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10/25/2013
1
Ecosystems
Chapter 42
42.1 Ecosystems
Ecosystem
• An array of organisms and their physical and
chemical environment
Inputs and outputs of energy and nutrients
• Energy flows one way, into and out of an
ecosystem
• Materials are cycled among resident species
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Energy Sources
Sunlight supplies energy to most ecosystems
Primary producers
• Convert energy of sunlight into chemical energy
(autotrophs)
• Take up nutrients that all living organisms require
Energy Sources
Consumers - get energy from food
• Herbivores – feed on producers
• Carnivores – eat herbivores and other consumers
• Flesh of animals
• Omnivores – eat animals and plants
• Decomposers – feed on organic waste and
remains. It is broken down into inorganic building
blocks
• Detritivores- eat small particles of organic matter
(crabs and earthworms)
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Fig. 42.2, p.734
Nutrient
cycling
Energy
input,
from
sun
Producers and then
consumers concentrate
nutrients in their tissues.
Some nutrients released by
decomposition get cycled
back to producers.
Energy inputs from the
environment flow through
producers, then consumers.
All energy that entered this
ecosystem eventually flows
out of it, mainly as heat.
Energy output (mainly metabolic heat)
Consumers
Detritivores, Decomposers
Primary Producers
Plants, Other Photoautotrophs
Energy efficiency is not 100%. All energy eventually lost
– most as heat from metabolism.
Trophic Levels
Organisms in an ecosystem are classified by
trophic levels (feeding levels)
• Organisms at the same trophic level are the same
number of steps away from the energy input
• Approximately 10% of the energy is transferred
from one energy level to the next.
A food chain shows who eats whom
• Path of energy and nutrient flow among
organisms
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Fig. 42.3b, p.735
big bluestem grass
Fourth Trophic Level
carnivore (third-level consumer)
coyote
Third Trophic Level
carnivore (second-level consumer)
Second Trophic Level
herbivore (primary consumer)
First Trophic Level
autotroph (primary producer)
sparrow
grasshopper
Food chains
or trophic
levels
Key Concepts:
ORGANIZATION OF ECOSYSTEMS
An ecosystem consists of a community and its
physical environment
A one-way flow of energy and a cycling of raw
materials among its interacting participants
maintain it
It is an open system, with inputs and outputs of
energy and nutrients
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42.2 Food Webs
Food chains interconnect as food webs
Most ecosystems support only four or five
trophic levels away from original energy source
• Efficiency of energy transfer is low
• Energy lost limits the length of the chain
42.2 Food Webs
Shorter in habitats that change widely over time
Longer in stable habitats
• Ocean depths
If there are a large number of connections then
there will be more herbivores
If there are fewer number of connections then
there will be more carnivores
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Types of Food Webs
Type of energy varies with season.
Most of the energy stored in producers moves
through the detrital food web.
42.3 Biological Magnification
A chemical substance is passed from organisms
at each trophic level to those above, becoming
increasingly concentrated in body tissues
• Pesticides (herbicides, insecticides, fungicides)
• Industrial pollutants
• Toxic metals (lead, mercury)
DDT – in raptors
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Key Concepts:
FOOD WEBS
Food chains are linear sequences of feeding
relationships, from producers through
consumers, decomposers, and detritivores
The chains cross-connect as food webs
Most energy that enters a food web returns to
the environment, mainly as metabolic heat
Key Concepts:
FOOD WEBS (cont.)
Most nutrients are cycled; some reenter the
environment
Biological magnification is the increasing
concentration of a substance in tissues of
organisms as it moves up food chains
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42.4 Energy Flow Through Ecosystems
Primary productivity of a system
• The rate at which producers capture and store
energy in their tissues
• Depends on number of producers and balance
between energy stored and energy used
• Varies with climate, seasonal changes, nutrient
availability, and other factors
42.4 Energy Flow Through Ecosystems
Gross primary production – all energy trapped
by the producers
Net primary production – the fraction of trapped
energy that producers funnel into growth and
reproduction.
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42.4 Energy Flow Through Ecosystems
Net ecosystem production – gross primary
production minus the energy that producers,
detritivores, and decomposers require.
