LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Ecosystems & Conservation
Chapter 55
Lectures by
Erin Barley
Kathleen Fitzpatrick
Ecosystem
• Ecosystem = all
organisms in a
community, as well as
abiotic factors with
which they interact
• Chemoautotrophic
bacteria, living below
Antarctic glacier
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• Ecosystems range from a microcosm, such as an
aquarium, to a large area such as a lake or forest
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Ecosystem Dynamics
• Regardless of ecosystem size,
dynamics involve 2 main processes:
energy flow & chemical cycling
• Energy flows through ecosystems
while matter cycles within them
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Physical laws govern energy flow and
chemical cycling
• Ecologists study transformations of energy and matter within
ecosystems
• Laws of physics and chemistry apply
– 1st law of thermodynamics (conservation of energy):
energy cannot be created or destroyed, only transformed
– Energy enters ecosystem as solar radiation, is conserved,
and lost from as heat
– 2nd law of thermodynamics (entropy): every exchange of
energy increases disorder of universe
– Energy conversions not completely efficient; some energy
always lost as heat
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Conservation of Mass
• Law of conservation of mass: matter cannot be created
or destroyed
• Chemical elements are continually recycled within
ecosystems
– Forest ecosystem – most nutrients enter as dust or solutes in
rain; and are carried away in water
• Ecosystems are open systems, absorbing energy
and mass and releasing heat and waste products
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Energy, Mass, and Trophic Levels
• Autotrophs build organic molecules using
photosynthesis or chemosynthesis as energy source
• Heterotrophs depend on biosynthetic output of
other organisms
• Energy and nutrients pass from primary producers
(autotrophs) to primary consumers (herbivores) to
secondary consumers (carnivores) to tertiary
consumers (carnivores that feed on other carnivores)
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• Detritivores, or decomposers
= consumers that derive
energy from detritus,
nonliving organic matter
• Prokaryotes and fungi
• Decomposition connects
trophic levels
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An overview of energy and nutrient dynamics in an ecosystem.
Sun
Key
Chemical cycling
Energy flow
Heat
Primary producers
Primary
consumers
Detritus
Secondary and
tertiary consumers
Microorganisms
and other
detritivores
Energy & other limiting factors control
primary production
• Primary production = amount of light energy
converted to chemical energy by autotrophs during a
given time period
– In some ecosystems, chemoautotrophs are primary
producers
– Titanic Pictures
• Extent of photosynthetic production sets spending
limit for ecosystem’s energy budget
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Global Energy Budget
• Amount of solar radiation reaching
Earth’s surface limits photosynthetic
output of ecosystems
• Small fraction of solar energy actually
strikes photosynthetic organisms; even
less is of usable wavelength
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Gross and Net Production
• Total primary production = gross primary production
(GPP) - conversion of chemical energy from
photosynthesis/unit time
• Net primary production (NPP) = GPP - energy used by
primary producers for respiration
• NPP is expressed as
 Energy per unit area per unit time (J/m2yr), or
 Biomass added per unit area per unit time
(g/m2yr)
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Net Primary Production
• NPP is amount of new biomass added in
given time period
• Only NPP is available to consumers
• Standing crop: total biomass of
photosynthetic autotrophs at a given
time
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TECHNIQUE
Percent reflectance
Determining 80
Primary
Production
using
60
Satellites
Snow
Clouds
Vegetation
40
Soil
20
Liquid water
0
400
600
Visible
800
1,000
Near-infrared
Wavelength (nm)
1,200
NPP Varies Greatly
• Tropical rain forests, estuaries, and coral
reefs are among most productive
ecosystems per unit area
• Marine ecosystems are relatively
unproductive per unit area, but
contribute much to global NPP because
of volume
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Figure 55.6
Global Net primary production
(kg carbon/m2yr)
3
2
1
0
Net Ecosystem Production
• Net ecosystem production (NEP): measure of total
biomass accumulation during given period
• NEP = GPP - total respiration of all organisms
(producers and consumers) in ecosystem
• NEP estimated by comparing net flux of CO2 and O2
in ecosystem (why these 2 molecules?)
• Release of O2 by system indicates storing CO2
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Figure 55.7
Impact: Ocean Production Revealed
Float surfaces
for 6–12 hours
to transmit data
to satellite.
Float descends
to 1,000 m
and “parks.”
