem,

and no central trunk. Shrubs have small but thick evergreenleaves that often are coated with a waxy material that pre-vents loss of moisture from the leaves. Their thick under-ground roots survive the dry summers and frequent firesand take deep moisture from the soil. Shrubs are adapted towithstand arid conditions and can also quickly sprout newgrowth after a fire. As a point of interest, you will recall thata shrub stage is a part of the process of both primary andsecondary succession.

Shrublands tend to occur along coasts that have drysummers and receive most of their rainfall in the winter. Ashrubland is found along the cape of South Africa, the west-ern coast of North America, and the southwest and southernshores of Australia, around the Mediterranean Sea, and incentral Chile. The dense shrubland that occurs in Californiais known as chaparral (Fig. 35.11). This type of shrubland,called the Mediterranean type, lacks an understory andground litter, and is highly flammable. The seeds of manyspecies require the heat and scarring action of fire to induce

germination. Other shrubs sprout from the roots after a fire.There is also a northern shrub area that lies west of the

Rocky Mountains. This area is sometimes classified as a colddesert, but the region is dominated by sagebrush and otherhardy plants. Some of the birds found here are dependentupon sagebrush for their existence.

GrasslandsGrasslands occur where rainfall is greater than 25 cm but isgenerally insufficient to support trees. Natural grasslands

once covered more than 40% of the earths land surface, butmany areas that once were grasslands are now used for thecultivation of crops, such as wheat and corn. In temperateareas, where rainfall is between 10 and 30 inches a year,grasslands occur. Here, it is too dry for forests and too wetfor deserts to form.

The grasses are well adapted to a changing environmentand can tolerate a high degree of grazing, flooding, drought,and sometimes fire. Where rainfall is high, large tall grassesthat reach more than 2 meters in height (e.g., pampas grass)can flourish. In drier areas, shorter grasses between 5 and 10cm are dominant. Low-growing bunch grasses (e.g., gramagrass) grow in the United States near deserts. Grasses alsogenerally grow in different seasons; some grassland animalsmigrate, and ground squirrels hibernate, when there is littlegrass for them to eat.

The temperate grasslands include the Russian steppes,the South American pampas, and the North Americanprairies (Fig. 35.12). When traveling across the United

States from east to west, the line between the temperatedeciduous forest and a tall-grass prairie is roughly alongthe border between Illinois and Indiana. The tall-grassprairie requires more rainfall than does the short-grassprairie that occurs near deserts. Large herds of bisones-timated at hundreds of thousandsonce roamed theprairies, as did herds of pronghorn antelope. Now, smallmammals, such as mice, prairie dogs, and rabbits, typi-cally live belowground, but usually feed aboveground.

Hawks, snakes, badgers, coyotes, and foxes feedon these mammals. Virtually all of these grass-lands, however, have been converted to agricul-tural lands.

Savannas, which are grasslands that containsome trees, occur in regions where a relativelycool dry season is followed by a hot, rainy one(Fig. 35.13). One tree that can survive the severedry season is the flat-topped acacia, which shedsits leaves during a drought. The African savanna

supports the greatest variety and number of largeherbivores of all the biomes. Elephants and gi-raffes are browsers that feed on tree vegetation.Antelopes, zebras, wildebeests, water buffalo, andrhinoceroses are grazers that feed on grasses. Anyplant litter that is not consumed by grazers is at-tacked by a variety of small organisms, amongthem termites. Termites build towering nests inwhich they tend fungal gardens, their source offood. The herbivores support a large populationof carnivores. Lions and hyenas hunt in packs,cheetahs hunt singly by day, and leopards huntsingly by night.


Figure 35.11 Shrubland.Shrublands, such as chaparral in California, are subject to raging

fires, but the shrubs are adapted to quickly regrow.


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Figure 35.13 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.

Figure 35.12 The prairie.Tall-grass prairies are seas of grasses dotted by pines and junipers. Bison, once abundant,

are now being reintroduced into certain areas.

zebra (in foreground), Equus quagga

cheetah,Acinonyx jubatus

wildebeest,Connochaetes sp.

giraffe,Giraffa camelopardalis

American bison,Bison bison

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DesertsAs discussed previously, deserts are usually found at lati-tudes of about 30, in both Northern and Southern Hemi-

spheres. The winds which descend in these regions lackmoisture. Therefore, the annual rainfall is less than 25 cm.Days are hot because a lack of cloud cover allows the sunsrays to penetrate easily, but the nights are cold because heatescapes easily into the atmosphere.

The Sahara, which stretches all the way from the At-lantic coast of Africa to the Arabian Peninsula, and a fewother deserts have little or no vegetation. But most have avariety of plants (Fig. 35.14). The best-known desert peren-nials in North America are the succulent, spiny-leafed cacti,which have stems that store water and carry on photosyn-thesis. Also common are nonsucculent shrubs, such as themany-branched sagebrush with silvery gray leaves and thespiny-branched ocotillo that produces leaves during wet pe-riods and sheds them during dry periods.

