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PowerLecture:
Chapter 25
Ecology and
Human Concerns
Learning Objectives

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Understand how materials and energy
enter, pass through, and exit an ecosystem.
Describe how communities are organized,
how they develop, and how they diversify.
Understand the various trophic roles and
levels.
Diagram the principal biogeochemical
cycles.
Learn the language associated with the
study of population ecology.
Learning Objectives (cont’d)




Understand the factors that affect
population density, distribution, and change.
Understand the meaning of logistic growth.
Know the problems associated with the
growth of human populations. Tell which
factors have encouraged growth in some
cultures and limited growth in others.
Understand the magnitude of pollution
problems in the United States.
Learning Objectives (cont’d)


Examine the effects modern agricultural
techniques have on different ecosystems.
Describe how our use of fossil fuels and
nuclear energy affects ecosystems.
Impacts/Issues
The Human Touch
The Human Touch
At one time as many as 15,000
people lived on Easter Island.




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The tiny island could not support
this many people.
Crop yields declined; soil nutrients
were depleted.
Large statues were erected to
appease the gods.
The population dwindled and
then disappeared as people
turned against each other.
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 Are
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

a. Yes, I would be willing to pay more for
sustainable products.
b. No, I would not be willing to pay more for
“green” products.
Section 1
Some Basic Principles
of Ecology
Some Basic Principles of Ecology

The biosphere encompasses the earth’s
crust, atmosphere, and waters that support
life; a biome is one of the major realms of
life, such as deserts or rain forests.
Figure 25.1
Some Basic Principles of Ecology
Ecology is the study of the interactions of
organisms with one another and with the
physical environment.




A habitat is the place where a species normally
lives; it is characterized by distinctive physical
features and vegetation.
Humans live in disturbed habitats, places we
have modified to suit our own purposes.
A community is the collection of all the
populations in a given habitat.
Some Basic Principles of Ecology

The niche refers to a range of physical and
biological conditions under which a species can
live and reproduce.
•
•
Specialist species have narrow niches.
Generalists have broad ranges of habitats and
niches.
Some Basic Principles of Ecology
An ecosystem consists of one or more
communities interacting with one another
and with the physical environment.


Communities
of organisms
make up the
biotic, or
living, portions
of an
ecosystem.
Figure 25.2
Some Basic Principles of Ecology

Succession is the
orderly progression of
species changes that
leads to a climax
community.
•
•
In primary succession,
changes begin when
pioneer species colonize
a barren habitat.
In secondary
succession, a
community reestablishes
itself toward a climax
state after a disturbance.
Figure 25.3
Section 2
Feeding Levels and
Food Webs
Feeding Levels and Food Webs
Many ecosystems exist, but they are all
similar in structure and function.



Producers (autotrophs) capture sunlight
energy and incorporate it into organic
compounds.
All other organisms in an ecosystem are
consumers (heterotrophs) that depend on
energy stored in the tissues of producers.
energy
input
from sun
Producers
Nutrient
Cycling
Consumers
energy lost (mainly heat)
Fig 25.4, p. 456
Feeding Levels and Food Webs
•
•
•
•


Herbivores eat plants (primary consumers).
Carnivores eat animals (secondary or tertiary
consumers).
Omnivores eat a variety of organisms.
Decomposers include fungi, bacteria, and small
invertebrates that extract energy from the remains or
products of organisms.
Ecosystems require energy and nutrient input
to continue to function.
Energy is generally lost from the system as
heat; some nutrients can also be lost.
Feeding Levels and Food Webs
Energy moves through a series of
ecosystem feeding levels.




Trophic levels (feeding levels) represent a
hierarchy of energy transfers.
Level 1 (closest to the energy source) consists
of primary producers, level 2 is composed of
herbivores, and levels 3 and above are
carnivores.
Decomposers and omnivores such as humans
feed on organisms from all levels.
Feeding Levels and Food Webs
Food chains and webs show who eats
whom.



