CHAPTER 3:
ECOSYSTEMS: WHAT ARE THEY AND HOW DO THEY WORK?
Objectives
1.
Define ecology. List and distinguish among five levels of organization of matter that are the focus of the realm of
ecology.
2. List the characteristics of life.
3. Distinguish among the following terms: lithosphere, hydrosphere, atmosphere, and ecosphere. Briefly describe how
the sun, gravity, and nutrient cycles sustain life on Earth. Compare the flow of matter and the flow of energy through
the biosphere.
4. Define soil horizon. Briefly describe six soil layers. Using Figure 3-21 on p. 51 in the text, compare soil profiles of
five important soil types.
5. Describe a fertile soil. In doing so, be sure to refer to soil texture, porosity, loam, and acidity.
6. Distinguish between an open system and a closed system. Name and describe three types of biogeochemical cycles.
7. Define abiotic component of an ecosystem. List three important physical factors and three important chemical
factors that have large effects on ecosystems.
8. Summarize the law of tolerance. Compare limiting factors in terrestrial and aquatic ecosystems.
9. Define biotic component of an ecosystem. Distinguish between producers and consumers. List and distinguish four
types of consumers. Distinguish among scavengers, detritus feeders, and decomposers. Distinguish between
photosynthesizers and chemosynthesizers, and between aerobic respiration and anaerobic respiration.
10. Distinguish between food chains and food webs, and between a grazing food web and a detrital food web. Apply the
second law of energy to food chains and pyramids of energy, which describe energy flow in ecosystems. Explain
how there may be exceptions to pyramids of numbers and biomass, but not energy.
11. Evaluate which ecosystems show the highest average net primary productivity and which contribute most to global
net primary productivity.
12. Briefly describe the historical development and distinguishing features of three approaches ecologists use to learn
about ecosystems: field research, laboratory research, and systems analysis.
13. Define ecosystem service. List five examples of ecosystem services. Distinguish among three types of biodiversity.
Briefly state two principles to sustain ecosystems.
14. Apply the law of conservation of matter to biogeochemical cycles, which describe the flow of matter through
ecosystems. Briefly describe the following cycles: carbon, nitrogen, phosphorous, and sulfur. Summarize the major
ways that humans affect each cycle.
15. Briefly describe the hydrologic cycle. Distinguish among the following: evaporation, transpiration, condensation,
precipitation, infiltration, percolation, and runoff.
Key Terms {(Terms are listed in the same font style as they appear in the text.)}
1. abiotic (p. 41)
12. biological diversity (p.
28. ecological efficiency (p.
2. aerobic respiration (p.
48)
52)
46)
13. biomass (p. 51)
29. ecology (p. 41)
3. A-horizon (p. 50)
14. biomes (p. 42)
30. ecosystem (p. 41)
4. ammonification (p. 58)
15. biosphere (p. 41)
31. field research (p. 59)
16. biotic (p. 41)
32. food chain (p. 50)
5. anaerobic respiration
(p. 47)
17. carbon cycle (p. 56)
33. food web (p. 51)
6. aquatic life zone (p. 42)
18. carnivores (p. 46)
34. gene (p. 39)
7. atmosphere (p. 42)
19. cells (p. 39)
35. genetic diversity (p. 41)
8. autotrophs (p. 46)
20. chromosome (p. 40)
36. geographic information
9. baseline data (p. 61)
21. clay (p. 51)
systems (GISs) (p. 59)
biodiversity (p. 48)
22. community (p. 41)
37. geosphere (p. 42)
23. consumers (p. 44)
38. gravel (p. 52)
10. biogeochemical cycles
(p. 54)
24. decomposers (p. 46)
39. greenhouse gases (p.
25. denitrification (p. 58)
42)
11. biological community
(p. 41)
26. detritivores (p. 46)
27. detritus (p. 46)
Ecosystems: What Are They and How Do They Work?
16
40. gross primary
productivity (GPP) (p.
53)
41. habitat (p. 41)
42. herbivores (p. 46)
43. heterotrophs (p. 46)
44. humus (p. 50)
45. hydrologic cycle (p. 54)
46. hydrosphere (p. 42)
47. infiltration (p. 51)
48. laboratory research (p.
60)
49. leaching (p. 51)
50. limiting factor (p. 44)
51. limiting factor
principle
(p. 44)
52. lithosphere (p. 38)
53. loam topsoil (p. 52)
54. mature soils (p. 50)
55. natural greenhouse
effect (p. 44)
56. net primary productivity
(NPP) (p. 53)
57. nitrate ions (NO3-) (p. 57)
58. nitrification (p. 57)
59. nitrite ions (NO2-) (p. 57)
60. nitrogen cycle (p. 57)
61. nitrogen fixation (p. 57)
62. nutrient cycles (p. 54)
63. O-horizon (p. 50)
64. omnivores (p. 46)
65. phosphate ion (PO4-) (p.
58)
66. phosphorus cycle (p. 58)
67. photosynthesis (p. 46)
68. population (p. 41)
69. producers (p. 46)
70. pyramid of energy flow
(p. 52)
71. range of tolerance (p.
41)
72. remote sensing (p. 59)
73. sand (p. 52)
74. silt (p. 52)
75. soil (p. 50)
76. soil horizons (p. 50)
77. soil profile (p. 50)
78. species (p. 41)
79. stratosphere (p. 42)
80. sulfur cycle (p. 59)
81. surface-litter layer (p.
50)
82. systems analysis (p. 60)
83. topsoil layer (p. 50)
84. transpiration (p. 55)
85. trophic level (p. 46)
86. troposphere (p. 42)
87. water cycle (p. 54)
Outline
3-1
3-2
What Is Ecology?
A Cells are the most basic unit of life.
1. The notion that all living things are made of cells is called cell theory.
a. Large and complex organic compounds make up the molecular units found in cells.
2. A chromosome is a single strand of DNA and associated proteins.
a. Chromosomes contain genes, which are sequences of nucleotides that provide the cell with instructions
for building proteins.
B A species is a group of organisms that generally resemble one another in their appearance, behavior, chemistry,
genetic makeup, and are able to mate and produce fertile offspring.
1. There are an estimated 4 to 100 million species of organisms on Earth.
a. Biologists have identified about 1.8 million species, about 54% of them insects.
C Ecology is the study of connections in the natural world. Ecologists try to understand interactions among
organisms, populations, communities, ecosystems, and the biosphere.
1. A population consists of a group of interacting individuals of the same species occupying a specific area.
2. Genetic diversity explains why these individuals may not behave nor look exactly alike.
3. The habitat is the place where a population or an individual usually lives. Its distribution or range is the area
over which a species may be found.
4. A community represents populations of different species living and interacting in a specific area. A biological
community consists of all the populations of different species interacting and living in a specific area; this is a
network of plants, animals, and microorganisms.
5. An ecosystem is a community of different species interacting with each other and with their nonliving
environment of matter and energy. All of the Earth’s diverse ecosystems comprise the biosphere.
What Keeps Us and Other Organisms Alive?
A Various interconnected spherical layers make up the Earth’s life-support system.
B The atmosphere is the thin membrane of air around the planet.
C The troposphere is the air layer about 11 miles above sea level.
D The stratosphere lies above the troposphere between 11–30 miles; it filters out the sun’s harmful radiation.
E The hydrosphere consists of Earth’s water, found in liquid water, ice, and water vapor.
F The lithosphere is the crust and upper mantle of the Earth’s soil. It contains nonrenewable fossil fuels, minerals,
and soil, and renewable soil chemicals needed for plant life.
G The biosphere includes most of the hydrosphere, parts of the lower atmosphere, and {parts of the?} upper
lithosphere. All parts of the biosphere are interconnected.
H The sun, cycles of matter, and gravity sustain life on Earth.
Ecosystems: What Are They and How Do They Work?
17
1.
3-3
The one-way flow of high-quality solar energy through materials and living things (as they eat) produces lowquality energy. Energy can’t be recycled.
2. Matter cycles through parts of the biosphere.
3. Gravity causes the downward movement of chemicals as matter cycles through the earth.
I Solar energy warms the atmosphere, evaporates and recycles water, generates wind, and supports plant growth.
J As solar radiation interacts with the Earth, infrared radiation is produced. Greenhouse gases trap the heat and
warm the troposphere. This natural greenhouse effect makes the planet warm enough to support life. Energy from
the sun supports photosynthesis.
Ecosystem Components
A The major components of ecosystems are abiotic (nonliving) water, air, nutrients, solar energy, and biotic (living)
plants, animals, and microbes.
B Ecosystem characteristics include a range of tolerance to physical and chemical environments by the ecosystem’s
populations.
1. The distribution of a species in an ecosystem is determined by the levels of one or more physical or chemical
factors being within the range tolerated by that species.
a. The limiting factor principle states that too much or too little of any abiotic factor can limit or prevent
growth of a population, even if all other factors are at or near the optimum range of tolerance.
b. Aquatic life zones can be limited by the dissolved oxygen (DO) content in the water or by the salinity.
C The major biological components of ecosystems are the producers/autotrophs that are self-feeders and the
consumers/heterotrophs.
D Autotrophs make their own food from compounds in the environment (organisms such as green plants and algae).
