Ecosystems: What Are They
and How Do They Work?
Chapter 3
Section 3-1
WHAT KEEPS US AND OTHER
ORGANISMS ALIVE?
Earth’s life-support system has
four major components
• The hydrosphere consists of earth’s water, found in
liquid water, ice, and water vapor.
• The geosphere is the hot core, a thick mantle, and thin
crust.
• The biosphere includes parts of the atmosphere,
hydrosphere, and geosphere.
Atmosphere
Biosphere
(living organisms)
Soil
Rock
Crust
Mantle
Geosphere
(crust, mantle, core)
Mantle
Core
Atmosphere
(air)
Hydrosphere
(water)
Fig. 3-2, p. 42
Solar
radiation
Radiated by
atmosphere
as heat
Reflected by
atmosphere
UV radiation
Lower Stratosphere
(ozone layer)
Most UV
absorbed
by ozone
Visible
light
Absorbed
by the earth
Troposphere
Heat added to
troposphere
Heat radiated
by the earth
Greenhouse
effect
Fig. 3-3, p. 42
Earth’s life-support system has
four major components
• The atmosphere is the thin membrane of air around the
planet.
– The troposphere is the air layer about 4–11 miles above sea
level. It contains greenhouse gases that absorb and release
energy which warms the inner layer of the atmosphere.
– The stratosphere lies above the troposphere between 11–31
miles; It contains ozone and it filters out the sun’s harmful
radiation.
Section 3-2
WHAT ARE THE MAJOR
COMPONENTS OF AN
ECOSYSTEM?
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
An individual living being
Cell
The fundamental structural and
functional unit of life
Molecule
Chemical combination of two or
more atoms of the same or different
elements
Atom
Smallest unit of a chemical element
that exhibits its chemical properties
Water
Hydrogen
Oxygen
Stepped Art
Fig. 3-4, p. 43
Oxygen (O2)
Precipitaton
Carbon dioxide (CO2)
Producer
Secondary
consumer
(fox)
Primary
consumer
(rabbit)
Producers
Water
Decomposers
Soluble mineral
nutrients
Fig. 3-5, p. 44
Ecosystems have several
important components
• Every organism belongs to a particular trophic
level depending on its source of nutrients.
• Producers, or autotrophs, use photosynthesis
to make nutrients from components in the
environment.
• Consumers, or heterotrophs, get their
nutrients by feeding on other organisms or their
remains.
• Consumers can be herbivores (feed on
plants), carnivores (feed on animals) or
omnivores (feed on both plants and animals).
Producers
Consumers
Ecosystems have several
important components
• Consumers can be primary, secondary or
tertiary consumers, depending upon their trophic
level.
• Decomposers (bacteria/fungi) break down
organic detritus into simpler inorganic compounds.
• Detritivores (detritus feeders) feed on waste or
dead bodies.
• Producers, consumers and decomposers utilize
chemical energy stored in organic molecules. In
most cells, this energy is released by aerobic
respiration.
Decomposers
Detritus feeders
Longhorned
beetle
holes
Carpenter Termite
ant
and
Bark beetle
galleries carpenter
engraving
ant work
Time progression
Dry rot
fungus
Wood
reduced
Fungi
to powder
Powder broken down
by decomposers into
plant nutrients in soil
Fig. 3-8, p. 45
Heat
Chemical nutrients
(carbon dioxide,
oxygen, nitrogen,
minerals)
Heat
Heat
Producers
(plants)
Decomposers
(bacteria, fungi)
Heat
Solar
energy
Consumers
(plant eaters,
meat eaters)
Heat
Fig. 3-9, p. 46
Section 3-3
WHAT HAPPENS TO ENERGY
IN AN ECOSYSTEM?
Energy flows through ecosystems
in food chains and food webs
What is a food chain?
Give me an example.
Energy flows through ecosystems
in food chains and food webs
• A food chain is a sequence of organisms,
each of which serves as a source of
nutrients and energy for the next
organisms. Organisms are assigned to
trophic levels in a food chain.
First
Trophic
Level
Second
Trophic
Level
Third
Trophic
Level
Producers
(plants)
Primary
consumers
(herbivores)
Secondary
consumers
(carnivores)
Heat
Heat
Heat
Fourth
Trophic
Level
Tertiary
consumers
(top carnivores)
Heat
Solar
energy
Heat
Heat
Heat
Decomposers and
detritus feeders
Stepped Art
Fig. 3-10, p. 47
Energy flows through ecosystems
in food chains and food webs
• A food web is a series of interconnected food
chains.
• Food webs occur in most ecosystems.
Organisms are also assigned to trophic levels in
food webs.
–
–
–
–
–
Producers are the first level.
