Ecosystems: What Are They and
How Do They Work?
Chapter 3
Core Case Study: Tropical Rain Forests
Are Disappearing
 Cover about 2% of the earth’s land surface
 Contain about 50% of the world’s known plant
and animal species
 Disruption will have three major harmful effects
• Reduce biodiversity
• Accelerate global warming
• Change regional weather patterns
Natural Capital Degradation: Satellite
Image of the Loss of Tropical Rain Forest
Santa Cruz, Boliva: June 1975
May 2003
3-1 What Is Ecology?
 Concept 3-1 Ecology is the study of how
organisms interact with one another and with
their physical environment of matter and energy.
Cells Are the Basic Units of Life
 Cell Theory – theory that all living things are
composed of cells
 Eukaryotic cell – membrane, nucleus,
organelles
 Prokaryotic cell – membrane
• bacteria
(a) Eukaryotic Cell
Nucleus
(DNA)
(b) Prokaryotic Cell
Energy
conversion
Protein
construction
DNA (no nucleus)
Cell membrane
Cell membrane
Protein construction and energy
conversion occur without specialized
internal structures
Stepped Art
Fig. 3-2, p. 52
Species Make Up the Encyclopedia of Life
 Species
 1.75 Million species identified
 Insects make up most of the known species
 Perhaps 10–14 million species not yet identified
 www.eol.org project started in 2007 to list and
describe all identified species.
Ecologists Study Connections in Nature
 Ecology – study of how organisms interact with
biotic and abiotic factors in their environment
 Levels of organization
• Population – same species in same place at same
time: ex. Field mice living in a cornfield
• Genetic diversity – variations in population
• Community – all populations of different species
living in same place
• Ecosystem – community of different species
interacting w/ one another & w/ nonliving environment
• Biosphere – parts of Earth’s air, water, & soil where
life if found
Biosphere
Parts of the earth's air, water, and
soil where life is found
Ecosystem
A community of different species
interacting with one another and with their
nonliving environment of matter and energy
Community
Populations of different species living in a
particular place, and potentially interacting
with each other
Population
A group of individuals of the same species
living in a particular place
Organism
Cell
Molecule
Atom
An individual living being
The fundamental structural and functional
unit of life
Chemical combination of two or more atoms
of the same or different elements
Smallest unit of a chemical element that
exhibits its chemical properties
Stepped Art
Fig. 3-3, p. 52
Population of Glassfish in the Red Sea
Genetic Diversity in a Caribbean
Snail Population
Science Focus: Have You Thanked
the Insects Today?
 Insects play a vital role in sustaining life on Earth
• Pollinators
• Eat other insects
• Loosen and renew soil
 Scientists estimate the value of ecological services
provided by insects in U.S. at $57 billion per year
 Reproduce rapidly
 Very resistant to extinction
 Insects don’t need humans, but we most certainly
need them
Importance of Insects
Pollinator
Pest Controller
3-2 What Keeps Us and Other
Organisms Alive?
 Concept 3-2 Life is sustained by the flow of
energy from the sun through the biosphere, the
cycling of nutrients within the biosphere, and
gravity.
The Earth’s Life-Support System Has
Four Major Components
 Atmosphere
• Troposphere
• Stratosphere
 Hydrosphere – liquid, gas, solid (permafrost too)
 Geosphere – core, mantle, crust
 Biosphere – thin layer of Earth ~ 9km thick
Vegetation
and animals
Atmosphere
Biosphere
Soil
Rock
Crust
Lithosphere
Mantle
Biosphere
(living organisms)
Atmosphere
(air)
Core
Mantle
Geosphere
(crust, mantle, core)
Crust
(soil and rock)
Hydrosphere
(water)
Fig. 3-6, p. 55
Life Exists on Land and in Water
 Biomes – large regions w/ distinct climate & species
(especially plants) adapted to live there
 Aquatic life zones
• Freshwater life zones
• Lakes and streams
• Marine life zones
• Coral reefs
• Estuaries
• Deep ocean
Major Biomes along the 39th Parallel
in the U.S.
Three Factors Sustain Life on Earth
 One-way flow of high-quality energy beginning with the sun –
through living things via feeding – into environment as low
quality energy (heat dispersed to air or water) – eventually
back into space as heat
• No round trips – high quality energy cannot be recycled
 Cycling of matter or nutrients throughout biosphere
• Earth a closed system (essentially fixed supply of nutrients)
• Nutrients are recycled
 Gravity
• Allows planet to hold onto atmosphere
• Enables movement & cycling of materials
What Happens to Solar Energy Reaching
the Earth?
