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Ecosystem Energy FlowProductivity
Studying organisms in their environment
organism
population
community
ecosystem
biosphere
Essential Questions:
 What limits the production in ecosystems?
 How do nutrients move in the ecosystem?
 How does energy move through the ecosystem?
Ecosystem
 All the organisms in a community plus abiotic
factors

ecosystems are transformers of energy
& processors of matter
 Ecosystems are self-sustaining

what is needed?
 capture energy
 transfer energy
 cycle nutrients
Ecosystem inputs
constant
energy flows
input
of
through
energy
nutrients cycle
Matter
cannot
Don’t forget
laws of or
bethe
created
Physics!
destroyed
nutrients
can only
cycle
biosphere
inputs
 energy
 nutrients
Generalized
Nutrient
cycling
consumers
producers
consumers
decomposers
nutrients
nutrients
ENTER FOOD
CHAIN
made
available
= made available
to producers
to producers
Decomposition
connects all
trophic levels
return to
abiotic
reservoir
abiotic
reservoir
geologic
processes
Carbon cycle
CO2 in
atmosphere
Combustion of fuels
Industry and home
Diffusion
Respiration
Photosynthesis
Plants
Animals
Dissolved CO2
Bicarbonates
Photosynthesis
Animals
Plants and algae
Carbonates in sediment
abiotic reservoir:
 CO2 in atmosphere
enter food chain:
 photosynthesis =
carbon fixation in
Calvin cycle
recycle:

return to abiotic:
 respiration
 combustion
Deposition of
dead material
Deposition
of dead
material
Fossil fuels
(oil, gas, coal)
Nitrogen cycle
abiotic reservoir:
 N in atmosphere
enter food chain:
 nitrogen fixation by soil & aquatic bacteria
recycle:
 decomposing & nitrifying bacteria
return to abiotic:
 denitrifying bacteria
Atmospheric
nitrogen
Carnivores
Herbivores
Birds
Plankton with
nitrogen-fixing
bacteria
Plants
Death, excretion, feces
Fish
excretion
Decomposing bacteria
amino acids
Ammonifying bacteria
loss to deep sediments
Nitrogen-fixing
bacteria
(plant roots)
Nitrogen-fixing
bacteria
(soil)
Nitrifying bacteria
soil nitrates
Denitrifying
bacteria
abiotic reservoir:
 rocks, minerals, soil
enter food chain:
 erosion releases
soluble phosphate
 uptake by plants
recycle:
 decomposing
bacteria & fungi
return to abiotic:
 loss to ocean
sediment
Phosphorus cycle
Plants
Land
animals
Animal tissue
Urine and feces
Soluble soil
phosphate
Decomposers
(bacteria and
fungi)
Loss in
drainage
Rocks and
minerals
Decomposers Phosphates
(bacteria & fungi) in solution
Animal tissue
and feces
Aquatic
animals
Plants and
algae
Precipitates
Loss to deep sediment
abiotic reservoir:
 surface & atmospheric water
enter food chain:
 precipitation & plant uptake
recycle:
 transpiration
return to abiotic:
 evaporation & runoff
Water cycle
Solar energy
Transpiration
Water vapor
Evaporation
Precipitation
Oceans
Runoff
Lakes
Percolation in soil
Groundwater
Aquifer
Transpiration
Why does
water flow
into, up
and out of
a plant?
We will discuss
process in
detail soon!
Energy flows through ecosystems
sun
Energy is
incorporated
into a
community by
what group?
secondary
consumers
(carnivores)
primary consumers
(herbivores)
producers (plants)
loss of
energy
loss of
energy
 Ecosystem dynamics involve two main processes: energy flow




(productivity) and chemical cycling (biogeochemical cycles)
Energy flows through ecosystems
Matter cycles within them
Physical laws govern energy flow and chemical cycling in
ecosystems
 Conservation of Energy (first law of thermodynamics)
 Energy enters from solar radiation and is lost as heat
 Conservation of matter - Chemical elements are continually
recycled within ecosystems
Ecosystems are open systems, absorbing energy and mass and
releasing heat and waste products
Productivity
 Primary productivity: Term for the rate
which producers photosynthesize
organic compounds in an ecosystem.


