Download Primary Production in Ecosystems

Ecology and
Ecosystems
•How energy flows through the ecosystem by understanding the
terms in bold that relate to food chains and food webs.
•The difference between gross primary productivity and net
primary productivity.
•The carbon and nitrogen biogeochemical cycles.
Ecosystems, Energy, and Matter
Ecosystems, Energy,
and Matter
• An ecosystem
consists of all the
organisms living in
a community
– As well as all the
abiotic factors with
which they interact
Ecosystems can range from a
microcosm, such as an
aquarium
•To a large area such as a
lake or forest
Life Depends on the Sun
Energy from the sun enters an ecosystem when a
plant uses sunlight to make sugar molecules
(carbohydrates) by a process called photosynthesis.
6CO2 + 6H2O + solar energy
C6H12O6
+ 6O2
Carbohydrates are energy-rich molecules which organisms use to
carry out daily activities, such as movement, growth, and repair.
As organisms consume food and use energy from carbohydrates,
the energy travels from one organism to another.
An exception to the Rule: Deep-Ocean Ecosystems
Bacteria use the hydrogen sulfide present in hot water that escapes
from cracks in the ocean floor to produce their own food. These
bacteria are eaten by the other underwater organisms, thus
supporting a thriving ecosystem in darkness.
An organism’s body breaks down its food to obtain the
energy stored in the food by a process called cellular
repiration.
C6H12O6
+ 6O2
6CO2
+
6H2O + energy
When cellular respiration occurs, the carbon-carbon
bonds found in carbohydrates are broken and the
carbon is combined with oxygen to form carbon
dioxide. This process releases the energy, which is
either used by the organism (to move its muscles, digest
food, excrete wastes, think, etc.) or the energy may be
lost as heat.
Ecosystem ecology emphasizes energy
flow and chemical cycling
• Ecosystem ecologists view
ecosystems
– As transformers of energy and
processors of matter
• Ecosystems are not
supernatural so…
– They abide by..
• Thermodynamics
• The Law of Conservation of
Energy
• The Law of Conservation of
Matter
Trophic Relationships
• Energy and
nutrients pass from
primary producers
(autotrophs)
– To primary
consumers
(herbivores) and
then to secondary
consumers
(carnivores)
Trophic Relationships
• Only ~10-20% of energy flows from one trophic
level to the next.
• Energy flows through an ecosystem
– Entering as light and exiting as heat
• Nutrients cycle within an ecosystem
Tertiary
consumers
Microorganisms
and other
detritivores
Detritus
Secondary
consumers
Primary consumers
Primary producers
Heat
Key
Chemical cycling
Energy flow
Figure 54.2
Sun
Decomposition
• Decomposition
– Connects all trophic levels
•Detritivores, mainly
bacteria and fungi,
recycle essential
chemical elements
Tertiary
consumers
Microorganisms
and other
detritivores
Detritus
Secondary
consumers
Primary consumers
Primary producers
Heat
Key
Chemical cycling
Energy flow
Figure 54.2
Sun
•By decomposing
organic material and
returning elements to
inorganic reservoirs
Detritivores obtain energy from
nonliving organic matter called
Detritus.
Physical and chemical factors limit
primary production in ecosystems
• Primary
production in
an ecosystem
–
Is the
amount of
light energy
converted to
chemical
energy by
autotrophs
during a
given time
period
Earth is bombarded with 1022 joules of solar energy every day.
•This is enough energy to meet human demands for 24years at our 2004
consumption level.