A linear sequence of who eats whom in an
ecosystem is called a food chain; simple
chains are rarely found in nature.
Cross-connecting food chains make up food
webs in which the same food resource is often
part of more than one food chain.
Marsh Hawk
Upland Sandpiper
Garter Snake
Cutworm
Plants
In-text Fig, p. 466
Marsh Hawk
Upland Sandpiper
Garter Snake
Cutworm
Plants
Stepped Art
In-text Fig, p. 466
Marsh Hawk
Higher
Feeding
Levels
A variety of
carnivores,
omnivores,
and other
consumers.
Many feed
at more
than one
level all
the time,
seasonally,
or when an
opportunity
presents
itself
Crow
Upland
Sandpiper
Garter Snake
Frog
Weasel
Spider
Second
Feeding
Level
Primary
consumers
(herbivores)
Badger
Ground
Squirrel
Clay-colored
Sparrow
Earthworms, Insects
(e.g.) Grasshoppers, Cutworms
First
Feeding
Level
Primary
producers
© 2007 Thomson Higher Education
Coyote
Prairie Vole
Pocket Gopher
Grass
Fig 25.5, p. 467
Section 3
Energy Flow
through Ecosystems
Energy Flow through Ecosystems
Producers capture and store energy.



Primary productivity is the total rate of
photosynthesis (trapping of energy) for the
ecosystem during a specified interval.
How much energy is trapped depends on many
factors.
•
•
The number of individual plants and the relative
balance between trapping energy and expending
energy to produce new plants.
Environmental factors such as availability of mineral
nutrients, rain fall, and temperature.
Earth’s Primary Productivity
Figure 25.6
Energy Flow through Ecosystems
Consumers subtract energy from
ecosystems.


An ecological pyramid describes the energy
relationships in an ecosystem.
•
•
Primary producers form the base.
Successive tiers of consumers are found above
them.
Energy Flow through Ecosystems

Ecological pyramids can be of two basic types:
•
•
Biomass is the combined weight of all of an
ecosystem’s organisms at each level of the pyramid;
a biomass pyramid can be “right-side up,” with
producers outnumbering consumers, or “upsidedown,” which is the opposite.
An energy pyramid reflects the trophic structure
more accurately because it is based on energy
losses at each level; energy pyramids are always
“right-side up.”
Figure 25.7a
1.5
third-level carnivores
(gar, large-mouth bass)
11
second-level consumers
(fishes, invertebrates)
37
first-level consumers
(herbivorous fishes, turtles,
invertebrates)
primary producers
(algae, eelgrass, rooted plants)
5
809
decomposers
(bacteria, crayfish)
Fig 25.7a, p.468
1.5
third-level carnivores
(gar, large-mouth bass)
11
second-level consumers
(fishes, invertebrates)
37
first-level consumers
(herbivorous fishes, turtles,
invertebrates)
primary producers
(algae, eelgrass, rooted plants)
5
809
decomposers
(bacteria, crayfish)
Stepped Art
Fig 25.7a, p.468
top carnivores
carnivores
herbivores
producers
21
Decomposers = 5,060
383
3,368
20,810
Fig 25.7b
Section 4
Biogeochemical Cycles—
An Overview
Biogeochemical Cycles
Biogeochemical cycles describe the
movement of nutrients from the
environment to organisms and then back to
the environment that serves as a reservoir
for them.
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Cycling is slowest through the reservoir.
The amount of nutrient being recycled through
major ecosystems is greater than the amount
entering or leaving in a given year.
Inputs to an ecosystem’s nutrient reserves are
by precipitation, metabolism, and rock
weathering; outputs include losses by runoff.
nutrient
reservoirs in
environment
fraction
available to
ecosystem
geochemical cycle
primary
producers
consumers
(herbivores,
carnivores,
parasites)
decomposers
Fig 25.8, p. 469
Biogeochemical Cycles
There are three categories of
biogeochemical cycles:


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In the global water cycle, oxygen and
hydrogen move as water molecules.
In the atmospheric cycles, elements such as
carbon and nitrogen move in gaseous phase.
In sedimentary cycles, solid, non-gaseous
nutrients move from land to the seafloor and
back to land through geological uplifting; this is
a very slow cycle.
Section 5
The Water Cycle
The Water Cycle
The hydrologic cycle (water cycle)
encompasses water in the oceans,
atmosphere, and land.

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
The ocean serves as the main water reservoir.
Evaporation moves water into the lower
atmosphere where it returns to Earth as
precipitation.
atmosphere
evaporation
from ocean
425,000
wind-driven water vapor
40,000
evaporation from
land plants
precipitation
(transpiration)
into ocean
71,000
385,000
precipitation
onto land
111,000
surface and
groundwater flow
40,000
ocean
land
Fig 25.9, p. 470
The Water Cycle
Water moves nutrients in or out of
ecosystems.

