Chapter 34 Lecture Outline
Introduction
A Mysterious Giant of the Deep
A. The ocean is a very special environment.
1. Exploration of the ocean’s depths requires special submersibles such as Alvin, seen in
Figure A. Unusual new species, such as giant squids have been discovered at these depths.
Review: Continental drift and the location of crustal plates (Modules 15.3).
2. Off the coast of Baja California between crustal plates, at depths of more than a mile and in
complete darkness, hydrothermal vents release hot, nutrient-rich gases (Figure B).
3. Around these vents are groups of organisms, the most obvious of which are large, yard-long
tube worms. A variety of other animals, including shrimps, crabs, clams, and a few fishes,
also live here (Figure C).
4. Most of the prokaryotes in hydrothermal vents are chemoautotrophs (Module 16.11).
Ultimately, all the other organisms depend on the food made by these prokaryotes because
energy sources dependent on sunlight never make it in any appreciable quantity to these
depths.
5. This setting hints at many of the topics concerning populations, communities, and nutrient
cycling that ecologists study.
B. Ecology is the scientific study of the interactions between organisms and their environments.
1. Dealing with humankind’s gravest biological crises hinges on a firm understanding of
ecological principles.
2. This unit starts with an overview of Earth’s different biological settings, details the
principles and mechanisms of ecology, and ends with a discussion of the impact of human
societies on the biosphere.
Module 34.1 Ecologists study how organisms interact with their environment at several levels.
Review: The hierarchical organization of life (Module 1.1) and the scientific process (Modules 1.7
and 1.8).
A. At the organism level, the focus is on how an individual organism interacts with aspects of its
immediate surroundings through either its physiology or behavior (Figure 34.1).
B. At the population level, ecologists focus on functioning among all the members of an
interbreeding group within a particular geographic area.
C. Studies at the community level focus on all the organisms of all species and their interactions
within one particular area.
D. The ecosystem level of study adds the nonliving factors (abiotic components, including
temperature, energy, water, inorganic nutrients, and other chemicals) to the picture, in addition
to relationships among the living factors (biotic components).
E. Ecology can be enormously complex because it studies multidimensional problems. Ecological
research still employs the scientific process (hypotheses, tests, and observations) but must often
take into account the complexities produced by the multidimensional nature of ecological
interactions. Studies can be done on idealized collections of organisms or environments
assembled in artificial setups in the laboratory, or by a careful examination of natural systems.
Mathematical and computer models are devised to test large-scale experiments that could not be
performed in the lab or field.
I. The Biosphere
Module 34.2 The biosphere is the total of all of Earth’s ecosystems.
A. The biosphere includes the atmosphere to an altitude of a few kilometers, the land to a soil
depth of a few meters, all lakes and streams, and the ocean to a depth of several kilometers.
B. The biosphere is isolated by space and is totally self-contained except for energy input from the
sun and heat loss to space (and input of solid matter in the form of meteorites) (Figure 34.2A).
C. The biosphere is erratic on many levels. At each level, the randomness is a result of variability
of habitats (specific environments where organisms live) (Figure 34.2B).
Preview: Randomness and human impact on this pattern are discussed in Chapter 38.
Module 34.3 Connection: Environmental problems reveal the limits of the biosphere.
Preview: Environmental issues are the subjects of Chapter 38.
A. Technological solutions, particularly those using chemicals, to agricultural and other problems
during the past 50 years have had environmental impacts.
B. Rachel Carson, author of Silent Spring (Figure 34.3), was one of the first observers to realize
the global dangers of the use of agricultural chemicals such as DDT.
Preview: See Module 38.4 for a discussion of the environmental impact of DDT and other
pollutants, such as CFCs.
C. Environmental degradation, famine, species endangerment, and extinction have been tied to
many human activities, including land misuse, expanding human population, incursions on
natural habitats, and the poisoning of soil and water by toxic wastes.