Gross and Net Primary Production
• Total primary production
in an ecosystem
– Is known as that
ecosystem’s gross
primary production
(GPP)
• Not all of this production
– Is stored as organic
material in the growing
plants
Gross and Net Primary Production
• Net primary
production (NPP)
– Is equal to GPP minus
the energy used by the
primary producers for
respiration
• Only NPP
– Is available to
consumers
NPP = GPP – R (respiration)
Different ecosystems vary considerably
in their net primary production
And in their contribution to the total NPP on Earth
Open ocean
Continental shelf
Estuary
Algal beds and reefs
Upwelling zones
5.2
0.3
0.1
0.1
Extreme desert, rock, sand, ice
4.7
Desert and semidesert scrub
Tropical rain forest
3.5
3.3
2.9
2.7
Savanna
Cultivated land
Boreal forest (taiga)
1.6
Tropical seasonal forest
Temperate deciduous forest
1.5
1.3
1.0
0.4
Temperate evergreen forest
Swamp and marsh
Lake and stream
Marine
500
3.0
90
10
0.04
0.9
22
900
7.9
9.1
600
9.6
800
600
700
5.4
3.5
0.6
140
1,600
1,200
1,300
2,000
250
20
30
(a) Percentage
40
50
60
of Earth’s
surface area
0
500 1,000 1,500 2,000 2,500
(b) Average
net primary
production (g/m2/yr)
Terrestrial
Freshwater (on continents)
0.9
0.1
2,200
0.4
0
5.6
1.2
2,500
1.7
Tundra
24.4
1,500
2.4
1.8
Temperate grassland
Woodland and shrubland
Key
125
360
65.0
Figure 54.4a–c
7.1
4.9
3.8
2.3
0.3
(c)
0
5
10
15
20
25
Percentage of Earth’s net
primary production
Open ocean
125
65.0
Continental shelf
360
5.2
Estuary
24.4
5.6
1,500
0.3
Algal beds and reefs
0.1
Upwelling zones
0.1
1.2
2,500
0.9
500
0.1
Extreme desert, rock, sand, ice
4.7
3.0
0.04
Desert and semidesert scrub
3.5
90
0.9
Tropical rain forest
3.3
Savanna
2.9
Cultivated land
2.7
Boreal forest (taiga)
2.4
Temperate grassland
1.8
Woodland and shrubland
1.7
Tundra
1.5
Temperate deciduous forest
1.3
Temperate evergreen forest
1.0
Swamp and marsh
0.4
Lake and stream
0.4
0
10
7.9
9.1
600
9.6
800
600
5.4
700
3.5
0.6
140
1,600
7.1
1,200
4.9
1,300
3.8
2,000
2.3
250
20
30
(a) Percentage
40
50
60
of Earth’s
surface area
0
500
1,000 1,500 2,000 2,500
Average net primary
production (g/m2/yr
Marine
Terrestrial
Freshwater (on continents)
22
900
1.6
Tropical seasonal forest
Key
2,200
Figure 54.4a–c
0.3
0
5
10
15
20
25
Percentage of Earth’s net
primary production
Overall, terrestrial ecosystems
Contribute about two-thirds of global NPP
and marine ecosystems about one-third
North Pole
60N
30N
Equator
30S
60S
South Pole
180
Figure 54.5
120W
60W
0
60E
120E
180
Primary Production in Marine and
Freshwater Ecosystems
• In marine and freshwater ecosystems
– Both light and nutrients are important in
controlling primary production
Limiting Nutrients
• A limiting nutrient is the element that must
be added
– In order for production to increase in a particular
area
• Nitrogen and phosphorous
– Are typically the nutrients that most often limit
marine production
Life Depends on the Sun
Energy from the sun enters an ecosystem when a
plant uses sunlight to make sugar molecules
(carbohydrates) by a process called photosynthesis.
6CO2 + 6H2O + solar energy
C6H12O6
+ 6O2
Carbohydrates are energy-rich molecules which organisms use to
carry out daily activities, such as movement, growth, and repair.
As organisms consume food and use energy from carbohydrates,
the energy travels from one organism to another.
An exception to the Rule: Deep-Ocean Ecosystems
Bacteria use the hydrogen sulfide present in hot water that escapes
from cracks in the ocean floor to produce their own food. These
bacteria are eaten by the other underwater organisms, thus
supporting a thriving ecosystem in darkness.
