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31
COMMUNITIES
AND
ECOSYSTEMS
CHAPTER REVIEW
In a community, different species (populations) interact with each other, and in an ecosystem they also interact with the physical environment. Communities
begin to develop on bare rock or on disturbed land and
the end result is a stable climax community. Certain
types of interactions, such as competition and predation, are well known between species. Mutualism also
plays a major role in the structure of a community.
Every species has a particular role to play—called
its niche—and some are keystone species because they
hold the community together in various ways. Exotic
species can greatly disrupt the balance of a community.
Whether an organism is an autotroph or heterotroph
determines its trophic level in a food web, characterized
by energy flow and chemical cycling. An ecological pyramid illustrates the energy losses that occur between trophic
levels. Chemicals cycle within an ecosystem through various biochemical cycles. Human activities significantly
alter the transfer rates in these cycles.
The major ecosystems of the world, for example,
forests, deserts, and oceans, make up the biosphere.
CHAPTER KEY TERMS
After studying the key terms of this chapter, match the phrases below with the alphabetized list of terms.
biogeochemical cycle
exotic species
biosphere
fossil fuel
climax community
greenhouse effect
commensalism
habitat
competitive exclusion principle
mutualism
decomposer
resource partitioning
detritus
transfer rate
eutrophication
trophic level
a. reradiation of solar heat toward the Earth, caused by gases in the atmosphere _______________________
b. partially decomposed organic matter derived from tissue and animal wastes _______________________
c. circulating pathway of elements _______________________
d. feeding level of one or more populations in a food web _______________________
e. species that is new to a community, nonnative _______________________
f. portion of the surface of the Earth where living things exist _______________________
g. organism that breaks down organic matter into inorganic nutrients _______________________
h. amount of a substance that moves from one component of the environment to another within a specified period of time _______________________
i. result when succession has come to an end _______________________
j. remains of once-living organisms that are burned to release energy _______________________
k. mechanism that increases the number of niches by apportioning the supply of a resource _______________________
l. symbiotic relationship; one species is benefited and the other is neither harmed nor benefited _______________________
m. place where an organism lives and is able to survive and reproduce _______________________
n. enrichment of water by inorganic nutrients used by phytoplankton _______________________
o. conclusion that no two species can occupy the same niche at the same time _______________________
p. symbiotic relationship in which both species benefit _______________________
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S T U DY E X E R C I S E S
Study the text section by section as you answer the questions that follow.
31.1 ECOLOGY
OF
COMMUNITIES (PP. 552–559)
• Communities are assemblages of interacting populations (species).
• In an ecosystem, species interact with one another and with the physical environment.
• Communities are characterized and compared in terms of species richness and diversity.
1. Which one is larger, a community or an ecosystem? Explain. ___________________________________________
2. Draw a line between the terms in the second column that pertain to those in the first column, and a line
between those in the third column that pertain to those in the second column.
a. composition
c. richness
e. relative abundance
b. diversity
d. evenness
f. number of species
ECOLOGICAL SUCCESSION (PP. 554–555)
• Ecological succession is a change in community composition and diversity over time.
3. Study the following diagram and answer the questions:
a. Is this an example of primary succession? Explain. __________________________________________________
b. If you wanted to use the illustration to exemplify secondary succession, what would you remove? _________
__________________________________________________________________________________________________________
c. Is this a snapshot of a single landscape or is it a series of communities in a single location over time? ______
__________________________________________________________________________________________________________
d. Why does ecological succession take time? _______________________________________________________________
e. The first plants are called pioneer species. Explain. _______________________________________________________
f. In general, do you find immature or mature plants in a climax community? Explain. _______________________
__________________________________________________________________________________________________________
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INTERACTIONS IN
•
•
•
•
COMMUNITIES (PP. 556–558)
Interactions between species include competition, predation, parasitism, commensalism, and mutualism.
An ecological niche is the role a species plays in its community.
Competition leads to resource partitioning, which reduces competition between species.
