Ecosystems: What Are They and How Do They Work

Chapter 3 (Miller and Spoolman, 2010)
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
 At least half have been destroyed.
 W/o strong conservation measures, most will be gone or
severely degraded in your lifetime.
 Disruption will have three major harmful effects
 Reduce biodiversity
 Accelerate global warming
 Change regional weather patterns
 Once a tipping point is reached, tropical rainforests will
become less diverse tropical grasslands
Figure 3-1 Natural capital degradation: satellite image of the loss of tropical rainforest,
cleared for farming, cattle grazing, and settlements, near the Bolivian city of Santa Cruz
between June 1975 (left) and May 2003 (right).
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 – smallest and most fundamental structural units
of life.
 Cell Theory
 Eukaryotic cell
 Prokaryotic cell
Figure 3.2
Natural capital: (a) generalized structure of a eukaryotic cell and (b) prokaryotic cell.
Note that a prokaryotic cell lacks a distinct nucleus and generalized structure of a
eukaryotic cell.
Species Make Up the Encyclopedia
of Life
 For a groups of sexually reproducing organisms, a
species is a set of individuals that can mate and
produce fertile offspring.
 1.8 Million species identified
Insects make up most of the known species
 Perhaps 10–14 million species not yet identified
 Scientists have developed a distinctive system for
classifying and naming each species.
Ecologists Study Connections in
 Ecology – derived from the Greek oikos and logos, is the
study of how organisms interact with their living (biotic)
environment and their nonliving environment (abiotic).
 Levels of organization
 Population (Figure 3-4)
Genetic diversity (Figure 3-5)
 Community
 Ecosystem
 Biosphere
Figure 3.3
Some levels of organization of
matter in nature. Ecology
focuses on the top five of these
Figure 3-4 Population (school) of glassfish in a cave in the Red Sea.
Figure 3-5 Genetic diversity among individuals in a population of a species of Caribbean
snail is reflected in the variations in shell color and banding patterns. Genetic diversity
can also include other variations such as slight differences in chemical makeup,
sensitivity to various chemicals, and behavior.
Science Focus: Have You Thanked
the Insects Today? (1)
Science Focus: Have You Thanked
the Insects Today? (2)
 Pollinators
 Eat other insects
 Loosen and renew soil
 Reproduce rapidly, and can rapidly develop new traits
 Very resistant to extinction
 According to E.O. Wilson, if all insects disappeared, parts of the
life support systems for us and other species would be greatly
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 (1)
 Atmosphere – envelope of gas that surrounds the
 Troposphere, extends to 17 km (11 mi) at tropics, 7 km (4
mi) at poles.
78 % N2, 21 % O2, and 1 % water vapor, CO2 and CH4
 Stratosphere, from 17-50 km (11-31 mi)
 Lower portion contains ozone (O3)
 Hydrosphere – all water on or near the earth’s surface.
 Most in oceans which cover 71 % of the globe.
 Liquid, ice, and water vapor
The Earth’s Life-Support System
Has Four Major Components (2)
 Geosphere
 Intensely hot core, a thick mantle, and thin outer crust.
 Upper portion contains nonrenewable fossil fuels and
minerals that we use as well as renewable soil.
 Biosphere – parts of the atmosphere, hydrosphere
and geosphere where life exists.
 From about 9 km (6 mi) above surface to bottom of the
Figure 3.6
Natural capital: general structure
of the earth showing that it
consists of a land sphere, air
sphere, water sphere, and life
Life Exists on Land and in Water
 Biomes – large regions such as forests, deserts, and
grasslands with distinct climates and certain species
(especially vegetation) adapted to them.
 Aquatic life zones – divisions of the watery parts of the
biosphere each containing numerous ecosystems.
