Transcript Document 7446900

OUR Ecological Footprint - 11
1.
11
The hierarchical nature and processes of
different levels of ecological systems:
• Individual organism: How do structure,
physiology, and behavior lead to the
individual’s survival and reproduction?
•
Population: What determines the number of
individuals and their variation in time and
space?
• Community: What determines the diversity
and relative abundance of organisms living
together?
• Ecosystem: How does energy flow and matter
cycle in the biotic and abiotic environment?
• Biosphere: How do air, water, and the energy
and chemicals they contain circulate globally?
Ecosystem Ecology: Interactions
between abiotic and biotic factors at
a given location as relates to:
energy flow and cycling of matter.
IB 452: Ecosystem Ecology
fall 2009
IB 440: Plants and Global Change
spring 2009
Energy flow in ecosystems
Objectives:
• The ecosystem obeys thermodynamic principles.
• Trophic pyramids for energy, biomass, numbers
• Primary production: efficiencies and factors
causing variation among biomes
• Secondary production:
•
Intertrophic transfers: efficiencies and food
chain length
•
Intratrophic transfers: efficiencies
Ecosystem: an energytransforming machine
• Exchanges of matter and energy among
components
• Obey thermodynamic principles that govern
energy transformations
• Law 1: Conservation of energy
• “balance the books”
• Law 2: Inefficient transformation of energy
• “heat tax”
Coupling of oxidations and reductions =
basis of energy flow in ecosystems.
Energy flows through biochemical
pathways.
Energy transfer decreases after each
transformation.
Heat is lost as energy flows through food
chain. Matter recycles…
Blue = matter
Red = energy
Energy flows through:
• Food chain – energy passes through
many steps or links
• Trophic level (feeding level) = each link
in food chain
• Two parallel food chains
– Plant-based
– Decomposer-based
Food chains represent energy
relationships.
Consumers
(heterotrophs)
Producers (autotrophs)
Figure 1
Food energy available to the human
population depends on their trophic level.
Figure 2
***Pyramids: Which can be inverted? Why?
Energy
Numbers
Biomass
Figure 3
Biomagnification:
Hazardous agents may accumulate in an inverse
pyramid and cause environmental diseases.
Primary Production:
• by plants
• process of converting light energy to
chemical bond energy in carbohydrates
(via photosynthesis!)
• for each g of C assimilated, 39 KJ energy
stored
• rate determines rate of energy supply to
rest of ecosystem
GrossPP = NetPP + Respiration
Day + night
Day
Figure 4
IRGA - Infrared gas analzyer:
measure CO2 in vs. out: in sunlight (NPP)
and dark (respiration); estimate GPP
Indirect measures of GPP
Figure 5
*** Measurements of PP by IRGA
Full sun: CO2 depleted from chamber at rate of
12 mg CO2 per 100 cm2 leaf area per hour
Dark: CO2 released by leaf into chamber at rate
of 1.5 mg CO2 per 100 cm2 leaf area per hour
What is the rate of NPP for this leaf? Explain.
What is the rate of respiration for this leaf?
Explain.
What is the rate of GPP for this leaf? Explain.
Figure 6
Limits on Productivity
• Photosynthetic efficiency (% energy from sun
converted to NPP)
= 1-2%
• Net production efficiency (NPP/GPP)
30% tropics 75-80% temperate
***why difference?
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Light
Temperature
Precipitation
Nutrients
CO2
NPP vs. Temperature and Precipitation
Figure 7
NPP vs. nitrogen (N in rubisco in PS)
Figure 8
NPP + > [CO2]
• To what extent is PS limited by
amount of CO2?
• To what extent does vegetation
act as a C sink?
Hypothesis: Sp richness and functional
diversity increase NPP (via more biomass).
Figure 9
Results
Figure 10
Remote sensing of primary production in
oceans.
1° productivity of aquatic ecosystems
depends on [nutrients].
