Ecosystem ProcessesCommunities to EcosystemsSlide 3Slide 4Thermodynamics in EcologyEcosystemsSlide 7Slide 8Slide 9Slide 10Gross & net primary production; respirationPrimary ProductionPhotosynthesis inputs & outputsSlide 14Measuring NPP & GPPSlide 16Effects of LightEffect of LightEffects of TempEffects of Water & TempWater limits GPPNutrients stimulate GPPSlide 23ProductivityNet primary production among ecosystemsSlide 26Energy TransfersSlide 28Slide 29Ecological EfficiencyIntratrophic Energy TransfersSlide 32Egestion example: undigestable plant materialSlide 34Slide 35Slide 36High metabolism expends assimilated energy (not available for growth)Slide 38Assimilation EfficiencySummaryGlobal trends in biodiversitySlide 42Slide 43Species abundance varies with latitudeDiversity correlated with complex habitatsSlide 46Diversity correlated with energy inputPatterns of BiodiversityEcosystem Processes 1. The ecosystem concept2. Productivity3. Energy transfers & pyramids4. Patterns of biodiversityCommunities to Ecosystems1. Natural Associations2. Direct & indirect links via feedingCommunities to EcosystemsSummerhayes & Elton 1923Communities to Ecosystems1. Natural Associations2. Direct & indirect links via feedingElton’s new concepts:food chainfood cycle (now called food web)pyramid of numbersThermodynamics in Ecology1. Size2. Productivity3. (in)efficiencyConservation of mass and energyenergy input from sunnutrientcyclingProducersConsumers & Decomposersenergy output (mainly heat)EcosystemsA community of organisms and their physical environment, interacting through a one-way flow of energy and cycling of materialsThermodynamics in EcologyOrigin of the trophic level conceptLindeman drove the point homeTrophic levels as a pyramidThermodynamics in EcologyThermodynamics in EcologyEnergy flow between trophic levelsGross & net primary production; respirationPrimary Production•Primary production is the capture of light energy and its conversion to chemical energy–primary productivity–6CO2 + 6H2O → C6H12O6 + 6O2The rate of primary production determines the rate of energy supply to the rest of the ecosystem:Photosynthesis inputs & outputsPrimary Production–Gross primary production = total energy assimilated by primary producers–Net primary production = energy accumulated (in stored form) by primary producers–gross - net = Respiration, the energy consumed by producers for maintenance and biosynthesisMeasuring NPP & GPP–harvest techniques determine dry mass accumulated (net production)–gas exchange techniques determine net uptake of CO2 in light (net production), production of CO2 in dark (respiration) and gross production as their sum It’s all about accounting.Measuring NPP & GPPIt’s all about accounting.Effects of Light•Light is rarely the limiting resouce in full sun.•In shade, PS may be reduced below its maximum.•Overall, photosynthetic efficiency of the ecosystem is typically 1-2%:–remaining energy is either reflected or absorbed and dissipatedEffect of LightEffects of Temp•Optimum temperature for photosynthesis varies with system:–about 16oC for many temperate species–as high as 38oC for some tropical species•Rate of photosynthesis increases with temperature, up to a point:–rate of respiration also increases with temperature–net assimilation may thus decrease at high temperaturesEffects of Water & TempWater limits GPP•Photosynthesis in terrestrial systems is water-limitedNutrients stimulate GPP•Terrestrial production may be nutrient -limited:–fertilizers–N often the limiterAdenostema – chaparral shrub; drought-resistant; western U.S.Others are annual grassesNutrients stimulate GPP•Aquatic systems are often strongly nutrient -limited:–especially true of open ocean (nitrogen, minerals)–freshwater usually phosphorus limited–inadvertent addition of nutrients may stimulate unwanted productionProductivityWhere’s the most productive ecosystem in the world?Net primary production among ecosystemsNet primary production across EarthEnergy Transfers•Autotrophs•HeterotrophsEnergy TransfersOnly 5% to 20% of energy passes between trophic levels.213833,36820,810 kilocalories/square meter/yeartop carnivorescarnivoresherbivoresproducersdecomposers + detritivores = 5,080marsh hawkcrowupland sandpipergarter snakefrogspiderweasel badger coyoteground squirrelpocket gopherprairie vole sparrowearthworms, insects First Trophic Level Second Trophic Level Higher Trophic Levels Part of the Tallgrass Prairie Food Webgrasses, composites Energy loss at each transfer limits the number of trophic levels to about 4 or 5Ecological Efficiency•Ecological efficiency is the % of energy transferred from one level to the next:–range of 5% to 20% is typical, as we’ve seen–where does energy go within a trophic level?Intratrophic Energy Transfers•ingestion (energy content of food ingested)Intratrophic Energy Transfers–egestion (energy content of indigestible materials regurgitated or defecated)Egestion example: undigestable plant materialIntratrophic Energy Transfers–assimilation (energy content of food digested and absorbed)Intratrophic Energy Transfers–excretion (energy content of organic wastes)Intratrophic Energy Transfers–respiration (energy consumed for maintenance; performs work or is lost as heat)High metabolism expends assimilated energy (not available for growth)Intratrophic Energy Transfers–production (residual energy content for growth and reproduction)Assimilation Efficiency•Assimilation efficiency = assimilation/ingestion •primarily a function of food quality:–seeds: 80%–young vegetation: 60-70%–plant foods of grazers, browsers: 30-40%–decaying wood: 15%–animal foods: 60-90%Summary•Primary productivity•Trophic levels•Intratrophic energy transfersGlobal trends in biodiversitySpecies richness across EarthNumber of species of ants Number of species of breeding birdsSpecies abundance varies with latitudeDiversity correlated with complex habitatsDiversity correlated with energy inputPatterns of Biodiversity Diversity on islands depends on:distance to the mainland island