Transcript video slide

Chapter 54
Ecosystems
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Do now 9/21
• Primary vs secondary succession
• Which is better for the ecosystem? Collecting
grass clippings or allowing them to compost
• To calculate net productivity what must be
subtracted from gross productivity?
• Where is most of oxygen produced?
• Define biological magnification
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Overview: Ecosystems, Energy, and Matter
• An ecosystem consists of all the organisms living
in a community, as well as the abiotic factors with
which they interact
• Ecosystems range from a microcosm, such as an
aquarium, to a large area such as a lake or forest
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Regardless of an ecosystem’s size, its dynamics
involve two main processes: energy flow and
chemical cycling
• Energy flows through ecosystems while matter
cycles within them
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Concept 54.1: Ecosystem ecology emphasizes
energy flow and chemical cycling
• Ecologists view ecosystems as transformers of
energy and processors of matter
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Ecosystems and Physical Laws
• Laws of physics and chemistry apply to
ecosystems, particularly energy flow
• Energy is conserved but degraded to heat during
ecosystem processes
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Trophic Relationships
• (1)Energy and nutrients pass from primary
producers (autotrophs) to primary consumers
(herbivores) and then to secondary consumers
(carnivores)
• Energy flows through an ecosystem, entering as
light and exiting as heat
• Nutrients cycle within an ecosystem
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LE 54-2
Tertiary
consumers
Microorganisms
and other
detritivores
Detritus
Secondary
consumers
Primary consumers
Primary producers
Heat
Key
Chemical cycling
Energy flow
Sun
Decomposition
• Decomposition connects all trophic levels
• Detritivores, mainly bacteria and fungi, recycle
essential chemical elements by decomposing
organic material and returning elements to
inorganic reservoirs
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 54.2: Physical and chemical factors limit
primary production in ecosystems
• (2)Primary production in an ecosystem is the
amount of light energy converted to chemical
energy by autotrophs during a given time period
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Ecosystem Energy Budgets
• The extent of photosynthetic production sets the
spending limit for an ecosystem’s energy budget
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The Global Energy Budget
• (1)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
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Gross and Net Primary Production
• (2a)Total primary production is known as the
ecosystem’s gross primary production (GPP)
• (2b)Net primary production (NPP) is GPP minus
energy used by primary producers for respiration
• Only NPP is available to consumers
• Ecosystems vary greatly in net primary production
and contribution to the total NPP on Earth
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LE 54-4
Open ocean
Continental shelf
Estuary
Algal beds and reefs
Upwelling zones
Extreme desert, rock, sand, ice
Desert and semidesert scrub
Tropical rain forest
Savanna
Cultivated land
Boreal forest (taiga)
Temperate grassland
Woodland and shrubland
Tundra
Tropical seasonal forest
Temperate deciduous forest
Temperate evergreen forest
Swamp and marsh
Lake and stream
5.2
0.3
0.1
0.1
4.7
3.5
3.3
2.9
2.7
2.4
1.8
1.7
1.6
1.5
1.3
1.0
0.4
0.4
0
Key
Marine
Terrestrial
125
360
65.0
10 20 30 40 50 60
Percentage of Earth’s
surface area
Freshwater (on continents)
24.4
5.6
1,500
2,500
1.2
0.9
0.1
0.04
0.9
500
3.0
90
22
2,200
7.9
9.1
9.6
5.4
3.5
900
600
800
600
700
140
0.6
7.1
4.9
3.8
2.3
0.3
1,600
1,200
1,300
2,000
250
0
500 1,000 1,500 2,000 2,500
Average net primary
production (g/m2/yr)
0
10 15 20 25
5
Percentage of Earth’s net
primary production
• Overall, terrestrial ecosystems contribute about
two-thirds of global NPP
• Marine ecosystems contribute about one-third
• (3)Oceans produce the most overall simply
because of size (net is low)
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LE 54-5
North Pole
60°N
30°N
Equator
30°S
60°S
South Pole
180°
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 control primary production
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Light Limitation
• (4a)Depth of light penetration affects primary
production in the photic zone of an ocean or lake
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Nutrient Limitation
• More than light, nutrients limit primary production
in geographic regions of the ocean and in lakes
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• 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 production