 UV, visible, and IR energy
 Radiation
•
•
•
•
Absorbed by ozone
Absorbed by the earth
Reflected by the earth
Radiated by the atmosphere as heat
 Natural greenhouse effect
Flow of Energy to and from the Earth
Active Figure: Energy flow
Animation: Energy flow in Silver Springs
Active Figure: Energy flow from the Sun
to Earth
3-3 What Are the Major Components
of an Ecosystem?
 Concept 3-3A Ecosystems contain living
(biotic) and nonliving (abiotic) components.
 Concept 3-3B Some organisms produce the
nutrients they need, others get their nutrients by
consuming other organisms, and some recycle
nutrients back to producers by decomposing the
wastes and remains of organisms.
Ecosystems Have Living and
Nonliving Components
 Abiotic
•
•
•
•
•
•
Water
Air
Nutrients
Rocks
Heat
Solar energy
 Biotic
• Living and once living, also waste products
Major Biotic and Abiotic Components
of an Ecosystem
Range of Tolerance for a Population of Organisms
INSERT FIGURE 3-10 HERE
Range of tolerance for a population of organisms, such as fish, to an abiotic environmental factor—in this case, temperature.
These restrictions keep particular species from taking over an ecosystem by keeping their population size in check
Several Abiotic Factors Can Limit
Population Growth
 Limiting factor principle
• 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 optimal
range of tolerance
• Water or lack thereof will limit plant growth in
a desert
• Soil nutrients can limit types of plants
• DO in aquatic ecosystems
• Salinity in aquatic ecosystems
Producers and Consumers Are the Living
Components of Ecosystems (1)
 Trophic (feeding) levels
 Producers, autotrophs
• Photosynthesis
• 6CO2 + 6H2O + solar energy
• Chemosynthesis
• Plants, phytoplankton, algae
 Consumers, heterotrophs
• Primary - herbivores
• Secondary - carnivores
• Third and higher level
 Decomposers – recycle nutrients
• Certain types of bacteria & fungi
C6H12O6 + 6O2
Producers and Consumers Are the Living
Components of Ecosystems (2)
 Detritivores
• Feed on wastes or dead bodies of other organisms
• Mites, earthworms, catfish, vultures
 Aerobic respiration
C6H12O6 + 6O2
6CO2 + 6H2O + ENERGY
 Anaerobic respiration, fermentation
End products could be methane gas, ethyl alcohol, acetic
acid, or hydrogen sulfide
Detritivores and Decomposers on a Log
Various detritivores and decomposers (mostly fungi and bacteria) can “feed on” or digest parts of a log and eventually convert
its complex organic chemicals into simpler inorganic nutrients that can be taken up by producers.
Energy Flow and Nutrient Cycling
Sustain Ecosystems and the Biosphere
 One-way energy flow
 Nutrient cycling of key materials
The Main Structural Components
of an Ecosystem
Natural capital: the main
structural components of an
ecosystem (energy, chemicals,
and organisms). Nutrient
cycling and the flow of
energy—first from the sun,
then through organisms, and
finally into the environment as
low-quality heat—link these
components.
Science Focus: Many of the World’s Most
Important Species Are Invisible to Us
 Microorganisms
•
•
•
•
Bacteria
Protozoa
Fungi
phytoplankton
 Some are harmful
 Most are beneficial
• Break down food we digest
• Purify water
• Produce food like bread, cheese, soy sauce
Active Figure: Roles of organisms in an
ecosystem
3-4 What Happens to Energy in
an Ecosystem?
 Concept 3-4A Energy flows through
ecosystems in food chains and webs.
 Concept 3-4B As energy flows through
ecosystems in food chains and webs, the
amount of chemical energy available to
organisms at each succeeding feeding level
decreases.
Energy Flows Through Ecosystems in
Food Chains and Food Webs
 Food chain
 Food web
A Food Chain
A food chain. The arrows show how chemical energy in nutrients flows through various trophic levels in energy transfers; most
of the energy is degraded to heat, in accordance with the second law of thermodynamics. See an animation based on this
figure at CengageNOW. Question: Think about what you ate for breakfast. At what level or levels on a food chain were you
eating?