Drift time: 9 days
Total cycle time:
10 days
O2 concentration is
recorded as float
ascends.
Primary Production in Aquatic
Ecosystems
• In marine and freshwater ecosystems, both light and nutrients
control primary production
• Depth of light penetration affects primary production in
photic zone of ocean or lake
• More than light, nutrients limit primary production in regions
of ocean and lakes
• Limiting nutrient = element that must be added for
production to increase
• Nitrogen and phosphorous are typically nutrients that most
often limit marine production
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Figure 55.8
Phytoplankton density
(millions of cells per mL)
RESULTS
30
Ammonium
enriched
24
Phosphate
enriched
18
Unenriched
control
Which element is the
limiting nutrient along
the Long Island coast?
12
6
0
A
B
C
D
E
Collection site
F
G
Table 55.1
Which element is the limiting nutrient in
the Sargasso Sea?
Production in Aquatic Ecosystems
• Upwelling of nutrient-rich waters in parts of oceans
contributes to regions of high primary production
• Addition of large amounts of nutrients to lakes has wide
range of ecological impacts
• Sewage runoff has caused eutrophication of lakes, which
can lead to loss of most fish species
• In lakes, phosphorus limits cyanobacterial growth more
often than nitrogen; phosphate-free detergents
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Production in Terrestrial Ecosystems
• Terrestrial ecosystems – temperature and
moisture affect primary production
• Primary production increases with
moisture
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Global relationship between NPP and mean annual precipitation for
terrestrial ecosystems
Net annual primary production
(above ground, dry g/m2 yr)
1,400
1,200
1,000
800
600
400
200
0
20
40
60
80 100 120 140 160 180 200
Mean annual precepitation (cm)
Evapotranspiration
• Water transpired by plants and
evaporated from a landscape
• Affected by precipitation, temperature,
solar energy
• Related to net primary production
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Nutrient Limitations and Adaptations
• On local scale, soil nutrient is often
limiting factor in primary production
• In terrestrial ecosystems, nitrogen is
most common limiting nutrient
• Phosphorus can also be limiting nutrient,
especially in older soils
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Adaptations help plants access
limiting nutrients
• Mutualisms with nitrogen-fixing bacteria
• Mutualisms with mycorrhizal fungi, which
supply plants with phosphorus and other
limiting elements
• Root hairs to increase surface area
• Release of enzymes that increase availability of
limiting nutrients
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Energy transfer ~10% efficient
• Secondary production is amount of chemical energy in
food converted to new biomass during given period of
time
• When caterpillar eats leaves, only about 1/6 of leaf’s
energy is used for secondary production
• Organism’s production efficiency = fraction of energy
stored in food not used for respiration
Production  Net secondary production  100%
efficiency
Assimilation of primary production
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Figure 55.10
Energy partitioning within a link of the food chain.
Plant material
eaten by caterpillar
200 J
67 J
Feces
100 J
Cellular
respiration
33 J
Not assimilated
Growth (new biomass;
secondary production)
Assimilated
• Birds and mammals have efficiencies of
13% because of high cost of
endothermy
– Fishes – around 10%
– Insects and microorganisms – 40% or more
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Trophic Efficiency and Ecological
Pyramids
• Trophic efficiency: % of production transferred from one
trophic level to next
• Usually about 10% (range of 5% to 20%)
• Trophic efficiency multiplied over length of food chain
• ~0.1% of chemical energy fixed by photosynthesis
reaches tertiary consumer
• Pyramid of net production represents loss of energy with
each transfer
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Figure 55.11
An idealized pyramid of net production
Tertiary
consumers
10 J
Secondary
consumers
100 J
Primary
consumers
1,000 J
Primary
producers
10,000 J
1,000,000 J of sunlight
• Biomass pyramid – each tier represents dry weight of
organisms in trophic level
• Most biomass pyramids show sharp decrease at
successively higher trophic levels
• Certain aquatic ecosystems have inverted pyramids:
producers (phytoplankton) consumed so quickly they
are outweighed by primary consumers
• Turnover time: ratio of standing crop biomass to
production
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Figure 55.12
Trophic level
Pyramids of biomass
(standing crop).