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
A watershed funnels rain or snow into a single
river.
Plants absorb nutrients to prevent their loss by
leaching.
Section 6
Cycling Chemicals from
the Earth’s Crust
Cycling Chemicals from the Earth’s Crust
There are two phases in the phosphorus
cycle:



In the geochemical phase, phosphorus moves
from land to sediments in the seas and back to
the land over long periods of time.
In the much more rapid ecosystem phase,
plants take up the phosphorus from the soil; it is
then transferred to herbivores and carnivores,
which excrete it in wastes and their own
decomposing bodies thus returning the
phosphorus to plants.
Cycling Chemicals from the Earth’s Crust

Excessive phosphorus compounds in runoff
water can lead to eutrophication of lakes
and streams, characterized by explosive
growth of algae and weeds.
mining
excretion
Fertilizer
Guano
agriculture
uptake by
autotrophs
Marine
Food Webs
weathering
Dissolved in
Ocean Water
uptake by
autotrophs
weathering
death,
decomposition
sedimentation
Land
Food Webs
death,
decomposition
settling out
Marine Sediments
Dissolved in
Soil Water,
Lakes, Rivers
leaching, runoff
Rocks
uplifting over
geologic time
© 2007 Thomson Higher Education
Fig 25.10, p. 471
Section 7
The Carbon Cycle
The Carbon Cycle
In the carbon cycle, sediments and rocks
hold most of the carbon; carbon moves also
through the oceans, soil, atmosphere, and
biomass.


Carbon enters the atmosphere as CO2
produced by aerobic respiration, fossil-fuel
burning, and volcanic eruptions.
The Carbon Cycle

Carbon in the ocean occurs as bicarbonate and
carbonate; carbon dioxide in the ocean is
carried to deep storage reservoirs on the
seafloor.
Figure 25.12
Cold, salty, deep current
Fig 25.12, p. 473
The Carbon Cycle



Carbon is removed from the atmosphere and
the ocean by photosynthesizers and shelled
organisms; carbon is held for different periods
of time in different ecosystems.
Decomposition of buried carbon compounds
millions of years ago caused the formation of
fossil fuels (natural gas, petroleum, and coal).
Burning of fossil fuels puts extra amounts of
carbon dioxide into the atmosphere, an
occurrence that may lead to global warming.
The Carbon Cycle
Figure 25.11
diffusion between
atmosphere and ocean
Bicarbonate and
Carbonate
Dissolved in
Ocean Water
photosynthesis
combustion of fossil fuels
Terrestrial
Rocks
aerobic
respiration
Marine Food Webs,
producers consumers,
decomposers
incorporation death,
into sediments sedimentation
uplifting over
geologic time
sedimentation
Marine Sediments, Including
Formations with Fossil Fuels
Soil Water
(dissolved carbon)
leaching,
runoff
Fig. 25.11a, p. 472
Atmosphere
combustion of
fossil fuels
photosynthesis
aerobic
respiration
combustion of
wood (for
cleaning land; or
for fuel)
sedimentation
Land Food Webs
producers, consumers,
decomposers
death, burial,
compaction
over geologic time
©2007 Thomson Higher Education
Peat,
Fossil Fuels
Fig. 25.11b, p. 473
Section 8
Global Warming
Global Warming
The greenhouse effect.


Molecules of gases such as carbon dioxide,
water, ozone, and others act like a pane of
glass over the surface of the Earth.
Figure 25.14
Concentration (parts per billion)
380
Carbon dioxide
360
340
320
300
1960
1965
1970
1975
1980
1985
1990
1995
Time (years)
© 2007 Thomson Higher Education
Fig 25.14a2, p. 475
Concentration (parts per trillion)
1200
CFCs
1000
800
600
400
200
1976
1980
1985
1990
1995
1998
Time (years)
© 2007 Thomson Higher Education
Fig. 25.14b, p. 475
1.80
Concentration (parts per billion)
Methane
1.70
1.60
1.50
1.40
1976
1980
1985
1990
1995
1998
Time (years)
© 2007 Thomson Higher Education
Fig. 25.14c, p. 475
Concentration (parts per billion)
320
Nitrous oxide (N2O)
310
300
290
280
270
260
1976
1980
1985
1990
1995
1998
Time (years)
© 2007 Thomson Higher Education
Fig. 25.14d, p. 475
Global Warming


