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Primary Production and Energy Flow.docx

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McMaster University
Kim Dej

November 14 , 2012 Biology 2F03: Fundamental and Applied Ecology Primary Production and Energy Flow Primary production and energy flow - terrestrial primary production is primarily limited by temperature and moisture - aquatic primary production is generally limited by nutrient availability - consumers affect the primary production rates - energy losses limit the number of trophic levels in ecosystems Primary production – definitions - primary production: energy fixed (biomass produced) by autotrophs (plants, algae, chemosynthetic microbes) - rate of primary production: the amount of energy (biomass) fixed over a time interval - gross primary production: the total amount of energy fixed - net primary production: the amount of energy left after autotrophs met their energetic needs - trophic level: a position in the food web determined by the number of energy transfers from primary producers Question - what are the main controls of primary production Productivity vs. water and temperature - actual evapotranspiration, AET, and net aboveground primary production – various ecosystems - AET increases with precipitation and temperature - Recall the link between the climate and biomes Nutrients also affect productivity - experimental addition of several nutrients (tundra) - does this mean that tundra has been underestimated - no, all biomes are limited by nutrients in a similar fashion but evapotranspiration exerts dominant control - all the range for all ecosystems: 50-3200 Question - are evapotranspiration and nutrients also the main controls in the aquatic systems Aquatic systems - in most freshwater ecosystems one nutrient limits primary production - if you recall Si:P ratio and competition among diatoms, you could predict where the greatest diversity is going to be Causes of high algal biomass - algal biomass and rate of primary production are linked (in temperate lakes) - possible alternative: longevity cells combined with the absence of graxing (cell accumulation) - why algae are abundant at high P Experimental evidence - a whole lake experiment demonstrates the effect of nutrient additions on phytoplankton biomass Question - therefore, where should one expect productivity in the oceans Geographic variation in marine primary production - where should productivity be highest - red = greatest primary production; blue = lowest - highest rates of production are on continental shelf and i
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