4 pc 520 420 81 sc 26 23 88 tc 3 3 99 these numbers

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Unformatted text preview: 26 23 88% TC 3 3 ~99% These numbers increase as you move up the trophic levels assimilation increases If you take amount of energy available to each level you can just plot them at each level, primary producers have a lot of energy, primary consumers less, secondary less, tertiary less..called trophic pyramids Nothing preys on lions b/c not enough lions (cant support another trophic leve) *****Relate these values to Fig. 18.16 Why is it advantageous to exploit herbivory? Energy flow to humans Lot of energy to support herbivores Takes energy to support herbivores which are then eaten More energy available for transfer 88% of world food supply is plant Most common plant is rice—comes from wetlands There are only 4 countries that use more animal U.S., Canada, Australia, New Zealand (all others get more calories from plants) A few terms: Biomass – organic matter found in a defined area, usually living Necromass – dead organic matter Production – the amount of energy stored by an individual, population, community or ecosystem per unit time o Primary production – autotrophs o Secondary production – heterotrophs o Gross production – all energy initially assimilated o Net production – (gross-respiration) energy remaining after respiration (it is the net primary production that is the energy available to consumers in an ecosystem) ******** NPP = GPP – R ******** ***Net primary production - amount of energy available to consumers in an ecosystem*** Ecosystem productivity: uses net productivity across ecosystems R. J. Whitaker NPP is measured as the energy stored or biomass (dry weight) added by producers per unit area OVER A GIVEN TIME SPAN. (g/m2y-1) grams per meter square per year Most productive- Wetlands and Salt marshes Least productive- desert (lack of water) and open ocean (lack of nutrients) Estuaries- lots of water, more nutrients (sesspools, too full of nutrients) Temperature, water, nutrients, pH limit primary productivity Factors affecting primary production: Abiotic – temperature, rainfall, photoperiod(how much sunlight an ecosystem is receiving), nutrients, disturbance, etc. Occur Over the growth season (rainfall outside growing season is not beneficial) Biotic – Plant (C3, C4, CAM) and animal biodiversity, community structure (is it grassland, shrub land is it forested?), animal utilization (grazing no grazing?) A few examples looking at abiotic and biotic factors affecting primary productivity: Figure 18.2 the effects of temp and precip. Temperature and precipitation are extremely important in regulation of primary productivity As evapotranspiration (amount of moisture evaporated off land surface over year) increases the net primary productivity increases—warm and moist is more productive Increase in aet increases net primary production Figure 18.3 Increased precipitation alone will increase net primary production increases (controls variation of primary production in ecosystem type) Total amount of water that evaporates or transpires off a landscape in a year Figuree 18.10 If you inc...
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