Gross primary productivity: total amount of photosynthetic
biomass production in an ecosystem
Net Primary Productivity = GPP – respiration cost
 Ecosystems with greater productivity are
more stable and diverse than ecosystems
with less productivity.

Which ecosystems are most productive?
Energy transfer between trophic levels
is typically only 10% efficient
 Net Primary Production (NPP) is the amount


of new biomass added in a given time period
Only NPP is available to consumers
Ecosystems vary greatly in NPP and
contribution to the total NPP on Earth

Limited by light, nutrients and other abiotic factors
 Secondary is the amount of chemical energy
in food converted to new biomass
Inefficiency of energy transfer
 Loss of energy between levels of food chain

To where is the energy lost? The cost of living!
sun
17%
growth
only this energy
moves on to the
next level in
the food chain
energy lost to
daily living
33%
cellular
respiration
50%
waste (feces)
Production Efficiency
 When a caterpillar feeds on a leaf, only about

one-sixth 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
Figure 55.10
Plant material
eaten by caterpillar
200 J
67 J
Feces
100 J
Cellular
respiration
33 J
Not assimilated
Growth (new biomass;
secondary production)
Assimilated
Trophic Efficiency and Ecological
Pyramids
 Trophic efficiency is the percentage of


production transferred from one trophic level
to the next
It is usually about 10% (“10% Law”), with an
actual range of 5% to 20%
Trophic efficiency is multiplied over the length
of a food chain
sun
Ecological pyramid
 Loss of energy between levels of food chain

can feed fewer animals in each level
10% energy
available for
next level
Notice only 1% of
sunlight energy
converted by plants
Interesting Energy production facts:
 Birds and mammals have efficiencies in the


range of 13%
Fishes have production efficiencies of around
10%
Insects and microorganisms have efficiencies
of 40% or more
 WHY??
Role of Humans in Energy flow and nutrient
cycling:
 Dynamics of energy flow in ecosystems have



important implications for the human population
Eating meat is a relatively inefficient in terms of
utilizing photosynthetic production (and water)
Worldwide agriculture could feed many more people
if humans ate only plant material
Fossil fuels used to produce foods
Humans in food chains-carbon cycle
 Dynamics of energy through ecosystems have
important implications for human populations
 How much energy does it take to feed a
human?
 if we are meat eaters?
 if we are vegetarian?
Better harvest?
Combustion and water/ ocean
pollution
Humans and the water cycle
 Deforestation breaks the water cycle

groundwater is not transpired to the
atmosphere, so precipitation is not
created
forest  desert
desertification
Effects of deforestation
40% increase in runoff
loss of water
loss into
surface water
80 nitrate levels in runoff
Concentration
of nitrate (mg/l )

 60x loss in nitrogen
 10x loss in calcium
40
loss out of
ecosystem!
4
Deforestation
2
Why is
0
nitrogen
1965 so
important?
1966
1967
Year
1968
What you need to be able to do:
 Using the laws of conservation of matter
and energy to do some basic accounting
and determine different aspects of energy
and matter usage in a community.
 Remember: Inputs have to equal outputs
Sample problem
 A caterpillar consumes 100 kcal of
energy. It uses 35 kcal for cell
respiration, and loses 50 kcal as waste.
Determine the trophic efficiency for its
creation of new biomass.
Total energy = 100 kcal
 Lost and Respired: 35 + 50 = 85 kcal
 Total energy for growth: 15 kcal

 Efficiency = part/total = 15/100 = .15 (or
15% transfer or 3/20 as fraction)
The “take home” energy defines ecology!