Primary consumers are the second.
Secondary consumers belong to the third.
Tertiary consumers are the fourth level.
Detritivores and decomposers process detritus from
all trophic levels.
Humans
Sperm whale
Blue whale
Elephant seal
Crabeater
seal
Adelie
penguin
Killer
whale
Leopard
seal
Emperor
penguin
Squid
Petrel
Fish
Carnivorous
zooplankton
Herbivorous
zooplankton
Krill
Phytoplankton
Fig. 3-11, p. 48
Usable energy decreases with
each link in a food chain or web
• There is less high-quality energy available
to organisms at each succeeding feeding
level because when chemical energy is
transferred from one trophic level to the
next, about 90% of the energy is lost as
heat
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)
Fig. 3-12, p. 49
Some ecosystems produce plant
matter faster than others do
• The rate of an ecosystem’s producers converting energy
into biomass is the gross primary productivity (GPP).
• 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.
• Ecosystems and aquatic life zones differ in their NPP.
The three most productive systems are …
• The three least productive are …
Terrestrial Ecosystems
Swamps and marshes
Tropical rain forest
Temperate forest
Northern coniferous forest
(taiga)
Savanna
Agricultural land
Woodland and shrubland
Temperate grassland
Tundra (arctic and alpine)
Desert scrub
Extreme desert
Aquatic Ecosystems
Estuaries
Lakes and streams
Continental shelf
Open ocean
Fig. 3-13, p. 49
Section 3-4
WHAT HAPPENS TO MATTER
IN AN ECOSYSTEM?
Nutrients cycle within and
among ecosystems
• Elements and compounds move through
air, water, soil, rock and living organisms
in biogeochemical, or nutrient, cycles.
The water cycle
http://www.youtube.com/watch?v=0gleTEA8eHY
The water cycle
• Solar energy evaporates water; the water
returns as precipitation (rain or snow),
goes through organisms, goes into bodies
of water, and evaporates again.
• Water is filtered and partly purified as it
moves through the hydrological cycle.
• Water can be stored as ice in glaciers or in
underground aquifers.
The water cycle
• Unique properties of water include…
The water cycle
• Humans alter the water cycle in 3 ways:
– Withdrawing freshwater at faster rates than
nature can replenish it.
– Clearing vegetation which increases runoff
and decreases replenishment of groundwater
supplies.
– Draining wetlands which interferes with flood
control (we’ve lost ~50% of our wetlands).
Condensation
Condensation
Ice and
snow
Transpiration
from plants
Precipitati
on to land
Evaporation of
surface water
Evaporation
from ocean
Runoff
Lakes and
reservoirs
Runoff
Infiltration
and
percolation
into aquifer
Groundwat
er
in aquifers
Increased runoff on
land covered with
crops,
buildings and
pavement
Runoff
Overpumpin
g
of aquifers
Precipitati
on to
ocean
Increased
runoff
from cutting
forests and
filling wetlands
Water pollution
Runoff
Ocean
Natural process
Natural reservoir
Human impacts
Natural pathway
Pathway affected by human activities
Fig. 3-14, p. 51
Carbon dioxide
in atmosphere
Respiration
Photosynthesis
Animals
(consumers)
Diffusion
Burning
fossil
fuels
Forest fires
Plants
(producers)
Deforestation
Transportation
Respiration
Carbon
in plants
(producers)
Carbon dioxide
dissolved in ocean
Carbon
in animals
(consumers)
Decomposition
Marine food webs
Producers, consumers,
decomposers
Carbon
in limestone
or dolomite
sediments
Carbon
in fossil
fuels
Compaction
Process
Reservoir
Pathway affected by humans
Natural pathway
Fig. 3-15, p. 53
The carbon cycle
• Carbon is the basic building block of carbohydrates,
fats, proteins, DNA, and other compounds.
• Carbon circulates through the biosphere,
hydrosphere, and atmosphere.
• Producers, consumers and decomposers circulate
carbon in the biosphere.
• Fossil fuels contain carbon.
• Humans are altering atmospheric carbon dioxide
mostly by our use of fossil fuels and our destruction
of the carbon-absorbing vegetation.
Process
Nitrogen in
atmosphere
Reservoir
Denitrification by bacteria
Nitrification by bacteria
Pathway affected by humans
Natural pathway
Nitrogen oxides
from burning fuel
and using inorganic
fertilizers
Nitrogen
in animals
(consumers)
Electrical storms
Volcanic
activity
Nitrogen
in plants
(producers)
Decomposition
Nitrates from
fertilizer
runoff and
decomposition
Uptake by plants
Nitrate in soil
Nitrogen loss
to deep ocean
sediments
Nitrogen
in ocean
sediments
Bacteria
Ammonia in soil
Fig. 3-16, p. 54
The nitrogen cycle: bacteria in action
• Nitrogen gas (N2), which makes up 78% of
the atmosphere, cannot be used directly
by most living organisms.
