Concept to UnderstandAs energy flows throughecosystems in food chains andwebs, the amount of chemicalenergy available to organisms ateach succeeding feeding leveldecreases.
Fig. 3-8, p. 46Trophic LevelsAt each level energy is transferred to thenext but some energy is “lost” in the formof heat
Energy Flow in EcosystemsFood chainSequence of organisms, eachof which serves as a source offood for the nextFood webNetwork ofinterconnected foodchainsMore complex than a foodchain
Usable Energy by Trophic LevelEnergy flow follows the second law ofthermodynamics, which is……2nd Law of Thermodynamics: Energycannot be created or destroyed, butchanged.But as energy is changed, someenergy is lost in the form of heat.
Usable Energy by Trophic LevelBiomass – dry weight of all organicmatter in plants and animals in anecosystem.Biomassdecreases withincreasingtrophic level
Fig. 3-10, p. 47Ecological efficiency – typically 10%(10% rule)
Two Kinds of Primary ProductivityGross primary productivity (GPP) – The rate at whichecosystems producers convert solar energy into chemicalenergy in the form of biomassSo the amount ofsolar energyconverted intocellskilocalories/squaremeter/year
Two Kinds of Primary ProductivityNet primary productivity (NPP) – is what energy is left overfor the consumers in the ecosystem.GPP minus the energy the producer need to survive
Two Kinds of Primary ProductivityPlanet’s NPP limits number of consumersHumans use, waste, or destroy 10-55% of earth’s totalpotential NPPHuman population is less than 1% of total biomass ofearth’s consumers
Temperate forestAquatic EcosystemsOpen oceanContinental shelfLakes and streamsEstuariesTerrestrial EcosystemsExtreme desertDesert scrubTundra (arctic and alpine)Temperate grasslandWoodland and shrublandAgricultural landSavannaNorthern coniferousforest (taiga)Swamps and marshesTropical rain forestFig. 3-11, p. 48Average net primary productivity (kcal/m2/yr)800 1,600 2,400 3,200 4,000 4,800 5,600 6,400 7,200 8,000 8,800 9,600