An organism’s body breaks down its food to obtain the
energy stored in the food by a process called cellular
repiration.
C6H12O6
+ 6O2
6CO2
+
6H2O + energy
When cellular respiration occurs, the carbon-carbon
bonds found in carbohydrates are broken and the
carbon is combined with oxygen to form carbon
dioxide. This process releases the energy, which is
either used by the organism (to move its muscles, digest
food, excrete wastes, think, etc.) or the energy may be
lost as heat.
Nutrient enrichment experiments
Confirmed that nitrogen was limiting
phytoplankton growth in an area of the ocean
Pollution from duck farms concentrated near
Moriches Bay adds both nitrogen and phosphorus to the coastal water
off Long Island. Researchers cultured the phytoplankton Nannochloris
atomus with water collected from several bays.
EXPERIMENT
30
21
19
15
5
4
Coast of Long Island, New York.
The numbers on the map indicate 2
the data collection stations.
Figure 54.6
11
Shinnecock
Bay
Moriches Bay
Atlantic Ocean
Nutrient Enrichment Experiments
RESULTS Phytoplankton abundance parallels the abundance of phosphorus in the water (a).
Inorganic
phosphorus
8
7
6
5
4
3
2
1
0
2
4
5
11 30 15 19 21
Station number
Great
Moriches
South Bay
Bay
30
Phytoplankton
(millions of cells per mL)
Phytoplankton
8
7
6
5
4
3
2
1
0
Inorganic phosphorus
(g atoms/L)
Phytoplankton
(millions of cells/mL)
Nitrogen, however, is immediately taken up by algae, and no free nitrogen is measured in the
coastal waters. The addition of ammonium (NH4) caused heavy phytoplankton growth in bay
water, but the addition of phosphate (PO43) did not induce algal growth (b).
24
Ammonium enriched
Phosphate enriched
Unenriched control
18
12
6
0
Shinnecock
Bay
(a) Phytoplankton biomass and phosphorus concentration
Starting 2
algal
density
4
5 11 30
Station number
15
(b) Phytoplankton response to nutrient enrichment
Since adding phosphorus, which was already in rich supply, had no effect on
Nannochloris growth, whereas adding nitrogen increased algal density dramatically, researchers
concluded that nitrogen was the nutrient limiting phytoplankton growth in this ecosystem.
CONCLUSION
Figure 54.6
19
21
Experiments in another ocean region
Showed that iron limited primary production
Table 54.1
Limiting Nutrients
• The addition of large amounts of nutrients
to lakes
– Has a wide range of ecological impacts
Limiting Nutrient
• In some areas, sewage runoff
– Has caused eutrophication of lakes, which can
lead to the eventual loss of most fish species
from the lakes
Eutrophication Video 1
Eutrophication Video 2
Eutrophication Video 3
Figure 54.7
Primary Production in Terrestrial and
Wetland Ecosystems
• In terrestrial and wetland
ecosystems climatic
factors
–
Such as temperature
and moisture, affect
primary production on a
large geographic scale
• The contrast between
wet and dry climates
–
Can be represented by
a measure called actual
evapotranspiration
Actual evapotranspiration
• Is the amount of water annually transpired by
plants and evaporated from a landscape
– Is related to net primary production
•Figure 54.8
shows…
•Tropical Forest
has the
greatest NPP
•Desert
Shrubland has
the least NPP
Net primary production (g/m2/yr)
3,000
Tropical forest
2,000
Temperate forest
1,000
Mountain coniferous forest
Desert
shrubland
Temperate grassland
Arctic tundra
0
0
500
1,000
1,500
Actual evapotranspiration (mm H2O/yr)
Figure 54.8
Soil Productivity
On a more local scale
EXPERIMENT
Over the summer of 1980, researchers added
phosphorus to some experimental plots in the salt marsh, nitrogen
to other plots, and both phosphorus and nitrogen to others. Some
Adding nitrogen (N)
plots were left unfertilized as controls.
boosts net primary
RESULTS
production.
