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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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slide1

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.
slide3

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

slide4

Trophic Structure???

2 Production

1 Production

slide5

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.
slide6

Major Primary Producers in Fresh Water

  • Algae
  • Diatoms
  • Cyanobacteria (aka, blue-green algae)
slide12

Reproduction of Cyanobacteria

  • Binary fission
  • Budding
  • Fragmentation
slide15

Attachment

Phytoplankton

Attached Algae

slide16

Picoplankton (< 5 μm)

Size

Macroplankton (> 500 μm)

slide17

Pigmentation

  • Chlorophyll: appears green
  • Carotenoids: appear red / orange
  • Billiproteins: pigment-protein complexes common in cyanobacteria.
slide19

Factors affecting pigment concentration

  • Shading
  • Photoinhibition
  • Physiological condition
slide20

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-
slide21

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?
slide23

Characteristics that reduce sinking rate

Small Size

Filamentous Structure

Gelatinous Sheath

slide25

Measuring primary production

Light

+

Pigment

  • 6CO2 + 12H2O  C6H12O6 + 6H2O + 6O2
  • Δ CO2
  • Δ O2
  • Uptake of 14C
slide27

Factors regulating primary productivity

  • Light
  • Inorganic nutrients and water chemistry
slide30

Factors regulating primary productivity

  • Light
  • Inorganic nutrients and water chemistry
  • Competition among species
slide31

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.
slide34

Factors regulating primary productivity

  • Light
  • Inorganic nutrients and water chemistry
  • Competition among species
  • Other
slide35

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
slide36

Emergent patterns in phytoplankton communities

  • Seasonal succession
  • Response to grazing by zooplankton