A few specialized producers can convert simple compounds to more complex compounds without sunlight, a
process called chemosynthesis.
E Consumers, or heterotrophs, feed on other organisms or their remains.
1. Decomposers break down organic detritus (bacteria/fungi) into simpler inorganic compounds.
2. Omnivores feed on both plants and animals.
3. Carnivores feed on animals.
4. Detritivores feed on dead organic matter and break it down into smaller molecules.
5. Herbivores feed on plants.
6.
Natural ecosystems produce little waste or no waste. In nature, waste becomes food.
F
3-4
3-5
Glucose and other organic compounds are broken down and energy is released by the process of aerobic
respiration, the use of oxygen to convert organic matter back to carbon dioxide and water. This process is a net
chemical change to that of photosynthesis.
G Some decomposers are able to break down organic compounds without using oxygen. This process is called
anaerobic respiration, or fermentation. The end products are compounds such as methane gas, ethyl alcohol, acetic
acid, and hydrogen sulfide.
H Matter is recycled; there is a one-way flow of energy.
What Is Biodiversity and Why Is It Important?
A Biodiversity is the amazing variety of Earth’s genes, species, ecosystems, and ecosystem processes.
1. The kinds of biodiversity are: genetic diversity, species diversity, ecological diversity, and functional
diversity.
2. Biodiversity keeps us alive and supports our economies.
3. Biodiversity is a renewable resource as long as humans live off the income, not destroy the capital.
What Happens to Energy in an Ecosystem?
A Food chains and food webs help us understand how eaters, the eaten, and the decomposed are interconnected in an
ecosystem.
B The sequence of organisms as they are eaten is a food chain.
1. Trophic levels are feeding levels for organisms within an ecosystem.
a. Producers belong to the first tropic level.
b. Primary consumers belong to the second tropic level.
c. Secondary consumers belong to the third tropic level.
d. Detritivores and decomposers process detritus from all trophic levels.
C Food webs are complex networks of interconnected food chains. They are maps of life’s interdependence.
D Energy flow in a food web/chain decreases at each succeeding organism in a chain or web.
E The dry weight of all organic matter within the organisms of a food chain/web is called biomass.
Evolution and Biodiversity
26
F
G
Ecological efficiency is the term that describes the %age of usable energy transferred as biomass from one trophic
level to another and ranges from 2–40 %, with 10 % being typical.
The greater number of trophic levels in a food chain, the greater loss of usable energy.
H The pyramid of energy flow visualizes the loss of usable energy through a food chain. The
lower levels of the trophic pyramid support more organisms. If people eat at a lower trophic
level (fruits, vegetables, grains directly consumed), Earth can support more people. There is a
large loss of energy between successive trophic levels.
3-6
3-7
1. Primary productivity of ecosystems.
2. Production of biomass takes place at different rates among different ecosystems.
I The rate of an ecosystem’s producers converting energy into biomass is the gross primary productivity (GPP).
J Some of the biomass must be used for the producers’ own respiration. Net primary productivity (NPP) is the rate
that producers use photosynthesis to store biomass minus the rate at which they use energy for aerobic respiration.
NPP measures how fast producers can provide biomass needed by consumers in an ecosystem.
K Ecosystems and life zones differ in their NPP. The three most productive systems are swamps and marshes,
tropical rain forest, and estuaries. The three least productive are tundra, desert scrub, and extreme desert.
1. The planet’s NPP limits the numbers of consumers who can survive on Earth.
a. The highly productive tropical rain forest cannot support agriculture as practiced in developed countries.
b. Marshes and swamps do not produce food that can be eaten directly by humans; they feed other aquatic
species that humans consume (fish, shrimp, clams).
L Humans are using, wasting, and destroying biomass faster than producers can make it.
Soils
A Soil provides nutrients needed for plant growth; it helps purify water. It is a thin covering that is made of eroded
rock, minerals, decaying organic matter, water, air, and billions of living organisms.
B Layers of soil, called soil horizons, vary in number, composition, and thickness.
C Soil provides nutrients for plant growth; it is the Earth’s primary filter for cleansing water and for decomposing
and recycling biodegradable wastes.
D The major layers of soil are the following:
1. Mature soils have developed over a long time, are arranged in soil horizons (series of horizontal layers), and
have distinct textures and compositions in these layers that vary among different types of soils.
2. Cross-sectional views of these layers are soil profiles.
3. The layers/horizons of mature soils have at least three parts.
a. The top part/layer is the surface-litter layer, or O-horizon. This layer is brown/black and composed of
leaves, twigs, crop wastes, animal waste, fungi, and other organic material.
b. The topsoil layer, or A-horizon, is composed of decomposed organic matter called humus, as well as
some inorganic mineral particles. Thick topsoil layers help hold water and nutrients. These two top layers
teem with bacteria, fungi, earthworms, and small insects.
1) Dark-brown/black topsoil is rich in nitrogen and organic matter.
2) Gray, yellow, or red topsoils need nitrogen enrichment.
E The B-horizon (subsoil) and the C-horizon (parent material) have most of the soil’s inorganic matter—sand, silt,
clay, and gravel. The C-horizon rests on bedrock.
F Air and water fill spaces between soil particles. Plant roots need oxygen for aerobic respiration.
1. Downward movement of water through the spaces in the soil is infiltration. Water moving downward
dissolves minerals and organic matter and carries them to lower levels; this process is leaching.
G Soil differences in texture are affected by the size of particles and the space between particles.
H To determine soil’s texture, do the following:
1. Take a small amount of topsoil, moisten, and rub between fingers and thumb.
a. A gritty feel means the soil has a lot of sand; this soil is easy to work.
b. A sticky feel means the soil has a lot of clay; this soil retains a lot of water.
c. A smooth feel means the soil is silt-laden.
d. A crumbly, spongy feel means the soil is heavily loam; this soil holds water.
2. Soil porosity is affected by soil texture. The average size of spaces or pores in soil determines soil
permeability.
What Happens to Matter in an Ecosystem?
A Nutrient cycles/biogeochemical cycles are global recycling systems that interconnect all organisms.
Evolution and Biodiversity
27
B
C
3-8
Nutrient atoms, ions, and molecules continuously cycle between air, water, rock, soil, and living organisms.
These cycles include the carbon, oxygen, nitrogen, phosphorus, and water cycles. They are connected to chemical
cycles of the past and the future.
D The water/hydrologic cycle collects, purifies, and distributes the Earth’s water in a vast global cycle.
1. Solar energy evaporates water; the water returns as rain/snow, goes through organisms, goes into bodies of
water, and evaporates again.
E Some water becomes surface runoff, returning to streams/rivers, causing soil erosion, and also being purified
itself.
F The water cycle is powered by energy from the sun. Winds and air masses transport water over the Earth’s
surface.
G Water is the primary sculptor of Earth’s landscape.
H Water is the major form of transporting nutrients within and between ecosystems.
I The water cycle is altered by man’s activities.
1. We withdraw large quantities of fresh water, clear vegetation, increase runoff, reduce filtering, increase
flooding, add nutrients to water, and contribute to global climate change.
J The carbon cycle circulates through the biosphere. Carbon moves through water and land systems, using
processes that change carbon from one form to another.
1. CO2 gas is an important temperature regulator on Earth.
K Photosynthesis in producers and aerobic respiration in consumers, producers, and decomposers circulates carbon
in the biosphere.
L Fossil fuels contain carbon; in a few hundred years we have almost depleted such fuels that have taken millions of
years to form.
M Carbon recycles through the oceans. Oceans act as a carbon sink, but when warming occurs, they release carbon
dioxide.
N Excess carbon dioxide’s addition to the atmosphere through our use of fossil fuels and our destruction of the
world’s photosynthesizing vegetation has contributed to global warming. The natural greenhouse effect is being
strengthened by increasing temperatures.
O Nitrogen is recycled through the Earth’s systems by different types of bacteria.
1. The nitrogen cycle converts nitrogen (N2) into compounds that are useful nutrients for plants and animals.
2. The nitrogen cycle includes the following steps:
a. Specialized bacteria convert gaseous nitrogen to ammonia in nitrogen fixation.
b. Special bacteria convert ammonia in the soil to nitrite ions and nitrate ions; the latter is used by plants as
a nutrient. This process is nitrification.
c. Decomposer bacteria convert detritus into ammonia and water-soluble salts in ammonification.
d. In denitrification, nitrogen leaves the soil. Anaerobic bacteria in soggy soil and bottom sediments of
water areas convert NH3 and NH4+ back into nitrite and nitrate ions, then nitrogen gas and nitrous oxide
gas are released into the atmosphere.
1) Phosphorus circulates through water, the Earth’s crust, and living organisms in the phosphorus cycle.
3. The major reservoirs of phosphorus on Earth are rock formations and ocean bottom sediments.
4. Phosphorus is transferred by food webs and is an important component of many biological molecules.
5. Phosphorus is often the limiting factor for plant growth.
a. Man interferes with the phosphorous cycle in harmful ways.
1) We mine phosphate rock to produce fertilizers and detergents.
2) We cut down tropical forests, and thereby reduce the phosphorus in tropical soils.
3) Phosphorus erodes from fertilized crops, enriching streams, oceans, and lakes; this stimulates
producer growth and upsets chemical cycling.