The introduction of exotic species can disrupt ecosystems.
4. Label the symbiotic relationships of species A to species B with these terms:
commensalism
competition
mutualism
parasitism
predation
a. ______________________ Species A consumed more of the resource than species B.
b. ______________________ Species A eats species B.
c. ______________________ Species A is cultivated by species B as a source of food.
d. ______________________ Species A infects species B.
e. ______________________ Species A rides along with species B to get food while species B hunts.
5. Place the appropriate letter next to each statement:
C—commensalism M–mutualism P—parasitism
a.
The clownfish lives safely within the poisonous tentacles of the sea anemone. If, as some suggest, the
clownfish attracts predators the sea anemone feeds on, the relationship is b. _________________.
c.
Humans get a tapeworm from eating raw pork.
d.
Epiphytes grow in branches of trees but get no nourishment from the trees.
e.
Flowers provide nourishment to a pollinator, and the pollinator carries pollen to another flower.
6. Which is larger, the habitat of an organism or its ecological niche? Explain. ______________________________
__________________________________________________________________________________________________________
7. A tropical rain forest contains many different species. No two species occupy the same niche as expected by
the a. ____________ principle. To reduce competition between all species, b. ____________ partitioning occurs.
8. Bats are pollinators and also disperse the seeds of certain tropical trees. Assuming the bats feed off the trees,
what type of relationship is this? a. ____________ If humans kill the bats, what happens to the trees?
b. ____________. A member of a community that has many such relationships with other members is a
c. ____________ species.
9. Why would an exotic species grow out of control in a new community? __________________________________
31.2 ECOLOGY
OF
ECOSYSTEMS (PP. 560–567)
• In the ecosystems, species are categorized by their food source. Autotrophs are producers, and heterotrophs are
consumers.
• Ecosystems are characterized by energy flow and chemical cycling among populations.
• Biogeochemical cycles are sedimentary (phosphorus) or gaseous (nitrogen, carbon). Human activity can alter
these cycles.
10. Match the descriptions to these biotic components of an ecosystem:
carnivores
a.
b.
c.
d.
e.
f.
consumers
______________________
______________________
______________________
______________________
______________________
______________________
decomposers
herbivores
omnivores
autotrophs
organisms of decay
feed only on other animals
producers in an ecosystem
heterotrophs
feed directly on green plants
feed on both plants and animals
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11. Label the following diagram using the alphabetized terms:
consumers
decomposers
inorganic nutrient pool
producers
h
t
t
y
a
Key:
energy
nutrients
heat
12. Energy doesn’t cycle in ecosystems.
a. Which populations contain the most energy? ________________________________________________
b. Which populations contain the least energy? ________________________________________________
c. What happened to the energy? Explain on the basis of the second law of thermodynamics. ________
__ ________________________________________________________________________________________
13. Chemicals do cycle in an ecosystem.
a. What two molecules do plants use to make glucose? __________________________________________
b. Glucose could conceivably pass from a producer population to the _____________________________
populations to the _________________________________ populations.
c. Eventually, the glucose is broken down, and what is returned to plants? ________________________
__________________________________________________________________________________
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The following is a food web diagram:
Key:
hawks
grazing food web
detrital food web
birds
chipmunks
fruits and nuts
mice
owls
snakes
leaf-eating
insects
leaves
fishers
rabbits
skunks
old leaves,
dead twigs
deer
shrews
foxes
salamanders
bacteria and fungi
invertebrates
carnivorous
invertebrates
14. a. How many trophic levels do you see in the grazing portion of this food web diagram?____________________
b. Name a population at the first trophic level. ________________________________________________________
c. Name two populations at the second trophic level. __________________________________________________
d. Name two populations at the third trophic level. ____________________________________________________
e. From these trophic levels, construct a grazing food chain. ___________________________________________
15. Construct a detrital food chain from the food web diagram.
_________________________________________________________________________________________________
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The following is an ecological pyramid diagram:
top carnivores
carnivores
herbivores
producers
16. a. Name two populations from the figure on page 303 that are at the same trophic level as the caterpillar.
