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WHAT IS AN ECOSYSTEM?

WHAT IS AN ECOSYSTEM?. Community + all abiotic factors affecting “Ecosystem” first proposed by Arthur Tansley Boundaries not fixed Energy flows Cycle nutrients. http://eesc.columbia.edu/courses/ees/life/lectures/lect02.html. LAWS OF THERMODYNAMICS. 1st LAW 2nd LAW:.

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WHAT IS AN ECOSYSTEM?

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  1. WHAT IS AN ECOSYSTEM? Community + all abiotic factors affecting “Ecosystem” first proposed by Arthur Tansley Boundaries not fixed Energy flows Cycle nutrients http://eesc.columbia.edu/courses/ees/life/lectures/lect02.html

  2. LAWS OF THERMODYNAMICS • 1st LAW • 2nd LAW:

  3. 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

  4. CHARLES ELTON & FOOD WEBS • 1920s, Charles Elton and others proposed: • Organisms living in same place not only have similar tolerances of physical factors, but • Feeding relationships link these organisms into single functional entity • Food web http://www.history.vt.edu/Barrow/Hist3144/readings/ecology/index.html

  5. http://www.nature.ca/ukaliq/images/a196_fwb_e.jpg

  6. Feeding relationships of the snowshoe hare-dominated food web in the boreal forest of northwestern Canada Dominant species in yellow

  7. ALFRED J. LOTKA AND THE THERMODYNAMIC CONCEPT • Alfred J. Lotka • Ecosystem as an energy-transforming machine • Equations representing exchanges of matter and energy among components

  8. LINDEMAN’S SYNTHESIS 1942 – Raymond Lindeman brought Lotka’s ideas of ecosystem as an energy-transforming machine to 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

  9. LINDEMAN’S FOUNDATIONS OF ECOSYSTEM ECOLOGY • Ecosystem is fundamental unity of ecology • Within an ecosystem, energy passes through many steps or links in food chain • Each link in the food chain is a trophic level (feeding level)

  10. ODUM’S ENERGY FLUX MODEL Recognized utility of energy and masses of elements as common “currencies” in comparative analysis of ecosystem structure and function Eugene Odum http://www.researchmagazine.uga.edu/summer2002/odum.htm

  11. 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

  12. AUTOTROPHS - PRODUCERS Photoautotrophs - Sunlight energy, Green plants Chemoautotrophs - Chemical energy, certain bacteria Primary producers – Transform sunlight energy to chemical energy Sugars, starch, ATP http://www.scienceclarified.com/images/uesc_01_img0028.jpg http://141.150.157.117:8080/prokPUB/figures/normal/p323-006.jpg

  13. 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 = • Net primary producion = • GPP – NPP = Respiration • Energy consumed by producers for maintenance and biosynthesis

  14. Energy lost and unavailable to consumers Partitioning gross primary productivity into respiration and net primary productivity GPP NPP

  15. NUTRIENTS STIMULATE PRIMARY PRODUCTION • Terrestrial production may be nutrient limited • Aquatic systems often strongly nutrient-limited • Open ocean • Addition of nutrients may stimulate unwanted production

  16. GLOBAL PRIMARY PRODUCTION • Correlates with annual precipitation (when light not limiting) • Note relationship among tundra, deserts, and tropics • Oceans – nutrient poor • CO2 Source of carbon • Follows 1st Law of Energy

  17. Grams carbon/m2/yr for globe, as calculated from satellite imagery. Oceans = 46%, land = 54%

  18. PRIMARY PRODUCTION VARIES AMONG ECOSYSTEMS • Maximum under favorable conditions • Intense sunlight • Warm temperatures • Abundant precipitation • Nutrients

  19. NPP vs. Temperature + Precipitation

  20. HETEROTROPHS - CONSUMERS Tertiary consumers Decomposers Secondary consumers Primary consumers Primary producers

  21. Tertiary consumers Decomposers Secondary consumers Primary consumers Primary producers

  22. ECOLOGICAL PYRAMIDS Elton Trophic levels placed in order Reflects: Numbers of organisms at each level Biomass of each level Energy at each level

  23. PYRAMID OF NUMBERS # CONSUMERS=TOP CARNIVORES # DECOMPOSERS # CONSUMERS # HERBIVORES # PRIMARY PRODUCERS

  24. PYRAMID OF BIOMASS kg CONSUMERS=TOP CARNIVORES kg CONSUMERS kG DECOMPOSERS kg HERBIVORES kg PRIMARY PRODUCERS

  25. PYRAMID OF ENERGY kJ CONSUMERS=TOP CARNIVORES kJ CONSUMERS kJ DECOMPOSERS kJ HERBIVORES kJ PRIMARY PRODUCERS

  26. ENERGY TRANSFER EFFICIENCY • ~10% Efficient between trophic levels • What happens to other 90% • How is it dispersed? • Is it lost? • Account for it

  27. ENERGY BUDGET

  28. ECOLOGICAL EFFICIENCY • Ecological Efficiency • Percentage of energy transferred from one trophic level to the next: • Range of 5-20% typical (avg = 10%) • Must understand the utilization of energy within a trophic level Not all food components can be assimilated - Undigested fibrous material from elephant dung

  29. FUNDAMENTAL ENERGY RELATIONSHIPS • Components of an animal’s energy budget are related by: • Assimilated Energy = Ingested Energy – Egested Energy • Production = Assimilated Energy – (Respiration-Excretion)

  30. ASSIMILATION EFFICIENCY • Assimilation Efficiency = Assimilation/Ingestion • Function of Food Quality:

  31. NET PRODUCTION EFFICIENCY • Net production efficiency = production/assimilation • depends on metabolic activity:

  32. What limits the length of the food chain?

  33. 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 • Dynamic stability hypothesis • Long food chains easily disrupted • Support is tentative • Ecosystem size • Species diversity higher

  34. Do aquatic or terrestrial ecosystems have more trophic levels? What factor contributes most to variation in food chain length among these ecosystems?

  35. http://www.yale.edu/post_lab/images/FCL_ecosize_large.gif

  36. 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!

  37. Readings • Quantifying Ecology 14.1, pp 293-294 • Field Studies, pp 300-301 • Ecological Issues p 315 • Quantifying Ecology 17.1, p 355 • Field Studies, pp 402-403 • Ecological Issues pp 638-639 • Sections 19.2, 19.3, 19.4; pp 394-401

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