• Nutrient enrichment experiments confirmed that
nitrogen was limiting phytoplankton growth in an
area of the ocean
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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 scale
• Actual evapotranspiration can represent the
contrast between wet and dry climates
• Actual evapotranspiration is the water annually
transpired by plants and evaporated from a
landscape
• It is related to net primary production
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• On a more local scale, a soil nutrient is often the
limiting factor in primary production
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Live, above-ground biomass
(g dry wt/m2)
LE 54-9
300
N+P
250
200
150
N only
100
Control
P only
50
0
0
June
July
August 1980
Concept 54.3: Energy transfer between trophic
levels is usually less than 20% efficient
• (1)Secondary production of an ecosystem is the
amount of chemical energy in food converted to
new biomass during a given period of time
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Production Efficiency
• When a caterpillar feeds on a leaf, only about onesixth of the leaf’s energy is used for secondary
production
• An organism’s production efficiency is the fraction
of energy stored in food that is not used for
respiration
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LE 54-10
Plant material
eaten by caterpillar
200 J
67 J
Feces
100 J
33 J
Growth (new biomass)
Cellular
respiration
Trophic Efficiency and Ecological Pyramids
• (2)Trophic efficiency is the percentage of
production transferred from one trophic level to the
next
• It usually ranges from 5% to 20%
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Pyramids of Production
• A pyramid of net production represents the loss of
energy with each transfer in a food chain
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LE 54-11
Tertiary
consumers
Secondary
consumers
Primary
consumers
Primary
producers
10 J
100 J
1,000 J
10,000 J
1,000,000 J of sunlight
Pyramids of Biomass
• In a biomass pyramid, each tier represents the dry
weight of all organisms in one trophic level
• Most biomass pyramids show a sharp decrease at
successively higher trophic levels
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LE 54-12a
Trophic level
Tertiary consumers
Dry weight
(g/m2)
1.5
Secondary consumers
11
Primary consumers
37
Primary producers
809
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.
• Dynamics of energy flow in ecosystems have
important implications for the human population
• (4)Eating meat is a relatively inefficient way of
tapping photosynthetic production
• Worldwide agriculture could feed many more
people if humans ate only plant material
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LE 54-14
Trophic level
Secondary
consumers
Primary
consumers
Primary
producers
The Green World Hypothesis
• (5)Most terrestrial ecosystems have large standing
crops despite the large numbers of herbivores
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The green world hypothesis proposes several
factors that keep herbivores in check:
– Plant defenses
– Limited availability of essential nutrients
– Abiotic factors
– Intraspecific competition
– Interspecific interactions
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Concept 54.4: Biological and geochemical processes move
nutrients between organic and inorganic parts of the ecosystem
• Life depends on recycling chemical elements
• Nutrient circuits in ecosystems involve biotic and
abiotic components and are often called
biogeochemical cycles
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A General Model of Chemical Cycling
• (1)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
• A model of nutrient cycling includes main
reservoirs of elements and processes that transfer
elements between reservoirs
• All elements cycle between organic and inorganic
reservoirs
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LE 54-16
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:
1. Each chemical’s biological importance
2. Forms in which each chemical is available or
used by organisms
3. Major reservoirs for each chemical
4. Key processes driving movement of each
chemical through its cycle
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LE 54-17a
Transport
over land
Solar energy
Net movement of
water vapor by wind
Precipitation
over ocean
Evaporation
from ocean
Precipitation
over land
Evapotranspiration
from land
Percolation
through
soil
Runoff and
groundwater
LE 54-17b
CO2 in atmosphere
Photosynthesis
Cellular
respiration
Burning of
fossil fuels
and wood
Higher-level
Primary consumers
consumers
Carbon compounds
in water
Detritus
Decomposition
LE 54-17c
N2 in atmosphere
Assimilation
Nitrogen-fixing
bacteria in root
nodules of legumes Decomposers
Ammonification
NH3