A soil nutrient is
often the
limiting factor
in primary
production
Live, above-ground biomass
(g dry wt/m2)
300
NP
250
200
N only
150
100
Control
P only
50
0
June
July
August 1980
Experimental plots receiving just
phosphorus (P) do not outproduce
the unfertilized control plots.
These nutrient enrichment experiments
confirmed that nitrogen was the nutrient limiting plant growth in
this salt marsh.
CONCLUSION
Energy transfer between trophic levels is
usually less than 20% efficient
• The secondary production of an ecosystem
– Is the amount of chemical energy in consumers’ food
that is converted to their own new biomass during a
given period of time
•When a caterpillar feeds on a
plant leaf
•Only about one-sixth of the
energy in the leaf is used for
secondary production
Plant material
eaten by caterpillar
200 J
67 J
Feces
100 J
33 J
Figure 54.10
Growth (new biomass)
Cellular
respiration
The production efficiency of an organism
– Is the fraction of energy stored in food that is
not used for respiration
Trophic Efficiency and
Ecological Pyramids
• Trophic efficiency
– Is the percentage of production transferred from one trophic level
to the next
– Usually ranges from 5% to 20%
•This loss of energy with
each transfer in a food
chain
Tertiary
consumers
Secondary
consumers
•Can be represented by a
pyramid of net production
Primary
consumers
Primary
producers
Figure 54.11
10 J
100 J
1,000 J
10,000 J
1,000,000 J of sunlight
Pyramids of Biomass
• One important ecological
consequence of low trophic
efficiencies
– Can be represented in a
biomass pyramid
Trophic level
• Most biomass pyramids
– Show a sharp decrease
at successively higher
trophic levels Dry weight
(g/m2)
Tertiary consumers
1.5
Secondary consumers
11
Primary consumers
37
Primary producers
(a) Most biomass pyramids show a sharp decrease in biomass at
successively higher trophic levels, as illustrated by data from
a bog at Silver Springs, Florida.
809
Exceptions to the Biomass Pyramid
• Certain aquatic ecosystems
– Have inverted biomass pyramids
Trophic level
Dry weight
(g/m2)
Primary consumers (zooplankton)
21
Primary producers (phytoplankton)
4
(b) In some aquatic ecosystems, such as the English Channel,
a small standing crop of primary producers (phytoplankton)
supports a larger standing crop of primary consumers
(zooplankton).
Figire 54.12b
Pyramids of Numbers
• A pyramid of numbers
– Represents the number of individual
organisms in each trophic level
Trophic level
Tertiary consumers
Number of
individual organisms
3
Secondary consumers
354,904
Primary consumers
708,624
Primary producers
Figure 54.13
5,842,424
Humans and Energy Efficiency
• The dynamics of energy flow through
ecosystems
– Have important implications for the human
population
• Eating meat
– Is a relatively inefficient way of tapping
photosynthetic production
Worldwide agriculture could
successfully feed many more people
If humans all fed more efficiently, eating only
plant material
Trophic level
Secondary
consumers
Primary
consumers
Primary
producers
Figure 54.14
The Green World Hypothesis
• According to the green world hypothesis
– Terrestrial herbivores consume relatively little plant biomass
because they are held in check by a variety of factors
• Most terrestrial ecosystems have large standing crops despite the
large numbers of herbivores
Figure 54.15
The green world hypothesis
• proposes several factors that keep
herbivores in check
– Plants have defenses against herbivores
– Nutrients, not energy supply, usually limit
herbivores
– Abiotic factors limit herbivores
– Intraspecific competition can limit herbivore
numbers
– Interspecific interactions check herbivore
densities
Biological and geochemical processes move