_______________________________________________________________________________________________
b. Name two populations at the same trophic level as the bird. __________________________________________
17. a. Why is each higher trophic level smaller than the one preceding it? ___________________________________
_______________________________________________________________________________________________
b. What is the so-called 10% rule of thumb? __________________________________________________________
_______________________________________________________________________________________________
18. Place a check beside the statements that correctly describe the results when producers take up phosphate:
a.
becomes a part of phospholipids
b.
becomes a part of ATP
c.
becomes a part of nucleotides
d.
becomes a part of the atmosphere
19. Indicate whether these statements are true (T) or false (F). Rewrite all false statements to be true statements.
a.
Excess phosphate in bodies of water may cause radiation poisoning. Rewrite: ____________________
_________________________________________________________________________________________
b.
Most ecosystems have plenty of phosphate. Rewrite: __________________________________________
_________________________________________________________________________________________
c.
The phosphorus cycle is a sedimentary cycle. Rewrite: ________________________________________
_________________________________________________________________________________________
d.
Phosphate enters ecosystems by being taken up by animals. Rewrite: ____________________________
_________________________________________________________________________________________
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20. Plants cannot use nitrogen gas. What are two ways in which plants receive a supply of nitrogen for
incorporation into proteins and nucleic acids? ________________________________________________________
21. When humans produce fertilizers, the gas a. _______________ is removed from the atmosphere and changed to
b. _______________, which enters the atmosphere. Acid deposition occurs when nitrogen oxides and
c. _______________ in the atmosphere are converted to acids that return to Earth.
22. In the carbon cycle (not shown), carbon dioxide is removed from the atmosphere by the process of
a. ____________ but is returned to the atmosphere by the process of b. ____________. Living things and dead
matter in soil are carbon c. ____________ and so are the d. ____________ because of shell accumulation. In
aquatic ecosystems, carbon dioxide from the air combines with water to produce e. ______________ that algae
can use for photosynthesis. In what way do humans alter the transfer rates in the carbon cycle?
f. ________________
31.3 ECOLOGY
OF
MAJOR ECOSYSTEMS (PP. 568–570)
• The Earth’s major aquatic ecosystems are of two types: freshwater or saltwater (marine).
• The Earth’s major terrestrial ecosystems are the tundra, the taiga, temperate forests, temperate grasslands,
deserts, tropical grasslands, and tropical rain forests.
23. Aquatic ecosystems can be divided into two major types: the a. ____________________ ecosystems that consist of
lakes, ponds, rivers, and streams, and the b.____________________ ecosystems along the coast and in the ocean.
24. For each biome listed, write a one- or two-word description for the temperature and rainfall:
Biome
Temperature
Rainfall
Tundra
Desert
Grassland
Taiga
Temperate deciduous forest
Tropical rain forest
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K E Y WO R D C RO S S WO R D
Review key terms by completing this crossword puzzle, using the following alphabetized list of terms:
1
2
3
4
5
6
7
8
9
10
11
biomass
commensalism
community
competitive exclusion
decomposer
ecological niche
ecological pyramid
ecosystem
fossil fuel
global warming
habitat
mutualism
trophic level
12
Across
1 principle that no two species can occupy the same
niche at the same time (two words)
5 feeding level of one or more populations in a food
web (two words)
7 pictorial graph based on energy content of various
trophic levels in a food web (two words)
11 number of organisms multiplied by their weight
12 location where the organism is able to survive and
reproduce
Down
1 symbiotic relationship in which one species is benefited and the other is neither harmed nor benefited
2
3
4
6
8
9
10
role an organism plays in a community (two words)
biological community together with the associated
abiotic environment
predicted increase in the Earth’s temperature (two
words)
remains of once-living organisms that are burned to
release energy (two words)
group of many different populations that interact with
one another
symbiotic relationship in which both species benefit
organism that breaks down organic matter into inorganic nutrients
CHAPTER TEST
OBJECTIVE QUESTIONS
Do not refer to the text when taking this test.