Module 34.4 Physical and chemical factors influence life in the biosphere.
A. Solar energy powers most surface terrestrial and shallow-water ecosystems. Ecosystems such as
hydrothermal vents and dark caves are dependent on energy extracted from inorganic materials
by prokaryotes. In nearly all environments, the availability of light is a critical factor that
affects the distribution of photosynthetic organisms and their dependents. In aquatic
environments, most photosynthesis occurs near the surface.
B. Water is essential to all life. In aquatic environments, water balance must be maintained in
diverse ionic concentrations. In terrestrial environments, water must be conserved.
Review: Osmoregulation (Modules 25.5–25.7).
C. Temperature affects rates of metabolism and the functioning of enzymes. Metabolism usually
occurs above 08C and below 458C, although some organisms can survive freezing or live at
temperatures around boiling.
Review: Thermoregulation (Modules 25.1–25.4).
D. Wind brings nutrients to some organisms, but it can cause damage, increase evaporation, and
lower effective temperatures.
E. Soil structure, pH, and nutrient content are important factors determining where plants and
other soil-dwelling organisms can live.
F. Fires and other catastrophes are infrequent and unpredictable in most ecosystems (Figure 34.4).
In grasslands and drier forests, fire may play an important recurring role in modifying the
physical, chemical, and biological parameters, enough so that some plants have adapted to
frequent fires.
Module 34.5 Organisms are adapted to abiotic and biotic factors by natural selection.
Review: Evolutionary principles are discussed in Chapter 13.
A. Species exist in a given area because they evolve there or disperse there. In either case, unique
adaptations that fit the local environment allow each species to live there.
B. Each organism can usually tolerate environmental fluctuations only within the set of conditions
to which it is adapted. For example, the pronghorn is a highly successful herbivore that evolved
on the open plains of North America (Figure 34.5).
C. The abiotic factors of the pronghorn’s environment include extreme daily and seasonal
temperature fluctuations, aridity, and wind. The pronghorn is well insulated by a coat of hollow
hairs and can obtain all the water it needs from the vegetation it eats.
D. Some biotic factors to which the pronghorn is adapted include its diet of coarse grasses and
woody shrubs and its predators—wolves, coyotes, and cougars. Pronghorns have teeth adapted
for biting and chewing these plants and a ruminant-type digestive system that depends on the
chemical digestion of cellulose by prokaryotes. Pronghorns can escape their predators by means
of great speed and endurance, are camouflaged, have keen eyesight, and increase their
environmental awareness by living in herds.
Module 34.6 Regional climate influences the distribution of biological communities.
A. Because of Earth’s curvature, different latitudes receive different amounts of solar energy. This
uneven heating drives winds and water currents. Seasonal differences in temperature exist
because Earth is tilted on its axis (Figures 34.6A and B). The tropics (between latitudes 23.58 N
and 23.58 S) have the most yearly input and the least seasonal variation in solar energy.
B. Uneven surface heating affects wind patterns and rainfall. Air over equatorial areas rises,
forming clouds and rain but no wind, known as the doldrums (Figure 34.6C). High-altitude air
masses spread to the north and south, descend at about 308 latitude, and flow on the surface
both north and south. The area around 308 includes the world’s major deserts because these
sinking air masses are very dry. The trade winds flowing toward the equator are generally
easterly (east to west) because of the high spin of Earth’s surface at the tropics. The winds
flowing through the temperate zones to the poles trend west to east (westerlies) because of the
slower spin of the surface at the higher latitudes (Figure 34.6D).
C. Ocean currents are produced from a combination of the prevailing winds, Earth’s rotational
spin, unequal heating of surface water, and the shapes of continents. The flow of warm and cold
currents can have a major effect on regions with water of contrasting temperature (Figure
34.6E).