Some animals are adapted to the desert environment.Reptiles and insects have waterproof outer coverings thatconserve water. A desert has numerous insects, which passthrough the stages of development from pupa to the next

pupa again when there is rain. Reptiles, especially lizardsand snakes, are perhaps the most characteristic group of ver-tebrates found in deserts, but running birds (e.g., the road-runner) and rodents (e.g., the kangaroo rat) are also wellknown (Fig. 35.14). Larger mammals, like the coyote, preyon the rodents, as do the hawks.


Figure 35.14 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.

bannertail kangaroo rat, Dipodomys spectabilis

greater roadrunner, Geococcyx californianus


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35.4 Aquatic BiomesAquatic biomes are classified as two types: freshwater (in-land) or saltwater (usually marine). Brackish water, however,

is a mixture of fresh and salt water. Figure 35.15 shows howthese communities are joined physically. In the water cycle,the suns rays cause seawater to evaporate and the salts areleft behind. The vaporized fresh water rises into the atmo-sphere, cools, and falls as rain either over the ocean or over theland. A lesser amount of water also evaporates from and re-turns to the land. Since land lies above sea level, gravity even-tually returns all fresh water to the sea, but in the meantime, itis contained within standing waters (lakes and ponds), flow-

ing waters (streams and rivers), and groundwater.When rain falls, some of the water sinks or percolates into

the ground and saturates the earth to a certain level. The top ofthe saturation zone is called the groundwater table, or simplythe water table. Wherever the earth contains basins or chan-nels, water will appear to the level of the water table. The

water within basins is called lakes and ponds, and the waterwithin channels is called streams or rivers. Sometimes ground-water is also located in underground rivers called aquifers.

Humans have the habit of channeling aboveground rivers

and filling in wetlands (lands that are wet for at least part ofthe year). These activities degrade ecosystems and eventuallycause seasonal flooding. Wetlands provide food and habitatsfor fish, waterfowl, and other wildlife. They also purify waters

by filtering them and by diluting and breaking down toxicwastes and excess nutrients. Wetlands directly absorb stormwaters and also absorb overflows from lakes and rivers. In thisway they protect farms, cities, and towns from the devastatingeffects of floods. There are now federal and local laws for the

protection of wetlands, but they are not always enforced.

Aquatic biomes can be classified as freshwater or

saltwater. The two sets of communities interact

and are joined by the water cycle.


stream

river

lake

salt marsh

delta

stonefly larva, Plecopterasp. red banded trout, Salmo gairdneri

carp,Cyprinus carpio

Figure 35.15 Streams and rivers.Mountain streams have cold, clear water that flows over waterfalls and rapids. The feet of this long-legged stonefly insect larva are clawed,

helping it to hold on to stones. Trout are found in occasional pools of the highly oxygenated water. As the streams merge, a river forms that gets

increasingly wider and deeper until it meanders across broad, flat valleys. Carp are adapted to water that contains little oxygen and has much

sediment. At its mouth, a river may divide into many channels where wetlands and estuaries are located.

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LakesLakes are bodies of fresh water often classified by their nu-trient status. Oligotrophic (nutrient-poor) lakes are charac-

terized by low organic matter and low productivity.Eutrophic (nutrient-rich) lakes are characterized by high or-ganic matter and high productivity. Such lakes are usuallysituated in naturally nutrient-rich regions or are enriched byagricultural or urban and suburban runoffs. Oligotrophiclakes can become eutrophic through large inputs of nutri-ents (Fig. 35.16). This process is called eutrophication.

In the temperate zone, deep lakes are stratified in thesummer and winter. In summer, lakes in the temperate zonehave three layers of water that differ in temperature (Fig.35.17). The surface layer, the epilimnion, is warm from solarradiation; the middle thermocline experiences an abrupt

drop in temperature; and the hypolimnion is cold. These dif-ferences in temperature prevent mixing. The warmer, lessdense water of the epilimnion floats on top of the colder,more dense water of the hypolimnion.

As the season progresses, the epilimnion becomesnutrient-poor, while the hypolimnion begins to be depletedof oxygen. The phytoplankton found in the sunlit epi-limnion use up nutrients as they photosynthesize. Photo-synthesis releases oxygen, giving this layer a ready supply.Detritus naturally falls by gravity to the bottom of the lake,and here oxygen is used up as decomposition occurs. De-composition releases nutrients, however.

In the fall, as the epilimnion cools, and in the spring, as

it warms, an overturn occurs. In the fall, the upper epi-limnion waters become cooler than the hypolimnion waters.This causes the surface water to sink and the deep water torise. The fall overturn continues until the temperature isuniform throughout the lake. At this point, wind aids in thecirculation of water so that mixing occurs. Eventually, oxy-gen and nutrients become evenly distributed.


b.

a.

epilimnion 2425C

thermocline 1318C

hypolimnion 58C

23C

most of lake4C

Summer Stratification

wind

Spring Overturn Fall Overturn

Winter Stratification

wind wind

windice

Figure 35.16 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.

Figure 35.17 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.