How Ecologists Study Ecosystems
A Ecologists do field research, which includes observing and measuring the ecosystem structure and function.
B New technologies such as remote sensing and geographic information systems (GISs) gather data that is fed into
computers for analysis and manipulation of the data. Computerized maps may be made of an area to examine
forest cover, water resources, air pollution emissions, coastal changes, and changes in global sea temperatures.
C Ecologists use tanks, greenhouses, and controlled indoor and outdoor chambers to study ecosystems (laboratory
research). This allows control of light, temperature, CO2, humidity, and other variables.
D Field and laboratory studies must be coupled together for a more complete picture of an ecosystem.
Evolution and Biodiversity
28
E
F
Systems analysis develops mathematical models and other models that simulate ecosystems that are large and
very complex; these models can’t be adequately studied with field and laboratory research. This allows the
analysis of the effectiveness of various alternate solutions to environmental problems and can help anticipate
environmental surprises.
We need baseline data about components, and physical and chemical conditions in order to determine how well
the ecosystem is functioning and anticipate how best to prevent harmful environmental changes.
CHAPTER 4
EVOLUTION AND BIODIVERSITY
Objectives
1. Briefly describe the evolution of life from chemical evolution to the development of eukaryotic cells.
2. Describe the tools available to researchers for learning the evolutionary history of life.
3. Briefly describe the theory of evolution, being sure to include the roles played by variation within the gene pool and
natural selection, extinction, speciation, and adaptive radiation.
4. Define natural selection and the three conditions that are necessary for evolution of a population by natural
selection. Summarize and address two common misconceptions about evolution.
5. Define coevolution.
6. Distinguish between a specialist and a generalist. Evaluate the conditions that favor these two approaches.
7. Define ecological niche. Distinguish between condition and resource, and between fundamental niche and realized
niche. List the factors that determine the realized niche.
8. Define speciation and compare allopatric speciation with sympatric speciation. Indicate which of these mechanisms
is more common.
9. Define extinction and distinguish between background extinction and mass extinction. Discuss the role of humans
on the rate of extinction at present.
10. Discuss the pros and cons of artificial selection and genetic engineering. Consider the possible environmental
impacts on resource use, pollution, and environmental degradation.
11. Indicate what it is that has allowed humans to have such a profound influence on their environment.
Key Terms {(Terms are listed in the same font style as they appear in the text.)}
1. adaptation (p. 65)
9. extinction (p. 70)
18. reproductive isolation
2. artificial selection (p. 71)
10. gene splicing (p. 71)
(p. 70)
11. generalist species (p. 68)
19. specialist species (p.
3. background extinction
(p. 71)
12. genetic engineering (p. 71)
68)
20. speciation (p. 69)
4. biological evolution
13. genetically modified
(evolution) (p. 64)
organisms (GMOs) (p. 71)
21. theory of evolution (p.
5. coevolution (p. 66)
14. geographic isolation (p. 69)
64)
15. mass extinction (p. 71)
6. differential reproduction
22. transgenic organisms
(p. 65)
16. mutation (p. 64)
(p. 71)
7. ecological niche (p. 68)
17. natural selection (p. 64)
8. endemic species (p. 70)
Outline
4-1 What Is Biological Evolution and How Does It Occur?
A Evolution is the description of how the Earth’s life changes over time through changes in genes of populations.
B The theory of evolution states that all species descend from earlier ancestral species.
C Populations evolve by becoming genetically different.
1. The gene pool consists of all the genes in a population’s offspring.
2. The population develops genetic variability brought about by mutations.
a. Mutations are random changes in the structure/number of DNA molecules in a cell.
b. Mutations occur in the following two ways:
1) Gene DNA is exposed to external agents like X-rays, chemicals (mutagens), or radioactivity.
2) Random mistakes occur in coded genetic instructions.
c. Only mutations in reproductive cells are passed to offspring.
D Natural selection occurs when members of a population have genetic traits that improve their ability to survive
and produce offspring with those specific traits.
Evolution and Biodiversity
29
1.
2.
3.
Adaptation or adaptive traits are heritable traits that help organisms to survive and reproduce better under
prevailing environmental conditions.
Environmental changes require adaptations also. Organisms must do the following:
a. Adapt to the new conditions.
b. Migrate to an area with more favorable environment.
c. Become extinct.
Natural selection can be summarized as genes mutate, individuals are selected, and populations evolve.
E
4-2
4-3
4-4
Interactions between species can result in microevolution in each of their populations, a process called
coevolution. Sometimes the predators have the advantage; sometimes the prey is better adapted.
How Do Geological and Climate Changes Affect Evolution?
A Geological process affects natural selection.
1. Tectonic plates have been moving apart for hundreds of millions of years.
a. The location of continents affects climate and species distribution.
b. Movement of plates allowed the spread and evolution of species.
B Climate change and catastrophes affect natural selection.
1. By defining the ecosystems on Earth, climate changes have molded species.
What Is an Ecological Niche?
A An ecological niche is a species’ way of life in an ecosystem, everything that affects its survival and reproduction.
B Some species have broad ecological roles and are termed generalist species.
1. Their living range is broad; it includes many different places.
2. They can eat a variety of foods and tolerate a wide range of environments.
3. If environment is changeable, the generalist may survive better than the specialist.
C Some species have narrow ecological roles and are termed specialist species.
1. Specialist species can live only in very specific environments.
2. This makes them more prone to extinction when environmental conditions change.
3. If the environment is constant, specialists have fewer competitors.
How Do Extinction, Speciation, and Human Activities Affect Biodiversity?
A Natural selection can lead to the development of an entirely new species.
1.
In speciation, two species arise from one when some members of a population cannot breed with other members to produce fertile
offspring.
a.
b.
4-5
Geographic isolation, physical separation for long time periods.
Reproductive isolation.
1) The gene pools are changed to the extent that members become so different in genetic makeup that
they cannot produce fertile offspring.
B When population members cannot adapt to changing environmental conditions, the species becomes extinct.
C When local environmental conditions change, some species will disappear at a low rate; this is called background
extinction.
D Mass extinction is a significant rise in extinction rates above the background extinction level. Usually, between
25–70% of species are lost. {Recent evidence suggests that there have been two mass extinctions on Earth. There
appears to have been five mass extinctions on Earth.}
E The Earth’s biodiversity is decreasing because of human activities.
1. Humans and their activities are also destroying/degrading ecosystems that might be centers for future
speciation.
How Might Genetic Engineering Affect Evolution?
A Man has used artificial selection to change the genetic characteristics of populations.
1. We use selective breeding to obtain specific desired traits.
2. Traditional crossbreeding is a slow process; it takes many generations of selection for the desired trait.
3. Genetic engineering/gene splicing are techniques that isolate, modify, multiply, and recombine genes from
different organisms. Genes from different species that would never interbreed in nature are being transferred
to each other.
4. Genetically modified organisms (GMOs)/transgenic organisms are the results of this gene splicing.
a. Gene splicing takes half as much time to develop a new crop/animal as does traditional crossbreeding.
B Genetic engineering is an unpredictable process and raises privacy, ethical, legal, and environmental issues. It is a
trial and error process.
Climate and Biodiversity
31
CHAPTER 5:
CLIMATE AND BIODIVERSITY
Objectives
1. Distinguish between weather and climate. Summarize how warm fronts, cold fronts, high-pressure air masses, and lowpressure air masses affect weather.
2. Describe at least five different factors that contribute to global air-circulation patterns.
3. Define greenhouse effect. Name greenhouse gases. State the significance of the greenhouse effect.
4. Describe the general effects of the following microclimates: windward and leeward sides of a mountain, forests, and cities.
5. Describe how climate affects the distribution of plant life on Earth. Draw connections between biomes and the following
plants, which are particularly adapted for different biomes: succulent plants, broadleaf evergreen plants, broadleaf deciduous
plants, and coniferous evergreen plants.
6. Compare the climate and adaptations of plants and animals in deserts, grasslands, and forests. Describe the distinctive
qualities of a chaparral ecosystem. Be sure to distinguish among the three major kinds of forests.
7. Compare the biodiversity and stratification in the three major kinds of forests.
8. Describe how a mountain ecosystem is like an “island of biodiversity.”
9. Summarize the distribution of light, salt, and temperature in different aquatic life zones.
10. Evaluate the significance of the ecological contributions of the oceans.
11. Briefly describe the characteristics and ecological significance of coral reefs. Describe environmental and economic problems
of coral reefs.
12. Distinguish between coastal and inland wetlands. Describe the ecological functions performed by wetlands. Describe
environmental problems associated with coastal and inland wetlands.
13. List and compare the four zones of a lake. Distinguish between oligotrophic and eutrophic lakes. Describe stratification and a
turnover in a lake.