Simplified Food Web in the Antarctic
Greatly simplified food web in the Antarctic. Many more
participants in the web, including an array of decomposer
and detritus feeder organisms, are not depicted here.
Question: Can you imagine a food web of which you are
a part? Try drawing a simple diagram of it.
Usable Energy Decreases with Each Link
in a Food Chain or Web
 Biomass
 Ecological efficiency
 Pyramid of energy flow
Usable energy available
at each trophic level
(in kilocalories)
Tertiary
consumers
(human)
10
Secondary
consumers
(perch)
100
Primary
consumers
(zooplankton)
Heat
Heat
Heat
Decomposers
Heat
1,000
Heat
10,000
Producers
(phytoplankton)
Generalized pyramid of energy flow showing the decrease in usable chemical energy available at each succeeding
trophic level in a food chain or web. In nature, ecological efficiency varies from 2% to 40%, with 10% efficiency
being common. This model assumes a 10% ecological efficiency (90% loss of usable energy to the environment, in
Stepped Art
the form of low-quality heat) with each transfer from one trophic level to another. Question: Why is a vegetarian diet
Fig. 3-15, p. 63
more energy efficient than a meat-based diet?
Some Ecosystems Produce Plant Matter
Faster Than Others Do
 Gross primary productivity (GPP)

rate at which ecosystem’s producers convert solar
energy into chemical energy as biomass (their tissues)

measured in energy production per unit area over time
kcal/m2/year
 Net primary productivity (NPP)
= GPP-R
• To stay alive, grow, & reproduce, producers must use
some of they energy stored in their biomass (R)
• Rate at which producers use photosynthesis to produce &
store chemical energy minus the rate they use some of
their stored energy through respiration
• Ecosystems and life zones differ in their NPP
• NPP = biomass available as nutrients for consumers
Estimated Annual Average NPP in Major Life Zones and
Ecosystems
Estimated annual average net primary productivity in major life zones and ecosystems, expressed as kilocalories of energy produced
per square meter per year (kcal/m2/yr). Question: What are nature’s three most productive and three least productive systems?
(Data from R. H. Whittaker, Communities and Ecosystems, 2nd ed., New York: Macmillan, 1975)
Animation: Prairie food web
Active Figure: Rainforest food web
Animation: Diet of a red fox
Animation: Prairie trophic levels
3-5 What Happens to Matter in
an Ecosystem?
 Concept 3-5 Matter, in the form of nutrients,
cycles within and among ecosystems and the
biosphere, and human activities are altering
these chemical cycles.
Nutrients Cycle in the Biosphere
 Biogeochemical cycles, nutrient cycles
•
•
•
•
•
Hydrologic
Carbon
Nitrogen
Phosphorus
Sulfur
 Connect past, present , and future forms of life
Water Cycles through the Biosphere
 Natural renewal of water quality: three major
processes
• Evaporation
• Precipitation
• Transpiration – evaporation from surfaces of plants
• Also Condensation, Infiltration, Runoff
 Alteration of the hydrologic cycle by humans
• Withdrawal of large amounts of freshwater at rates
faster than nature can replace it
• Clearing vegetation
• Increased flooding when wetlands are drained
Hydrologic Cycle Including Harmful Impacts of Human
Activities
Natural capital: simplified model of the hydrologic cycle with major harmful impacts of human activities shown in red. See an
animation based on this figure at CengageNOW. Question: What are three ways in which your lifestyle directly or indirectly
affects the hydrologic cycle?
Science Focus: Water’s Unique
Properties
 Properties of water due to hydrogen bonds
between water molecules:
• Exists as a liquid over a large range of
temperature
• Changes temperature slowly
• High boiling point: 100˚C
• Adhesion and cohesion
• Expands as it freezes
• Solvent
• Filters out harmful UV
Carbon Cycle Depends on
Photosynthesis and Respiration
 C is basic building block of carbohydrates, fats,
proteins, DNA, & other organic compounds
 Link between photosynthesis in producers and
respiration in producers, consumers, and
decomposers
 Additional CO2 added to the atmosphere
• Tree clearing
• Burning of fossil fuels
Natural Capital: Carbon Cycle with Major Harmful Impacts
of Human Activities
Natural capital: simplified
model of the global carbon
cycle, with major harmful
impacts of human
activities shown by red
arrows. See an animation
based on this figure at
CengageNOW. Question:
What are three ways in
which you directly or
indirectly affect the carbon
cycle?