• Subtracted because it is NOT availabel to next
trophic level
Ecological Pyramids
Energy pyramids and biomass pyramids
• Depict how energy and organic compounds are
distributed among organisms of an ecosystem
Energy pyramids are largest at their base
• Usually primary producers
• Always largest at the base
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Ecological Pyramids
Biomass pyramids
• Dry weight of all organisms at each trophic level
in a specific ecosystem
• Common
• Primary producers – most biomass
• Carnivores – least biomass
• may be upside down
• Consumer biomass can exceed that of producers
• Producers are eaten almost as fast as they grow
and reproduce and cannot accumulate
Fig. 42.10a, p.740
1.5 top carnivores
(gar and bass)
carnivores (smaller
fishes, invertebrates)
herbivores
(plant-eating fishes,
invertebrates, turtles)
producers (mainly
algae and eel grass)
detritivores (crayfish) and
decomposers (bacteria)
5
809
37
11
Small biomass (g/m squared) on
aquatic system of Florida. Producers
bulk.
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Ecological Efficiency
Only about 10% of energy transferred from
trophic level to trophic level
Influences amount of energy transferred
• Proportion of digestible biomass
• Amount of energy lost by the animals
• Warm-blooded loose faster then cold blooded
• Active animals loose mere than less active
animals
Higher efficiency of transfer allows for longer
food chains
Key Concepts:
PRIMARY PRODUCTIVITY
Primary productivity is the rate at which an
ecosystem’s producers capture and store
energy in their tissues during a given interval
The number of producers and the balance
between photosynthesis and aerobic respiration
influence the amount stored
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42.5 Biogeochemical Cycles
In biogeochemical cycles, water or a nutrient
moves from an environmental reservoir, through
organisms, then back to the environment
• Hydrologic cycle
• Carbon cycle
• Nitrogen cycle
• Phosphorus cycle
42.5 Biogeochemical Cycles
Transfer to and from reservoirs are far slower
than rates of exchange among organisms of an
ecosystem.
• Minerals enter and leave rocks slowly
• Nutrient cycles depend on decomposers
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42.5 Biogeochemical Cycles
Hydrologic cycle – oxygen and hydrogen moving
at a global scale
Atmospheric cycle – gaseous form of a nutrient
available to ecosystems
• Carbon and nitrogen
Sedimentary cycle – nutrients that do not often
occur as gases
• Phosphorus
42.5 Biogeochemical Cycles
Cycles –
• Hydrologic cycle
• Carbon cycle
• Nitrogen cycle
• Phosphorus cycle
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42.6 The Hydrologic Cycle
Evaporation, condensation, and precipitation
move water from its main reservoir (oceans) into
the atmosphere, onto land, and back to oceans
42.6 The Hydrologic Cycle
Evaporation –
• driven by the sun
• Liquid to a vapor
Transpiration-
• Evaporation of water from plant parts
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42.6 The Hydrologic Cycle
Condensation-
• Water vapors form drops as it cools
• Gives rise to clouds
Precipitation – clouds releasing water
• Rain
• Snow
• Hail
42.6 The Hydrologic Cycle
Evaporation, condensation, and precipitation move
water from its main reservoir (oceans) into the
atmosphere, onto land, and back to oceans
• A watershed area drains into a waterway
• Valley to Amazon river basin
• Aquifers – permeable rock layers that hold water
• Groundwater includes water in soil and aquifers
• Runoff flows over ground into a waterway when
saturated
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The Hydrologic Cycle - FYI
A Global Water Crisis
Humans are disrupting the water cycle
• Salinization of soil due to uptake of water and
evaporation
• Stunts plant growth and decreases yields
• Pollution of groundwater drinking supplies
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A Global Water Crisis
• Contaminants disrupt aquatic ecosystems, drive
vulnerable species to local extinction
• Desalinization of seawater increases freshwater
supplies, but uses fossil fuels
• EXSPENSIVE
A Global Water Crisis
• Water overdrafts from aquifers (saltwater
intrusion)
• Water is drawn from aquifers faster than natural
processes replenish it.
• Near the coast salt water is drawn into aquifer
• Ogallala aquifer is half depleted
• Supplies 20% of nations crops
• Withdrawal exceeds replenishment by a factor of
10
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A Global Water Crisis
• Water to regulate political behavior –
• Turkey has built dam sites at headwaters of
Tigris and Euphrates rivers
• In the words of one of the dam site
managers, “Turkey can shut off water flow
into Syria and Iraq ‘ to regulate their
political behavior.’”
