Trophic Trophic Structure & Food WebsStructure & Food Webs1946, Riley published a simple food web model:PP = 153T - 120P - 7.3N - 9.1Z + 67131947, simplified it to:dN/dt = N(Ph - R) - GTrophic Trophic Structure & Food WebsStructure & Food Webs1946, Riley published a simple food web model:PP = 153T - 120P - 7.3N - 9.1Z + 67131947, simplified it to:dN/dt = N(Ph - R) - GPhytoplanktonNutrientsZooplanktonTrophic Trophic TerminologyTerminologyTop Down Control:Top Down Control:Regulation of ecosystems by predationRegulation of ecosystems by predationBottom Up Control:Bottom Up Control:Regulation of ecosystems by physicsRegulation of ecosystems by physicsTrophic Trophic CascadesCascadesInfluencing any one Influencing any one ““boxbox”” cascades to other cascades to otherboxes, not always linearlyboxes, not always linearlyThe concept of r-K strategyThe concept of r-K strategyFood webs versus food chainsFood webs versus food chainsr versus K strategies r versus K strategiesBased on the concept of ‘maximizing’ reproductiveefficiency by balancing offspring versus parenting r < ---------------------------------------------------------------> KRapid Growth Slow growthMultiple offspring Fewer offspringShort Life Long LifeSmall body size Large body sizeInvasive/Transient EstablishedGeneralists SpecialistMargalefMargalef’’s Mandalas MandalaRamon Margalef(1978) updated theidea of r-Kstrategies for theocean…said thatyou can definespecies successionbased on a “phasespace” defined byenergy (turbulence)and nutrientsEcosystems and Energy TransferEcosystems and Energy TransferEcosystemEcosystem: biotic community + environment: biotic community + environmentProducersProducersConsumersConsumersDecomposersDecomposersEcosystems and Energy TransferEcosystems and Energy TransferEnergy is Energy is alwaysalways lost! lost!Ecosystems and Energy TransferEcosystems and Energy TransferTrophic Trophic Levels:Levels: each level of organismeach level of organismTrophic Trophic Transfer:Transfer: percentage of energy percentage of energyFood Chains:Food Chains: short, direct transfer of energyshort, direct transfer of energyfrom phytoplankton to apex predatorsfrom phytoplankton to apex predatorsNZPNPZ Models of BiologyNPZ Models of BiologyCirculation/physicsRemineralization timeFeeding efficiencyRespiration, excretionMichaelis-Menten RespirationTemperatureLightMicrobial Food WebMicrobial Food WebFirst recognized byFirst recognized by Azam Azam, extended by, extended byothers (Pomeroy, others (Pomeroy, WiebeWiebe,, Hobbie Hobbie))1977:1977: Hobbie Hobbie introduces introduces Acridine Acridine Orange OrangeDirect Counts (AODC)Direct Counts (AODC)•• 1980s-90s: 1980s-90s:Viruses discoveredViruses discovered•• 2000: 2000: Archaea Archaea!!The Microbial WebThe Microbial WebViruses can account for aViruses can account for amajor source ofmajor source ofphytoplankton mortalityphytoplankton mortalityBacteria canBacteria canprovide 50% ofprovide 50% ofphytoplanktonphytoplanktonnutrientsnutrientsSome ecosystemsSome ecosystemscan be netcan be netheterotrophicheterotrophicUp to 20% of thebiomass in theoceans may beassociated witharchaea.What are theydoing?Illustration by S. Cook, Scripps Institution of OceanographyWhat is DOM?Operational definition: organic matter that passes a GF/F filter(nominal pore size of 0.7 µm)DOM = Dissolved Organic Matter; DOC = Dissolved OrganicCarbon; DON= Dissolved Organic Nitrogen; DOP=DissolvedOrganic PhosphorousIncludes1. All (most) viruses2. 50% of bacteria3. Some phytoplankton (chlorophyll)4. Many "submicron particles," e.g. colloidsItems 1-3 generally not big part of DOM pool.Hansell, D.A. and C.A. Carlson (ed) 2002. Biogeochemistry ofMarine Dissolved Organic Matter. Academic Press.Deep water DOC is ca.6000 years old.Same concentration ofdeep DOC is also insurface layer becauseoceans circulate on orderof 1000 years• Divide the DOC poolinto threecomponents:1) Refractory DOM2) Semi-labile DOM3) Labile DOMCole et al. (1988) Mar. Ecol. Progr. Ser 43: 1-10Bacterial Production and NPPBacterial Production and NPPare generally relatedare generally relatedPrimary Production (mg C m-2 d-1)200 400 600 800 1000 1200 1400Bacterial Production (mg C m-2 d-1)0100200300400500N.PacificSubarcticEquatorN. AtlanticNA RingsIndianArcticAntarcticaBacteria roughly follow phytoplanktonSource of organic CLakes & EstuariesArcticSo what is the microbial web?So what is the microbial web?About 50% of NPP goes through bacterialAbout 50% of NPP goes through bacterialdegradation (formation of DOM,degradation (formation of DOM,respiration back to inorganic compounds)respiration back to inorganic compounds)For For eacheach size class of producer, there size class of producer, there’’s ans anequivalent consumerequivalent consumerIn terms of new versus regeneratedIn terms of new versus regeneratedproduction, the microbial web is production, the microbial web is HOWHOW the thematerial is regenerated, and the microbialmaterial is regenerated, and the microbialcommunity is community is WHOWHO is responsible is responsibleHow do we measure it?How do we measure it?WhoWho’’s theres thereFlowFlow Cytometry CytometryMicroscopy (withMicroscopy (withstains)stains)SEM/TEM (viruses)SEM/TEM (viruses)Chemical analysisChemical analysisWhatWhat’’s theres thereChemical analysisChemical analysisRadio-datingRadio-datingNMR, mass spec, etc.NMR, mass spec, etc.Rates (producers)Rates (producers)3H-3H-ThymidineThymidine3H-3H-LeucineLeucineRespirationRespirationRates (consumers)Rates (consumers)Fluorescently LabeledFluorescently LabeledBacteria (FLB)Bacteria (FLB)Grazer DilutionGrazer DilutionInfection/Infection/LysisLysisWho Cares?Who Cares?• Air-Sea flux of:CO2, methane, DMS,oxygen, nitrogen gas• Regeneration ofnutrients• Repackaging oforganic matter• Recycling andoxidation (rather thanexport)SummarySummaryIn the 1970s, the importance of the In the 1970s, the importance of the ‘‘microbialmicrobiallooploop’’ (web) was discovered (web) was discoveredFor each size class of producer, there is anFor each size class of producer, there is anequivalent consumerequivalent consumerApproximately 50% of NPP goes through thisApproximately
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