D. Landforms also affect local climate by influencing wind speed and precipitation. For example,
moist air flowing off the Pacific Ocean across the mountains of Pacific northwestern North
America produces, first, relatively warm, extremely wet climates and then, in the rain shadow
of the Cascade Range, continental climates that are almost desertlike (Figure 34.6F). The rain
forests and deserts of Washington State are ecosystems commonly found throughout the world.
They are referred to as biomes. Biomes are grouped into two types, aquatic or terrestrial.
II. Aquatic Biomes
Module 34.7 Oceans occupy most of Earth’s surface.
A. Evaporation from the ocean surface loads the air with moisture that provides most of the world’s precipitation.
Photosynthesis of marine algae provides much of the biosphere’s O2.
B. The intertidal zone characterizes all areas exposed to fluctuations in tidal height. Most
pronounced are the intertidal zones of temperate coastlines with rocky shores, which may
include tidepools (Figure 34.7A). The continental shelf is that portion of a continent under
water (Figure 34.7B).
C. The pelagic zone of the open ocean includes all the water and is a major habitat for
phytoplankton and zooplankton and highly motile marine invertebrates, fishes, and mammals. It
is divided between the photic zone, where photosynthesis can occur and which is usually rich in
life forms, and the aphotic zone, which is generally less rich in life forms.
D. The seafloor is called the benthic zone and is characterized by communities of invertebrates and
fishes. Depending on its depth, it may include photosynthetic organisms.
E. Underlying the photic zone is the aphotic zone, the most extensive part of the biosphere. The
aphotic zone contains a diverse array of life whose sources of energy include organic remains
that sink from the photic zone and the hydrothermal vents discussed earlier (Opening Essay).
F. Coral reefs are a diverse ecosystem found in tropical waters above the continental shelf. Coral
reefs are extremely fragile and are destroyed easily by pollution, native and introduced
predators, and souvenir collectors (Figure 34.7C).
G. Estuaries are flat, shallow areas where broad expanses of fresh water meet seawater (Figure
34.7D). They are among the most productive of all environments on Earth. Estuaries and
intertidal zones are among the most threatened ecosystems as a result of overharvesting,
pollution, and the removal of habitat by human development of coastal areas. Laws in many
countries now severely regulate activities in these areas in an attempt to restore and conserve
these regions.
H. Mudflats and salt marshes are two types of wetland that border estuaries. Wetlands have
characteristics intermediate between aquatic and terrestrial ecosystems. Most wetlands have
permanently or periodically saturated soils.
NOTE: Most wetlands have specialized vegetation, can be highly productive, or play pivotal
roles in the maintenance of nearby aquatic ecosystems.
Module 34.8 Freshwater biomes include lakes, ponds, rivers, streams, and wetlands.
A. Light and the scarcity of dissolved inorganic ions have a major effect on ponds, lakes, rivers,
and streams.
Review: Osmoregulation (Module 25.4).
B. All but the most shallow ponds and lakes have photic and aphotic zones. Because of the lack of
currents, environments in the aphotic and benthic zones may be low in, or lack, oxygen.
C. Temperature stratification has important effects on oxygenation and on organismal distribution
in lakes and ponds, particularly in temperate zones. Stratification can impede the mixing of
surface and deep water, except during times when surface temperatures are changing rapidly,
during spring and fall.
D. The presence and distribution of inorganic ions (particularly nitrogen and phosphorus) can limit
organismal growth and distribution. Increased amounts of nutrients affected by inputs from
sewage or agricultural runoff can lead to phytoplankton blooms. When these algae die and
decompose, a pond or lake suffers from oxygen depletion.
NOTE: Of particular danger is the increase in respiration by blooms overnight. This can deplete
oxygen on a daily cycle and lead to the suffocation of many associated organisms, including
fish.
E. Streams and rivers support different communities than ponds and lakes. Near sources, water is
usually cold, clear, and low in nutrients, and currents are swift. Near outlets, water is usually
warmer, murkier, and high in nutrients, and currents are slower. These differences support
different species (Figure 34.8A).
