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.
Lindemann RL. 1942. The trophic-dynamic aspects of ecology. Ecology 23: 399-418.
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
Trophic Structure??? 2 Production 1 Production
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.
Major Primary Producers in Fresh Water • Algae • Diatoms • Cyanobacteria (aka, blue-green algae)
Reproduction of Cyanobacteria • Binary fission • Budding • Fragmentation
Stromatolites: formed in shallow water by cyanobacteria that trap and bind sedimenting grains.
Attachment Phytoplankton Attached Algae
Picoplankton (< 5 μm) Size Macroplankton (> 500 μm)
Pigmentation • Chlorophyll: appears green • Carotenoids: appear red / orange • Billiproteins: pigment-protein complexes common in cyanobacteria.
Factors affecting pigment concentration • Shading • Photoinhibition • Physiological condition
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-
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?
Characteristics that reduce sinking rate Small Size Filamentous Structure Gelatinous Sheath
Measuring primary production Light + Pigment • 6CO2 + 12H2O C6H12O6 + 6H2O + 6O2 • Δ CO2 • Δ O2 • Uptake of 14C
Factors regulating primary productivity • Light • Inorganic nutrients and water chemistry
Vertical profiles of primary production in different lake types Light Nutrients
Factors regulating primary productivity • Light • Inorganic nutrients and water chemistry • Competition among species
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.
Factors regulating primary productivity • Light • Inorganic nutrients and water chemistry • Competition among species • Other
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
Emergent patterns in phytoplankton communities • Seasonal succession • Response to grazing by zooplankton