14. Define watershed. List and distinguish the three zones of a river system.
Key Terms {(Terms are listed in the same font style as they appear in the text.)}
1. abyssal zone (p. 99)
27. desert (p. 82)
53. phytoplankton (plant) plankton (p. 92)
2. alpine tundra (p. 86)
28. drainage basin (p. 102)
54. polar grasslands (p. 84)
3. altitude (p. 76)
29. estuaries (p. 94)
55. polyps (p. 98)
4. aquatic life zones (p. 92)
30. euphotic zone (p. 98)
56. prairie potholes (p. 102)
5. arctic tundra (p. 84)
31. eutrophic lake (p. 101)
57. profundal zone (p. 100)
6. barrier beaches (p. 96)
32. evergreen coniferous forests
58. rain shadow effect (p. 79)
7. barrier islands (p. 96)
(p. 89)
59. rocky shores (p. 96)
8. bathyal zone (p. 99)
33. floodplain zone (p. 102)
60. runoff (p. 102)
9. benthic zone (p. 100)
34. floodplains (p. 102)
61. salinity (p. 92)
10. benthos (p. 92)
35. forest (p. 86)
62. savanna (p. 84)
11. biomes (p. 80)
36. freshwater life zones (p. 100)
63. seasonal wetlands (p. 102)
12. boreal forests (p. 89)
37. grasslands (prairies) (p. 84)
64. short-grass prairies (p. 84)
13. broadleaf deciduous trees (p. 89)38. grazing (p. 84)
65. source zone (p. 102)
14. broadleaf evergreen plants
39. human-enhanced climate change (p.
66. surface water (p. 102)
(p. 86)
79)
67. swamps (p. 102)
15. browsing (p. 84)
40. inland wetlands (p. 102)
68. taigas (p. 89)
16. climate (p. 76)
41. intertidal zone (p. 96)
69. tall-grass prairies (p. 84)
17. coastal coniferous forests (p. 90)42. lakes (p. 100)
70. temperate deciduous forests (p. 89)
18. coastal wetlands (p. 94)
43. latitude (p. 76)
71. temperate deserts (p. 82)
19. coastal zone (p. 94)
44. limnetic zone (p. 100)
72. temperate grassland (p. 84)
20. cold deserts (p. 82)
45. littoral zone (p. 100)
73. transition zone (p. 102)
21. coniferous evergreen trees
46. marshes (p. 102)
74. tropical deserts (p. 82)
(p. 89)
47. mountains (p. 90)
75. tropical rain forests (p. 86)
22. continental shelf (p. 94)
48. natural greenhouse effect (p. 79) 76. watershed (p. 102)
23. coral reefs (p. 97)
49. nekton (p. 92)
77. weather (p. 76)
24. currents (p. 78)
50. oligotrophic lake (p. 101)
78. wet arctic tundra (p. 102)
25. decomposers (p. 92)
51. open sea (p. 98)
79. zooplankton (animal plankton) (p. 92)
26. density (p. 78)
52. permafrost (p. 86)
80. zooxanthellae (p. 98)
Climate and Biodiversity
32
Outline
5-1 What Factors Influence Climate?
A Weather is short-term atmospheric conditions in an area. It is typically considered in hours or days.
B The amount of incoming solar energy per unit area of land, air circulation over the surface of the Earth, and water
circulation determine the different climates that occur.
C The following four major factors determine global air circulation patterns:
1. There is uneven heating of Earth’s surface; the equator is heated more than the poles. This is due to the angle of the
sun’s rays on different parts of the Earth.
2. Rotation of the Earth on its axis results in the Earth moving faster beneath air masses at the equator and slower at the
poles. Belts of prevailing winds are the result.
3. Properties of air, water, and land affect global air circulation. Water evaporation sets up cyclical convection cells.
These occur both vertically and from place to place in the troposphere. The result is an irregular distribution of
climates and patterns of vegetation from pole to pole.
4. Ocean currents and winds influence climate by redistributing heat received from the sun from one place to another.
a. Differences in water density and heat create ocean currents that are warm/cold.
D Currents redistribute absorbed solar heat from one place to another and influence vegetation and climate near coastal
regions.
E Currents also help mix ocean waters to distribute nutrients and dissolved oxygen needed for aquatic organisms.
F Winds moving away from coastal regions result in upwelling of cold, nutrient-rich bottom waters as surface water moves
offshore. These nutrients support large populations of phytoplankton, zooplankton, fish, and fish-eating sea birds.
G Gases such as water vapor, carbon dioxide, methane, and nitrous oxide play key roles in determining Earth’s average
temperatures and climate.
H These gasses are known as greenhouse gasses. They allow mostly visible light, some infrared radiation, and ultraviolet
radiation to pass through the troposphere. This natural warming is the greenhouse effect.
I The Earth would be a cold, mostly lifeless place without this effect.
J Human activities have added to the carbon dioxide, methane, and nitrous oxide in the atmosphere. The fear is that this can
increase the natural greenhouse effect and lead to global warming.
K Precipitation patterns, sea levels, and crop growing areas could be altered.
L Various topographic features can create local and regional climates different from the general climate of a region.
1. One example of this is the rain shadow effect, where an air mass moves inland from an ocean, reaches a mountain
range, and as the air is forced to rise, it cools and loses moisture on the windward side. The leeward side of the
mountain will be drier due to the loss of moisture on the windward side.
2. Bricks, asphalt, and other building materials create distinct microclimates in cities that are warmer, and have more
haze and smog and lower wind speeds than the countryside around them.
5-2 Biomes: Climate and Life on Land
A Different climates lead to different communities of organisms, especially vegetation.
B Differences in average temperature and precipitation due to global air and water circulation lead to differences in climate.
C Scientists divide the world into 12 major biomes.
1. Average annual precipitation, temperature, and soil type are the most important factors in producing tropical,
temperate, or polar deserts, grasslands, and forests.
2. Biomes are actually a mosaic of different biological communities, but with similarities unique to the biome (forest,
grassland, and desert).
3. Climate and vegetation vary with latitude and altitude of an area. Latitude measures distance from the equator; altitude
measures elevation above sea level.
5-3 Desert Biomes
A Deserts have little precipitation and little vegetation. They are found in tropical, temperate, and polar regions.
B Deserts cover about 30% of the Earth’s land surface, mostly in tropical and subtropical regions. The largest ones are found
in the interior of continents. Others form because of the rain shadow effect on the down side of mountains.
1. Tropical deserts are hot and dry most of the year with few plants, rocks, and sand.
2. Temperate deserts have high day temperatures in the summer and low temperatures in the winter with more rain than
in tropical deserts. Plants are widely spaced, mostly drought-resistant shrubs and cacti/succulents.
3. Cold deserts have cold winters and warm summers with low rainfall.
C Deserts take a long time to recover from disturbances.
1. Plant growth is slow.
2. There is low species diversity.
Community and Population Ecology
41
D
E
F
3. Nutrient cycling is slow and there is a lack of water.
Human impact on deserts due to overgrazing and off-road vehicles may take decades to overcome.
Grasslands/prairies have enough water to support grasses, but few, if any, trees.
1.
They persist because of seasonal drought, grazing by large herbivores, and occasional fires that keep shrubs and trees from growing.
2.
The three main types of grasslands are tropical, temperate, and polar (tundra).
A savanna usually has warm temperatures year-round and two long, dry seasons with much rain the rest of the year.
1.
2.
3.
4.
5.
G
Large herds of grazing/browsing animals feed here.
There are a number of different niches in the savanna.
Competition for plant materials has been minimized due to specialized eating habits.
Many of these animals are killed for coats, tusks, and ivory, for example.
Human attempts to raise cattle on savannas may result in converting them to desert areas. Cattle need more water so
they move between water holes, causing loss of vegetation and soil compaction.
6. Cattle fecal materials kill grass beneath them as they dry; native herbivores have dry fecal pellets that readily
decompose, recycling nutrients.
Temperate grasslands have cold winters, hot, dry summers, and deep, fertile soils.
H
They are widely distributed in North and South America, Europe, and Asia. Rain falls unevenly throughout the year.
1.
2.
3.
4.
5.
6.
7.
8.
5-4
Organic matter accumulates, producing fertile soil as aboveground plant parts die each year.
Soil is held in place by a network of intertwined root.
Natural grasses are adapted to fire.
North American grasslands are tall-grass prairies and short-grass prairies.
Evaporation is rapid, winds blow most of the time, and fires occur in summer and fall.
Humans have used these lands to raise cattle and crops. They are often flat areas, easily plowed.
Plowing makes soil vulnerable to erosion and blowing.
Overgrazing of a number of areas has led to sagebrush desert instead of grassland.
I
Polar grasslands, or arctic tundra, are treeless, cold plains. Long, dark winters and low precipitation are the norm.
J
1. There is a thick, spongy mat of low-growing vegetation (grasses, mosses, dwarf woody shrubs).
2. Most growth occurs within 6–8 weeks of summer in long days.
3. Permafrost is a permanently frozen layer of soil when water freezes.
4. Tundra is waterlogged during summer, with hordes of insects.
Alpine tundra occurs above the tree line, but below the permanent snow line.
K
This area gets more sunlight than arctic tundra and has no permafrost. Vegetation is similar to that in arctic tundra.
Forest Biomes
A Forests are found in areas with a moderate to high average of annual rainfall. Three main types of forest are tropical,
temperate, and boreal (polar).
B Tropical rain forests are near the equator, have hot, humid conditions and almost daily rainfall.
