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Ecosystem energetics

Ecosystem energetics

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Ecosystem energetics

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  1. Ecosystem energetics Outline: • Limits on primary production • Relationship between primary and secondary productivity • Trophic efficiency Readings: Chapters 20

  2. Laws of thermodynamics govern energy flow

  3. Laws of thermodynamics govern energy flow

  4. Energy flow in ecosystems

  5. Ecosystem energetics - terminology • Standing crop biomass – amount of accumulated organic matter found in an area at a given time [g/m2] • Productivity – rate at which organic matter is created by photosynthesis [g/m2/yr] • Primary productivity – autotrophs • Secondary - heterotrophs • Gross versus net primary productivity

  6. Estimating primary productivity in aquatic ecosystems

  7. Factors limiting primary productivity in terrestrial ecosystems • Temperature • Precipitation • Light • Nutrients

  8. Controls on primary production in terrestrial ecosystems

  9. Controls on primary production in terrestrial ecosystems

  10. Controls on primary production in terrestrial ecosystems

  11. Controls on primary production in terrestrial ecosystems

  12. Controls on primary production in terrestrial ecosystems

  13. Primary production as a function of latitude Despite much variation, there is a general trend of increasing net primary productivity with decreasing latitude. a), Grassland and tundra ecosystems. b) Cultivated crops. c) Lakes

  14. Global map of primary productivity

  15. Factors limiting primary productivity in aquatic ecosystems • Light • Nutrients

  16. Controls on primary production in aquatic ecosystems

  17. Controls on primary production in aquatic ecosystems

  18. Controls on primary production in aquatic ecosystems

  19. Global map of primary productivity

  20. Energy allocation

  21. Primary production varies with time

  22. Primary production varies with time

  23. Primary production varies with time

  24. Primary productivity limits secondary productivity

  25. Primary productivity limits secondary productivity

  26. Secondary production by trophic level n Amt respired by trophic level n Production efficiency = 14/70 Amt egested as feces (waste) by trophic level n Amt assimilated (i.e. absorbed into body) by trophic level n Assimilation efficiency 70/200 Amt ingested by trophic level n Consumption efficiency = 200/1000 Amt produced by trophic level n-1 Efficiency of energy transfer

  27. Efficiency of production • I = ingested • A = assimilated through gut wall • W = expelled as waste product • Of A, • R = respired • P = production

  28. Food chains

  29. Consumption efficiency determines pathways of energy flow through ecosystem

  30. FOREST • Note: • Detrital food chain accounts for most biomass produced in a community • LCS plays greatest role in phytoplankton-based food chains

  31. GRASSLAND

  32. PLANKTON - OCEAN

  33. STREAM COMMUNITY

  34. Energy loss between trophic levels

  35. Secondary production by trophic level n Amt respired by trophic level n Amt egested as feces (waste) by trophic level n Amt assimilated (i.e. absorbed into body) by trophic level n Amt ingested by trophic level n Amt produced by trophic level n-1 Example: a herbivore (level n) feeding on a plant (level n-1); values = kilocalories. Trophic Efficiency = 0.2*0.35*0.2 = 14/1000 = 0.014 Efficiency of energy transfer

  36. Decomposition and Nutrient cycling Outline: • Process of decomposition • Types of decomposers • Controls on decomposition • Decomposition in lakes and rivers • Nutrient cycling: generalities • Nutrient cycles • Carbon • Nitrogen • Phosphorus Readings: Chapters 21, 22

  37. Decomposition • Most material = plant • Involves: • Release of chemical energy • Mineralization (= organic --> inorganic) • Note immobilization = reverse of mineralization • Net mineralization rate = mineralization - immobilization

  38. Decomposition involves a variety of organisms • Microfauna & microflora [<100 μm]– bacteria and fungi; nematodes, protozoa • Mesafauna [100 μm – 2mm] – mites, potworms • Macrofauna [2-20 mm] - millipedes • Megafauna [> 20 mm]- earthworms, snails

  39. Fungi: microfauna

  40. Mites: mesofauna

  41. Megafauna

  42. Vertebrate scavengersConsumers of animal carrion

  43. Factors influencing decomposition rates (highest lignin content) (lowest lignin content)