nutrients between organic and inorganic
parts of the ecosystem
• Life on Earth
– Depends on the recycling of essential chemical
elements
• Nutrient circuits that cycle matter through an
ecosystem
– Involve both biotic and abiotic components and
are often called biogeochemical cycles
A General Model of Chemical
Cycling
• Gaseous forms of carbon, oxygen, sulfur, and nitrogen
– Occur in the atmosphere and cycle globally
• Less mobile elements, including phosphorous, potassium,
Reservoir a
Reservoir b
and calcium
– Cycle on a more local level
Organic
materials
available
as nutrients
Organic
materials
unavailable
as nutrients
Fossilization
A general model of
nutrient cycling
Includes the main
reservoirs of elements
and the processes that
transfer elements
between reservoirs
Figure 54.16
Living
organisms,
detritus
Assimilation,
photosynthesis
Coal, oil,
peat
Respiration,
decomposition,
excretion
Burning
of fossil fuels
Reservoir c
Reservoir d
Inorganic
materials
available
as nutrients
Inorganic
materials
unavailable
as nutrients
Atmosphere,
soil, water
Weathering,
erosion
Formation of
sedimentary rock
Minerals
in rocks
Biogeochemical Cycles
• All elements
– Cycle between organic and inorganic
reservoirs
Biogeochemical Cycles
THE CARBON CYCLE
THE WATER CYCLE
• The water cycle and the carbon cycle
CO2 in atmosphere
Transport
over land
Photosynthesis
Solar energy
Cellular
respiration
Net movement of
water vapor by wind
Precipitation
over ocean
Evaporation
from ocean
Precipitation
over land
Burning of
fossil fuels
and wood
Evapotranspiration
from land
Percolation
through
soil
Runoff and
groundwater
Figure 54.17
Carbon compounds
in water
Higher-level
Primary consumers
consumers
Detritus
Decomposition
Water Cycle (Read Page 1196)
The Carbon Cycle (Read Page 1196)
The Nitrogen Cycle (Read Page 1197)
The Phosphorus Cycle (Read Page 1197)
Decomposition and Nutrient
Cycling Rates
• Decomposers (detritivores) play a key role
– In the general pattern of chemical cycling
Consumers
•The rates at which
nutrients cycle in
different ecosystems
•Are extremely
variable, mostly as
a result of
differences in rates
of decomposition
Producers
Decomposers
Nutrients
available
to producers
Abiotic
reservoir
Figure 54.18
Geologic
processes
Vegetation and Nutrient Cycling: The Hubbard
Brook Experimental Forest
• Nutrient cycling
– Is strongly regulated by
vegetation
•
The research team
constructed a dam on the site
– To monitor water and
mineral loss
• Long-term ecological research
projects
– Monitor ecosystem dynamics
over relatively long periods of
time
• The Hubbard Brook
Experimental Forest
– Has been used to study nutrient
cycling in a forest ecosystem
since 1963
(a) Concrete
dams and weirs built across
streams at
the bottom of watersheds enabled
researchers to monitor the outflow of
water and nutrients from the ecosystem.
Experiment: Human Disturbances and how
they effect nutrient cycles
• In one experiment, the trees in one valley
were cut down
– And the valley was sprayed with herbicides
Figure 54.19b
(b) One watershed was clear cut to study the effects of the loss
of vegetation on drainage and nutrient cycling.
Experiment: Human Disturbances and how
they effect nutrient cycles
•
Net losses of water and minerals were studied
–
These results showed how human activity
–
Can affect ecosystems
Nitrate concentration in runoff
(mg/L)
•
And found to be greater than in an undisturbed area
80.0
60.0
40.0
20.0
4.0
3.0
2.0
1.0
0
Deforested
Completion of
tree cutting
1965
(c)
Figure 54.19c
Control
1966
1967
1968
The concentration of nitrate in runoff from the deforested
watershed was 60 times greater than in a control (unlogged)
watershed.