1. Dominant plants are broadleaf evergreens with shallow roots.
2. A dense canopy blocks most sunlight from reaching lower levels.
3. Vines often drape individual trees.
4. Epiphytes such as orchids and bromeliads are found on trunks and branches. They get nutrients from falling materials
and water from humid air.
5. There is great biological diversity found in many specialized niches within the forest.
6. Most animal life is found in the sunny canopy layer of the forest.
C
Temperate deciduous forests grow in areas with moderate average temperatures, abundant rainfall, and long, warm summers.
1.
2.
3.
D
Broadleaf, deciduous trees dominate this biome. Leaves drop in fall, trees become dormant, and new leaves grow in
spring.
These areas have fewer species of trees.
More sunlight penetrates the canopy so there is richer diversity of ground level plant life.
Evergreen coniferous forests/boreal forests are located in areas just south of arctic tundra around the northern sub-arctic regions of the Earth.
1.
5-5
Long, dry, extremely cold winters with 6–8 hours sunlight are the norm. Summers are short, with 19 hours of daily
sunlight.
2. Dominant trees are coniferous (cone-bearing) spruce, hemlock, fir, cedar, and pine.
3. There is low plant diversity.
Aquatic Environments
A Saltwater and freshwater aquatic zones cover about 71% of the Earth’s surface. These are the equivalent of terrestrial
biomes.
B Salinity of the water determines the major types of organisms found in an aquatic environment.
Community and Population Ecology
42
C
5-6
There are four major types of organisms in aquatic systems:
1. Plankton are free-floating, weakly swimming, generally one-celled organisms. There are two major types of plankton:
phytoplankton (plant plankton) and zooplankton (animal plankton).
2. Nekton is a second group of organisms. These are fish, turtles, and whales.
3. Benthos are bottom dwellers, a third group of organisms. Barnacles, oysters, worms, lobsters, and crabs are examples
of benthos organisms.
4. Decomposers are a fourth group. These organisms break down organic matter into simple nutrients for use by
producers.
D Aquatic-environment living has both advantages and disadvantages. Physical boundaries are less fixed, making it more
difficult to manage/count aquatic populations of organisms.
1. Food webs are longer and more complex than on land due to the fluidity of medium habitats and variety of bottom
habitats.
2. Size and lack of visibility make them more difficult to study.
E Three layers of aquatic life zones can be used: surface, middle, and bottom.
1. Temperature, sunlight availability, dissolved oxygen levels, and nutrient availability determine types and numbers of
producers found in these zones.
2. The euphotic zone describes the upper layer where sunlight can penetrate. Clouding or excessive algal growth reduces
the depth of the euphotic zone.
3. Dissolved oxygen levels are higher near the surface due to photosynthesis in this area.
4. CO2 levels are lower near the surface and higher in deeper, dark layers due to aerobic respiration.
5. Open oceans tend to have limited amounts of nitrates, phosphates, iron, and other nutrients that limit productivity.
6. Shallow waters are generally well supplied with nutrients for growth.
7. Deep-dwelling species depend on animal and plant material that die/fall to the bottom. Large fish are vulnerable to
overfishing depletion.
Saltwater Life Zones
A Oceans have two major life zones: the coastal zone and the open sea.
B The coastal zone interacts with the land, making it more easily affected by human activities.
1. Ecosystems in coastal zones have a high net primary productivity per unit area. They constitute 10% of the oceans and
contain 90% of all marine species.
2. There is ample sunlight, and nutrients flow from land and wind/currents distribute them.
3. The coastal zone extends from the high-tide mark on land to the edge of the continental shelf.
4. Estuaries and coastal wetlands are subject to tidal rhythms, runoff from land, and seawater mixing with freshwater and
nutrients from rivers and streams.
5. Mangrove forest swamps grow in sheltered regions of tropical coasts. They collect mud and anaerobic sediment.
6. Coastal wetlands/estuaries make nutrients available due to constant stirring of bottom sediment.
7. These areas filter toxic pollutants and excess plant nutrients, reduce storm damage, and provide nursery sites for
aquatic species.
8. Humans are destroying/degrading these ecosystems; one-third has already been lost.
C Organisms living in the intertidal zone have adapted ways to survive the daily changes in wet/dry conditions and changes
in salinity.
D Barrier beaches/sandy shores are gently sloping. Organism’s tunnel or burrow in the sand to survive daily changes in
conditions.
E Low, sandy, narrow islands that form offshore from a coastline are barrier islands. They generally run parallel to the shore.
1. The islands help protect the mainland, estuaries, and coastal wetlands from heavy storm damage.
2. People want to live on these islands, but do not recognize how much they are subject to damage. In spite of this,
almost one-fourth of barrier islands are developed.
3. Sand is constantly shifting due to winds and parallel currents along the islands.
4. Undisturbed beaches have one or more rows of sand dunes on them. Grass roots hold the sand in place, and the dune is
a first line of defense against storms. It is safer to build behind the second set of dunes if any building occurs.
5. Developers want to build on the islands and do not consider the protective services that the dunes provide. Large
storms can and have swept away or severely damaged seaside buildings.
6. Governments often provide funds for rebuilding and provide insurance at fairly low rates for building on the dunes.
7. Some people think that persons building in such risky places should accept all responsibility for repair or replacement
due to storm damage.
F Coral reefs in shallow coastal zones of tropical and subtropical oceans support a very diverse, complex ecosystem.
Community and Population Ecology
43
1.
2.
5-7
They grow slowly and are vulnerable to damage.
They thrive in clear, warm, fairly shallow water with a high salinity. The ideal water temperature is between 18–30oC
and will bleach if the water warms above this by as little as 1 oC.
3. Severe storms, freshwater floods, and invasions of predatory fish adversely affect the reefs. They have survived natural
disturbances for a long geologic history.
4. The greatest threats to coral reefs today are sediment runoff and other human activities. Coral reef systems may not
have enough time to adapt to these rapidly changing conditions.
5. There are indications that recovery is possible when restrictions are imposed and pollution is reduced.
G The open sea is divided into three vertical zones based primarily on penetration of light.
1. The euphotic zone is lighted, has floating phytoplankton carrying on photosynthesis, and has low nutrient levels,
except at upwellings.
2. The dissolved oxygen level is high.
3. Large, fast-swimming predatory fish like swordfish, sharks, and bluefin tuna live in this zone.
4. The bathyal zone is the dimly lit middle zone; no producers are in this zone. Zooplankton and smaller fish live in this
zone.
5. The abyssal zone is dark and very cold with little dissolved oxygen. The nutrients on the ocean floor occult support
about 98% of species living in the ocean.
6. Organisms in this area are deposit feeders, or filter feeders.
7. Low average primary productivity and NPP occurs, but oceans are so large they make the largest contribution to NPP
overall.
H About 40% of the world population lives along coasts. Over half of the U.S. population lives within 62 miles of the coast.
Freshwater Life Zones
A Freshwater life zones contain less than 1% by volume of salt. These zones include standing (lentic) bodies such as lakes,
ponds, and wetlands, and flowing (lotic) systems such as streams and rivers.
B Lakes are large natural bodies of standing water found in depressions.
1. Rainfall, melting snow, and stream drainage feed lakes.
2. Lakes generally consist of three distinct zones depending on depth and distance from shore.
a. The littoral zone is open, sunlit surface water away from shore and is the most productive area for food and
oxygen production.
b. The profundal zone is deep open water too dark for photosynthesis. Oxygen levels are lower.
c. The benthic zone consists of decomposers and detritus feeders. Fish swim from one zone to another. Sediment
washing and dropping detritus feed this area.
C Waters flowing from mountains to the sea create different aquatic conditions and habitats.
1. Surface water does not sink into the ground.
2. Runoff is surface water that flows into streams and rivers, and the area it drains is called a watershed or drainage basin.
D Three aquatic life zones, each with different conditions, can be identified along stream flow.
1. The source zone is narrow and fast moving.
2. The transition zone forms wider, deeper streams, flowing down gentler slopes.
3. The floodplain zone has wider, deeper rivers.
E Streams are fairly open ecosystems and receive many nutrients from surrounding lands.
F Farms, power plants, cities, and recreation areas are often found in floodplains. This also increases excessive nutrient input
and pollutant input into the river system.
G Inland wetlands cover the land for a part or all of each year. Wetlands include swamps, marshes, prairie potholes,
floodplains, and arctic tundra in summer.
1. Scientists also use soil composition and plant life to define whether a particular area is a wetland.
2. Wetlands provide a number of free ecological services, such as filtering toxic wastes/pollutants, absorbing/storing
excess water from storms, and providing habitats for a variety of species.
H Human activities have four major impacts on freshwater systems.
1. Dams and diversions of canals fragment 60% of world’s large rivers and destroys habitats.
2. Flood control dikes and levees alter rivers and destroy aquatic habitats.
3. Cities and farmlands add pollutants.
4. Wetlands have been drained or covered with buildings. The U.S. has lost more than 50% of its wetlands since the
1600s.
5. These systems are able to recover when destructive practices are stopped or reduced.
Community and Population Ecology
44
CHAPTER 6:
COMMUNITY AND POPULATION ECOLOGY
Objectives
1. Describe the three characteristics that describe a biological community.
2. Distinguish among the following roles played by species and give one example of each: native species, nonnative
species, indicator species, and keystone species. Explain why these labels are important.