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As winter approaches, the water cools. Ice formation be-gins at the top, and the ice remains there because ice is lessdense than cool water. Ice has an insulating effect, prevent-ing further cooling of the water below. This permits aquaticorganisms to live through the winter in the water beneaththe surface of the ice.

In the spring, as the ice melts, the cooler water on topsinks below the warmer water on the bottom. The springoverturn continues until the temperature is uniform

through the lake. At this point, wind aids in the circulationof water as before. When the surface waters absorb solar ra-diation, thermal stratification occurs once more.

This vertical stratification and seasonal change of temper-atures in a lake basin influence the seasonal distribution of fishand other aquatic life in the lake basin. For example, coldwaterfish move to the deeper water in summer and inhabit the up-per water in winter. In the fall and spring just after mixing oc-curs, phytoplankton growth at the surface is most abundant.

Life ZonesIn both fresh and salt water, free-drifting microscopic organ-isms, called plankton,are important components of the com-munity. Phytoplankton are photosynthesizing algae that

become noticeable when a green scum or red tide appears onthe water. Zooplanktonare animals that feed on the phyto-plankton. Lakes and ponds can be divided into several lifezones. The littoral zone is closest to the shore, the limnetic zoneforms the sunlit body of the lake, and theprofundal zone is be-low the level of light penetration (Fig. 35.18). The benthic zoneincludes the sediment at the soil-water interface. Aquaticplants are rooted in the shallow littoral zone of a lake, andvarious microscopic organisms cling to these plants and to

rocks. Some organisms such as the water strider live at thewater-air interface and can literally walk on water. In the lim-netic zone, small fishes, such as minnows and killifish feedon plankton and also serve as food for large fishes. In the pro-fundal zone, there are zooplankton and fishes such as white-fish that feed on debris that falls from above. Pike species arelurking predators. They wait among vegetation around themargins of lakes and surge out to catch passing prey.

A few insect larvae are in the limnetic zone, but they are

far more prominent in both the littoral and profundal zones.Midge larvae and ghost worms are common members of thebenthos. The benthos are animals that live on the bottom inthe benthic zone. In a lake, the benthos include crayfish,snails, clams, and various types of worms and insect larvae.


Figure 35.18 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-repellent feet. Crayfishes and mollusks are in the profundal zone and also the littoral zone.

Pike are top carnivores prized by fishermen.

clingingorganisms

bottom-dwelling organisms

BenthicZone

Limne

ticZo

ne

Littoral Zone

Profun

dalZ

one

fishes

surfaceorganisms insect

larvae

zooplankton

phytoplanktonfloatingo

rganism

s

pike, Esox Iucius

water strider, Gerris sp.

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Coastal CommunitiesNear the mouth of a river, a salt marsh in the temperate zoneand a mangrove swamp in the subtropical and tropical zonesare likely to develop. Also, the silt carried by a river mayform mudflats. It is proper to think of seacoasts and mud-flats, salt marshes, and mangrove swamps as belonging to

one ecological system.

EstuariesAn estuary is a partially enclosed body of water wherefresh water and seawater meet and mix (Fig. 35.19). Ariver brings fresh water into the estuary, and the sea, be-cause of the tides, brings salt water. Coastal bays, tidalmarshes, fjords (an inlet of water between high cliffs),some deltas (triangular-shaped areas of land at themouths of rivers), and lagoons (a body of water separated

from the sea by a narrow strip of land) are all examples ofestuaries.

Organisms living in an estuary must be able to with-stand constant mixing of waters and rapid changes insalinity. Not many organisms are suited to this environ-ment, but for those that are suited, there is an abundanceof nutrients. An estuary acts as a nutrient trap because thesea prevents the rapid escape of nutrients brought by ariver.

Although only a few small fish permanently reside in anestuary, many develop there, so that there is always anabundance of larval and immature fish. It has been esti-mated that well over half of all marine fishes develop in theprotective environment of an estuary, which explains why


Marine snails, at the base of salt

marsh cordgrass, feed on algae.

b.

a.

Figure 35.20 Types of estuaries.Many types of regions qualify as estuaries, such as the salt marsh

depicted in Figure 35.19 and (a) mudflats, which are frequented bymigrant birds, and (b) mangrove swamps skirting the coastlines of

many tropical and subtropical lands. The tangled roots of mangrove

trees trap sediments and nutrients that sustain many immature forms

of sea life.

Figure 35.19 Estuary structure and function.Since an estuary is located where a river flows into the ocean, i t receives nutrients from land. Estuaries serve as a nursery for the spawning and

rearing of the young for many species of fishes, shrimp and other crustaceans, and mollusks.

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estuaries are called the nurseries of the sea. Estuaries are alsofeeding grounds for many birds, fish, and shellfish becausethey offer a ready supply of food.

Salt marshes dominated by salt marsh cordgrass are of-ten associated with estuaries. So are mudflats and mangrove

swamps, where sediment and nutrients from the land collect(Fig. 35.20).