1. A community is made up of all the
a. members of a given population.
b. plant populations of a given area.
c. populations of a given area.
d. populations of a given area plus the abiotic
habitat in which they live.
2. Which is a facet of species diversity?
a. species richness
b. species evenness
c. composition only
d. Both a and b are correct.
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3. Competition
a. always eliminates one or the other species.
b. widens niche breadth.
c. narrows niche breadth and increases species
diversity.
d. None of these are correct.
4. In which relationship do both species benefit?
a. mutualism
b. commensalism
c. symbiosis
d. Both b and c are correct.
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5. Choose the scenario that best represents secondary succession.
a. trees—shrubs—grasses—perennial grasses
b. annual weeds and grasses—perennial grasses—
shrubs—trees
c. shrubs—annual weeds—perennial grasses—
trees
d. All of these are correct.
6. A complex of interconnected food chains in an
ecosystem is called a(an)
a. ecosystem.
b. ecological pyramid.
c. trophic level.
d. food web.
7. Wolves and lions are at the same trophic level because they both
a. are large mammals.
b. eat only when they are hungry.
c. eat primary consumers.
d. live on land.
e. Both b and c are correct.
In questions 8–11, indicate whether the statements are true
(T) or false (F).
8. Energy flows through a food chain because it is
constantly lost when organic food is processed.
9. A food web contains many food chains.
10. The weathering of rocks is one way that phosphate
ions are made available to plants.
11. Respiration returns carbon to the atmosphere.
For questions 12–14, refer to the following food chain:
grass → rabbits → snakes → hawks
12. Each population
a. is always larger than the one before it.
b. supports the next level.
c. is an herbivore.
d. is a carnivore.
13. Rabbits are
a. consumers.
b. herbivores.
c. more plentiful than snakes.
d. All of these are correct.
14. Hawks
a. are top carnivores.
b. give off O 2 that will be taken up by rabbits.
c. contain phosphate that will eventually be taken
up by grass.
d. Both a and c are correct.
15. Which of the following contribute(s) to the carbon cycle?
a. respiration
b. photosynthesis
c. fossil fuel combustion
d. All of these are correct.
16. The largest reserve of unincorporated carbon is in
a. the soil.
b. the atmosphere.
c. the ocean.
d. deep sediments.
17. The greenhouse effect
a. is caused by particles in the air.
b. is caused in part by carbon dioxide.
c. will cause temperatures to increase.
d. will cause temperatures to decrease.
e. Both b and c are correct.
18. The form of nitrogen most plants make use of is
a. atmospheric nitrogen.
b. nitrogen gas.
c. organic nitrogen.
d. nitrates.
19. Which of these characterizes a keystone species?
a. exotic species
b. interacts with other species
c. harms other species, such as eating their seeds
d. helps maintain the health of a community
e. Both b and d are correct.
20. In keeping with the competitive exclusion principle and resource partitioning, you would expect
a. a community to have many different species
in a given area.
b. very few species in a community.
c. species to be closely adapted to their way of
life.
d. many exotic species to invade an area.
e. Both a and c are correct.
CRITICAL THINKING QUESTIONS
The introduction to this chapter is about nitrogen buildup in the atmosphere.
21. Human beings alter the transfer rates in biogeochemical cycles. Give an example from the introduction to the
chapter in the text. __________________________________________________________________________________________
22. What is the chief reason, studied in another ecology chapter, that humans need to grow more food on less
land? _______________________________________________________________________________________________________
23. Ecologists often say “there is no free lunch” and “everything affects everything else.” Why does production of
artificial fertilizers support these sayings? __________________________________________________________________
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24. All the various interactions between species support the biosphere. Should we be concerned when the growth
of the human population causes species to become extinct? Explain. _________________________________________
25. If the human population expands until the biosphere can’t support it anymore, what will be the end result? ____
_____________________________________________________________________________________________________________
Test Results: ______ number correct ÷ 25 = ______ × 100 = ______ %
EXPLORING
THE
INTERNET
ARIS, the Essentials of Biology website: http://www.mhhe.com/maderessentials
ARIS, the website for Essentials of Biology, offers access to a wide variety of tools to help students learn biological
concepts and to reinforce their knowledge. Online study aids such as practice quizzes, interactive activities, animations, labeling exercises, flashcards, and much more are organized according to the major sections of each chapter.