3. Distinguish among the following species interactions and give one example of each: interspecific competition,
predation, and symbiosis. Distinguish between interference competition and exploitation competition. Summarize
the competitive exclusion principle. List two strategies species use to reduce competition.
4. List two strategies that predators use to capture their prey. List at least five strategies that prey use to defend
themselves against predators.
5. Distinguish among three forms of symbiotic relationships and give one example of each: parasitism, mutualism, and
commensalism.
6. Define succession. Distinguish between primary and secondary succession. Describe how humans affect
communities.
7. Define birth rate, death rate, immigration, and emigration. Write an equation to mathematically describe the
relationship between these rates and the rate of population change.
8. Define limiting factor. Give an example of a resource that would be limiting in an ecosystem.
9. Define exponential growth.
10. Compare a J-shaped growth curve with an S-shaped growth curve and comment on the factors that produce the
sigmoid (S-shaped) curve.
11. Define carrying capacity and explain what determines the carrying capacity of an ecosystem.
12. Define r-selected species and K-selected species and compare the two. Give an example for each type of species
reproductive pattern.
13. List the eight major ways that humans have altered natural ecosystems and comment on the effects of these
alterations for the future of the planet.
Key Terms {(Terms are listed in the same font style as they appear in the text.)}
1. age structure (p. 118)
14. indicator species (p. 108)
28. predation (p. 112)
2. alien species (p. 108)
15. inertia (p. 107)
29. primary succession
3. biotic potential (p. 118)
(p. 115)
16. interspecific competition
4. carnivores (p. 112)
(p.111)
30. resilience (p. 107)
5. carrying capacity (K) (p.
17. intrinsic rate of increase
31. resource partitioning
118)
(p. 118)
(p. 111)
6. climax community (p. 116)
18. invasive species (p. 108)
32. r-selected species (p.
7. commensalism (p. 114)
19. keystone species (p. 110)
119)
8. constancy (p. 107)
20. K-selected species (p.
33. secondary succession
9. ecological succession (p.
119)logistic growth (p. 118)
(p. 115)
115)
21. mimicry (p. 113)
34. species diversity (p.
22. mutualism (p. 114)
106)
10. environmental resistance
(p. 118)
23. native species (p. 108)
35. species evenness (p.
11. epiphytes (p. 114)
24. niche structure (p. 106)
106)
12. exponential growth (p.
25. nonnative species (p. 108)
36. species richness (p.
118)
26. parasite (p. 113)
106)
13. herbivores (p. 112)
27. parasitism (p. 113)
Outline
6-1 How Does Species Diversity Affect the Sustainability of a Community?
A Species diversity.
1. Species diversity is a combination of numbers of different species (richness) and abundance of individuals
within each species (species evenness).
2. Niche structure refers to the number of ecological niches, their resemblance or difference from each other,
and the interaction of species with each other.
B There are three aspects of system sustainability: persistence, constancy, and resilience.
6-2 What Role Do Species Play in a Community?
A Species in a community play many different roles in its ecology.
Community and Population Ecology
45
1.
2.
3.
4.
5.
6.
Native species are those whose original home is in this particular ecosystem.
Nonnative species originally evolved in a different ecosystem and migrated, or were introduced to a new
ecosystem.
Indicator species alert us to harmful changes taking place in biological communities.
Birds are excellent biological indicators because they are everywhere and are quickly affected by
environmental change.
Some amphibians are also considered indicator species.
a. Their disappearance may be a warning of serious declining environmental quality.
b. Vulnerability in different parts of an amphibian lifecycle suggests degrees of environmental
decline/disruption.
c. They are born and live in water and are prey to water-born pollutants.
d. As adults they live on land; they are unprotected because their skins readily absorb pollutants.
e. Frogs as a threatened species are harmed by habitat loss, drought, pollution, parasitism, disease, overhunting, ultraviolet radiation, etc.
The importance of amphibian species’ becoming extinct rests on the following three likelihoods:
a. This extinction suggests that the health of the environment is deteriorating.
b.
6-3
Adult amphibians play important ecological roles in the world community.
1) Extinction of one species leads to extinction of other species.
2) Their biological niche controls insect populations.
c. Amphibians represent the possibility of hundreds of potential pharmaceutical products.
B Keystone species help ecological communities run smoothly; they determine the type and number of community
species.
1. Keystone species have a larger effect on both the types and number of other species in a community.
2. Keystone species fill important ecological roles: pollinating and regulating populations of other species.
3. Loss of a keystone species has far-reaching ramifications for other species in a community; alligators are an
example.
C Foundation species shape communities by creating and enhancing habitat that benefits other species.
1. Elephants, in breaking and uprooting trees, create forest openings in African savanna grasslands and
woodlands.
2. Grazing species benefit from the new growth of grasses and other forage plants.
3. The rate of nutrient cycling is increased.
How Do Species Interact?
A Five basic species interactions are competition, predation, parasitism, mutualism, and commensalism.
B Competition between different species for food, sunlight, water, soil, space, nest sites, etc. is interspecific
competition.
1. With intense competition for limited resources, one species must migrate, shift its feeding habits/behavior, or
face extinction.
2. As humans take more and more space, other species are compromised.
C In competitive situations, some species evolve adaptations, which reduce/avoid competition for resources.
1. Over a long time, species evolve more specialized traits that allow them to use shared resources at different
times, in different ways, or in different places; this is termed resource partitioning. An example is that of
insect-eating warblers in Maine forests that eat insects in specific parts of a spruce tree. Owls hunt at night;
hawks hunt during the day.
D Predator-prey relationships define one species (the predator) feeding/preying on another. Individually, prey is
harmed, but predation can help the population by eliminating the sick, weak, and old.
E Predators have a variety of ways to capture prey. Herbivores feed on immobile plant species; carnivores use
pursuit of prey or ambush to capture prey. Some predators use camouflage and others use chemical warfare
(venom) to capture prey or deter predators.
F Prey species escape predators in a number of different ways such as using swift movement or protective shells,
camouflage, or chemicals to repel or poison their predators.
G Parasites live on or in another species. The host of this arrangement is obviously harmed, but the parasite can
contribute to biodiversity by controlling the size of specific species populations.
H Mutually beneficial interactions also exist in ecological environments.
1. Mutualism is a relationship that benefits both species; these benefits can be in dispersing pollen and seeds for
reproduction, or in receiving food and/or receiving protection.
Applying Population Ecology: The Human Population
48
2.
I
6-4
6-5
Mutualism is not cooperation; each species exploits the other.
Some species interaction helps one species but does nothing for the other; this is termed commensalism.
How Do Communities Respond to Changing Environmental Conditions?
A With new environmental conditions, community structure and composition can change.
1. Ecological succession is the gradual change in species composition of a given area.
2. Primary ecological succession is the gradual establishment of biotic communities on lifeless ground. This
process generally takes a very long time.
3. Secondary ecological succession defines a series of communities with different species developing in places
with soil or bottom sediment. The soil or sediment remains after the natural community of organisms has
been disturbed, removed, or destroyed.
B The classic view of ecological succession is that it is an orderly sequence, each stage leading to the next, more
stable stage until a climax community is reached. Such a community would represent the balance of nature, one
dominated by a few long-lived plant species that are in balance with their environment.
C Scientists can’t predict the course of a given succession in a community toward a stable climax community in
balance with its environment.
D The precautionary principle states that when evidence exists that suggests that an activity can harm human health
or the environment, we should stop it.
What Limits Growth of Populations?
A Populations change in size, density, and age distribution; most members of populations live together in clumps or
groups, which offer safety, food supply, and mating opportunities.
B Four variables influence/govern population size: births, deaths, immigration, and emigration.
C Increase in population occurs by birth and immigration.
D Decrease in population occurs by death and emigration.
E
No population can grow indefinitely due to limited resources, such as light, water, and nutrients, because of competitors or predators.
1.
2.
F
The biotic potential is the population’s capacity for growth.
The intrinsic rate of increase (r) is the rate of population growth with unlimited resources.
Environmental resistance consists of factors that limit population growth.
1.
G
H
I
Carrying capacity (K) is determined by biotic potential and environmental resistance. This is the number of a
species’ individuals that can be sustained indefinitely in a specific space.
2. As a population reaches its carrying capacity, its growth rate will decrease because resources become scarcer.
A population can grow rapidly with ample resources.
1. With few resource limitations, a population will have exponential growth. This is a fixed rate of growth that
will take a J-shaped growth curve as the base size of population increases. This represents its intrinsic rate of
increase (r) or biotic potential.
2. This exponential growth is converted to logistic growth when the populations get larger and face
environmental resistance. In logistic growth, the growth rate levels-off as population size reaches or nears
carrying capacity.
3. The sigmoid (s-shaped) population growth curve shows that the population size is stable at or near its
carrying capacity.
When population size exceeds its carrying capacity, organisms die unless they move or switch to new resources.
1. Exponential growth leads to logistic growth and may lead to the population overshooting the environment’s
carrying capacity.
a. Overshooting an environment’s resources is often a result of a reproductive time lag.
b. The reproductive time lag can produce a dieback/crash of organisms unless the organisms can find new
resources or move to an area with more resources.