F. Freshwater wetlands are similar to the intertidal zones with respect to the diversity of species
and the protective qualities for the environment. They are easily harmed, and efforts are under
way to protect and restore freshwater wetlands (Figure 34.8B).
III. Terrestrial Biomes
Module 34.9 Terrestrial biomes reflect regional variations in climate.
A. Biomes can be divided into nine major types (Figure 34.9).
B. Biomes are usually named for their predominant vegetation but are characterized by distinct
groups of organisms from all kingdoms.
C. Each biome is a type, not a distinct assemblage.
D. Biomes are distributed in broad patterns across planet Earth. Some occur in wide bands. Others
are found in widely separated areas. The assembly of species found in the separated examples
of the same type may show convergence of traits in evolutionarily unrelated forms of plants and
animals.
E. Biomes do not abruptly change from one to another, but grade into each other.
NOTE: Such biome gradients are referred to as ecoclines.
F. Fires are important in maintaining certain biomes, such as grasslands.
Preview: Module 37.8 discusses the role of fire in ecosystems.
G. Many natural biomes have been broken up by human activity (Chapter 38).
Module 34.10 Tropical forests cluster near the equator.
A. Tropical forests are found near the equator where temperatures are warm, and days are
uniformly 11–12 hours long year-round in the tropical forest. Rainfall is variable and defines
subtypes of this biome.
B. Tropical thorn forests are common in equatorial lowlands, such as eastern Africa and
northwestern India. They are characterized by scarce rainfall. The plants found here are thorny
shrubs and trees.
C. Tropical deciduous forests dominate areas where there are distinct wet and dry seasons of about
equal length, such as central West Africa, India, and Southeast Asia. The deciduous trees and
shrubs of these forests drop their leaves during the dry season and releaf during the wet season.
D. Tropical rain forests are the most complex of all biomes, with very high diversity (particularly
of plant species—as many as 300 tree species per hectare) and complex structure (Figure
34.10). Larger animals are tree dwellers, and there is little organic soil because of high
decomposition and recycling rates. Tropical rain forests are stratified, with an upper canopy of
the largest trees, a lower layer of trees, the shrub understory, the herbaceous plants at ground
level, the forest floor, and the root layer. Tropical rain forests occur in humid equatorial areas
(e.g., Indonesia and the Amazon River basin) where rainfall ranges between 200 and 400 cm
per year and there is a short season of reduced rainfall.
E. The impact of humans on the tropical rain forest is currently of great concern. The deforestation
of these areas may cause large-scale changes in world climate, as well as the loss of numerous
species (Chapter 38).
Module 34.11 Savannas are grasslands with scattered trees.
A. Savannas cover wide areas of the tropics in South America, central and southern Africa, and
temperate North America and have between 30 and 50 cm of rain each year (Figure 34.11).
B. In temperate North America, the grasslands of the west merge with the temperate forests of the
east.
C. Savannas are simpler in structure and lower in diversity than tropical forests and are
characteristic of areas of low but consistent rainfall.
D. Frequent fires and grazing animals inhibit invasion by trees and maintain the wind-pollinated
grasses and nonwoody insect-pollinated dicots.
Preview: Module 37.8 discusses the role of fire in ecosystems.
E. Rapid grass growth makes the savanna home to many of the world’s largest herbivores and their
predators. Particularly famous are those of Africa (e.g., giraffes, zebras, antelope, baboons,
lions, and cheetahs) and Australia (e.g., kangaroos). Savanna habitat in North America (home to
bison, deer, black bear, coyotes, and wolves) has largely been replaced by farms. During the
seasonal drought, large mammals must migrate to find suitable grazing and water.
F. Other animals characteristic of this region are burrowing animals (e.g., mice, moles, gophers,
snakes, ground squirrels, worms, and arthropods), which must go underground to find shelter in
a region with few trees.
