1. The hierarchical nature and processes of different levels of ecological systems:

2. 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?

3. 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 2011
IB 440: Plants and Global Change
spring 2011

4. Energy flow in ecosystem Objectives:
Ecosystem obeys thermodynamic principles.
Trophic pyramid for energy
Primary production: efficiencies and
factors causing variation among biomes
Secondary production:
Intertrophic transfers: efficiencies and
food chain length
Intratrophic transfers: efficiencies
Net ecosystem production: C gain - C loss

5. Food energy available to the human population depends on their trophic level.
C Eating meat is inefficient way of tapping PS productivity. Humans obtain far more calories by eating grains directly as a primary consumer than by prcessing that same amount of grain through another trophic level. We could feed many more people if we all consumed only plant material, feeding more efficiently as primary consumers
224 billion tons of plant production/year
59% = terrestrial
35-40% used by humans directly (as plants) or indirectly (by feed animals first)
Food supplies can be increased and more
people can be supported by eating lower on
food chain
Figure 1 5

6. Ecosystem: an energy-transforming 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”
Law 1: energy neither created nor destroyed: have to ‘balance the books’

7. ‘Universal’ model of energy flow through ecosystems.

8. Coupling of oxidations and reductions = basis of energy flow in ecosystems.

9. Energy flows through biochemical pathways
Energy flows through biochemical pathways. Energy transfer decreases after each transformation.

10. Heat is lost as energy flows through food chain. Matter recycles…
Blue = matter
Red = energy
What do red and blue arrows =? Blue = matter; red = energy

11. 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

12. GrossPP = NetPP + Respiration
Day + night
Day
Figure 2

13. IRGA - Infrared gas analzyer: measure CO2 in vs
IRGA - Infrared gas analzyer: measure CO2 in vs. out: in sunlight (NPP) and dark (respiration); estimate GPP
B15.14

14. Indirect measures of GPP
Figure 3

15. How measure assimilation and respiration of CO2 over
large spatial scales? Use eddy flux covariance towers
Sensors quantify vertical movement of CO2 in atmosphere above vegetation.
How temp and precip control primary proudction affect respiration of plants
Helps to predict how ecosystem productivity migh change in response to climate change.

16. Abiotic Limits on Productivity
Photosynthetic efficiency
(% energy from sun converted to NPP)
= 1-2%
Net production efficiency (NPP/GPP)
30% tropics % temperate
***why difference?
Variables affecting productivity:
Light
Temperature
Precipitation
Nutrients
CO2

17. Photosynthesis and light…
Figure 4

18. NPP vs. Temperature and Precipitation
Effects of Temperature
Optimum varies from 16 to 38
Rate of PS increases with T, but so does respiration
Net assimilation may decrease at high temperatures
Effects of Water
PS on land is water-limited
Water-use efficiency: 2 g production per kg of water transpired
Water use efficiency =
G NPP per kg water transpired
Figure 5

19. NPP vs. nitrogen (N in rubisco in PS)
Nutrients stimulate primary production
N = most common limiting element; then P on land
Aquatic systems often nutrient-limited
Nutrient use efficiency =
g production per g N assimilated
Figure 6

20. NPP + > [CO2] To what extent is PS limited by amount of CO2?
To what extent does vegetation
act as a C sink?

21. Remote sensing of primary production in oceans.
Spectral instrument estimates chlorophyll conc and converts data to contrasting artificial colors.

22. 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

23. PP in aquatic ecosystems - highest where nutrients regenerated in sediments reach light zone.
Figure 7

24. 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.

25. Southern Ocean Iron Enrichment Experiment
Southern Office Iron Enrichment Experiment (SO FEX) in areas of high and low silicon concentrations 25

27. Results: satellite images
White = cloud
False-color satellite images of each experimental area showing greatly increased phytoplankotn proudciton (as indiciate by chlorophylll a reflectance. 27

28. What is the conclusion? Figure 8
Fe fertilization increases ocean as C sink…but it also stimulates zooplankton production which releases CO2 to atmosphere and counters C sink argument.
The So FE exp were more promising as much C precipitated below water mixing zone
What is the conclusion?
Figure 8

29. Global variation in estimated NPP
Figure 9

30. NPP varies among habitats:30

31. Energy flow between trophic levels

32. 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 32

33. Food chains represent energy relationships.
Consumers
(heterotrophs)
Ecosystem trophic structure model: Spatial pattern set by autotrophs
Decomposers blur the pattern
Predators link components, stabilize system
Producers (autotrophs) 33

34. Energy Pyramid: 10% law of energy transfer; 2nd law limits number of levels.
90% lost at each level .1 1 10
100
Figure 10

35. Energy transfer between trophic levels depends on:
NPP
efficiencies of transfer between trophic levels
residence time
longer time--> > accumulation of energy
Monitor energy fluxes by considering various efficiencies and residence times of energy and results from food chain processing of energy by animals.
Residence time varies: short in aquatic zooplankton; long in land
Longer residence time - greater time to accumulate energy (biomass)

36. Ecological (food chain) efficiency = net production of trophic level_n net production of trophic level n-1 10 15 20 1
sun
Figure 11

37. 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%)

38. What limits the length of the food chain?

39. 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.
Microcosms - useful for such tests…replicate essential features of ecosystem. Control all variables except ones of interest
Get pix of 1.20

40. Do aquatic or terrestrial ecosystems have more trophic levels
***Do aquatic or terrestrial ecosystems have more trophic levels? What factor contributes most to variation in food chain length among these ecosystems? Community NPP Consumer Ecological # Trophic Ingestion Efficiency% Levels Open ocean Coastal marine Grassland Tropical forest
Figure 12

41. Secondary production By non-photosynthesizers
Amount of chemical energy in consumer’s food converted to biomass /unit time
Secondary production

42. Energy flow within a trophic level Secondary production = assimilated energy – respiration – excretion
Figure 13

43. 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.

44. Net Ecosystem Production (NEP) = carbon gain - carbon lost
Measures net carbon accumulation -->
carbon ‘sequestered’ in organic cmpds in
soil and living biomass -->
no ‘greenhouse’ warming effect
Positive NEP represents carbon sink -->
removes CO2 from atmosphere

45. Exam ? Energy (kcal m-2 yr-1)
Energy production Primary Primary Secondary
__or removal_____ Producers Consumers Consumers
Non-consumed production
Removed by consumers
Respiration
Gross production (totals) ____ ____ ____
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?
N.B. NPP - non-consumer+ consumed
Ecological Efficiency = net 2ndP/net P so 104/880=11.8% and 13/104=12.5%