Wavelengths of visible light easily pass
downward to Earth, but infrared wavelengths—
heat—are impeded from passing back into
space.
The warming of the lower atmosphere is called
the greenhouse effect.
Figure 25.13
Rays of sunlight
penetrate the lower
atmosphere and warm
the earth’s surface.
a
Surface radiates heat
(infrared wavelengths) to the
lower atmosphere. Some heat
escapes into space. But
greenhouse gases and water
vapor absorb some infrared
energy and radiate a portion of it
back toward earth.
b
Increased concentrations
of greenhouse gases trap
more heat near Earth’s
surface. Sea surface
temperature rises, more
water evaporates into the
atmosphere, and Earth’s
surface temperature rises.
c
Fig 25.13, p. 474
Global Warming
Global warming.



Concentrations of greenhouse gases are
increasing and may be at the highest levels
they have been at for 420,000 to 20 million
years.
The result is a long-term rise in temperature—
global warming; irreversible climate changes
are already underway, such as melting of the
polar ice caps and retreating of glaciers.
Global Temperature
Figure 25.15
Video: Kyoto Protocol
 This
video clip is available in CNN Today
Videos for Environmental Science, 2004,
Volume VII. Instructors, contact your local
sales representative to order this volume,
while supplies last.
Section 9
The Nitrogen Cycle
The Nitrogen Cycle
Gaseous nitrogen (N2) makes up about
80% of the atmosphere, which is the largest
reservoir; this form of nitrogen can only be
brought into the nitrogen cycle by certain
species of bacteria.


In nitrogen fixation, bacteria convert N2 to
ammonia, which is then used in the synthesis of
proteins and nucleic acids to be assimilated into
plant, then animal, tissues.
The Nitrogen Cycle




Decomposition of dead nitrogen fixers releases
nitrogen-containing compounds.
Nitrification is a type of chemosynthesis where
ammonia and ammonium ions are converted to
nitrite; nitrite is turned to nitrates by bacteria for
uptake by plants.
Denitrification is the release of nitrogen gas to
the atmosphere by the action of bacteria.
Nitrogen can be lost from ecosystems
through leaching.
Consumers
Nitrogen Fixation
by industry for
agriculture
Nitrogen gas
in Atmosphere
Food Webs on
Land
Fertilizers
Nitrogen
Fixation
by bacteria
Ammonia,
Ammonium
in Soil
loss by
leaching
uptake by
autotrophs
excretion, death,
decomposition
uptake by
autotrophs
Nitrogen-rich wastes,
Remains in soil
Nitrate
in Soil
Ammonification
bacteria, fungi convert
residues to NH3; this
dissolves to form NH4
Nitrification
Loss by
Denitrification
Nitrification
Nitrate
in Soil
loss by
leaching
© 2007 Thomson Higher Education
Fig 25.16, p. 476
Section 10
Biological Magnification
Biological Magnification
DDT is a synthetic organic pesticide that
was first used during World War II in the
fight against malaria and typhus; after the
war it continued to be used as a pesticide to
control agricultural and forest pests.



DDT is insoluble in water, but it is fat soluble.
Vapor forms and small particles in water can
carry DDT through an environment; from the
environment it can be absorbed into tissues.
Biological Magnification
Biological magnification describes the
increased concentration of slowly
degradable substances in organisms as it is
passed upward in a food chain.



Each organism in a chain essentially assumes
the absorbed DDT in each organism it feeds on
lower in the chain.
With DDT, organisms at the very top of the food
chain, such as bald eagles and other predatory
birds, suffered the most and some were pushed
almost to extinction.
Biological Magnification

DDT is banned in the US, but this is not true
outside of the US.
Figure 25.18
DDT Residues (ppm wet weight of whole live organism)
Ring-billed gull fledgling (Larus delawarensis)
Herring gull (Larus argentatus)
Osprey (Pandion haliaetus)
Green heron (Butorides virescens)
Atlantic needlefish (Strongylura marina)
Summer flounder (Paralychthys dentatus)
Sheepshead minnow (Cyprinodon variegatus)
Hard clam (Mercenaria mercenaria)
Marsh grass shoots (Spartina patens)
Flying insects (mostly flies)
Mud snail (Nassarius obsoletus)
Shrimps (composite of several samples)
Green alga (Cladophora gracilis)
Plankton (mostly zooplankton)
Water
75.5
18.5
13.8
3.57
2.07
1.28
0.94
0.42
0.33
0.30
0.26
0.16
0.083
0.040
0.00005
Data for a Long Island, NY, estuary in 1967
Fig 25.17a, p. 477
Section 11
Human
Population Growth
Human Population Growth
The human population is growing rapidly.