SeashoresBoth rocky and sandy shores are constantly bombarded bythe sea as the tides roll in and out (Fig. 35.21). The littoralzone lies between the high and low water marks. The lit-toral zone of a rocky beach is divided into subzones. In theupper portion of the littoral zone, barnacles are glued so

tightly to the stone by their own secretions that their cal-careous outer plates remain in place even after the enclosedshrimplike animal dies. In the midportion of the littoralzone, brown algae known as rockweed may overlie the bar-nacles. In the lower portions of the littoral zone, oysters and

mussels attach themselves to the rocks by filaments calledbyssal threads. Also present are snails called limpets andperiwinkles. But periwinkles have a coiled shell and securethemselves by hiding in crevices or under seaweeds, whilelimpets press their single flattened cone tightly to a rock.

Below the littoral zone, macroscopic seaweeds, which arethe main photosynthesizers, anchor themselves to the rocks

by holdfasts.Organisms cannot attach themselves to shifting, unsta-

ble sands on a sandy beach; therefore, nearly all the perma-nent residents dwell underground. They either burrowduring the day and surface to feed at night, or they remainpermanently within their burrows and tubes. Ghost crabsand sandhoppers (amphipods) burrow themselves above

the high tide mark and feed at night when the tide is out.Sandworms and sand (ghost) shrimp remain within theirburrows in the littoral zone and feed on detritus wheneverpossible. Still lower in the beach, clams, cockles, and sanddollars are found.


upper littoral zone

mid littoral zone

lower littoral zone

a.

b.

c.

Figure 35.21 Seacoasts.a. 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. b. Some organisms of a rocky coast live

in tidal pools. c.A sandy shore looks devoid of life except for the

birds that feed there. However, a number of invertebrate species

burrow in the sand and sediment beneath the sand.


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OceansClimate is driven by the sun, but the oceans play a majorrole in redistributing heat in the biosphere. Water tends to be

warm at the equator and much cooler at the poles because ofthe distribution of the suns rays, as we have discussed be-fore (see Fig. 35.1a). Air takes on the temperature of the wa-ter below, and warm air moves from the equator to thepoles. In other words, the oceans make the winds blow. (Theland masses also play a role, but the oceans hold heat longerand remain cool longer during periods of changing temper-ature than do solid continents.)

When the wind blows strongly and steadily across agreat expanse of ocean for a long time, friction from the

moving air begins to drag the water along with it. Once thewater has been set in motion, its momentum, aided by thewind, keeps it moving in a steady flow we call a current. Be-cause the ocean currents eventually strike land, they movein a circular pathclockwise in the Northern Hemisphereand counterclockwise in the Southern Hemisphere (Fig.35.22). As the currents flow, they take warm water from theequator to the poles. One such current, called the GulfStream, brings tropical Caribbean water to the east coast of

North America and the higher latitudes of western Europe.Without the Gulf Stream, Great Britain, which has a rela-

tively warm temperature, would be as cold as Greenland. Inthe Southern Hemisphere, another major ocean currentwarms the eastern coast of South America.

Also, in the Southern Hemisphere a current called the

Humboldt Current flows toward the equator. The Hum-boldt Current carries phosphorus-rich cold water north-ward along the west coast of South America. During aprocess called upwelling, cold offshore winds cause coldnutrient-rich waters to rise and take the place of warmnutrient-poor waters. In South America, the enriched waterscause an abundance of marine life that supports the fisheriesof Peru and northern Chile. Birds feeding on these organ-isms deposit their droppings on land, where it is mined asguano, a commercial source of phosphorus. When the Hum-

boldt Current is not as cool as usual, upwelling does not oc-cur, stagnation results, the fisheries decline, and climatepatterns change globally. This phenomenon, which is dis-cussed in the accompanying reading, is called ElNioSouthern Oscillation.

Major ocean currents move heat from the equator

to cooler parts of the biosphere. The Gulf Stream

warms the east coast of North America and parts

of Europe.


Asia

Australia

SouthAmerica

NorthAmerica

Africa

Europe

GulfS

tream

equatorequatorial countercurrent

JapanCu

rrent

warm currents

cold currents

west wind driftwestwinddrift

east wind drift

Antarctica

Figure 35.22 Ocean currents.The arrows on this map indicate the locations and directions of the major ocean currents set in motion by the global wind circulation. By carrying

warm water to cool latitudes (e.g., Gulf Stream) and cool water to warm latitudes (e.g., Humboldt Current), these currents have a major effect on

the worlds climates.


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SouthAmerica

cold water

warm water

cold water

warm water

Pacific OceanPacific Ocean

Australiatrade winds trade winds

ocean currentsocean currents

equatorequator

a. b.

where funds to import replacement supplies of food are limited.There can even be a backward movement of winds and ocean

currents so that the waters can warm to more than 14 above nor-

mal along the west coast of the Americas. Now a severe El Nio

has occurred, and the weather changes are dramatic in the Amer-

icas also. Southern California is hit by storms and even hurri-

canes, and the deserts of Peru and Chile receive so much rain

that flooding occurs. A jet stream (strong wind currents) can

carry moisture into Texas, Louisiana, and Florida, with flooding

a near certainty. Or the winds can turn northward and depositsnow in the mountains along the west coast so that flooding

occurs here in the spring. Some parts of the United States, how-

ever, benefit from an El Nio. The Northeast is warmer than

usual, few if any hurricanes hit the east coast, and there is a lull

in tornadoes throughout the Midwest. Altogether, a severe El

Nio affects the weather over three-quarters of the globe.

