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Chapter 55
Ecosystems
PowerPoint® Lecture Presentations for
Biology
Eighth Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Overview: Observing Ecosystems
• An ecosystem consists of all the organisms living
in a community, as well as the abiotic factors with
which they interact
• Ecosystems can range in size, but regardless of
an ecosystem’s size, its dynamics involve two
main processes: energy flow and chemical cycling
• Energy flows through ecosystems (IN ONE
DIRECTION) while matter cycles within them
(IN ALL DIRECTIONS)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Concept 55.1: Physical laws govern energy flow and
chemical cycling in ecosystems.
• All living systems require a constant input of free
energy, and organisms use free energy to
maintain organization, grow and reproduce.
• Ecologists study the transformations of energy
and matter within their system, and use these
studies to suggest the health of an
ecosystem.
• Laws of physics and chemistry apply to
ecosystems, particularly energy flow.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Conservation of Mass
• The law of conservation of mass states that
matter cannot be created or destroyed
• Chemical elements must therefore be
continually recycled within ecosystems
• Ecosystems are open systems, absorbing
energy and mass and releasing heat and waste
products
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 55-4
Tertiary consumers
Microorganisms
and other
detritivores
Detritus
Secondary
consumers
Primary consumers
Primary producers
Heat
Key
Chemical cycling
Energy flow
Sun
Fig. 55-3
Concept 55.2: Energy and other limiting factors
control 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.
– The extent of photosynthetic production sets the
spending limit for an ecosystem’s energy budget
– The amount of solar radiation reaching the Earth’s
surface limits photosynthetic output of ecosystems.
– Only a small fraction of solar energy actually strikes
photosynthetic organisms, and even less is of a usable
wavelength.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Gross and Net Primary Production
• Total primary production is known as the
ecosystem’s gross primary production (GPP)
• Net primary production (NPP) is GPP minus
energy used by primary producers for respiration
• Only NPP is available to consumers
• Ecosystems vary greatly in NPP and contribution
to the total NPP on Earth
NPP = GPP - R
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 55-6
Net primary production (kg carbon/m2·yr)
·
0
1
2
3
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 a lake or ocean
– More than light, nutrients limit primary production in
geographic regions of the ocean and in lakes
– A limiting nutrient is the element that must be added
for production to increase in an area
– Nitrogen and phosphorous are typically the
nutrients that most often limit marine and
freshwater production
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 55-7
EXPERIMENT
B
C
D
E
F
G
Shinnecock
Bay
Moriches Bay
Atlantic Ocean
A
Phytoplankton density
(millions of cells per mL)
RESULTS
30
Ammonium
enriched
24
Phosphate
enriched
18
Unenriched
control
12
6
0
A
B
C
D
E
Collection site
F
G
Primary Production in Terrestrial Ecosystems
• In terrestrial ecosystems, temperature and
moisture affect primary production on a large
scale:
•
Tropical rainforests, with their warm, wet
conditions that promote plant growth, are the most
productive of all terrestrial ecosystems.
•
Low productivity terrestrial ecosystems are
generally dry (deserts or the arctic tundra).
•
Temperate forest and grassland ecosystems have
moderate climates and intermediate productivity.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Concept 55.3: Energy transfer between trophic
levels is typically only 10% efficient.
• Secondary production of an ecosystem is the
amount of chemical energy in food converted
to new biomass during a given period of time.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Trophic Efficiency and Ecological Pyramids
• Trophic efficiency is the percentage of
production transferred from one trophic level to
the next
• It usually ranges from 5% to 20%
• Trophic efficiency is multiplied over the length
of a food chain
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 55-10
Tertiary
consumers
Secondary
consumers
10 J
100 J
Primary
consumers
1,000 J
Primary
producers
10,000 J
1,000,000 J of sunlight
PYRAMID OF NUMBERS
Fig. 55-11
Trophic level
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)
Meadow Habitat: Occupies 50.2 km2. Primary Producer
Biomass – distributed uniformly and totals 3200 kg/km2.
What would be the most likely immediate result of a
disturbance that reduced the primary producer’s biomass
by 50% AND removed all rabbits and insects? Long term
result?
How much carbon (in g/m2) is released into the atmosphere as a
result of the metabolic activity of herbivores?
What % of the biomass in the forest community is tied up
in the shrub layer?
Concept 55.4: Biological and geochemical processes cycle
nutrients between organic and inorganic parts of an ecosystem.