Module 34.12 Deserts are defined by their dryness.
A. Deserts have daytime temperatures reaching 548C, and nighttime temperatures dropping below
freezing. Rainfall is less than 30 cm per year, and evaporation is rapid. Rainfall often occurs at
one short time (or not at all, in some years) (Figure 34.12).
B. Deserts are centered at about 308 north and south latitudes in regions of descending, dry air
masses. Most famous are the Sahara (where evaporation exceeds rainfall), Arabian, and
Kalahari Deserts and the desert areas of North America in Mexico and the southwestern United
States. Areas in rain shadows of mountains in more temperate areas may also be deserts.
C. Cycles of growth and reproduction are keyed to rainfall. Desert plants are adapted to conserve
water and to produce great numbers of seeds that may remain dormant for several years before
rain triggers germination. Desert animals are adapted to drought and temperature extremes.
Many are burrowers and seed-eaters (e.g., ants, birds, and rodents). Lizards, snakes, and hawks
are important predators.
D. The size of many deserts is increasing (desertification), principally because of the pressures of
overgrazing and dry-land farming. This process is especially evident in the savannas of central
Africa.
Module 34.13 Spiny shrubs dominate the chaparral.
A. The climate of the chaparral results from cool, offshore ocean currents that produce mild, rainy
winters and long, hot, dry summers (Figure 34.13).
B. Important regions of chaparral include regions around the Mediterranean, coastal Chile,
southwestern Africa, southwestern Australia, California, and northwestern Mexico (all
chaparrals are mid-latitude coastal areas).
C. Perennial shrubs and annual plants are adapted to periodic fires and require occasional fires to
maintain their overall structure.
Preview: Module 37.8 discusses the role of fire in ecosystems.
D. Characteristic animals include browsers (e.g., deer), fruit-eating birds, and seed-eating rodents.
Lizards and snakes are important predators.
Module 34.14 Temperate grasslands include the North American prairie.
A. Temperate grasslands are mostly treeless. This biome is maintained in regions with relatively
cold winter temperatures, seasonal drought, occasional fires, and grazing by large mammals
(Figure 34.14). These factors prevent the establishment of woody shrubs and trees.
Preview: Module 37.8 discusses the role of fire in ecosystems.
B. Temperate grasslands include areas known as veldts in South Africa, pampas in Argentina and
Uruguay, steppes in Asia, and prairies in central North America.
C. The area covered by grasslands increased dramatically following the ice age. In North America,
little native grassland remains because vast portions of it are used for grain production.
D. The amount of rainfall determines the height of the grassland vegetation. In addition to grazing
mammals (e.g., bison and pronghorn of North America, gazelles and zebras of Africa, and wild
horses and sheep of Asia), common animals include burrowing animals and carnivores such as
badgers, skunks, and foxes. The rich soil supports a great diversity of microorganisms, annelids,
arthropods, and burrowing mammals.
Module 34.15 Broadleaf trees dominate temperate forests.
A. Temperate broadleaf forests occur where there is enough precipitation to support trees. The
seasonal temperature range can be great, ranging from 2308C to 1308C (Figure 34.15).
Review: These forests are threatened by global warming (Modules 7.13 and 38.5).
B. Temperate forests are in the eastern United States, most of central Europe, and parts of eastern
Asia and Australia. A small amount can be found in southern South America. In many
temperate zones, human occupation of this biome has drastically altered the region.
C. Worldwide, the mix of broadleaf tree species varies. Trees that dominate include maples, oaks,
hickory, and beech. The diversity of species may be high, but not nearly as high as in tropical
rain forests. The growing season usually lasts 5–6 months, and the trees become dormant in
autumn. Leaf drop conserves water during cold, sometimes dry, winters.
D. Temperate forest soils are rich in organic and inorganic nutrients and support a diversity of
species.