 Freshwater life zones
 Lakes and streams
 Marine life zones
 Coral reefs
 Estuaries
 Deep ocean
Figure 3.7
Major biomes found along the 39th parallel across the United States. The differences
reflect changes in climate, mainly differences in average annual precipitation and
Three Factors Sustain Life on Earth
 One-way flow of high-quality energy beginning with
the sun
 Cycling of matter or nutrients
 Gravity
 Holds on to the atmosphere and enables the movement
and cycling of chemicals through the air, water, soil, and
What Happens to Solar Energy
Reaching the Earth?
 UV, visible, and IR energy
 Much is reflected by the atmosphere, only 1 % reaches surface
 Lights the earth during the day, warms the air, evaporates and cycles
water through the biosphere.
 1 % generates the wind, and only 0.1 % is harnessed by photosynthetic
 Radiation
 Absorbed by ozone , including 95 % of harmful UV
 Absorbed by the earth
 Reflected by the earth
 Radiated by the atmosphere as heat
 Natural greenhouse effect
 Carbon dioxide, methane (CH4), nitrous oxide (N2O), and ozone (O3)
 Human activities are increasing these gases.
Figure 3.8
Solar capital: flow of energy to and from the 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
Ecosystems Have Living and
Nonliving Components (1)
 Abiotic
 Water
 Air
 Nutrients
 Rocks
 Heat
 Solar energy
 Biotic
 Living and once living biological components—plants
animals and microbes.
 Dead organisms, dead part of organisms, and waste products
of organisms.
Figure 3.9
Major living (biotic) and nonliving (abiotic) components of an ecosystem in a field.
Ecosystems Have Living and
Nonliving Components(2)
 Different species AND their populations thrive under
different physical and chemical conditions.
 Some need bright light, or warmer temperatures, or
higher humidity or pH, for example, than others.
 Each population in an ecosystem has a range of
tolerance to variations in the physical and chemical
 Likewise individuals in population can vary in their
tolerance to environmental factors because of small
differences in genetic makeup(i.e. genetic variation).
Figure 3.10
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.
Question: Which scientific principle of sustainability (see back cover) is related to the
range of tolerance concept?
Several Abiotic Factors Can Limit
Population Growth
 Limiting factor – specific factor(s) important in
regulating the growth of a population.
 Terrestrial ecosytems: precipitation, soil nutrients,
 Aquatic ecosystems: temperature, sunlight, nutrients,
DO, and salinity.
 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
 One way in which population control (one of the
scientific principles of sustainability) is achieved
Producers and Consumers Are the
Living Components of Ecosystems (1)
 Trophic level
 Producers, or autotrophs
 Photoautotrophs: plants, algae, aquatic plants, and phytoplankton,
 Chemoautotrophs: mostly specialized bacteria
Chemosynthesis (see p. 59 for details)
 Consumers, or heterotrophs
 Primary
 Secondary
 Third and higher level
 Omnivores
 Decomposers
 Primarily bacteria and fungi
 Detritus feeders, or detritivores
 Mites, earthworms, some insects, catfish, and larger scavengers like
Figure 3.11
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.
Producers and Consumers Are the
Living Components of Ecosystems (2)
 Organisms use the chemical energy stored in glucose
and other organic compounds to fuel their life
 In most cells, energy released by aerobic respiration.
Though the steps differ, the net chemical rxn is essentially the
opposite of that for photosynthesis.
 Anaerobic respiration, or fermentation
End products include CH4, ethyl alcohol (C2H6O), acetic acid
(C2H4O2), or hydrogen sulfide (H2S).
Energy Flow and Nutrient Cycling
Sustain Ecosystems and the Biosphere
 Ecosystems and the biosphere are sustained through a
combination of one-way energy flow from the sun
through these systems and nutrient cycling of key
materials within them.
 These two principles of sustainability (see back cover of
textbook) arise from
Structure and function of natural ecosystems
Law of conservation of matter, and
Two law of thermodynamics.
Figure 3.12
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
Science Focus: Many of the World’s Most
Important Species Are Invisible to Us
 Microorganisms, or microbes, are a vital part of
earth’s natural capital. Explain.