Eventually an El Nio dies out and normal conditions return.

The normal cold-water state off the coast of Peru is known as La

Nia (the girl). Figure 35B contrasts the weather conditions of a

La Nia with those of an El Nio. Since 1991, the sea surface hasbeen almost continuously warm and there have been two

recording-breaking El Nios. What could be causing more of the

El Nio state rather than the La Nia state? Some scientists are

seeking data to relate this environmental change to global

warming. Global warming is a rise in environmental tempera-

ture due to greenhouse gases, like carbon dioxide, in the atmo-

sphere. Like the glass of a greenhouse, the gases allow the suns

rays to pass through, but trap the heat. Greenhouse gases are

pollutants that human beings have been pumping into theatmosphere since the industrial revolution.

El NioSouthern Oscillation

Figure 35B a. La Nia Upwelling off the west coast of South America brings cold

waters to the surface.

High barometric pressure over southeastern Pacific.

Monsoons associated with Indian Ocean occur.

Hurricanes off the east coast of the U.S.

b. El Nio

Great ocean warming off the west coast of the Americas.

Low barometric pressure over southeastern Pacific.

Monsoons associated with Indian Ocean fail.

Hurricanes off the west coast of the U.S.

Climate largely determines the distribution of life on earth.Short-term variations in climate, which we call weather, also

have a pronounced effect on living things. There is no better ex-

ample than an El Nio. Originally, El Nio referred to a warm-

ing of the seas off the coast of Peru at Christmas timehence its

name El Nio, the boy child for the Christ child Jesus.

Now scientists prefer the term El Nio-Southern Oscillation

(ENSO) for a severe weather change brought on by an interac-

tion between the atmosphere and ocean currents. Ordinarily the

southeast trade winds move along the coast of South Americaand turn west because of the earths daily rotation on its axis. As

the winds drag warm ocean waters from east to west, there is an

upwelling of nutrient-rich cold water from the oceans depths

that results in a bountiful Peruvian harvest of anchovies. When

the warm ocean waters reach their western destination, the

monsoons bring rain to India and Indonesia. Scientists have

noted that these events correlate with a difference in the baro-

metric pressure over the Indian Ocean and the southeastern

Pacificthe barometric pressure is low over the Indian Ocean

and the barometric pressure is high over the southeastern

Pacific. But when a southern oscillation occurs and the baro-

metric pressures switch, an El Nio begins.

During an El Nio, both the northeast and the southeast trade

winds slacken. Upwelling no longer occurs and the anchovy fish-

ery off the coast of Peru plummets. During a severe El Nio, wa-

ters from the east never reach the west and the winds lose their

moisture in the middle of the Pacific instead of over the Indian

Ocean. The monsoons fail and there is drought in India, Indonesia,

Africa, and Australia. Harvests decline, cattle must be slaugh-tered, and famine is likely in highly populated India and Africa,


738 Part 7 Behavior and Ecology 35 22
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Pelagic Division

The oceans cover approximately three-quarters of ourplanet. The geographic areas and zones of an ocean areshown in Figure 35.23. It is customary to place the organ-

isms of the oceans into either the pelagic division (open wa-ters) or the benthic division (ocean floor).

The pelagic division includes the neritic province andthe oceanic province. The neritic province has a greaterconcentration of organisms than the oceanic province be-cause the neritic province is sunlit and has a supply of in-organic nutrients for photosynthesizers. Phytoplankton,consisting of suspended algae, is food not only for zoo-plankton but also for small fishes. These small fishes inturn are food for commercially valuable fishesherring,cod, and flounder.

The oceanic province lacks the inorganic nutrients of theneritic province, and therefore does not have as high a con-centration of phytoplankton, even though the epipelagic

zone is sunlit. Still, the photosynthesizers are food for a largeassembly of zooplankton, which are food for herrings and

bluefishes. These, in turn, are eaten by larger mackerels, tu-nas, and sharks. Flying fishes, which glide above the surface,are preyed upon by dolphins (not to be confused with por-

poises, which also are present). Whales are other mammalsfound in the epipelagic zone. Baleen whales strain krill(small crustacea) from the water, and the toothed spermwhales feed primarily on the common squid.

Animals in the mesopelagic zone are carnivores, areadapted to the absence of light, and tend to be translucent,red colored, or even luminescent. There are luminescentshrimps, squids, and fishes, such as lantern and hatchetfishes.

