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

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 mattercycle 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 ecosystemObjectives: • 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. Figure 1

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”

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 transfer decreases after each transformation.

10. Heat is lost as energy flows through food chain. Matter recycles… Blue = matter Red = energy

11. PrimaryProduction: • 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. out: in sunlight (NPP) and dark (respiration); estimate GPP

14. Indirect measures of GPP Figure 3

15. How measure assimilation and respiration of CO2 over large spatial scales? Useeddy flux covariance towers

16. Abiotic 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? Variables affecting productivity: • Light • Temperature • Precipitation • Nutrients • CO2

17. Photosynthesis and light… Figure 4

18. NPP vs. Temperature and Precipitation Water use efficiency = G NPP per kg water transpired Figure 5

19. NPP vs. nitrogen (N in rubisco in PS) 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.

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

27. Results: satellite images

28. What is the conclusion? Figure 8

29. Global variation in estimatedNPP Figure 9

30. NPP varies among habitats:

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

33. Food chains represent energy relationships. Consumers (heterotrophs) Producers (autotrophs)

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 levelsdepends on: • NPP • efficiencies of transfer between trophic levels • residence time longer time--> > accumulation of energy

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.

40. ***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% LevelsOpen ocean 500 0.1 25 7.1Coastal marine 8000 10.0 20 5.1Grassland 2000 1.0 10 4.3Tropical forest 8000 10.0 5 3.2 Figure 12

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

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 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?