 Bacteria
 Protozoa
 Fungi
 Phytoplankton
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
Energy Flows Through Ecosystems
in Food Chains and Food Webs
 Chemical energy stored as nutrients in the bodies and
wastes of organisms flows through ecosystems from
one trophic level (feeding level) to another.
 Food chain – a sequence of organisms, each of which
serves as a source of food or energy for the next.
 Primarily through photosynthesis, feeding and
 Food web – complex network of interconnected food
Figure 3.13
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. Question: Think about what you ate for
breakfast. At what level or levels on a food chain were you eating?
Figure 3.14
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 – the dry weight of all organic matter
contained in its organisms.
 Chemical energy stored in biomass is transferred up the
food web.
Inefficient. Decrease in energy available at each succeeding
trophic level.
 Ecological efficiency – percentage of usable chemical
energy transferred as biomass from one trophic level
to the next.
 Ranges from 2 to 40 %, but 10 % is average.
Figure 3.15
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
the form of low-quality heat) with each transfer from one trophic level to another.
Question: Why is a vegetarian diet more energy efficient than a meat-based diet?
Some Ecosystems Produce Plant
Matter Faster Than Others Do (1)
 Ultimately, the biomass of an ecosystem depends on
the amount of energy captured and stored by
 Gross primary productivity (GPP) – the rate at
which an ecosystems producers convert solar energy
into chemical energy.
 Usually measured in energy production per unit area per
unit time, e.g. kcal/m2/yr.
 To stay alive producers must use some of this stored
chemical energy for their own respiration.
Some Ecosystems Produce Plant
Matter Faster Than Others Do (2)
 Net primary productivity – rate at which producers
use photosynthesis to produce and store energy minus
the rate at which they use this stored energy for
aerobic respiration.
 Ecosystems and aquatic life zones differ in their NPP
(Fig. 3-16).
 Decreases from equator to pole.
 Estuaries are high
 Upwellings (water moving up from depths to surface)
 Open ocean, low NPP, but high absolute amount. Why?
Figure 3.16
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)
Some Ecosystems Produce Plant
Matter Faster Than Others Do (3)
 Should be clear that the planet’s NPP ultimately limits
the number of consumers (including humans) that can
survive on the earth.
 Ecologists estimated that humans use, waste, or
destroy about 20-32% of the earth’s total potential
 Remarkable considering that humans make up on 1% of
the total biomass of all of the earth’s consumers.
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, or nutrient cycles – the cycling
of elements and compounds through air, water, soil, rock,
and living organisms in ecosystems and in the biosphere.
 Driven directly and indirectly by the sun and gravity.
 Human activities are altering them.
 Include: Hydrologic, Carbon, Nitrogen, Phosphorus, and
Sulfur Cycles.
 Atoms and compounds moving in this cycle may accumulate
in one portion of the cycle indefinitely. These atmospheric,
oceanic, and underground deposits are called reservoirs.
 Connect past, present , and future forms of life
Water Cycles through the
 The hydrologic cycle, or water cycle, collects, purifies, and
distributes the earth’s fixed supply of water.
 Powered by energy from the sun, involves three major processes:
 Evaporation
84% of water in atmosphere comes from the ocean.
 Precipitation
Surface runoff, infiltration, and percolation to aquifers
 Transpiration
On land, 90% of water reaches atmosphere from plants.
 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
Figure 3.17
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 of water due to hydrogen bonds between
water molecules:
 Exists as a liquid over a large range of temperature
 Changes temperature slowly (High heat capacity)
 High boiling point: 100˚C
 Takes lots of energy to evaporate (High heat of
Adhesion and cohesion
Expands as it freezes
Filters out harmful UV
Carbon Cycle Depends on
Photosynthesis and Respiration
 Carbon cycle – carbon circulates through the biosphere,
the atmosphere, and parts of the hydrosphere.