There is even an online tutorial service!
ANSWER KEY
CHAPTER KEY TERMS
a. greenhouse effect b. detritus c. biogeochemical cycle
d. trophic level e. exotic species f. biosphere g. decomposer h. transfer rate i. climax community j. fossil fuel
k. resource partitioning l. commensalism m. habitat
n. eutrophication o. competitive exclusion principle p. mutualism
STUDY EXERCISES
1. An ecosystem is larger because it includes populations
and the physical environment. 2. Draw lines between:
b and c, b and d, e and d, f and c 3. a. yes, because it
begins with bare rock b. remove the rock, lichens/mosses,
and start with the grasses c. series of communities
d. Plants have to invade an area, establish themselves, and
then grow. e. Pioneers are first and prepare the way for
others. f. Mature plants are found because the last community is there the longest. 4. a. competition
b. predation c. mutualism d. parasitism e. commensalism 5. a. C b. M c. P d. C e. M 6. The ecological niche
is larger because it includes the habitat (where it lives),
plus how it makes its living. 7. a. competitive exclusion
b. resource 8. a. mutualistic b. They die. c. keystone
9. because there is no competition, no predators, and no
parasites in the new environment 10. a. decomposers
b. carnivores c. autotrophs d. consumers e. herbivores
f. omnivores 11. a. producers b. consumers c. decomposers d. inorganic nutrient pool 12. a. producers
b. consumers c. It dissipates. With every transformation, as when the energy in food is converted to ATP,
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there is always a loss of usable energy. Eventually, all solar
energy taken in by plants becomes heat. 13. a. carbon
dioxide and water b. consumer, decomposer c. carbon dioxide and water 14. a. three b. tree c. birds, chipmunks
d. foxes, fishers e. tree → rabbits → snakes 15. old
leaves and dead twigs → bacteria and fungi of decay →
chipmunks → hawks 16. a. rabbits and deer b. foxes
and snakes 17. a. Less energy is available to be passed
on. b. In general, only about 10% of the energy of one
trophic level is available to the next trophic level. 18. a,
b, c 19. a. F, . . . may cause algal bloom b. F, . . . have
a limited supply of phosphate c. T d. F, . . . taken up by
plants 20. nitrogen-fixing bacteria in nodules and nitrate in soil 21. a. N 2 b. NO 3 c. sulfur dioxide
22. a. photosynthesis b. respiration c. reservoirs d. oceans
e. bicarbonate ions f. add CO 2 from fossil fuel combustion to the atmosphere 23. a. freshwater b. saltwater
24.
Temperature
Rainfall
Cold
Little
Hot days/cold
nights
Little
Moderate
Limited
Cool
Moderate
Moderate
Rather high
Hot
High
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CHAPTER TEST
KEYWORD CROSSWORD
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C
O
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1. c 2. d 3. c 4. a 5. b 6. d 7. c 8. T 9. T
10. T 11. T 12. b 13. d 14. d 15. d 16. c 17. e
18. d 19. e 20. e 21. They change atmospheric nitrogen
to nitrates for use in fertilizers. 22. The human population is very large and is getting larger every day.
23. Artificial fertilizer helps cause pollution, which is
detrimental to all species in the biosphere. 24. yes, because they keep the biosphere functioning 25. Collapse
of the biosphere and extinction of human beings, along
with most other species.
12
H
A
B
I
T
A
T
G
E
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