• Freshwater lakes:
• P often limiting;
• with low N/P, blue-green algae increase NPP
because they can fix additional N;
• with high N/P, green algal ‘blooms’ occur
• Open ocean:
• near shore: N often limiting
• open ocean: silica and Fe more limiting
Question: Is NPP in the open ocean
limited by nutrients (e.g Fe)?
•Hypothesis: NPP in the open ocean is limited
by availability of iron.
•Experimental setup?
•Prediction: Amount of chlorophyll a
increases both at surface and 30 m deep in
area with added Fe relative to area without Fe.
Figure 11
What is the conclusion?
Figure 12
Global variation in estimated NPP
NPP in different biomes:
(blue = water
green = land)
% area
Figure 13
X
NPP/area = % of total
NPP
Secondary production
• By non-photosynthesizers
• Amount of chemical energy in
consumer’s food converted to biomass
/unit time
Energy flow within and between
trophic levels
Figure 14
Energy transfer between trophic levels
depends on:
• NPP
• efficiencies of transfer between trophic
levels
• residence time
longer time--> > accumulation of energy
Energy Pyramid: 10% law of energy transfer;
2nd law limits number of levels.
.1
1
10
100
90% lost at
each level
Ecological (food chain) efficiency =
net production of trophic level_n
net production of trophic level n-1
10
15
20
1
sun
Figure 15
Ecological (food chain ) efficiency
•  Production of each trophic level =
5 – 20% that of level below it
• Replaces the “10% law”= an average;
not fixed
• Often lower on land (5-15%) than
aquatic (15-20%)
Energy (kcal m-2 yr-1)
Energy production
Primary
Primary
Secondary
__or removal_____
Producers Consumers Consumers
Non-consumed production 704
70
13
Removed by consumers
176
34
0
Respiration
234
44
18
Gross production (totals) 1114____ 148 ____
31____
1) Calculate NPP.
_____
2) Calculate Ecological Efficiency during 2 transfers
(= food chain efficiency).
______
______
3) What ultimately happens to 1) the energy and 2) the
biomass that is not consumed in this lake?
Figure 16
What limits the length of the food
chain?
Figure 17
What limits length of food chain?
• H1: Energetics
• Availability of energy limits to 5-7 levels
• Depends on:
NPP
energy needed by consumers
average ecological efficiency
• H2: Dynamic stability
Longer chains less stable because:
Fluctuations at lower trophic levels magnified at
higher levels --->
extinction of top predators.
***Do aquatic or terrestrial ecosystems have
more trophic levels?
What factor contributes most to variation in
food chain length among these ecosystems?
Community
NPP
Open ocean
500
Coastal marine 8000
Grassland
2000
Tropical forest 8000
Consumer Ecological
Ingestion Efficiency%
0.1
10.0
1.0
10.0
25
20
10
5
# Trophic
Levels
7.1
5.1
4.3
3.2
Figure 18
Energy flow within a trophic level
Figure 19
Intratrophic energy transfers:
• Exploitation Efficiency =
ingestion by trophic level n___
production of trophic level n-1
• Herbivores 20% and carnivores 30%
• If production and consumption aren’t balanced, energy
accumulates;
• E.g. Non-consumed production of plants and herbivores
1) accumulates as (lake) sediments or
2) undergoes respiration by decomposers.
• Assimilated energy =
ingestion – egestion
• Assimilation efficiency =
assimilation / ingestion
• primarily a function of food quality;
• i.e. amount of non-digestible material
• Secondary production =
assimilated energy – respiration – excretion
Net production efficiency =
Production/Assimilation
Net production efficiency
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Depends on metabolic activity
Most active animals have lowest values
Cost of maintenance and activity greatest
Warm-blooded vertebrates :
birds <1%
small mammals <6%
Cold-blooded animals: 15-75%
Some general rules
• Assimilation efficiency increases at higher
trophic levels.
• Net and gross production efficiencies
decrease at higher trophic level.
• Ecological efficiency averages about 10%.
• About 1% of NPP ends up as production
on third trophic level;
• The pyramid of energy narrows quickly.