plants and pollinators - linn–benton community college
TRANSCRIPT
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Ecosystems
Chapter 27
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Chapter 28 At a Glance
• 28.1 How Do Energy and Nutrients
Move Through Ecosystems?
• 28.2 How Does Energy Flow Through
Ecosystems?
• 28.3 How Do Nutrients Cycle Within and
Among Ecosystems?
• 28.4 What Happens When Humans
Disrupt Nutrient Cycles?
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Ecosystem
An association of organisms and their
physical environment, interconnected by
ongoing flow of energy and a cycling of
materials
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Modes of Nutrition
• Autotrophs
– Capture sunlight or chemical energy
– Producers
• Heterotrophs
– Extract energy from other organisms or
organic wastes
– Consumers, decomposers, detritivores
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O2
CO2
H2O
sugar
plant tissues
other
nutrients
energy
from
sunlight
photosynthesis
Producers
Fig. 28-1
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Simple
Ecosystem
Model
Autotrophs (plants,
other self-
feeding organisms)
Heterotrophs
(animals, most
fungi,
many protists,
many bacteria)
(mainly metabolic heat)
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Energy Flow, Nutrient Cycling,
and Feeding Relationships in
Ecosystems
Fig. 28-2
solar energy
heat
heat
heat
heat
nutrients
heat energy
energy stored in chemical bonds
detritus feeders
and decomposers
primary consumers
higher-level
consumers
producers
energy from sunlight
nutrients
O S P
N
Mg H
Ca H
2O
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Diet of an omnivore (red fox)
• Herbivores
• Carnivores
• Parasites
• Omnivores
• Decomposers
• Detritivores
Seasonal variation in the diet of an
omnivore (red fox)
rodents,
rabbits
fruits insects
birds
rodents,
rabbits
fruits
insects
birds
rodents,
rabbits
rodents,
rabbits
birds
birds
insects
insects
fruits
fruits
WINTER
FALL
SUMMER
SPRING
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Trophic Levels
• All the organisms at a trophic level are
the same number of steps away from
the energy input into the system
• Producers are closest to the energy
input and are the first trophic level
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Trophic Levels in Prairie
5th
4th
3rd
2nd
1st
Fourth-level consumers (heterotrophs):
Top carnivores, parasites,
detritivores, decomposers
Third-level consumers (heterotrophs): Carnivores, parasites, detritivores,
decomposers
Second-level consumers (heterotrophs):
Carnivores, parasites, detritivores,
decomposers
First-level consumers
(heterotrophs):
Herbivores, parasites, detritivores,
decomposers
Primary producers (autotrophs):
Photoautotrophs, chemoautotrophs
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Food Chain
• A straight line
sequence of who
eats whom
• Simple food chains
are rare in nature
marsh hawk
upland sandpiper
garter snake
cutworm
flowering plant
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Food Chains on Land
Fig. 28-4a
(a) A simple terrestrial food chain
tertiary consumer
(4th trophic level)
producer
(1st trophic level)
primary consumer
(2nd trophic level)
secondary consumer
(3rd trophic level)
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Food Web marsh hawk
crowupland
sandpiper
garter snake
frog
spider
weasel badger coyote
ground squirrelpocket
gopherprairie vole
clay-colored
sparrow
earthworms, insects (e.g.,
grasshoppers, cutworms)
grasses, composites
HIGHER TROPHIC LEVELS
Complex array of carnivores,
omnivores and other consumers.
Many feed at more than one trophic level continually,
seasonally, or when an
oppportunity presents itself
SECOND TROPHIC LEVEL Primary
consumers (e.g., herbivores,
detritivores, and decomposers)
FIRST TROPHIC LEVEL
Primary producers
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Primary Productivity
• Gross primary productivity is
ecosystem’s total rate of photosynthesis
• Net primary productivity is rate at which
producers store energy in tissues in
excess of their aerobic respiration
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Energy Losses
• Energy transfers are never 100 percent
efficient
• Some energy is lost at each step
• Limits the number of trophic levels in an
ecosystem
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Primary Productivity Varies
• Seasonal variation
• Variation by habitat
• The harsher the environment, the
slower plant growth, the lower the
primary productivity
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28.2 How Does Energy Flow
Through Ecosystems? • Energy pyramids illustrate energy
transfer between trophic levels
– The net energy transfer between trophic levels is roughly 10% efficient and is known as the “10% law”
• An energy pyramid, which shows maximum energy available at the base and steadily diminishing amounts at higher levels, illustrates the general energy relationships between tropic levels
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Silver Springs:
Annual Energy
Flow
ENERGY INPUT
17,000,000 kilocalories
energy transfers through ecosystem
incoming solar energy not harnessed:
producers
herbivores
carnivores
top carnivores
decomposers, detritivores
1,679,190 (98.8%)
20,810 (1.2%)
transferred to the next trophic level:
energy still in organic wastes and remains:
energy losses as metabolic heat and as net export from the ecosystem:
ENERGY OUPUT: TOTAL ANNUAL ENERGY FLOW:
4,245 3,368
13,197
383
21
720
272
16 5
5,060
2,265
90
1,700,000 (100%)
20,810 + 1,679,190
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Silver Springs Study
• Aquatic ecosystem in Florida
• Site of a long-term study of a grazing food web
5
decomposers, detritivores
(bacteria, crayfish)
1.5
11
37
third-level carnivores
(gar, large-mouth bass)
second-level consumers
(fishes, invertebrates)
first-level consumers
(herbivorous fishes,
turtles, invertebrates)
primary producers (algae,
eelgrass, rooted plants) 809
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All Heat in the End
• At each trophic level, the bulk of the
energy received from the previous level
is used in metabolism
• This energy is released as heat energy
and lost to the ecosystem
• Eventually, all energy is released as
heat
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Biogeochemical Cycles
