Chapter 18
Interdependence: A Key Theme
in Ecology
• Organisms and
Their Environments
– Species interact
with both other
species and their
nonliving
environment.
– Interdependence
is a theme in
ecology—one
change can affect
all species in an
ecosystem.
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Chapter 18
Section 1 Introduction to Ecology
Levels of Organization in studying an
ecological system
• Ecologists recognize a hierarchy of organization in
the environment: biosphere, ecosystem, community,
population, and organism.
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Chapter 18
Section 1 Introduction to Ecology
Levels of Organization
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Chapter 18
Section 1 Introduction to Ecology
Levels of Organization, continued
• The Biosphere
– The broadest, most inclusive level of organization
is the biosphere, the thin volume of Earth and its
atmosphere that supports life.
– All organisms are found in the biosphere
– Extends from ~ 5-6 miles above earth to the
deepest part of the oceans.
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Chapter 18
Section 1 Introduction to Ecology
Levels of Organization, continued
• Ecosystems
– The biosphere is composed of smaller units called
ecosystems.
– An ecosystem includes all of the organisms and
the nonliving environment found in a particular
place.
• BIOTIC FACTORS--A pond ecosystem
includes all of the fish, turtles, insects, aquatic
plants, algae and bacteria (all living things)
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Chapter 18
Section 1 Introduction to Ecology
Ecosystem
•ABIOTIC FACTORS--A pond
ecosystem also includes all of
the physical and chemical
aspects of the pond that
influence its inhabitants.
ie pH, levels of dissolved
oxygen, carbon dioxide, nitrogen
as well as the amount of
sunlight. Temperature, humidity,
salinity, precipitation
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Chapter 18
Section 1 Introduction to Ecology
Levels of Organization, continued
• Communities, Populations, and Organisms
– A community is all the interacting organisms
living in an area.
– Below the community level of organization is the
population level, where the focus is on the
individual organisms of a single species.
• Size, density, and dispersion are characteristics
of populations
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Chapter 18
Section 1 Introduction to Ecology
Community
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Population Growth
Logistic vs ExponentialLogistic limited by
resources
Exponential steady
growth rate
Exponential
Logistic
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Chapter 18
Section 2 Ecology of Organisms
Objectives
• Compare abiotic factors with biotic factors, and list
two examples of each.
• Describe two mechanisms that allow organisms to
survive in a changing environment.
• Explain the concept of the niche.
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Chapter 18
Section 2 Ecology of Organisms
Ecosystem Components
•
Biotic and Abiotic Factors
– Both biotic, or living, factors and abiotic, or nonliving, factors
influence organisms. Examples of abiotic factors are climate,
sunlight, and pH.
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Chapter 18
Section 2 Ecology of Organisms
The Niche
• A niche is a way of life, or a role (What’s your job?)
in an ecosystem.
– Range of conditions the organism can tolerate
– The resources it uses
– Method of obtaining resources
– Number of offspring
– Time of reproduction
– All interactions with its environment
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Chapter 18
Section 2 Ecology Of Organisms
Earthworm Niche
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Chapter 18
Section 3 Energy Transfer
Objectives
• Summarize the role of producers in an ecosystem.
• Identify several kinds of consumers in an ecosystem.
• Explain the important role of decomposers in an ecosystem.
• Compare the concept of a food chain with that of a food web.
• Explain why ecosystems usually contain only a few trophic
levels.
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Chapter 18
Section 3 Energy Transfer
Producers
• Most producers are photosynthetic and make
carbohydrates by using energy from the sun.
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Chapter 18
Section 3 Energy Transfer
Producers, continued
• Measuring Productivity
– Gross primary productivity is the rate at which
producers in an ecosystem capture the energy of
sunlight by producing organic compounds.
– The rate at which biomass accumulates is called
net primary productivity.
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Chapter 18
Section 3 Energy Transfer
Consumers
• Consumers obtain energy by eating other organisms
and include herbivores, omnivores, carnivores,
detritivores, and decomposers.
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Chapter 18
Section 3 Energy Transfer
Comparing Consumers and Producers
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Chapter 18
Section 3 Energy Transfer
Energy Flow
• When one organism eats another, organic
molecules are metabolized and energy
transferred.
• Food Chains and Food Webs
– A single pathway of energy transfer is a food
chain.
– A network showing all paths of energy transfer is a
food web.
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Chapter 18
Section 3 Energy Transfer
Food Chains and Food Webs
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Chapter 18
Section 3 Energy Transfer
Food Chain in an Antarctic Ecosystem
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Chapter 18
Section 3 Energy Transfer
Food Web
in an
Antarctic
Ecosystem
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Chapter 18
Section 3 Energy Transfer
Energy Flow, continued
• Energy Transfer
– Ecosystems contain only a few trophic levels because there
is a low rate of energy transfer between each level.