The human population is disrupting
chemical cycles throughout the
biosphere
• As the human
population has
grown in size
– Our activities
have disrupted
the trophic
structure, energy
flow, and
chemical cycling
of ecosystems in
most parts of the
world
Nutrient Enrichment
• In addition to transporting nutrients from
one location to another
– Humans have added entirely new materials,
some of them toxins, to ecosystems
Nutrient Enrichment
• In addition to transporting nutrients from one
location to another
– Humans have added entirely new materials, some of
them toxins, to ecosystems
• Agriculture
constantly removes
nutrients from
ecosystems
– That would
ordinarily be cycled
back into the soil
Figure 54.20
Nutrient Enrichment
• Nitrogen is the main nutrient lost through
agriculture
– Thus, agriculture has a great impact on the
nitrogen cycle
• Industrially produced fertilizer is typically
used to replace lost nitrogen
– But the effects on an ecosystem can be
harmful
Contamination of Aquatic
Ecosystems
• The critical load
for a nutrient
• When excess nutrients
are added to an
– Is the amount
ecosystem, the critical
of that nutrient
that can be
load is exceeded
absorbed by
plants in an
ecosystem
without
damaging it
– And the remaining
nutrients can
contaminate
groundwater and
freshwater and
marine ecosystems
• Sewage runoff
contaminates
freshwater (and
saltwater)
ecosystems
– Causing cultural
eutrophication,
excessive algal
growth, which can
cause significant
harm to these
ecosystems
This is happening in your
backyard!!!!
Click Picture to learn about
the NY/NJ Harbor Estuary
studies and action plans
Acid Precipitation
• Combustion of fossil fuels
– Is the main cause of acid precipitation
• North American and
European ecosystems
downwind from
industrial regions
– Have been damaged
by rain and snow
containing nitric and
sulfuric acid
Figure 54.21
4.6
4.3
4.6
4.3
4.6
4.1
4.3
4.6
Europe
North America
Acid Precipitation
• By the year 2000
– The entire contiguous United States was affected
by acid precipitation
Figure 54.22
Field pH
5.3
5.2–5.3
5.1–5.2
5.0–5.1
4.9–5.0
4.8–4.9
4.7–4.8
4.6–4.7
4.5–4.6
4.4–4.5
4.3–4.4
4.3
Toxins in the Environment
• Humans release an immense variety of
toxic chemicals
– Including thousands of synthetics previously
unknown to nature
• One of the reasons such toxins are so
harmful
– Is that they become more concentrated in
successive trophic levels of a food web
Biological Magnification
Polychlorinated Biphenyl (PCB)
PCBs belong to a broad family of man-made organic
chemicals known as chlorinated hydrocarbons. PCBs were
domestically manufactured from 1929 until their
manufacture was banned in 1979. They have a range of
toxicity and vary in consistency from thin, light-colored
liquids to yellow or black waxy solids. Due to their nonflammability, chemical stability, high boiling point, and
electrical insulating properties, PCBs were used in
hundreds of industrial and commercial applications
including electrical, heat transfer, and hydraulic equipment;
as plasticizers in paints, plastics, and rubber products; in
pigments, dyes, and carbonless copy paper; and many
other industrial applications.