The world population reached the 6.3 billion
mark in 2004.
•
•

It took 2.5 million years for the world’s human
population to reach 1 billion.
It took less than 200 years for it to reach 6 billion.
The growth rate is determined mainly by the
balance between births and deaths.
•
•
The total fertility rate (TFR) is the average number
of children born to a woman.
Many developed countries have a TFR at or below
2.1 (replacement rate), but some developing
countries have a TFR two or three times this rate.
6
Estimated size by
10,000 years ago 5 million
5
By 1904
By 1927
By 1960
By 1974
By 1987
By 1999
Projected for 2050
4
1 billion
2 billion
3 billion
4 billion
5 billion
6 billion
8.9 billion
3
2
domestication of plants,
animals 9000B.C. (about
11,000 years ago)
14,000
12,000
10,000
8,000
beginning of
industrial,
scientific
revolutions
agriculturally based
urban societies
6,000
4,000
2,000
BC AD
1
2,000
© 2007 Thomson Higher Education
Fig. 25.19, p. 478
Human Population Growth
Population statistics help predict growth.


Demographics influence a population’s growth
and impact on ecosystems.
•
•
•
Population size is the number of individuals in the
population’s gene pool.
Population density is the number of individuals per
unit of area or volume.
Population distribution refers to the general pattern
in which the population members are distributed,
such as clustering in towns or cities.
292 million
population in
2003
177 million
134 million
population in
2050 (projected)
351 million
211 million
206 million
population
under age 15
population
above age 65
21%
30%
44%
13%
Gold: U.S.
6%
Brown: Brazil
3%
2.0
2.2
total fertility rate
Ivory: Nigeria
5.8
infant mortality
rate
6.9 per 1,000 births
33 per 1,000 births
75 per 1,000 births
77 years
69 years
life expectancy
52 years
per capita
income in 2001
$34,280
$7,070
$800
© 2007 Thomson Higher Education
Fig. 25.20a, p. 479
Human Population Growth

Age structure defines the relative proportions
of individuals of each age.
•
•
The three categories are: prereproductive,
reproductive, and postreproductive.
The reproductive base (prereproductive and
reproductive members) for a human population will
determine the future growth rate of a population.
Figure 25.21
UNITED STATES
INDIA
Fig 25.21, p. 479
Section 12
Nature’s Controls on
Population Growth
Nature’s Controls on Population Growth
The human population has been growing
exponentially since the mid-1700s.
There is a limit on how many people the
Earth can sustain.




The biotic potential of a population is its
maximum rate of increase under ideal—
nonlimiting—conditions.
Limiting factors on population growth could
include any essential resource that is in short
supply such as food, water, or living space;
predation and pathogens can also be limiting.
Nature’s Controls on Population Growth


The number of individuals that can be
sustained by the resources in a given area is
the carrying capacity.
The carrying capacity can vary over time and is
expressed graphically in the S-shaped curve
pattern called logistic growth.
Figure 25.22
Number of individuals
initial carrying capacity
TIME A
new carrying capacity
B
C
D
E
Fig 25.22, p. 480
Nature’s Controls on Population Growth
Some natural population controls are
related to population density.



Density-dependent controls (such as
diseases) are limiting factors that exert their
effects with respect to the number of individuals
present.
Density-independent controls, such as
natural disasters, tend to increase the death
rate without respect to the number of
individuals present.
Section 13
Assaults on Our Air
Assaults on Our Air
Pollutants are substances that adversely
affect health, activities, or survival of a
population.



