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Lecture Goals

Lecture Goals . To review the concept of trophic structure – how energy moves through ecosystems. To discuss primary production in freshwater ecosystems – who does it, how do they do it, and what controls it. Lindemann RL. 1942. The trophic-dynamic aspects of ecology. Ecology 23: 399-418.

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Lecture Goals

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  1. Lecture Goals • To review the concept of trophic structure – how energy moves through ecosystems. • To discuss primary production in freshwater ecosystems – who does it, how do they do it,andwhat controls it.

  2. Lindemann RL. 1942. The trophic-dynamic aspects of ecology. Ecology 23: 399-418.

  3. Detritivore Sp. 11 Trophic Structure Sp. 10 2 Production Sp. 7 Sp. 9 Sp. 8 1 Production Sp. 1 Sp. 2 Sp. 3 Sp. 4 Sp. 6 Sp. 5

  4. Trophic Structure??? 2 Production 1 Production

  5. Productivity is a Rate • Production of biomass over time (e.g., mg C / hr) • Snap-shots only capture “standing stock”. • Rate of “turn-over” affects the distribution of biomass among layers.

  6. Major Primary Producers in Fresh Water • Algae • Diatoms • Cyanobacteria (aka, blue-green algae)

  7. Algae

  8. Reproduction of Algae

  9. Diatoms

  10. Diatom Reproduction is Cool

  11. Cyanobacteria

  12. Reproduction of Cyanobacteria • Binary fission • Budding • Fragmentation

  13. Stromatolites: formed in shallow water by cyanobacteria that trap and bind sedimenting grains.

  14. Other ways of classifying freshwater primary producers

  15. Attachment Phytoplankton Attached Algae

  16. Picoplankton (< 5 μm) Size Macroplankton (> 500 μm)

  17. Pigmentation • Chlorophyll: appears green • Carotenoids: appear red / orange • Billiproteins: pigment-protein complexes common in cyanobacteria.

  18. Light absorption by different algal pigments

  19. Factors affecting pigment concentration • Shading • Photoinhibition • Physiological condition

  20. General physiological requirements • Light of specific wavelength • Nutrients: • - N and P • - Si for diatoms • - Mg for chlorophyll • Carbon forms: • - CO2 • - Carbonic acid: H2CO3 • - Hydrogen carbonate: HCO3- • - Carbonate: CO32-

  21. Movement and Buoyancy • Light is in the epilimnion. • To stay in epilimnion, need to (1) not sink, and (2) deal with water circulation. • How do they do it?

  22. Movement with Flagella

  23. Characteristics that reduce sinking rate Small Size Filamentous Structure Gelatinous Sheath

  24. Gas Vacuoles

  25. Measuring primary production Light + Pigment • 6CO2 + 12H2O  C6H12O6 + 6H2O + 6O2 • Δ CO2 • Δ O2 • Uptake of 14C

  26. Factors regulating primary productivity • Light

  27. Factors regulating primary productivity • Light • Inorganic nutrients and water chemistry

  28. Lake classifications based on nutrient levels

  29. Vertical profiles of primary production in different lake types Light  Nutrients

  30. Factors regulating primary productivity • Light • Inorganic nutrients and water chemistry • Competition among species

  31. Leibig’s Law of the Minimum • The population growth rate of an organism is determined by the abundance of the nutrient that relative to the needs of that organismis least abundant in the environment.

  32. Competition for a limiting resource

  33. Competition for multiple resources

  34. Factors regulating primary productivity • Light • Inorganic nutrients and water chemistry • Competition among species • Other

  35. Other factors regulating primary productivity • Change over time: dC/dt = rpC – (S + G + Pa + D) • > C = algal cell concentration • > rp = rate of photosynthesis • > S = sinking out of algae below photic zone • > G = zooplankton grazing • > Pa = parasitism and disease • > D = natural death

  36. Emergent patterns in phytoplankton communities • Seasonal succession • Response to grazing by zooplankton

  37. Seasonal succession in phytoplankton biomass and community composition

  38. Phytoplankton productivity in the summer

  39. Effect of grazing on phytoplankton community composition

  40. Algal Defenses

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