Nitrogen-fixing
soil bacteria
NO3–
Nitrifying
bacteria
Nitrification
NO2–
NH4+
Nitrifying
bacteria
Denitrifying
bacteria
LE 54-17d
Rain
Geologic
uplift
Weathering
of rocks
Plants
Runoff
Consumption
Sedimentation
Soil
Leaching
Plant uptake
of PO43–
Decomposition
Decomposition and Nutrient Cycling Rates
• Decomposers (detritivores) play a key role in the
general pattern of chemical cycling
• (3)Rates at which nutrients cycle in different
ecosystems vary greatly, mostly as a result of
differing rates of decomposition
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LE 54-18
Consumers
Producers
Decomposers
Nutrients
available
to producers
Abiotic
reservoir
Geologic
processes
Concept 54.5: The human population is disrupting
chemical cycles throughout the biosphere
• As the human population has grown, our activities
have disrupted the trophic structure, energy flow,
and chemical cycling of many ecosystems
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Nutrient Enrichment
• (1)In addition to transporting nutrients from one
location to another, humans have added new
materials, some of them toxins, to ecosystems
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Agriculture and Nitrogen Cycling
• Agriculture removes nutrients from ecosystems
that would ordinarily be cycled back into the soil
• (2)Nitrogen is the main nutrient lost through
agriculture; thus, agriculture greatly impacts the
nitrogen cycle
• Industrially produced fertilizer is typically used to
replace lost nitrogen, but effects on an ecosystem
can be harmful
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Contamination of Aquatic Ecosystems
• Critical load for a nutrient is the amount that plants
can absorb without damaging the ecosystem
• When excess nutrients are added to an
ecosystem, the critical load is exceeded
• Remaining nutrients can contaminate groundwater
and freshwater and marine ecosystems
• (3)Sewage runoff causes cultural eutrophication,
excessive algal growth that can greatly harm
freshwater ecosystems
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Acid Precipitation
• (4)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
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LE 54-21
4.6
4.3
4.6
4.3
4.6
4.1
4.3
4.6
Europe
North America
• By the year 2000, acid precipitation affected the
entire contiguous United States
• Environmental regulations and new technologies
have allowed many developed countries to reduce
sulfur dioxide emissions
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LE 54-22
5.0
5.3
5.4
5.2
5.5
5.2
5.5
5.6
5.4
5.2
5.3
5.3
5.5
6.0
5.9 5.5
5.3
5.2
5.3
5.4
5.4
5.3 5.0
5.05.1 4.9 5.4
5.1
6.3
5.7
5.6
4.9
5.4
5.3
5.0
5.2
5.4
5.1
5.5
5.2 4.8
5.3
4.5 4.6 4.7
5.4
5.2 5.15.0
4.8
4.7
5.2
4.5 4.6
4.8
4.3 4.5 4.5
5.2 4.9
5.5
4.5
5.6
4.5 4.5 4.6
4.9 4.7
4.7
4.3 4.4
4.5
4.6
5.1 4.7
4.6
4.5
4.7
5.4
4.5
4.1 4.4
5.3
5.3
4.4 4.4
4.6 4.8
4.3
4.6
4.6
4.6 4.5
4.4
4.5
4.7
4.5
4.5 4.5
4.7
4.7
4.6
4.8
4.6
5.4
4.6
4.8 4.6
4.5
5.0
4.5 4.5
4.7
4.8
4.9
4.5
4.6
4.5
Field pH
4.7
4.5
5.0
4.7
4.8 4.7 4.7
5.0
4.8 5.1 4.7
5.3
4.7
4.7
5.2–5.3
5.0
5.4
4.7 4.6
4.7
4.9
5.1–5.2
4.8
4.7
4.8
5.3
4.8
4.9
5.0–5.1
4.8
4.7
4.9–5.0
4.9
4.8
4.7
5.6
6.1
5.2
5.3
5.3
5.2
5.7
5.0 5.0
5.1
5.1
5.7
5.1
5.0
5.0
4.8
4.7
4.7
4.7
4.9
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 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
• (6)In biological magnification, toxins concentrate
at higher trophic levels, where biomass is lower
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LE 54-23
Concentration of PCBs
Herring
gull eggs
124 ppm
Lake trout
4.83 ppm
Smelt
1.04 ppm
Zooplankton
0.123 ppm
Phytoplankton
0.025 ppm
Atmospheric Carbon Dioxide
• (7)One pressing problem caused by human
activities is the rising level of atmospheric carbon
dioxide
• Greenhouse effect
• Due to the burning of fossil fuels and other human
activities, the concentration of atmospheric CO2
has been steadily increasing
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The Greenhouse Effect and Global Warming
• The greenhouse effect caused by atmospheric
CO2 keeps Earth’s surface at a habitable
temperature
• Increased levels of atmospheric CO2 are
magnifying the greenhouse effect, which could
cause global warming and climatic change
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Depletion of Atmospheric Ozone
• Life on Earth is protected from damaging effects of
UV radiation by a protective layer or ozone
molecules in the atmosphere
• Satellite studies suggest that the ozone layer has
been gradually thinning since 1975
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LE 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)
• Destruction of atmospheric ozone probably results
from chlorine-releasing pollutants produced by
human activity
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LE 54-28
October 1979
October 2000