The bathypelagic zone is in complete darkness exceptfor an occasional flash of bioluminescent light. Carnivoresand scavengers are found in this zone. Strange-lookingfishes with distensible mouths and abdomens and small,tubular eyes feed on infrequent prey.


high tide marklow tide mark

sublittoralzone

continentalshelf

bath

yalzone

continentalslo

pe

littoral

NeriticProvince

OceanicProvince

Benthic

Division

Divisions of the Ocean

Pelagic Division

Neritic province(above continental shelf)

Oceanic province

(the oceanic basins)

Benthic Division

Continental shelf(in sublittoral shelf)

Continental slope(in bathyal zone)

Abyssal plain(in abyssal zone)

epipelagic zone

bathypelagic zone

abyssal zone

abyssal plain

abyssalplain

mesopelagic zone

120 m

1,200 m

3,000 m

4,000 m

depth(meters)

PelagicDivision

Figure 35.23 Marine environment.Organisms reside in the pelagic division (blue), where waters are divided as indicated. Organisms also reside in the benthic division (brown), withsurfaces divided and in the zones indicated.


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Benthic DivisionThe benthic division includes organisms thatlive on or in the soil of the continental shelf

(sublittoral zone), the continental slope (bathy-al zone), and the abyssal plain (abyssal zone)(Fig. 35.24). These are the organisms of the sub-littoral, bathyal, and abyssal zones.

Seaweed grows in the sublittoral zone, andit can be found in batches on outcroppings asthe water gets deeper. There is more diversityof life in the sublittoral and bathyal zones thanin the abyssal zone. In these first two zones,clams, worms, and sea urchins are preyed

upon by starfishes, lobsters, crabs, and brittlestars. Photosynthesizing algae occur in thesunlit sublittoral zone, but benthic organismsin the bathyal zone are dependent on the slowrain of detritus from the waters above.

The abyssal zone is inhabited by animalsthat live at the soil-water interface of theabyssal plain (Fig. 35.24). It once was thoughtthat few animals exist in this zone because of

the intense pressure and the extreme cold. Yetmany invertebrates live here by feeding on de-bris floating down from the mesopelagic zone.Sea lilies rise above the seafloor; sea cucumbersand sea urchins crawl around on the sea bot-tom; and tube worms burrow in the mud.

The flat abyssal plain is interrupted byenormous underwater mountain chains calledoceanic ridges. Along the axes of the ridges,crustal plates spread apart and molten magma

rises to fill the gap. At hydrothermal vents,seawater percolates through cracks and isheated to about 350C, causing sulfate to reactwith water and form hydrogen sulfide (H2S).Chemosynthetic bacteria that obtain energyfrom oxidizing hydrogen sulfide exist freely ormutualistically within the tissues of organ-isms. They are the start of food chains for acommunity that includes huge tube worms

and clams. It was a surprise to find communi-ties of organisms living so deep in the ocean,where light never penetrates. Unlike photo-synthesis, chemosynthesis does not requirelight energy.

Chapter 35 Biosphere 73935 23

phytoplankton zooplankton

flying fish

sea turtle dolphins

shark

jellyfish

ocean bonito mackerel

baleenwhale

Epipelagic Zone(0120 m)

squid

tuna

giantsquid

prawnmidshipman

lanternfish

Mesopelagic Zone(1201,200 m)

viperfish

hagfish

anglerfish

sperm whale

swallowers

Bathypelagic Zone(1,2003,000 m)

deep-seashrimp

tripodfish

glasssponges

sea cucumber

brittle stars

gulper

Abyssal Zone(3,000 mbottom)

Figure 35.24 Pelagic division.Organisms of the epipelagic, mesopelagic, and bathypelagic zones are shown. The

abyssal zone is a part of the benthic division.

The neritic province and the

epipelagic zone of the oceanic

province receive sunlight and contain

the organisms with which we aremost familiar. The organisms of the

benthic division are dependent upon

debris that floats down from above.


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Coral ReefsCoral reefs (Fig. 35.25) are areas of biological abundancefound in shallow, warm, tropical waters just below the sur-

face of the water. Their chief constituents are stony corals,animals that have a calcium carbonate (limestone) exoskele-ton, and calcareous red and green algae. Corals do not usu-ally occur individually; rather, they form colonies derivedfrom an individual coral that has reproduced by means of

budding. Corals provide a home for a microscopic algacalled zooxanthellae. The corals, which feed at night, andthe algae, which photosynthesize during the day, are mutu-alistic and share materials and nutrients. The close relation-ship of corals and zooxanthellae may be the reason why

coral reefs form only in shallow sunlit water

the algae uti-lize sunlight for photosynthesis.

A reef is densely populated with life, perhaps becausereefs are areas of intermediate disturbance (p. 713). The largenumber of crevices and caves provide shelter for filter feed-ers (sponges, sea squirts, and fan worms) and for scavengers(crabs and sea urchins). The barracuda, moray eel, andsharks are top predators in coral reefs. There are many typesof small beautifully colored fishes. Parrot fishes feed directly

on corals, and others feed on plankton or detritus. Smallfishes become food for larger fishes like snappers that arecaught for human consumption.

gy

Figure 35.25 Coral reefs.A coral reef is a rich community of marine organisms.