– ~10% of energy is transferred to the next trophic level
• Some organisms in one trophic level escape being eaten
• When they die, they are eaten by decomposers, but the
energy does not go to a higher trophic level
• Energy transfer is never 100 % efficient when changing
form
• There are many more organisms in lower trophic levels
because higher levels contain less energy and can not
support as many organisms.
• Trophic level = feeding level in an ecosystem
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Chapter 18
Section 3 Energy Transfer
Energy Transfer Through Trophic Levels
There are about 1000 zebras for every lion. There are many
grasses.
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Chapter 18
Section 3 Energy Transfer
Energy Pyramid
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Chapter 18
Section 4 Ecosystem Recycling
Objectives
• List four major biogeochemical cycles.
• Summarize three important processes in the water cycle.
• Outline the major steps in the carbon cycle.
• Describe the role of decomposers in the nitrogen cycle.
• Summarize the major steps of the phosphorus cycle.
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• Since stratospheric ozone is produced by solar UV radiation,
one might expect to find the highest ozone levels over the
tropics and the lowest over polar regions. The same argument
would lead one to expect the highest ozone levels in the
summer and the lowest in the winter. The observed behavior is
very different: most of the ozone is found in the mid-to-high
latitudes of the northern and southern hemispheres, and the
highest levels are found in the spring, not summer, and the
lowest in the autumn, not winter in the northern hemisphere
The ozone layer can be depleted by free radical
catalysts, including nitric oxide (NO), nitrous oxide
(N2O), hydroxyl (OH), atomic chlorine (Cl), and
atomic bromine (Br).
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Chapter 18
Section 4 Ecosystem Recycling
The Water Cycle
• Key processes in the water cycle are evaporation,
transpiration, and precipitation.
• Transpiration is a process similar to evaporation. It
is a part of the water cycle, and it is the loss of water
vapor from parts of plants (similar to sweating),
especially in leaves (stomata) but also in stems.
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Chapter 18
Section 4 Ecosystem Recycling
Water Cycle
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Chapter 18
Section 4 Ecosystem Recycling
Water Cycle
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Chapter 18
Section 4 Ecosystem Recycling
The Carbon Cycle
• Photosynthesis and cellular respiration are the two
main steps in the carbon cycle.
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Chapter 18
Section 4 Ecosystem Recycling
Carbon Cycle
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Chapter 18
Section 4 Ecosystem Recycling
Carbon Cycle
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In the last 150 years the concentration of
atmospheric carbon dioxide has risen more than
30%. This has increased the temperature about 1⁰C
since 1900.
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Chapter 18
Section 4 Ecosystem Recycling
Nitrogen Cycle
• N2 gas makes up 78% of the atmosphere, but
plants cannot use nitrogen unless it is in the form
of nitrate.
• Nitrogen-fixing bacteria are important in the
nitrogen cycle because they change nitrogen gas
into this usable form of nitrogen for plants-nitrogen
fixation.
• The plants supply carbohydrates to the bacteria.
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Chapter 18
Section 4 Ecosystem Recycling
Nitrogen Cycle
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Chapter 18
Section 4 Ecosystem Recycling
Nitrogen Cycle
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Chapter 18
Section 4 Ecosystem Recycling
Phosphorus Cycle
• In the phosphorus cycle, phosphorus moves from
phosphate deposited in rock, to the soil, to living
organisms, and finally to the ocean.