Reproductive patterns can be classified into two fundamental reproductive patterns: r-selected and K-selected
species.
1. R-selected species have a high rate of reproduction with little parental care. They have many, usually small
offspring. Massive loss of offspring is compensated for by the large numbers of offspring produced in each
reproductive cycle.
2. R-selected species are opportunists; they reproduce when conditions are favorable or when disturbance opens
a niche for invasion. Most species of this type go through irregular and unstable boom-and-bust cycles in
population size.
a. Competitor or K-selected species are at the other extreme. They produce later in life, have a small
number of offspring, are born fairly large, are cared for and protected by parents, and mature more
slowly.
Applying Population Ecology: The Human Population
49
3.
K-selected species generally follow a logistic growth curve. Many of the larger species with long generation
times/low reproductive rate are prone to extinction.
4. Availability of suitable habitat for individuals of a population ultimately determines the population size.
J Humans are not exempt from population overshoots and diebacks.
1. Human populations have been riddled with famines, plagues, and epidemics throughout our history.
2. We have extended the Earth’s carrying capacity for the human species by our technological, social, and
cultural changes, but we may someday approach the absolute carrying capacity.
K By 1900 U.S. white-tailed deer populations were low, but by mid-century had rebounded, and currently there are
25–30 million deer in the U.S.
1. Questions linger regarding how to manage the U.S. deer population.
CHAPTER 7: APPLYING POPULATION ECOLOGY: HUMAN POPULATION AND
URBANIZATION
Objectives
1. Define birth rate, death rate, emigration rate, and immigration rate. Write an equation to mathematically describe
the relationship between these rates and the rate of population change.
2. Define fertility rate. Describe how fertility rate affects population growth. List at least five factors that affect birth
rate and five factors that affect death rate.
3. Compare rates of population growth in developed and developing countries. Explain the differences you find.
Briefly describe the state of teenage pregnancy in the United States.
4. Using population age structure diagrams, explain how the age structure of a country creates population growth
momentum. Summarize social impacts resulting from declining populations.
5. List five approaches to slowing human population growth. List the four stages of the demographic transition. Briefly
describe the controversies that surround controlling population size through controlling migration and family
planning.
6. Summarize India’s and China’s experiences. Describe the three major shifts in population distribution in U.S.
history.
7. List seven resource and environmental problems faced by urban areas. Briefly describe the process of ecological
land-use planning.
8. Evaluate the costs and benefits of the automobile on U.S. society. List three alternative forms of transportation to the
car, and evaluate the costs and benefits of each.
9. Describe your conception of a sustainable urban environment.
Key Terms {(Terms are listed in the same font style as they appear in the text.)}
1. age structure (p. 131)
8. family planning (p. 134)
14. replacement-level
2. birth rate (p. 127)
9. fertility (p. 127)
fertility (p. 127)
3. crude birth rate (p. 127)
10. infant mortality rate (p.
15. smart growth (p. 146)
4. crude death rate (p. 127)
128)
16. total fertility rate
5. death rate (p. 127)
11. life expectancy (p. 129)
(TFR)
12. migration (p. 130)
(p. 127)
6. demographic transition
(p. 134)
13. population change (p. 127)
17. urban sprawl (p. 138)
7. demographic trap (p. 134)
Outline
7-1 What Factors Influence Population Size?
A Population increases through births and immigration and decreases through deaths and emigration. [population
change = (Births + Immigration) – (Deaths + Emigration)]
1. The crude birth rate is the number of live births per 1,000 people in a population in a specific year.
2. The crude death rate is the number of deaths per 1,000 people in a population in a specific year.
B There are currently more births than deaths throughout the world.
1. The annual rate of natural population change expressed in %age equals the birth rate minus the death rate,
divided by 1,000 persons, and multiplied by 100.
2. The rate of the world’s population growth has decreased.
Applying Population Ecology: The Human Population
50
The populations of China and India comprise 37% of the world’s population. The next most populated country is
the United Stated, with 4.6% of the world’s population.
D Doubling time is one measure of population growth. The rule of 70 is a quick way to calculate doubling time in
years. If the population grew by 1.25% in 2005, divide 70 by 1.25 to find the doubling time, equaling 58 years.
E Fertility is the number of births that occur to an individual woman or in a population.
1. The changing nature of fertility rates affects population growth.
a. Replacement-level fertility is the number of children needed to replace their parents.
b. Total fertility rate (TFR) is the average number of children that a woman has during her fertile years.
2. There are apt to be between 7.2–10.6 billion people by 2050, with 97% of this growth to be in developing
countries. These countries have acute poverty as a way of life for about 1.4 billion people.
F From 1946–1964 the United States had a sharp rise in birth rate, called the baby-boom period.
G At its peak, the TFR reached 3.7 children per woman. There has been a gradual decline since then.
H The population growth of the United States is still greater than any other developed country and is not close to
leveling off.
I About 2.7 million people were added to the U.S. population in 2004. Fifty-five % of this population growth comes
from more births than deaths, and 45% comes from immigration.
1. Other major developed countries have slower population growth and most are expected to have declining
populations after 2010.
2. The high U.S. per capita resource rate produces enormous environmental impact.
J Many factors influence birth and fertility rates.
1. More children work in developing countries; they are important to the labor force.
2. The economic cost of raising and educating children determines their numbers. The more children cost, the
less children people tend to have.
K If there are available private/public pension systems, adults have fewer children because they don’t need children
to take care of them in old age.
L People in urban areas usually have better access to family planning, so have fewer children.
M If women have educational and economic choices, they tend to have fewer children.
N When the infant mortality rate is low, people have fewer children because children are not being lost to death.
O The older the age at which women marry, the fewer children they bear.
P If abortions are available and legal, women have fewer children.
Q The availability of reliable birth control allows women to space children and determines the number of children
they bear.
R Factors that have caused a decline in death rates are the following:
1. Better food supplies and nutrition, and safer water supplies contribute to people’s living longer.
2. Advances in medicine and public health, improved sanitation, and improved personal hygiene also contribute
to people living longer.
S Measures of overall health are the following:
1. Life expectancy is the average number of years a newborn can expect to live.
2. Infant mortality rate is the number of babies out of every 1,000 born who die before their first birthday.
a. This rate reflects a country’s level of nutrition and health care.
3. U.S. infant mortality rate is higher than 35 other countries because of the following:
a. Inadequate health care for poor women and for their babies.
b. Drug addiction among pregnant women.
c. High birth rate among teenagers.
T Arguments to limit immigration into the U.S. are the following:
1. Limitations would aid in stabilizing the population sooner.
2. Limitations would help reduce the U.S.’s enormous environmental impact.
U Arguments for generous immigration policies in the U.S. are the following:
1. Historically, the U.S. has been the land of opportunity for the world’s poor.
2. Immigrants do work that Americans won’t do or handle jobs for which there are not enough trained natives.
3. Immigrants contribute to the economy and pay taxes.
Population Age Structure: What are age structure diagrams? They are visual aids that show the distribution of males
and females in each age group.
A The %ages of male and females in the total population are divided into the following age categories:
1. Pre-reproductive ages span birth to 14 years of age.
C
7-2
Environmental Problems, Their Causes, and Sustainability
51
7-3
2. Reproductive ages include 15 through 44.
3. Post-reproductive ages include ages 45 and up.
B The major determining factor in a country’s future population growth is the number of people under the age of 15.
1. In 2005, 30% of the planet’s population was under 15.
2. The world is demographically divided.
C Changes in the distribution of a country’s age groups have long-lasting economic and social impacts. An example
of this is the “baby boom” generation in the U.S.
D Such a group can dominate the population’s demands for goods and services.
E They influence elections, legislation, and economic demand.
F Retirement of baby boomers in the U.S. may create a shortage of workers.
G The “baby bust” generation compared to that of the “baby boom” generation.
H There will be fewer people to compete for education, jobs, and services.
I Too few people in the labor force may increase wages.
J It may be more difficult to get job promotions because a larger baby-boom group will occupy most upper-level
positions.
K There is an echo-boom consisting of people born since 1977.
L These fluctuations in population age structure have social and economic effects for decades.
M Reduced fertility and population decline can have long-term consequences, especially if the decline is rapid.
1. In a gradual population decline, its harmful effects can usually be managed.
2. There can be a sharp rise in the proportion of older people.
3. It may also produce a sharp rise in public services, cost of healthcare, etc.
4. It may greatly reduce the number of working taxpayers and cause labor shortages.
5. It may make it necessary to raise retirement age, raise taxes, cut retirement benefits and increase legal
immigration, which are generally unpopular moves.
N If population declines because of deaths, the consequences are serious.
1. Deaths from disease such as AIDS disrupt a country’s social and economic structure.
2. A large number of people in a particular age group are removed from the country’s future.
O Life expectancy drops.
P In the case of AIDS, the deaths are mostly young adults; those who usually help run the country and everyday life
for millions.
Q Two major goals are to reduce the spread of HIV through education and health care and to provide financial help
for education, health care, volunteer teachers, and social workers to compensate for the lost young adults.
How Can We Slow Population Growth?
A The demographic transition hypothesis states that as countries become industrialized, their death rates and then
their birth rates decline in four stages.