Pollution of fresh water comes from twosources. Point sources, like paper millsor other industries that discharge pollu-tants directly into nearby rivers and bod-ies of water, are easily identifiable.Nonpoint sources, which are simply dueto runoff from the land, are not easily iden-tifiable. Although the public generally be-lieves that big corporations are stillcausing most of the freshwater pollution,

this is not the case. Instead, nonpointsources are causing most of the problem.Agricultural fertilizers are the chief causeof nitrate contamination of drinking-waterwells. Excessive nitrates in a babys blood-stream can lead to a slow suffocationknown as blue-baby syndrome. Agricul-tural herbicides are suspected carcinogensin the tap water of scattered communitiescoast to coast. A 1993 runoff from a dairy

farm carried a parasite called cryp-tosporidium to the drinking water of Mil-waukee, Wisconsin, sickening thousandsof people, and killing a few. What can bedone? Some farmers are already using irri-

gation methods that deliver water directlyto plant roots, no-till agriculture that re-duces the loss of top soil and cuts back onherbicide use, and integrated pest man-agement that relies heavily on good bugsto kill bad bugs. Perhaps more should doso. Encouragedin some casescompelledby state and federal agents,dairy farmers have built sheds, concretecontainments, and underground liquid

storage tanks to hold the wastes fromrainy days. Then, the manure can betrucked to fields and spread as fertilizer.

Home owners, like business golf clubsand ski resorts, also contribute to the prob-lem. The manicuring of lawns, the use ofmotor vehicles, and the construction anduse of roads and buildings all add contam-inants to streams, lakes, and aquifers. Citi-zens around Grand Traverse Bay on the

eastern shore of Lake Michigan have got-ten the message, especially because theywant to keep on enjoying water-dependentactivities like boating, bathing, and fishing.

James Haverman, a concerned member of

the Traverse Bay Watershed Initiative says,If we cant change the way people livetheir everyday lives, we are not going to beable to make a difference. Builders in Tra-verse County are already required to con-trol soil erosion with filter fences, steerrainwater away from exposed soil, buildsediment basins, and plant protective

buffers. Should similar restrictions hold forhome builders? Presently they must have a

25-foot setback from wetlands and a 50-foot setback from lakes and creeks. Theyare also encouraged to pump out their sep-tic systems every two years.

Questions1. Do you approve of legislation that

requires farmers and homeowners toprotect freshwater supplies? Why or whynot?

2. Should landscapers and gardeners be

required to follow certain restrictions?Why or why not?3. Do you approve of legislation that

restricts the number of homes in aparticular area? Why or why not?

Coral reefs, which are areas of biologicalabundance, occur in tropical seas.


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Summarizing the Concepts

35.1 Climate and the BiosphereBecause the earth is a sphere, the suns rays at the poles are spread out

over a larger area than the vertical rays at the equator. The temperatureat the surface of the earth therefore decreases from the equator to each

pole. The earth is tilted on its axis, and the seasons change as the earth

rotates annually about the sun.

Warm air rises near the equator and loses its moisture and then de-

scends at about 30 north and south latitude, and so forth to the poles.

When the air descends, it is dry, and therefore the great deserts of the

world are formed at 30 latitudes. Because the earth rotates on its axis

daily, the winds blow in opposite directions above and below the equa-

tor. Topography also plays a role in the distribution of moisture. Air ris-

ing over coastal ranges loses its moisture on the windward side,making the leeward side arid.

35.2 Biomes of the WorldThe term biome is used to refer to terrestrial and aquatic communities.

Biomes are distributed according to climate; that is, temperature and

rainfall influence the pattern of biomes about the world. The signifi-

cance of temperature is also seen by observing that the same sequence

of biomes is seen when traveling to northern latitudes as traveling up a

mountain.

35.3 Terrestrial BiomesThe tundra is the northernmost biome and consists largely of short

grasses and sedges and dwarf woody plants. Because of the cold win-

ters and short summers, most of the water in the soil is frozen the year

round. This is called the permafrost.

The taiga, a coniferous forest, has less rainfall than other types of

forests. The temperate deciduous forest has trees that gain and lose

their leaves because of the alternating seasons of summer and winter.

Tropical rain forests are the most complex and productive of all biomes.

Shrublands usually occur along coasts that have dry summers and

receive most of their rainfall in the winter. Among grasslands, the sa-

vanna, a tropical grassland, supports the greatest number of different

types of large herbivores. The prairie, found in the United States, has a

limited variety of vegetation and animal life.

Deserts are characterized by a lack of waterthey are usually

found in places with less than 25 cm a year. Some plants, such as cacti,

are succulents, and others are shrubs with thick leaves they often lose

during dry periods.

35.4 Aquatic Biomes

Rain falls in mountains, and streams develop that join to form a riverwhich runs into the sea. Streams, rivers, lakes, and wetlands are differ-

ent communities.

