Download ENERGY

ENERGY
PATTERNS OF ENERGY
FLOW IN ECOSYSTEMS
WHAT IS AN ECOSYSTEM?
• Biological community plus all abiotic factors
affecting the community
• “Ecosystem” first proposed by Arthur
Tansley
• Boundaries not fixed
• Energy flows
• Cycle nutrients
LAWS OF
THERMODYNAMICS
• 1st LAW:
• 2nd LAW:
ENERGY SOURCES IN
BIOSPHERE
• Sunlight energy – driving force
– Energy distribution and carbon dioxide
in atmosphere shape ecosystems and
biosphere
• Biosphere energy and CO2 shape world
climate and weather
CHARLES ELTON &
FOOD WEBS
• 1920s, Charles Elton and others proposed:
– Organisms living in the same place not only
have similar tolerances of physical factors, but
– Feeding relationships link these organisms into
a single functional entity
• Food web
http://www.history.vt.edu/Barrow/Hist3144/readings/ecology/index.html
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OLD FIELD FOOD WEB
http://www.nature.ca/ukaliq/images/a196_fwb_e.jpg
Feeding relationships of the snowshoe hare-dominated food web
in the boreal forest of northwestern Canada
Dominant
species in
yellow
ALFRED J. LOTKA AND THE
THERMODYNAMIC
CONCEPT
• Alfred J. Lotka
– Ecosystem as an energytransforming machine
– Set of equations representing
exchanges of matter and energy
among components
– Characterize transfer of body mass
using series of equations describing
how system works
LINDEMAN’S SYNTHESIS
• 1942 – Raymond Lindeman
brought Lotka’s ideas of the
ecosystem as an energytransforming machine to the
attention of ecologists
• Incorporated:
– Lotka’s thermodynamic concepts
– Elton’s food web concept
– Tansley’s ecosystem concept
http://www.cedarcreek.umn.edu/people/photo/LindemanRaymond1942.jpg
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LINDEMAN’S FOUNDATIONS
OF ECOSYSTEM ECOLOGY
• Ecosystem is fundamental unity of ecology
• Within an ecosystem, energy passes through
many steps or links in a food chain
Cedar Bog Lake in Minnesota…site of Raymond Lindemen’s classic research paper
in 1942: "The Trophic-Dynamic Concept in Ecology“. Ecology 23:399-418
ODUM’S ENERGY FLUX
MODEL
• Recognized the utility of energy
and masses of elements as
common “currencies” in
comparative analysis of
ecosystem structure and function
Eugene Odum
ttp://www.researchmagazine.uga.edu/summer2002/odum.htm
ODUM EXTENDED HIS MODELS
TO INCORPORATE NUTRIENT
CYCLING
• Fluxes of energy and materials are closely linked in
ecosystem function
• But:
– Energy enters ecosystems as light and is
degraded into heat
– Nutrients cycle indefinitely, converted from
inorganic to organic forms and back again
• Studies of nutrient cycling provides index of energy
fluxes
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Single trophic level
Example food chain
Odum’s “universal” model of energy flow, which can
be applied to any organism
Energy dissipated as heat
AUTOTROPHS - PRODUCERS
SUN
Producers
• Photoautotrophs - Sunlight energy, Green
plants
• Chemoautotrophs - Chemical energy, certain
bacteria
• Primary producers – capture energy from
sunlight
Consumers
Detritus + Decomposers
Inorganic nutrients
Import
Energy Flow
Nutrient
pool
Export
Nutrient Cycling
http://www.scienceclarified.com/images/uesc_01_img0028.jpg
Energy lost and
unavailable to
consumers
PRIMARY PRODUCTION
• Producers capture energy of light
• Transform sunlight energy into energy of chemical
bonds in carbohydrates
• 6CO2 + 6H2O → C6H12O6 + 6O2
– For each g of C assimilated, 39 kj energy stored
• Gross primary production = total energy assimilated
by primary producers
• Net primary producion = energy accumulated (in
stored form) by primary producers
• GPP – NPP = Respiration
– Energy consumed by producers for maintenance
and biosynthesis
http://141.150.157.117:8080/prokPUB/figures/normal/p323-006.jpg
Partitioning
gross
primary
productivity
into
respiration
and net
primary
productivity
GPP
NPP
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NUTRIENTS STIMULATE
PRIMARY PRODUCTION
Effects of fertilization with N & P on primary production in a
salt marsh dominated Carex subspathecea in southern
Hudson Bay, Canada.
• Terrestrial production may
be nutrient limited
– N most common limiting
element
• Aquatic systems often
strongly nutrient-limited
– Open ocean
– Addition of nutrients may
stimulate unwanted
production
AQUATIC ECOSYSTEMS
RESPONSIVE TO
PHOSPHORUS
1975
1994
http://www.umanitoba.ca/institutes/fisheries/eutro.html
GLOBAL PRIMARY
PRODUCTION
Slow-moving coastal plain stream choked with algal
bloom caused by nitrogen and phosphorus from
upstream farmland.