• Nitrogen-fixing bacteria convert N2 into
compounds that are useful nutrients for
plants and animals.
The nitrogen cycle: bacteria in action
• The nitrogen cycle includes the following steps:
– Specialized bacteria convert gaseous nitrogen to
ammonia in nitrogen fixation.
– Specialized 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.
– Decomposer bacteria convert detritus into ammonia
and water-soluble salts in ammonification.
– In denitrification, anaerobic bacteria in soggy soil and
bottom sediments of water areas convert NH3 and
NH4+ back into nitrite and nitrate ions, then into
nitrogen gas and nitrous oxide gas, which are
released into the atmosphere.
The nitrogen cycle: bacteria in action
• Human activities have more than doubled
the annual release of nitrogen from the
land into the rest of the environment,
mostly from the greatly increased use of
inorganic fertilizers to grow crops. This
excessive input of nitrogen into the air and
water contributes to pollution and other
problems.
Process
Reservoir
Pathway affected by humans
Natural pathway
Phosphates
in sewage
Phosphates in
mining waste
Phosphates
in fertilizer
Runoff
Plate
tectonics
Runoff
Sea
birds
Runoff
Erosion
Animals
(consumers)
Phosphate
dissolved
in water
Plants
(producers)
Phosphate in
rock (fossil
bones,
guano)
Ocean food
webs
Phosphate in
shallow ocean
sediments
Phosphate in
deep ocean
sediments
Bacteria
Fig. 3-17, p. 54
The phosphorus cycle
• Phosphorus circulates through water, Earth’s crust, and
living organisms in the phosphorus cycle. Phosphorus
does not cycle through the atmosphere.
• The major reservoirs of phosphorus on Earth are rock
formations and ocean bottom sediments.
• Phosphorus is transferred by food webs and is an
important component of many biological molecules.
• Phosphorus is often the limiting factor for plant growth.
• Human activity removes phosphate from the earth to
make fertilizer and reduces phosphate levels in tropical
soils by clearing forests. Phosphate-rich runoff from the
land can produce huge populations of algae, which can
upset chemical cycling and other processes.
Sulfur dioxide in
atmosphere
Smelting
Burning
coal
Sulfuric acid and
Sulfate
deposited
as acid rain
Refining
fossil fuels
Sulfur in
animals
(consumers)
Dimethyl
Sulfide
a bacteria
byproduct
Sulfur
in plants
(producers)
Mining and
extraction
Uptake
by plants
Sulfur
in ocean
sediments
Decay
Decay
Process
Reservoir
Sulfur
in soil, rock
and fossil fuels
Pathway affected by
humans
Natural pathway
Fig. 3-18, p.56
The sulfur cycle
• Much of the earth’s sulfur is stored underground
in rocks and minerals.
• Hydrogen sulfide (H2S) is released from
volcanoes and anaerobic decomposition of
organic matter in bogs and swamps.
• Humans have been increasing atmospheric
sulfur dioxide by burning sulfur-containing fuels,
refining sulfur-containing fuels, and converting
sulfur containing metallic mineral ores into free
metals.
Section 3-5
HOW DO SCIENTISTS STUDY
ECOSYSTEMS?
Some scientists study nature directly
• Field research (“muddy-boots biology”) involves
making direct measurements and observations
of ecosystems in natural settings.
• Remote sensing devices can gather data on the
earth’s surface that can be converted into usable
forms by geographic information systems (GIS),
such as computerized maps of an area that are
used to examine forest cover, water resources,
air pollution emissions, coastal changes, and
changes in global sea temperatures.
Some scientists study
ecosystems in the laboratory
• Ecologists use tanks, greenhouses, and
controlled indoor and outdoor chambers to
study ecosystems in laboratory research.
This allows control of light, temperature,
CO2, humidity, and other variables.
We need to learn more about the
health of the world’s ecosystems
• Mathematical models and computer simulations
can help scientists understand large and very
complex systems.
• Simulations are no better than the data and
assumptions used to develop models.
• We need more 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.
Three Big Ideas
• Life is sustained by the flow of energy from the
sun through the biosphere, the cycling of
nutrients within the biosphere, and gravity.
• Some organisms produce the nutrients they
need, some survive by consuming other
organisms, and others recycle nutrients back to
producers.
• Human activities are altering the flow of energy
through food chains and webs, and the cycling
of nutrients within ecosystems and the
biosphere.