In deep lakes of the temperate zone, the temperature and the con-

centration of nutrients and gases in the water vary with depth. The en-

tire body of water is cycled twice a year, distributing nutrients from the

bottom layers. Lakes and ponds have three life zones. Rooted plants

and clinging organisms live in the littoral zone, plankton and fishes are

in the sunlit limnetic zone, and bottom-dwelling organisms like cray-

fishes and mollusks are in the profundal zone.

Estuaries (e.g., salt mashes, mudflats, mangrove forests) are nearthe mouth of a river. Estuaries are the nurseries of the sea. Marine com-

munities are divided into coastal communities and the oceans. The

coastal communities, especially estuaries, are more productive than the

oceans.

An ocean is divided into the pelagic division and the benthic divi-

sion. The oceanic province of the pelagic division (open waters) has

three zones. The epipelagic zone receives adequate sunlight and sup-

ports the most life. The mesopelagic zone contains organisms adapted

to minimum and no light, respectively. The benthic division (ocean

floor) includes organisms living on the continental shelf in the sublit-

toral zone, the continental slope in the bathyal zone, and the abyssal

plain in the abyssal zone. Coral reefs are extremely productive com-

munities found in shallow tropical waters.

Studying the Concepts

1. Tell how a spherical earth and the path of the earth about thesun affect climate. 71819

2. Describe the air circulation about the earth; tell why desertsare apt to occur at 30 north and south of the equator.Why does the Pacific coast of California get plentifulrainfall? 719

3. Name the terrestrial biomes you would expect to find whengoing from the base to the top of a mountain. 721

4. Describe the location, the climate, and the populations of theArctic tundra, coniferous forests (both taiga and temperaterain forest), temperate deciduous forests, tropical forests,shrubland, grasslands (both prairie and savanna), and

deserts. 722

24, 726

305. Describe the overturn of a temperate lake, and the life zonesof a lake, and the organisms you would expect to find in eachzone. 73233

6. Describe the coastal communities, and discuss the impor-tance of estuaries to the productivity of the ocean. 73435

7. Describe the ocean currents and how the Gulf Streamaccounts for Great Britain having a mild temperature. 736

8. Describe the zones of the open ocean and the organisms youwould expect to find in each zone. 73839

9. Describe a coral reef, including the varied organisms foundthere. 740

Testing Yourself

Choose the best answer for each question.1. The seasons are best explained by

a. the distribution of temperature and rainfall in biomes.b. the tilt of the earth on its axis as it rotates about the sun.c. the daily rotation of the earth on its axis.

d. the fact that the equator is warm and the poles arecold.

2. The mild climate of Great Britain is best explained bya. the winds called the westerlies.

b. the spinning of the earth on its axis.c. Great Britain being a mountainous country.d. the flow of ocean currents.

3. The location of deserts at 30 is best explained by whichstatement?a. Warm air rises and loses its moisture; cool air descends

and becomes warmer and drier.b. Ocean currents give up heat as they flow from the equator

to the poles.c. Cool ocean breezes cool the coast during the day.d. All of these are correct.

p



8/13/2019 Chapt 35

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4. Which of these is mismatched?a. tundrapermafrost

b. savannaacacia treesc. prairieepiphytesd. coniferous forestevergreen trees

5. All of these phrases describe the tundra excepta. low-lying vegetation.

b. northernmost biome.c. short growing season.d. many different types of species.

6. The forest with a multilevel understory is thea. tropical rain forest.

b. coniferous forest.c. tundra.d. temperate deciduous forest.

7. All of these phrases describe a tropical rain forest excepta. nutrient-rich soil.

b. many arboreal plants and animals.c. canopy composed of many layers.d. broad-leaved evergreen trees.

8. Phytoplankton are more likely to be found in which life zoneof a lake?a. limnetic zone c. benthic zone

b. profundal zone d. All of these are correct.9. An estuary acts as a nutrient trap because of the

a. action of rivers and tides.b. depth at which photosynthesis can occur.c. amount of rainfall received.d. height of the water table.

10. Which area of an ocean has the greatest concentration ofnutrients?a. epipelagic zone and benthic zone

b. epipelagic zone onlyc. benthic zone onlyd. neritic province

Understanding the Terms

alpine tundra 721Arctic tundra 722

benthic division 739biome 721biosphere 718chaparral 728climate 718

coral reef 740desert 730El NioSouthern Oscillation

736epiphyte 726estuary 734eutrophication 732fall overturn 732hydrothermal vent 739lake 732

montane coniferous forest 721pelagic division 738permafrost 722phytoplankton 733plankton 733rain shadow 719savanna 728

shrubland 728spring overturn 733taiga 723temperate deciduous

forest 724temperate rain forest 723tropical rain forest 726upwelling 736zooplankton 733

Match the terms to these definitions:a. End of a river where fresh water and salt water

mix as they meet.

b. Major terrestrial community characterized bycertain climatic conditions and dominated by particular typesof plants.

c. Ocean floor, which supports a unique set of organisms in contrast to the pelagic division.

d. Terrestrial biome that is a grassland

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