• Life depends on recycling chemical elements
• Nutrient circuits in ecosystems involve biotic
and abiotic components and are often called
biogeochemical cycles
– Gaseous carbon, oxygen, sulfur, and nitrogen
occur in the atmosphere and cycle globally
– Less mobile elements such as phosphorus,
potassium, and calcium cycle on a more local
level
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 55-13
Reservoir A
Reservoir B
Organic
materials
available
as nutrients
Organic
materials
unavailable
as nutrients
Fossilization
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
• In studying cycling of water, carbon, nitrogen,
and phosphorus, ecologists focus on four
factors:
– Each 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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 55-14a
Transport
over land
Solar energy
Net movement of
water vapor by wind
Precipitation Evaporation
over ocean
from ocean
Precipitation
over land
Evapotranspiration
from land
Percolation
through
soil
Runoff and
groundwater
Fig. 55-14b
CO2 in atmosphere
Photosynthesis
Photosynthesis
Cellular
respiration
Burning of
fossil fuels Phytoand wood plankton
Higher-level
consumers
Primary
consumers
Carbon compounds
in water
Detritus
Decomposition
Fig. 55-14c
N2 in atmosphere
Assimilation
NO3–
Nitrogen-fixing
bacteria
Decomposers
Ammonification
NH3
Nitrogen-fixing
soil bacteria
Nitrification
NH4+
NO2–
Nitrifying
bacteria
Denitrifying
bacteria
Nitrifying
bacteria
Fig. 55-14d
Precipitation
Geologic
uplift
Weathering
of rocks
Runoff
Consumption
Decomposition
Plant
uptake
of PO43–
Plankton Dissolved PO43–
Uptake
Sedimentation
Soil
Leaching
Decomposition and Nutrient Cycling Rates
• Decomposers (detritivores) play a key role in
the general pattern of chemical cycling
• Rates at which nutrients cycle in different
ecosystems vary greatly, mostly as a result of
differing rates of decomposition
• The rate of decomposition is controlled by
temperature, moisture, and nutrient availability
• Rapid decomposition results in relatively low
levels of nutrients in the soil
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Ecosystem type
EXPERIMENT
Arctic
Subarctic
Boreal
Temperate
Grassland
A
Mountain
G
M
T
P
E,F
N
U
D
B,C
H,I
S
O
L
J
K
R
Q
RESULTS
80
Percent of mass lost
Fig. 55-15
70
60
K
J
50
40
D
30
20
C
A
10
0
–15
–10
BE
F
G
P
N
M
L
I
U
R
O Q
T
S
H
–5
0
5
10
Mean annual temperature (ºC)
15
Fig. 55-16
(a) Concrete dam
and weir
Nitrate concentration in runoff
(mg/L)
(b) Clear-cut watershed
80
60
40
20
4
3
2
1
0
Deforested
Completion of
tree cutting
1965
Control
1966
(c) Nitrogen in runoff from watersheds
1967
1968
Concept 55.5: Human activities now dominate most
chemical cycles on Earth.
• As the human population has grown, our
activities have disrupted the trophic structure,
energy flow, and chemical cycling of many
ecosystems
• In addition to transporting nutrients from one
location to another, humans have added new
materials, some of them toxins, to ecosystems
• Disruptions that deplete nutrients in one area
and increase them in other areas can be
detrimental to ecosystem dynamics.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 55-17: Agriculture & Nitrogen Cycling
Fig. 55-18 – Contamination of Aquatic Ecosystems
Winter
Summer
Acid Precipitation
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Toxins in the Environment
• Humans release many toxic chemicals,
including synthetics previously unknown to
nature
• In some cases, harmful substances persist for
long periods in an ecosystem
• One reason toxins are harmful is that they
become more concentrated in successive
trophic levels
• Biological magnification concentrates toxins
at higher trophic levels, where biomass is lower
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 55-20
Herring
gull eggs
124 ppm
Lake trout
4.83 ppm
Smelt
1.04 ppm
Zooplankton
0.123 ppm
Phytoplankton
0.025 ppm
Greenhouse Gases and Global Warming
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 55-23
Ozone layer thickness (Dobsons)
350
300
250
200
100
0
1955 ’60
’65
’70
’75
’80 ’85
Year
’90
’95 2000 ’05
Fig. 55-24
Chlorine atom
O2
Chlorine O3
ClO
O2
ClO
Cl2O2
Sunlight
Fig. 55-25
(a) September 1979
(b) September 2006