 Based on CO2, which make up 0.038% of atmosphere.
 Link between photosynthesis in producers and aerobic
respiration in producers, consumers, and decomposers.
 Key component of earth’s thermostat (a GHG).
 Additional CO2 added to the atmosphere
 Tree clearing
 Burning of fossil fuels
 Computer models suggest that it is very likely (90-99%
probability) that human activities are enhancing the green
house effect.
Figure 3.18
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?
Nitrogen Cycles through the
Biosphere: Bacteria in Action (1)
 Major reservoir, the atmosphere; N2 makes up 78%
 Nitrogen is a crucial component of proteins, vitamins and nucleic
 Two processes convert N2 to more usable forms:
 Electrical charges, such as lightning.
 Nitrogen-fixing bacteria; process called nitrogen fixation.
Special bacteria in soil and blue-green algae (cyanobacteria)
Combine N2 and H2 to make ammonia (NH3)  to NH4+ that can be used by
 Nitrification – ammonia is converted by other bacteria to nitrate
ions (NO3-).
 Ammoniafication – specialized decomposers convert detritus into
simpler nitrogen-containing compounds like NH3 and NH4+.
 Denitrification – specialize bacteria in waterlogged soils and
sediments of aquatic ecosystems convert ammonia and ammonium
ions back into nitrite and nitrate ions and then into N2 and N2O.
Figure 3.19
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
Nitrogen Cycles through the
Biosphere: Bacteria in Action (2)
 Human intervention in the nitrogen cycle:
1. Burn fuels at high temperatures, creates nitric oxide (NO) 
nitrogen dioxide (NO2)  nitric acid vapor (HNO3)  acid
deposition, or acid rain.
2. Anaerobic bacteria action on livestock waste and commercial
inorganic fertilizer  nitrous oxide (N2O)  ghg forces
warming and can destroy stratospheric ozone (O3)
3. Destruction of forest, grasslands, and wetlands  releases
large quantities of nitrogen as gaseous compounds.
4. Add excess nitrates to bodies of water from agricultural runoff
and municipal sewage systems  cultural eutrophication.
5. Deplete nitrogen from topsoil when we harvest nitrogen-rich
crops, irrigate crops and burn and clear grasslands and
Figure 3.20
Global trends in the annual inputs of nitrogen into the environment from human
activities, with projections to 2050. (Data from 2005 Millennium Ecosystem Assessment)
Phosphorus Cycles through the
 Phosphorus circulates through water, the earth’s crust, and
living organisms; does not include the atmosphere.
 Component of nucleic acids and energy molecules, ATP.
 Major reservoir, phosphorus salts containing (phosphate ions,
PO4-3) in terrestrial rock formations and ocean sediments.
 Limiting factor for plant growth in terrestrial and aquatic
 Impact of human activities
 Clearing forests
 Removing large amounts of phosphate from the earth to make
 Runoff from land can lead to further cultural eutrophication of
lakes and coastal areas.
Figure 3.21
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?
Sulfur Cycles through the
 Sulfur is stored in rocks and minerals and ocean sediments.
 H2S released from volcanoes and anaerobic bacteria
decomposition in flooded swamps, bogs and tidal flats.
SO2 released from volcanoes and processing and burning fossil
Sulfate (SO4-2) salts from sea spray, dust storms, and forest fires.
Certain marine algae produce DMS, serves as nuclei for
condensation for water into droplets found in clouds.
DMS in atmosphere  SO2  SO3 and H2SO4  acid
Human activities affect the sulfur cycle mostly by release of SO2.
 Burn sulfur-containing coal and oil
 Refine sulfur-containing petroleum
 Convert sulfur-containing metallic mineral ores
Figure 3.22
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?
3-6 How Do Scientists Study
 Concept 3-6 Scientists use field research, laboratory
research, and mathematical and other models to learn
about ecosystems.
Some Scientists Study Nature
 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
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
 Doctor-patient analogy

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