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Chapter 18
Standardized Test Prep
Multiple Choice
1. What are the levels of organization in ecology?
A. cell, tissue, organ, organ system, body
B. organ, organism, population, community
C. organism, population, community, ecosystem,
biosphere
D. population, habitat, ecosystem, biogeochemical
system, planet
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Chapter 18
Standardized Test Prep
Multiple Choice, continued
1. What are the levels of organization in ecology?
A. cell, tissue, organ, organ system, body
B. organ, organism, population, community
C. organism, population, community, ecosystem,
biosphere
D. population, habitat, ecosystem, biogeochemical
system, planet
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Chapter 18
Standardized Test Prep
Multiple Choice, continued
2. What makes up an ecosystem?
F. all the habitat types on Earth
G. all parts of Earth where life exists
H. all members of a species in the same area
J. all the living and nonliving factors in an
environment
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Chapter 18
Standardized Test Prep
Multiple Choice, continued
2. What makes up an ecosystem?
F. all the habitat types on Earth
G. all parts of Earth where life exists
H. all members of a species in the same area
J. all the living and nonliving factors in an
environment
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Chapter 18
Standardized Test Prep
Multiple Choice, continued
3. Which of the following are abiotic factors?
A. plants
B. animals
C. sunlight
D. microorganisms
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Chapter 18
Standardized Test Prep
Multiple Choice, continued
3. Which of the following are abiotic factors?
A. plants
B. animals
C. sunlight
D. microorganisms
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Chapter 18
Standardized Test Prep
Multiple Choice, continued
4. How do decomposers benefit an ecosystem?
F. by returning nutrients to the soil
G. by manufacturing energy from sunlight
H. by removing excess nutrients from the soil
J. by removing predators from the ecosystem
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Chapter 18
Standardized Test Prep
Multiple Choice, continued
4. How do decomposers benefit an ecosystem?
F. by returning nutrients to the soil
G. by manufacturing energy from sunlight
H. by removing excess nutrients from the soil
J. by removing predators from the ecosystem
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Chapter 18
Standardized Test Prep
Multiple Choice, continued
5. Which organisms are most critical in the nitrogen
cycle?
A. plants
B. nitrates
C. animals
D. bacteria
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Chapter 18
Standardized Test Prep
Multiple Choice, continued
5. Which organisms are most critical in the nitrogen
cycle?
A. plants
B. nitrates
C. animals
D. bacteria
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Chapter 18
Standardized Test Prep
Multiple Choice, continued
Use the illustration below to answer question 6. The
illustration represents a trophic pyramid.
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Chapter 18
Standardized Test Prep
Multiple Choice, continued
6. What is the term for the kinds of organisms that make
up the trophic level labeled C?
F. producers
G. consumers
H. detritivores
J. decomposers
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Chapter 18
Standardized Test Prep
Multiple Choice, continued
6. What is the term for the kinds of organisms that make
up the trophic level labeled C?
F. producers
G. consumers
H. detritivores
J. decomposers
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Chapter 18
Standardized Test Prep
Multiple Choice, continued
Complete the following analogy:
7. bear : omnivore :: vulture :
A. producer
B. herbivore
C. detritivore
D. decomposer
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Chapter 18
Standardized Test Prep
Multiple Choice, continued
Complete the following analogy:
7. bear : omnivore :: vulture :
A. producer
B. herbivore
C. detritivore
D. decomposer
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Chapter 18
Standardized Test Prep
Multiple Choice, continued
Use the illustration to
answer question 8.
The illustration
represents a food
chain.
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Chapter 18
Standardized Test Prep
Multiple Choice, continued
8. What role do the krill have in this food chain?
F. They are producers.
G. They are consumers.
H. They are detritivores.
J. They are decomposers.
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Chapter 18
Standardized Test Prep
Multiple Choice, continued
8. What role do the krill have in this food chain?
F. They are producers.
G. They are consumers.
H. They are detritivores.
J. They are decomposers.
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Chapter 18
Standardized Test Prep
Short Response
Give two reasons why the destruction of tropical
rain forests can contribute to an increase in
carbon dioxide levels in the atmosphere.
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Chapter 18
Standardized Test Prep
Short Response, continued
Give two reasons why the destruction of tropical
rain forests can contribute to an increase in
carbon dioxide levels in the atmosphere.
Answer: The burning of vegetation releases CO2
into the atmosphere and removes plants that
could have absorbed the CO2 already in the
atmosphere.
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Chapter 18
Standardized Test Prep
Extended Response
Base your answers to parts A & B on the information
below.
Some species are generalized with regard to their niche,
and other species are specialized.
Part A Compare the niche of a generalist species with
one of a specialist species.
Part B Predict how two different herbivores can share
the same plant resource.
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Chapter 18
Standardized Test Prep
Extended Response, continued
Answer:
Part A Generalist species have a broad niche, as
they can tolerate a wide range of conditions
and use a wide variety of resources. Specialist
species can only use specific resources and
have more narrowly defined niches.
Part B Two herbivores might eat different parts
of the plant, or might eat the plant at different
times of the year.
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Chapter 18
Section 2 Ecology of Organisms
Organisms in a Changing Environment
• Acclimation
– Some organisms can adjust their tolerance to
abiotic factors through the process of acclimation.
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Chapter 18
Section 2 Ecology of Organisms
Organisms in a Changing Environment,
continued
• Control of Internal Conditions
– Conformers are organisms that do not regulate
their internal conditions; they change as their
external environment changes.
– Regulators use energy to control some of their
internal conditions.
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Chapter 18
Section 2 Ecology of Organisms
Organisms in a Changing Environment,
continued
• Escape from Unsuitable Conditions
– Some species survive unfavorable environmental
conditions by becoming dormant or by migrating.
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