Active Figure: Carbon cycle
Nitrogen Cycles through the Biosphere:
Bacteria in Action (1)
 N major component of proteins, many vitamins, & DNA but
can’t be used as found in atmosphere
 Nitrogen fixed into useful compounds
• Lightning
• Nitrogen-fixing bacteria – produce NH3
 Nitrification – specialized soil bacteria convert NH3 and NH4+
to nitrate ions (NO3-)
 Denitrification – specialized bacteria in waterlogged soil & in
bottom sediments of lakes, oceans, etc. convert NH3 and
NH4+ back nitrate & nitrite ions & then to nitrogen gas (N2) &
nitrous oxide gas (N2O) which are released to atmosphere
Nitrogen Cycles through the Biosphere:
Bacteria in Action (2)
 Human intervention in the nitrogen cycle
• Additional NO when fuel burned at high temps
(this can lead to acid rain)
• Add N2O (greenhouse gas) through livestock
wastes & inorganic fertilizers in soil
• Destruction of forest, grasslands, and wetlands
release stored nitrogen to atmosphere
• Add excess nitrates to bodies of water
• Remove nitrogen from topsoil when harvest Nrich crops, irrigation, burn/clearing
Nitrogen Cycle in a Terrestrial Ecosystem
with Major Harmful Human Impacts
Natural
capital:
simplified
model of the
nitrogen cycle
with major
harmful human
impacts shown
by red arrows.
See an
animation
based on this
figure at
CengageNOW.
Question:
What are three
ways in which
you directly or
indirectly affect
the nitrogen
cycle?
Annual Increase in Atmospheric N2 Due
to Human Activities
Global trends in the annual inputs of
nitrogen into the environment from
human activities, with projections to
2050. (Data from 2005 Millennium
Ecosystem Assessment)
Active Figure: Nitrogen cycle
Phosphorus Cycles through the
Biosphere
 Cycles through water, the earth’s crust, and
living organisms
 Phosphates stored in sediment and rocks
 May be limiting factor for plant growth
 Impact of human activities
• Clearing forests
• Removing large amounts of phosphate from the
earth to make fertilizers
Phosphorus Cycle with Major Harmful
Human Impacts
Natural capital:
simplified model of
the phosphorus
cycle, with major
harmful human
impacts shown by
red arrows.
Question: What are
three ways in which
you directly or
indirectly affect the
phosphorus cycle?
Animation: Phosphorus cycle
Sulfur Cycles through the Biosphere
 Sulfur found in organisms, ocean sediments, soil, rocks, and
fossil fuels
 SO2 in the atmosphere from volcanoes also release H2S
 H2S also from anaerobic decomposition
 H2SO4 and SO4- - sulfuric acid & sulfate salts = acid
deposition
 Human activities affect the sulfur cycle
• Burn sulfur-containing coal and oil
• Refine sulfur-containing petroleum
• Convert sulfur-containing metallic mineral ores (Pb, Zn)
Natural Capital: Sulfur Cycle with Major
Harmful Impacts of Human Activities
Natural capital:
simplified model of
the sulfur cycle, with
major harmful
impacts of human
activities shown by
red arrows. See an
animation based on
this figure at
CengageNOW.
Question: What are
three ways in which
your lifestyle directly
or indirectly affects
the sulfur cycle?
Active Figure: Sulfur cycle
3-6 How Do Scientists Study
Ecosystems?
 Concept 3-6 Scientists use field research,
laboratory research, and mathematical and other
models to learn about ecosystems.
Some Scientists Study Nature Directly
 Field research: “muddy-boots biology”
 New technologies available
• Remote sensors
• Geographic information system (GIS) software
• Digital satellite imaging
 2005, Global Earth Observation System of
Systems (GEOSS) – 10 year program
Some Scientists Study Ecosystems
in the Laboratory
 Simplified systems carried out in
•
•
•
•
Culture tubes and bottles
Aquaria tanks
Greenhouses
Indoor and outdoor chambers
 Supported by field research
Some Scientists Use Models to
Simulate Ecosystems
 Computer simulations and projections
 Field and laboratory research needed for
baseline data
We Need to Learn More about the Health
of the World’s Ecosystems
 Determine condition of the world’s ecosystems
 More baseline data needed