• The flow of a nutrient from the
environment to living organisms and
back to the environment
• Main reservoir for the nutrient is in the
environment
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Nutrient Flow:
Land Ecosystem
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Three Categories
• Hydrologic cycle
– Water
• Atmospheric cycles
– Nitrogen and carbon
• Sedimentary cycles
– Phosphorus and sulfur
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Hydrologic Cycle
evaporation
from ocean
425,000
precipitation
into ocean
385,000
evaporation from land
plants
(evapotranspiration)
71,000
precipitation
onto land
111,000
wind-driven water vapor
40,000
surface and
groundwater flow
40,000
Atmosphere
Oceans Land
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Hubbard Brook Experiment
• A watershed was experimentally
stripped of vegetation
• All surface water draining from
watershed was measured
• Removal of vegetation caused a six-fold
increase in the calcium content of the
runoff water
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Hubbard Brook Experiment
losses from disturbed
watershed plot
time of deforestation
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Aquifer Depletion
• Green signifies high
overdrafts
• Gold, moderate
overdrafts
• Yellow, insignificant
withdrawals
• Shaded areas show
groundwater pollution
• Blue squares: saltwater
intrusion
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Carbon Cycle
• Carbon moves through the atmosphere
and food webs on its way to and from
the ocean, sediments, and rocks
• Sediments and rocks are the main
reservoir
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Carbon Cycle
photosynthesis TERRESTRIAL
ROCKS
volcanic action
weathering
diffusion
Bicarbonate,
carbonate
Marine food webs
Marine Sediments
Atmosphere
Terrestrial
rocks
Soil water Peat, fossil
fuels
Land food
webs
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Carbon in the Oceans
• Most carbon in the ocean is dissolved
carbonate and bicarbonate
• Ocean currents carry dissolved carbon
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Greenhouse Effect
• Greenhouse gases impede the escape
of heat from Earth’s surface
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Carbon Dioxide Increase
• Carbon dioxide levels fluctuate
seasonally
• The average level is steadily increasing
• Burning of fossil fuels and deforestation
are contributing to the increase
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Carbon in Atmosphere
• Atmospheric carbon is mainly carbon
dioxide
• Carbon dioxide is added to
atmosphere
– Aerobic respiration, volcanic action,
burning fossil fuels
• Removed by photosynthesis
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Other Greenhouse Gases
• CFCs - synthetic gases used in plastics
and in refrigeration
• Methane - produced by termites and
bacteria
• Nitrous oxide - released by bacteria,
fertilizers, and animal wastes
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Greenhouse Gases
carbon
dioxide
methane
CFCs
nitrous oxide
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Climate Change
• Long-term increase in the temperature
of Earth’s lower atmosphere
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Global Warming Parallels
Atmospheric CO2 Increases
Fig. 28-15
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Biological Magnification
A nondegradable or slowly degradable
substance becomes more and more
concentrated in the tissues of
organisms at higher trophic levels of a
food web
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DDT in Food Webs
• Synthetic pesticide banned in the United
States since the 1970s
• Birds that were top carnivores
accumulated DDT in their tissues
• Mercury in the fish today
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Minamata Bay Disease
(mercury poisoning)
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Nitrogen Cycle
• Nitrogen is used in amino acids and
nucleic acids
• Main reservoir is nitrogen gas in the
atmosphere
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Nitrogen Cycle
gaseous nitrogen in atmosphere
food webs on landnitrogen fixation
fertilizers
uptake by autotrophs uptake by autotrophsexcretion, death,
decomposition
ammonia, ammonium in soil nitrate in soil
nitrate in soil
nitrification
nitrification
ammonification
nitrogen-rich wastes,
remains in soil
loss by
leaching
loss by leaching
loss by
dentrification
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Nitrogen Fixation
• Plants cannot use nitrogen gas
• Nitrogen-fixing bacteria convert
nitrogen gas into ammonia (NH3)
• Ammonia and ammonium can be
taken up by plants
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Ammonification & Nitrification
• Bacteria and fungi carry out
ammonification, conversion of
nitrogenous wastes to ammonia
• Nitrifying bacteria convert ammonium to
nitrites and nitrates
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Nitrogen Loss
• Nitrogen is often a limiting factor in
ecosystems
• Nitrogen is lost from soils via leaching
and runoff
• Denitrifying bacteria convert nitrates
and nitrites to nitrogen gas
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Human Effects
• Humans increase rate of nitrogen loss
by clearing forests and grasslands
• Humans increase nitrogen in water and
air by using fertilizers and by burning
fossil fuels
• Too much or too little nitrogen can
compromise plant health
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Phosphorus Cycle
• Phosphorus is part of phospholipids and
all nucleotides
• It is the most prevalent limiting factor in
ecosystems
• Main reservoir is Earth’s crust; no
gaseous phase
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Phosphorus Cycle
GUANO
FERTILIZER
ROCKS
LAND
FOOD
WEBS
DISSOLVED
IN OCEAN
WATER
MARINE
FOOD
WEBS
MARINE SEDIMENTS
excretion
weathering
mining
agriculture
uptake by
autotrophs
death,
decomposition
sedimentation setting out leaching, runoff
weathering
uplifting over
geologic time
DISSOLVED IN
SOILWATER,
LAKES, RIVERS
uptake by
autotrophs
death,
decomposition
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Human Effects
• In tropical countries, clearing lands for
agriculture may deplete phosphorus-
poor soils
• In developed countries, phosphorus
runoff is causing eutrophication of
waterways