1. The pre-industrial stage produces high birth and death rates because living conditions are harsh.
2. The transitional state sees food production rise and improvement in health care. Death rates drop and birth
rates remain high.
3. The industrial stage causes birth rates to drop, followed by a drop in death rates because of widespread
industrialization, medical advances, and modernization.
4. The postindustrial stage moves to the birth rate equaling the death rate, resulting in zero population growth.
Population size will begin to slowly decrease.
B Some countries run the risk of getting caught in the transitional state, and economic conditions will not be
available to sustain the population.
1. There can be a shortage of skilled workers to sustain the country’s economy.
2. There will not be capital and resources to support rapid developing economies.
a. International debt takes much of a country’s resources.
b. Developed countries are not helping developing countries economically.
C Family planning helps reduce the number of births and abortions throughout the world.
D Information is given on birth spacing, birth control, and health care.
E Family planning has been responsible for at least 55% of the drop in TFRs in developing countries.
F Family planning has also reduced both legal and illegal abortions per year.
1. Services come through educational and clinical services.
a. Almost one-half of pregnancies in developing countries are unplanned, and 26% end in abortion.
b. Women want to limit their pregnancies but have no access to contraceptives.
Environmental Problems, Their Causes, and Sustainability
52
2.
7-4
Family planning success can be improved through the following methods:
a. Target programs to teenagers and unmarried, sexually active women.
b. Develop programs for educating men about their responsibilities for the children they father.
c. Provide more effective means of birth control for men.
d. Advocate that pro-choice and pro-life groups join to reduce unplanned birth and abortions.
3. Empower women by providing education and paying jobs, and by supporting their human rights.
a. Women work 66% of all the hours worked, but receive 10% of the world’s income.
b. Empowering women with these things would slow population growth, promote human rights, reduce
poverty, and slow environmental degradation.
G Reducing population growth can best be achieved by investing in family planning, reducing poverty, and
elevating the status of women.
H India has tried to control its population growth for years.
1. Overpopulation ills of poverty, malnutrition, and environmental problems abound in India.
2. Almost one-half of India’s labor force is unemployed; half of its cropland is degraded due to soil erosion; and
two-thirds of its water is seriously polluted, with inadequate sanitation services.
3. Efforts to limit population have not been especially successful because of the following:
a. Poor couples believe they need several children for work and care.
b. There is a strong preference for male children, so many do not use birth control.
I Population growth in China has been controlled by a strongly enforced government program.
1. Between 1972 and 2005, China’s birthrate was cut in half.
2. Couples with one child are rewarded with extra food, larger pensions, better housing, bonuses, free school
tuition, and preferential employment treatment for the child.
J Eighty-three % of married women use modern contraception, provided free by the government.
K China’s population has an enormous environmental impact that may affect its production of food.
L The health clinics that used to provide basic health care for rural farm population collapsed in the 1980s; now nine
of ten rural Chinese have no health insurance or social safety net.
Population Distribution: Urbanization and Urban Growth
A Urban populations are attracting more and more people throughout the world, developing into centers of poverty.
1. About one-half of the world’s people live in cities/densely populated urban areas, drawn there for better jobs
and a better life.
2. Cities provide jobs, food, housing, a better life, entertainment, and freedom from religious, racial, and
political conflicts of village life.
3. People are pushed to cities by poverty, lack of land, declining work, famine, and war.
B Urban trends that affect urban growth include the following:
1. The number/proportion of people living in urban areas is growing.
a. Most urban areas are along countries’ coastal areas.
b. Most huge urban areas are in developing countries.
2. The number of large cities (a million or more people) is increasing rapidly.
a. Megacities or megalopolises contain 10 million-plus people.
b. Megalopolis is a merger of a city (cities) and adjacent urban areas; two such areas are Bowash (BostonWashington) and Chipitts (Chicago-Pittsburgh).
3. Urban population is rapidly increasing in developing countries.
C Urban growth is much more rapid in developing countries, but developed countries will be 84% urbanized by
2030.
D Poverty is becoming more common in urban areas, especially in developing countries.
E Three of four Americans live in urban areas; about half of them live in suburban areas. These urban areas are
cities with at least a population of 50,000 people.
1. People first migrated from rural areas to large central cities.
2. Then, people migrated from large central cities to suburbs/smaller cities.
F Next, people migrated from the North and East to the South and West (1980–).
G Lastly, some have migrated away from urban areas back to rural areas (1990–).
H Urban life’s quality in America has improved, but problems remain.
1. Overall, people have better working and housing conditions as well as improved air and water quality. City
services have improved.
2. Older cities have deteriorating services and aging infrastructures.
Environmental Problems, Their Causes, and Sustainability
53
7-5
a. Budget cuts compromise services and infrastructures.
b. Poverty in cities is rising, as is unemployment.
I Urban areas tend to sprawl outward and eat up surrounding countryside; the process is termed urban sprawl.
1. Low-density development is growing and encouraging dependence on cars.
J Sprawl is a byproduct of affordable land and cars, poor urban planning, and cheap gas.
K Problems caused by sprawl have been decreased energy efficiency; increased urban flooding; destruction of
cropland, forest, and open space; and longer travel time.
L The advantages of urbanization include the following:
1. Cities are centers of economic development, jobs, commerce, and transportation.
2. Urban populations are generally healthier with better access to medical care, family planning information,
education, and social services.
3. Recycling is more feasible, and environmental protection is better supported.
4. People concentrated in an area preserve biodiversity and wildlife habitats.
M The disadvantages of urbanization include the following:
1. Cities do not sustain themselves; they concentrate pollutants and noise, spread infectious diseases, and are
centers of crime, poverty, and terrorism.
2. They threaten biodiversity, produce huge wastes, and consume about 75% of the world’s resources.
3. Cities’ huge use of resources depletes the environments around them. Flooding is a problem because of
location and water runoff.
N The heat produced in cities creates urban heat islands that affect the climate over a large area and keep polluted air
from being cleaned.
O The urban poor and the rural poor both live in unhealthy conditions.
1. Large cities have squatter settlements and shantytowns for the poor—places that provide metal, plastic sheets,
scrap wood, and discarded packing crates to build shelters. Some places develop communities with hope for a
better life.
2. These urban settlements have the worst/nonexistent services: lack of clean water, sewers, electricity, etc.
There are often severe air, water, and hazardous waste pollutants.
3. Governments often force people away; they resettle somewhere else and the cycle begins again.
4. The rural poor tend to have more children and less educational opportunity.
5. Mexico City is an environmental nightmare and an urban disaster.
a. The negatives of Mexico City are overwhelming: rapid population growth, severe pollution, disease, and
poverty.
b. About one in every six Mexicans lives in the city; they suffer from high unemployment, noise, traffic
congestion, soaring crime, etc. Barrios are the slum settlements.
c. Lack of sewage services has produced bacteria-laden, dried human excrement, which is spread by the
wind; it is called fecal snow and causes widespread salmonella and hepatitis.
d. Breathing the air in Mexico City is the same as smoking three packs of cigarettes per day.
e. The city’s air and water pollution causes 100,000 premature deaths per year.
Transportation and Urban Development
A The amount of available land determines if a city grows outward or upward, as well as the type of transportation
systems used.
1. Those in compact cities growing upward use mass transit systems, walk, or ride bicycles.
2. Those people in sprawling cities use individual automobile transportation.
B Cars rule in the United States because of large areas of relatively cheap land.
1. The U.S. is overrun with automobiles, using 32% of the world’s cars and consuming 43% of the world’s gas.
C Cars have advantages and disadvantages.
1. Cars make people mobile and fuel the economy.
2. Cars kill people, pollute, and waste time when traffic jams occur.
D To reduce automobile use, users must pay for the car’s harm by paying greater gasoline taxes, giving up the
government subsidies for cars, subsidizing mass transit systems, and raising use fees.
E Political pressures and the love of the automobile interfere with efforts to decrease the importance/presence of
automobiles. Fast, efficient, and reliable mass transit is not available; people live all over, not in well-defined
areas.
F The use of any alternative to automobile transportation—bicycles, walking, scooters, buses, subways, rail
systems, etc.—would benefit the U.S. environment.
Environmental Problems, Their Causes, and Sustainability
54
G
7-6
The United States had an efficient streetcar system that was bought and destroyed by an alliance of companies that
wanted to promote car and bus sales.
How Can Cities Become More Sustainable and Livable?
A Smart growth discourages urban sprawl, protects ecologically sensitive land and water, and develops
environmentally sustainable urban areas. These methods help channel growth to areas where it does less harm.
B Ecocities are people-oriented; they preserve biodiversity, and they emit low pollution.
1. Buildings, vehicles, and appliances meet high energy-efficient standards.
2. Native trees and plants abound for noise buffers, pollution reduction, and animal sanctuaries.
3. Urban sprawl is not allowed to gobble-up nearby forests, grasslands, wetlands, and farms.
4. Food is raised in the city in community gardens, window boxes, and garden rooftops and comes from nearby
organic farms and solar greenhouses.
C There are ecocities all over the world: Curitiba in Brazil, Waitakere City in New Zealand, Leicester in England,
Portland in Oregon, and Chattanooga in Tennessee.
Environmental Problems, Their Causes, and Sustainability
55