E. Animal life is diverse because of the diverse habitats and includes arthropods, birds, and
mammals (e.g., whitetail deer, bobcats, foxes, black bears, and mountain lions).
F. Unlike drier areas, temperate forests tend to recover after a disturbance.
Preview: The role of disturbances in community maintenance is discussed in Module 37.7.
Module 34.16 Coniferous forests are often dominated by a few species of trees.
A. Coniferous forests are dominated by cone-bearing trees such as spruce, pine, fir, and hemlock.
B. Prior to human disturbance, much of the southeastern United States was dominated by
coniferous forest.
C. Fire is essential to this biome. Without periodic fires, deciduous trees will tend to replace the
conifers.
Preview: Module 37.8 discusses the role of fire in ecosystems (also see Module 37.7).
D. The taiga forms a broad band across North America and Eurasia (Figure 34.16). In more
southerly regions, it is located at higher elevations, below alpine areas. There is little taiga in
the southern hemisphere.
E. Harsh winters; short, warm summers; and considerable precipitation, often as snow,
characterize the region. Snow insulates the thin and acidic soil during the winter.
F. Taiga is usually characterized by a few species of conifer, whose shape and resiliency protect
them from heavy snow loads. Scattered deciduous trees (birch, willow, aspen, and alder) are
common, especially near openings.
G. Animals are adapted to cold winters, often remaining active in tunnels under the snow in winter
(e.g., mice). Squirrels and birds feed on conifer seeds. Browsers include deer, moose, elk,
snowshoe hares, beavers, and porcupines. Predators include bears, wolves, lynxes, and
wolverines.
H. Actually, northwestern North American coniferous forests are temperate rain forests (Chapter
31, Introduction). Warm, moist air from the Pacific Ocean supports this biome. In particularly
wet areas, both broadleaf trees and conifers are dominant.
Module 34.17 Long, bitter-cold winters characterize the tundra.
A. Tundra is found from the northern edge of the taiga to the northern limits of land and encircles
the North Pole. Alpine tundras occur at high elevation, above the treeline and below permanent
rock and ice, throughout all climatic regions (Figure 34.17).
B. Vegetation is dominated by low-growing herbs and shrubs, and lichens and bryophytes. During
short but warm summers, vascular plants grow and flower quickly.
C. The arctic tundra is characterized by permafrost, a permanently frozen layer of ground
beginning a few meters deep and ranging from several meters to more than a kilometer in depth.
In many tundra areas, there is little precipitation, which is mostly snow. But poor drainage due
to permafrost and slow rates of evaporation retain the moisture and keep the soil saturated.
D. Animals are adapted to the cold by thick fur, or by migratory behavior. Large herbivores
include musk ox and caribou. The main smaller mammal is the lemming. There are a few
predators, such as the arctic fox and the snowy owl. Many species found in the tundra,
especially the birds, use it as a summer breeding ground. Huge populations of blood-eating
insects, such as the mosquito, develop in mid-summer and then experience an abrupt decline in
population size as winter approaches.
Preview: Population dynamics (Chapter 36).
Module 34.18 Talking about Science: Ecologist Ariel Lugo studies tropical forests in Puerto Rico.
A. Dr. Ariel Lugo is a tropical ecologist who works in Puerto Rico (Figure 34.18B). He tempers
his concerns about the rain forest organisms with an understanding of the social and economic
needs of the people who live in and use these forests.
B. The main force causing deforestation at present is not the need for lumber or the destructive
effects of a hurricane (Figure 34.18A), but the need for land to grow food. Unfortunately, in the
tropics, once the forest is cut, the remaining land can be farmed only a short time before it is
infertile. Increasing populations in tropical areas also adds to the problem.
C. Lugo believes it is critical that land use in these areas remains sustainable, and this depends on
the cultural awareness of the people living there. Any deforestation that occurs needs to be
planned, controlled, and integrated into the ecosystem mechanisms in the area to avoid losing
species and degrading soil and water resources.