Tertiary consumers
Secondary consumers
Primary consumers
Primary producers
Dry mass
(g/m2)
1.5
11
37
809
(a) Most ecosystems (data from a Florida bog)
Trophic level
Primary consumers (zooplankton)
Primary producers (phytoplankton)
Dry mass
(g/m2)
21
4
(b) Some aquatic ecosystems (data from the English Channel)
• Dynamics of energy flow in ecosystems have
important implications for humans
• Eating meat: relatively inefficient way of
tapping photosynthetic production
• Worldwide agriculture could feed many more
people if humans ate only plant material
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Biological and geochemical processes
cycle nutrients and water
• Life depends on recycling elements
• Nutrient circuits in ecosystems involve
biotic and abiotic components – called
biogeochemical cycles
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Biogeochemical Cycles
• Gaseous carbon, oxygen, sulfur, nitrogen occur in
atmosphere and cycle globally
• Less mobile elements include phosphorus,
potassium, and calcium
• Elements cycle locally in terrestrial systems, but
more broadly in aquatic systems
• Model of nutrient cycling includes main reservoirs of
elements and processes that transfer elements
between reservoirs
• Elements cycle between organic & inorganic
reservoirs
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Figure 55.13
Reservoir A
Organic materials
available as
nutrients
A
general
model of
nutrient
cycling.
Living
organisms,
detritus
Reservoir B
Organic
materials
unavailable
as nutrients
Fossilization
Peat
Coal
Oil
Respiration,
decomposition,
excretion
Reservoir D
Inorganic materials
unavailable
as nutrients
Assimilation,
photosynthesis
Weathering,
erosion
Minerals
in rocks
Burning of
fossil fuels
Reservoir C
Inorganic materials
available as
nutrients
Atmosphere
Water
Formation of
sedimentary
rock
Soil
In studying cycling, ecologists
focus on 4 factors:
• Chemical’s biological importance
• Forms in which each chemical is available
or used by organisms
• Major reservoirs for each chemical
• Key processes driving movement of each
chemical through its cycle
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Water Cycle
• Essential to all organisms
• Liquid water - 1° physical phase which is used
• Oceans contain 97% of water; 2% in glaciers and
polar ice caps; 1% in lakes, rivers, groundwater
• Water moves by evaporation, transpiration,
condensation, precipitation, and movement
through surface and groundwater
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Figure 55.14a
Movement over
land by wind
Precipitation
over ocean
Evaporation
from ocean
Precipitation
over land
Evapotranspiration from land
Runoff and
groundwater
Percolation
through
soil
Carbon Cycle
• Organic molecules – essential to organisms
• Photosynthetic organisms convert CO2 to organic
molecules that are used by heterotrophs
• Reservoirs: fossil fuels, soils and sediments,
solutes in oceans, plant and animal biomass,
atmosphere, and sedimentary rocks
• CO2 taken up and released (photosynthesis &
respiration); volcanoes & burning of fossil fuels
contribute CO2 to atmosphere
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Figure 55.14b
CO2 in
atmosphere
Photosynthesis
Photo- Cellular
synthesis respiration
Burning
of fossil
fuels and
wood Phytoplankton
Consumers
Consumers
Decomposition
Nitrogen Cycle
• Component of amino acids, proteins, nucleic acids
• Main reservoir is atmosphere (N2); this must be
converted to NH4+ or NO3– for uptake by plants (nitrogen
fixation by bacteria)
• Organic nitrogen decomposed to NH4+ by
ammonification; NH4+ is decomposed to NO3– by
nitrification
• Denitrification converts NO3– back to N2
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Figure 55.14c
N2 in
atmosphere
Reactive N
gases
Industrial
fixation
Denitrification
N fertilizers
Fixation
NO3–
Dissolved
organic N
NH4+
Runoff
NO3
–
Terrestrial
cycling
N2
Aquatic
cycling
Denitrification
Decomposition
and
sedimentation
Assimilation
Decomposition
Uptake
of amino
acids
Fixation
in root nodules
Ammonification
NH3
NO3–
Nitrification
NH4+
NO2–
Phosphorus Cycle
• Major constituent of nucleic acids, phospholipids, and
ATP
• Phosphate (PO43–) is most important inorganic form of
phosphorus
• Largest reservoirs – sedimentary rocks of marine origin,
oceans, and organisms
• PO43– binds with soil particles; movement often localized
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Figure 55.14d
Wind-blown
dust
Geologic
uplift
Weathering
of rocks
Runoff
Consumption
Decomposition
Plankton Dissolved
PO43–
Uptake
Leaching
Plant
uptake
of PO43–
Sedimentation
Decomposition
Decomposition & Nutrient Cycling Rates
• Decomposers (detritivores) play key role in
pattern of chemical cycling
• Rates at which nutrients cycle in different
ecosystems vary greatly (differing rates of
decomposition)
• Rate of decomposition controlled by
temperature, moisture, nutrient availability
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Figure 55.15
EXPERIMENT
Ecosystem type
Arctic
Subarctic
Boreal
Temperate
Grassland
Mountain
A
G
M
D
B,C
T
H,I
S
E,F
O
L
N
U
J
K
Q
R
RESULTS
80
Percent of mass lost
How does
temperature
affect litter
decomposition
in an
ecosystem?