42.7 The Carbon Cycle
Carbon cycle
• Carbon moves from reservoirs in rocks and
seawater, through its gaseous form (CO2) in the
atmosphere, and through ecosystems
Carbon-oxygen cycle
• Carbon moves in and out of ecosystems
combined with oxygen in carbon dioxide,
bicarbonate, and carbonate
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Fig. 42.15a, p.744
sedimentation
bicarbonate and carbonate dissolved in ocean water
marine food webs producers, consumers,
decomposers, detritivores
marine sediments, including formations with fossil fuels
diffusion between atmosphere and ocean
photosynthesis aerobic respiration
incorporation into sediments
death, sedimentation
uplifting over geologic time
combustion of fossil fuels
F
Y
I
Fig. 42.15b, p.745
volcanic action
terrestrial
rocks
weathering
soil water
(dissolved carbon)
leaching,
runoff
photosynthesis
atmosphere
(mainly carbon dioxide)
land food webs producers, consumers,
decomposers, detritivores
death, burial, compaction over geologic time peat,
fossil fuels
deforestation
combustion of wood (for clearing
land; or for fuel)
aerobic respiration
combustion of fossil
fuels
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Carbon Cycling
between Ocean and Atmosphere
Deforestation and burning of wood and fossil
fuels are adding more carbon dioxide to the
atmosphere than oceans can absorb
The Greenhouse Effect
Natural processes and human activities add
more greenhouse gases to the atmosphere
• Gases that can profoundly influence the average
temperatures of the Earth’s surface
• Carbon dioxide, CFCs, methane, nitrous oxide
• Greenhouse Effect-
• Named because gasses act as a pane of glass in a
greenhouse
•
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The Greenhouse Effect
• Gasses absorb wavelengths of visible light and
transmit them toward Earth’s surface
• The surface absorbs the wavelength and then
emits longer , infrared wavelengths – heat.
• Greenhouse gasses impede the escape of heat
energy form Earth into space and increases
temperature.
• It has to have some gasses or the Earth would be
too cold to support life.
42.8 The Greenhouse Effect
Greenhouse gases trap heat in the lower
atmosphere
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The Greenhouse Effect
CO2 follow annual cycles of primary production
• Decline in summer due to photosynthesis
increase
• Rise in winter when photosynthesis declines
Global Warming
Global Warming
• Long term increase in temperature near Earth’s
surface
• Evaporation increases – precipitation increases
• Causing flooding in some areas and droughts in
others
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42.9 The Nitrogen Cycle
Plants can’t use atmospheric N2
Nitrogen fixation (soil bacteria) takes up N2 (gas)
and forms ammonia
Denitrification (denitrifying bacteria) returns
some nitrogen to the atmosphere
42.9 The Nitrogen Cycle
Denitrification (denitrifying bacteria) returns
some nitrogen to the atmosphere
Farmers must counter act loss of nitrogen when
they plant crops that use a lot of nitrogen
• Plant rotation
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The Nitrogen Cycle - FYI
Disruption by Human Activities
Human activities add nitrogen to ecosystems
• Examples: Fertilizer application and fossil fuel
burning (releases nitrogen oxides)
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42.10 The Phosphorus Cycle
Phosphorus moves in a sedimentary cycle
• Mainly stored as phosphate in rocks
• Earth’s crust is the largest reservoir
Phosphorus is often the limiting factor for plant
growth and algal producers
Required for energy (ATP adenosine
triphosphate)
42.10 The Phosphorus Cycle
Subtropical and tropical ecosystems have limited
amounts of phosphorus available for plants
• Most is tied up in plants
Developed countries have too much phosphorus
• Heavily fertilized fields
• At one point soaps –
• Moves to water ways and causes algal blooms
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The Phosphorus Cycle - FYI
Eutrophication
Excessive nutrient
enrichment of an
ecosystem
• Example:
Phosphorus in
aquatic ecosystems
Natural
But, exacerbated by
humans
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Key Concepts:
CYCLING OF WATER AND NUTRIENTS
Availability of water, carbon, nitrogen, phosphorus, and other substances influences primary productivity
Ions or molecules of these substances move slowly in global cycles, from environmental reservoirs, into food webs, then back to reservoirs
Human activities can disrupt these cycles