Herring
gull eggs
124 ppm
Concentration of PCBs
– Toxins
concentrate at
higher trophic
levels because
at these levels
biomass tends
to be lower
Lake trout
4.83 ppm
Smelt
1.04 ppm
Zooplankton
0.123 ppm
Phytoplankton
0.025 ppm
Atmospheric Carbon Dioxide
• One pressing problem caused by human
activities
– The concentration of
atmospheric CO2 has
been steadily increasing
390
1.05
380
0.90
0.75
370
Temperature
0.60
360
0.45
350
0.30
340
CO2
330
0
320
0.15
310
 0.30
300
1960 1965 1970 1975
Figure 54.24
0.15
Temperature variation (C)
• Due to the increased
burning of fossil fuels
and other human
activities
CO2 concentration (ppm)
– Is the rising level of atmospheric carbon
dioxide
 0.45
1980 1985 1990 1995 2000 2005
Year
National Geographic Video on
Global Warming
Click on picture for 3min
video
The Greenhouse Effect and
Global Warming
• The greenhouse effect is caused by many
gases, but atmospheric CO2 plays a major
role
– But is necessary to keep the surface of the
Earth at a habitable temperature
• Increased levels of atmospheric CO2 are
magnifying the greenhouse effect
– Which could cause global warming and
significant climatic change
Depletion of Atmospheric
Ozone
• Life on Earth is protected from the
damaging effects of UV radiation
– By a protective layer or ozone molecules (O3)
present in the atmosphere
• Satellite studies of
the atmosphere
– Suggest that the
ozone layer has
been gradually
thinning since 1975
Figure 54.26
Ozone layer thickness (Dobson units)
350
300
250
200
150
100
50
0
1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
Year (Average for the month of October)
The destruction of atmospheric
ozone
Probably results from chlorine-releasing
pollutants produced by human activity
1 Chlorine from CFCs interacts with ozone (O3),
forming chlorine monoxide (ClO) and
oxygen (O2).
Chlorine atoms
O2
Chlorine
O3
ClO
O2
Figure 54.27
3 Sunlight causes
Cl2O2 to break
down into O2
and free
chlorine atoms.
The chlorine
atoms can begin
the cycle again.
ClO
Cl2O2
Sunlight
2 Two ClO molecules
react, forming
chlorine peroxide (Cl2O2).
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
What Is the Ecosystem Approach to Ecology?
1.Describe the relationship between autotrophs and heterotrophs in an ecosystem.
2.Explain how decomposition connects all trophic levels in an ecosystem.
3.Explain how the first and second laws of thermodynamics apply to ecosystems.
Primary Production in Ecosystems
4.Explain why the amount of energy used in photosynthesis is so much less than the
amount of solar energy that reaches Earth.
5.Define and compare gross primary production and net primary production. 6.Define
and compare biomass and standing crop.
7.Compare primary productivity in marine, freshwater, and terrestrial ecosystems.
Secondary Production in Ecosystems
8.Explain why energy is said to flow rather than cycle within ecosystems. Use the
example of insect caterpillars to illustrate energy flow.
9.Define, compare, and illustrate the concepts of production efficiency and trophic
efficiency.
10.Distinguish between energy pyramids and biomass pyramids. Explain why both
relationships are in the form of pyramids. Explain the special circumstances of
inverted biomass pyramids.
How Specific Immunity Arises
11.Explain why food pyramids usually have only four or five trophic levels 12.Define
the pyramid of numbers.
13.Explain why worldwide agriculture could feed more people if all humans consumed
only plant material.
14.Explain the green-world hypothesis. Describe six factors that keep herbivores in
check.
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The Cycling of Chemical Elements in Ecosystems
15.Describe the four nutrient reservoirs and the processes that transfer the
elements between reservoirs.
16.Explain why it is difficult to trace elements through biogeochemical
cycles.
17.Describe the hydrologic water cycle.
18.Describe the nitrogen cycle and explain the importance of nitrogen
fixation to all living organisms.
19.Describe the phosphorus cycle and explain how phosphorus is recycled
locally in most ecosystems.
20.Explain how decomposition affects the rate of nutrient cycling in
ecosystems.
21.Describe the experiments at Hubbard Brook that revealed the key role
that plants play in regulating nutrient cycles.
Human Impact on the Chemical Dynamics of the Biosphere
22.Describe how agricultural practices can interfere with nitrogen cycling.
23.Explain how "cultural eutrophication" can alter freshwater ecosystems.
24.Describe the causes and consequences of acid precipitation.
25.Explain why toxic compounds usually have the greatest effect on toplevel carnivores.
26.Describe how increased atmospheric concentrations of carbon dioxide
could affect Earth.
27.Describe how human interference might alter the biosphere.