P
70
60
50
K
J
40
D
30
20
10
0
–15
C
A
B E
F
G
P
N
M
L
I
U
R
O Q
T
S
H
–10
–5
0
5
10
Mean annual temperature (C)
15
• Rapid decomposition results in relatively
low levels of nutrients in soil
– Tropical rain forest – material decomposes
rapidly; most nutrients tied up in trees
• Cold, wet ecosystems store large
amounts of undecomposed organic
matter
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Case Study: Nutrient Cycling
• Hubbard Brook Experimental Forest – used to study
nutrient cycling in forest since 1963
• Research team constructed dam to monitor loss of
water and minerals
• 60% of precipitation exits through streams and 40%
lost by evapotranspiration
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Figure 55.16
(a) Concrete dam
and weir
(b) Clear-cut watershed
Nitrate concentration in runoff
(mg/L)
Nutrient
cycling in
the Hubbard
Brook
Experiment
al Forest:
an example
of long-term
ecological
research.
80
60
40
20
4
3
2
1
0
Deforested
Completion of
tree cutting
1965
1966
(c) Nitrate in runoff from watersheds
Control
1967
1968
Hubbard Experimental Forest
• In one experiment, the trees in one valley were cut down, and
the valley was sprayed with herbicides
• Net losses of water were 3040% greater in the deforested
site than the undisturbed (control) site
• Nutrient loss was also much greater in the deforested site
compared with the undisturbed site
– For example, nitrate levels increased 60 times in the outflow
of the deforested site
• These results showed how human activity can affect
ecosystems
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Restoration ecologists help return degraded
ecosystems to a more natural state
• Given enough time, biological communities can
recover from many types of disturbances
• Restoration ecology seeks to initiate or speed up the
recovery of degraded ecosystems
• Two key strategies are bioremediation and
augmentation of ecosystem processes
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Figure 55.17
A gravel and clay mine site in New Jersey,
before and after restoration.
(a) In 1991, before restoration
(b) In 2000, near the completion of restoration
Bioremediation
• Use of living organisms to detoxify ecosystems
• Organisms most often used are prokaryotes, fungi, or
plants
• Organisms can take up, & sometimes metabolize,
toxic molecules
– Bacterium Shewanella oneidensis can metabolize
uranium and other elements to insoluble forms; less
likely to leach into streams and groundwater
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Bioremediation of groundwater
contaminated with uranium at
Oak Ridge National
Laboratory, Tennessee.
Concentration of
soluble uranium (M)
6
5
4
3
2
1
0
0
50
100
150
200
250
300
Days after adding ethanol
350
400
Biological Augmentation
• Uses organisms to add
essential materials to a
degraded ecosystem
– For example, nitrogenfixing plants can increase
the available nitrogen in
soil
– For example, adding
mycorrhizal fungi can
help plants to access
nutrients from soil
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Restoration Projects Worldwide
• The newness and complexity of restoration ecology
require that ecologists consider alternative solutions
and adjust approaches based on experience
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Figure 55.19a
Exploring: Restoration Ecology Worldwide
Equator
Figure 55.19b
Kissimmee River, Florida
Figure 55.19c
Truckee River, Nevada
Figure 55.19d
Tropical dry forest, Costa Rica
Figure 55.19e
Rhine River, Europe
Figure 55.19f
Succulent Karoo, South Africa
Figure 55.19g
Coastal Japan
Figure 55.19h
Maungatautari, New Zealand