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, and what controls it.

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

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

4. Trophic Structure??? 1  Production 2  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. PhytoplanktonAttached Algae Attachment

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

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: - CO 2 - Carbonic acid: H 2 CO 3 - Hydrogen carbonate: HCO 3 - - Carbonate: CO 3 2-

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

24. Gas Vacuoles

25. Measuring primary production 6CO 2 + 12H 2 O   C 6 H 12 O 6 + 6H 2 O + 6O 2 Light + Pigment Δ CO 2 Δ O 2 Uptake of 14 C

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 organism is 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 = r p C – (S + G + Pa + D) > C = algal cell concentration > r p = 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