Air pollutants include oxides of carbon, sulfur,
and nitrogen as well as CFCs.
Over 700,000 metric tons of pollutants are
released into the atmosphere every day in the
United States alone.
Assaults on Our Air

Pollutants may be trapped in the atmosphere to
produce two types of smog:
•
•

Industrial smog is gray air found in industrial cities
that burn fossil fuels.
Photochemical smog is brown air found in large
cities in warm climates; for example, gases from car
exhaust.
Burning of fossil fuels produces oxide particles
that can fall to the earth as acid rain.
Assaults on Our Air
The ozone layer has been damaged.


Ozone (O3) in the lower stratosphere absorbs
most of the ultraviolet radiation from the sun.
•
•
Ozone thinning has produced an ozone hole over
Antarctica; in 2001 an ozone hole appeared over the
Arctic.
Chlorofluorocarbons (CFCs) seem to be the cause—
one chlorine atom can destroy 10,000 molecules of
ozone.
Assaults on Our Air

While most CFC production is being phased
out, it will take 100 to 200 years for the ozone
layer to fully recover once all production and
use ceases.
Figure 25.23
Section 14
Water, Wastes, and
Other Problems
Water, Wastes, and Other Problems
Problems with water are serious.



Three out of four humans do not have enough
clean water to meet basic needs.
About one third of all food is raised on irrigated
land, leading to salt buildup (salinization) and
depletion of ground water systems.
Figure 25.24
Water, Wastes, and Other Problems

Humans waste limited water supplies and
pollute much of the remaining water through
agricultural and industrial runoff; even garbage
and debris is dumped into our waterways.
Water, Wastes, and Other Problems
Where will we put solid wastes and produce
food?



Finding enough space to bury our wastes is
becoming a problem, and the dump sites can
leak toxic materials into the soil and water.
Almost one quarter of all the land on Earth is
used for agriculture.
•
•
The green revolution has increased crop yields but
uses many times more energy and mineral
resources.
Large-scale desertification is caused by
overgrazing on marginal lands.
Water, Wastes, and Other Problems
Deforestation has global repercussions.


Deforestation, the removal of all trees from
large tracts of land, can reduce fertility, change
rainfall patterns, increase temperatures, and
increase carbon dioxide levels.
Water, Wastes, and Other Problems

Clearing large tracts of tropical forests may
have global repercussions due to leaching and
shifting rates of evaporation and sunlight
penetration.
Figure 25.25
Section 15
Concerns about Energy
Concerns about Energy
The Earth has abundant energy, but the net
amount of energy left after subtracting the
energy it costs to find, process, and deliver
this energy is relatively small.


Some forms of energy are renewable, such as
solar energy; coal and petroleum are examples
of non-renewable energy.
Figure 25.26a
Concerns about Energy

People in developed countries use far more
energy per person than those in developing
countries.
Figure 25.26b
Concerns about Energy
Fossil fuels are going fast.




Fossil fuels include oil, coal, and natural gas;
these sources represent the fossilized remains
of ancient forests and organisms.
Petroleum and natural gas reserves may be
depleted during this century.
Extraction and use of abundant reserves of coal
are not environmentally attractive.
Concerns about Energy
Can other energy sources meet the need?


Nuclear power can produce electricity at
relatively low cost, but there are risks.
•
•

Meltdowns may release large amounts of
radioactivity to the environment.
Waste is so radioactive that it must be isolated for
10,000 years.
Solar energy can be converted to the
mechanical energy of wind to run turbines;
solar cells could be used to generate electricity
for producing hydrogen gas.
Concerns about Energy


Hybrid cars are currently available, which work
on a combination of gasoline and the electricity
from batteries.
Fusion power has potential, but many obstacles
make the technology a distant possibility.
Section 16
Loss of Biodiversity
Loss of Biodiversity
Humans have become a major factor in the
premature extinction of more and more
species.



Extinction is irreversible and greatly decreases
biodiversity.
Speciation cannot balance rapid extinction.
Loss of Biodiversity
Tropical deforestation is the greatest source
of extinction of species, followed closely by
destruction of coral reefs.



Loss of plant diversity directly hurts consumers
by removing an important part of every food
chain; plant loss also affects our sources of
natural medicines.
The underlying causes of such destruction are
human population growth and poor economic
policies.
1620
1850
1850 (pocket only)
1990
Fig 25.29, p. 487
Loss of Biodiversity

To end the trend, we must collectively fight
to reduce deforestation, global warming,
ozone depletion, and poverty.
Figures 25.27 and 25.28