• Correlates with annual precipitation (when light not
limiting)
• Note relationship among tundra, deserts, and tropics
– Oceans – nutrient poor
• CO2 Source of carbon
http://wps.prenhall.com/wps/media/objects/57/58641/51_8089ic.gif
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Grams carbon/m2/yr for globe, as calculated
from satellite imagery. Oceans = 46%, land = 54%
PRIMARY PRODUCTION VARIES
AMONG ECOSYSTEMS
NPP vs. Temperature + Precipitation
• Maximum under
favorable
conditions
– Intense sunlight
– Warm
temperatures
– Abundant
precipitation
– Nutrients
HETEROTROPHS - CONSUMERS
•
•
•
•
•
Get energy from external sources
“Animals”
Primary consumers
Secondary consumers
Tertiary consumers
– Carnivores
• Decomposers
– Detritivores
– Eat dead organic matter
Tertiary consumers
Secondary consumers
Decomposers
Primary consumers
Primary producers
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ECOLOGICAL PYRAMIDS
Tertiary consumers
Secondary consumers
Decomposers
Primary consumers
• Trophic levels placed in order
• Reflects:
– Numbers of organisms at each level
– Biomass of each level
– Energy at each level
Primary producers
ECOLOGICAL PYRAMIDS
• Elton observed predators tended to be larger
and less numerous than their prey - described
as the ‘pyramid’ of numbers or biomass
• Elton hypothesized that this occurred because
predators have to be larger than prey
PYRAMID OF NUMBERS
# CONSUMERS=TOP CARNIVORES
# DECOMPOSERS
# CONSUMERS
# HERBIVORES
# PRIMARY PRODUCERS
PYRAMID OF BIOMASS
kg CONSUMERS=TOP CARNIVORES
kg CONSUMERS
kG DECOMPOSERS
kg HERBIVORES
kg PRIMARY PRODUCERS
PYRAMID OF ENERGY
kJ CONSUMERS=TOP CARNIVORES
kJ CONSUMERS
kJ DECOMPOSERS
kJ HERBIVORES
kJ PRIMARY PRODUCERS
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NUMBERS PYRAMID
NUMBERS PYRAMID
http://www.bbc.co.uk/schools/gcsebitesize/img/bi01010.gif
BIOMASS PYRAMID
BIOMASS PYRAMID
ENERGY PYRAMID
BIOMASS
AND
(NUMBERS)
PYRAMID
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Heat is lost as energy flows through food chain
Energy pyramids
can never be
inverted, but
biomass
pyramids can be
inverted when
lower trophic
levels are
dominated by
palatable and
small organisms
that turnover
rapidly
ENERGY TRANSFER
EFFICIENCY
• 10% Efficient between trophic levels
• What happens to other 90%
– How is it dispersed?
– Is it lost?
– Account for it
What % of energy is available to the next tropic level?
ENERGY BUDGET
Energy Budget – energy flow & distribution through
ecosystem
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ONLY 5% TO 20% OF ENERGY
PASSES BETWEEN TROPHIC
LEVELS
• Energy reaching each trophic level depends on:
– Net primary production (base of food chain)
– Efficiencies of transfers between trophic levels
• Plants use 15-70% of light energy assimilated for
maintenance
• Herbivores and carnivores expend more energy on
maintenance than plants:
-
ECOLOGICAL EFFICIENCY
• Ecological Efficiency
– Percentage of
energy transferred
from one trophic
level to the next:
– Range of 5-20%
typical
– Must understand the
utilization of energy
within a trophic level
Not all food components can
be assimilated - Undigested
fibrous material from
elephant dung
FUNDAMENTAL ENERGY
RELATIONSHIPS
• Components of an animal’s energy budget are
related by:
• Assimilated Energy = Ingested Energy – Egested
Energy
• Production = Assimilated Energy – (RespirationExcretion)
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NET PRODUCTION EFFICIENCY
ASSIMILATION EFFICIENCY
• Assimilation Efficiency = Assimilation/Ingestion
• Function of Food Quality:
– SEEDS: 80%
– YOUNG VEGETATION: 60-70%
– PLANT FOODS OF GRAZERS, BROWSERS:
30-40%
– DECAYING WOOD: 15%
– ANIMAL FOODS: 60-90%
• Net production efficiency =
production/assimilation
• depends on metabolic activity:
– birds: <1%
– small mammals: <6%
– sedentary ectotherms: as much
as 75%
• Gross production efficiency =
assimilation efficiency x net
production efficiency
– = production/ingestion, ranges
from below 1% (birds and
mammals) to >30% (aquatic
animals).
What limits the length of the food chain?
Detritus Food Chains
• Ecosystems support two
parallel food chains:
– herbivore-based (relatively
large animals feed on leaves,
fruits, seeds)
– detritus-based (microorganisms
and small animals consume
dead remains of plants and
indigestible excreta of
herbivores)
– herbivores consume:
Temperate
deciduous forest
Tropical rain
forest
• 1.5-2.5% of net primary
production in temperate forests
• 12% in old-field habitats
• 60-99% in plankton
communities
Food chain length may be limited by:
• Energy constraint hypothesis
– Energy is lost with each transfer
– Food chain length should be related to productivity
– Not supported by research
Do aquatic or terrestrial ecosystems have
more trophic levels?
What factor contributes most to variation in
food chain length among these ecosystems?
• Dynamic stability hypothesis
– Long food chains easily disrupted
– Support is tentative
• Ecosystem size
– Species diversity higher
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SOME GENERAL RULES
• Assimilation efficiency increases at higher
trophic levels.
• GPP and NPP efficiencies decrease at higher
trophic levels.
• Ecological efficiency ~ 10%.
• ~ 1% of NPP ends up as production on the third
trophic level – the energy pyramid narrows
quickly.
• To increase human food supplies means eating
lower on the food chain!
http://www.yale.edu/post_lab/images/FCL_ecosize_large.gif
Food energy available to the human
population depends on their trophic level.
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