Ecosystem Production Objectives Describe the concept of the ecosystem Relate the laws of...
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Transcript of Ecosystem Production Objectives Describe the concept of the ecosystem Relate the laws of...
Ecosystem Production ObjectivesEcosystem Production Objectives
Describe the concept of the ecosystem
Relate the laws of thermodynamics to ecology
Define the types of ecological production
Discuss how plants allocate net primary production
Tell how net primary production varies among world ecosystems and why
Describe secondary production and its allocation
Compare assimilation & production efficiencies of poikilotherms & homeotherms
Ecosystem ConceptEcosystem Concept
Organisms physical environmentOrganisms Organisms (Intra-specific competition)Organisms Organisms (Inter-specific competition)
Community structure= biota only Communities abiotic = Ecosystem
Ecosystem: biological and physical components of the environment as a single interactive systemSpatial concept: defined boundaries, often difficult to define
Focus of Ecosystem EcologyFocus of Ecosystem Ecology
Ecosystem ecology: focus on the exchange of energy and matter
Inputs: exchanges from surrounding environmentOutputs: exchanges from inside the ecosystem to the surrounding environment
– Closed ecosystem: no inputs– Open ecosystems: with inputs
Three Basic ComponentsThree Basic Components
Autotrophs (Producers) Largely green plants that use energy of sun in photosynthesis to transform inorganic compounds into organic compounds
Heterotrophs: Use the organic compounds of producers as a source of food; eventually break down organic into inorganicConsumers: feed on living tissueDecomposers: break down dead material
AbioticSoil, sediments, particulate matter, dissolved organic matter, litterEnergy source driven from sunlight
Energy FlowEnergy Flow
Production involves fixation and transfer of energy from sun
Energy exists in two forms:Potential energy (PE): stored energy that is capable of doing workKinetic energy (KE): energy in motion, performing work at the expense of PEWork : 1) storage of energy or 2) ordering of matter
First Law of ThermodynamicsFirst Law of Thermodynamics Energy is neither created nor destroyed
May change in form, pass from one place to another, or act upon matter in various waysHowever, no gain or loss of energy occurs
Exothermic reaction: energy lost from the system to surrounding environment:
Wood burning: PE of molecular bonds KE of heat Endothermic: energy from outside is put into a system
to raise to a higher energy statePhotosynthesis products (sugar) store more energy than the reactants that combined to form the products
EntropyEntropy
Total energy is maintained in a reaction, but tends to disperse randomly and in disorder
PE of wood molecules disperse as KE of heat that disperse and incapable of doing further work
Second Law of ThermodynamicsSecond Law of Thermodynamics When energy is transferred or transformed, part of the
energy is assumes a form that can’t pass on any further
Entropy increase– Boiler Coal steam+heat, some heat dispersed to air, incapable
to do work in that system– Same is true for transfer of energy from one organism to another
in the form of food, some of the energy is lost as heat, unable to do work, some is stored as tissue, able to to work.
Primary ProductionPrimary Production Primary production
Energy accumulated by plants via photosynthesis Primary productivity
Rate energy is accumulated by plants (kcal/m2 or g/m2) Gross primary production (GPP)
Total energy assimilated by the plant through photosynthesis Net primary production (NPP):
Energy remaining after respiration (R), for living processesNPP stored at organic matterNPP = GPP – R
Standing Crop biomass (g/m2 or cal/m2)NPP accumulates over a given time as biomass in a given areaInstantaneous versus NPP is a rate
Energy AllocationEnergy Allocation Annual Plants: begin above ground life cycle in spring
Photosynthates to leaves leaves photosynthesisAt flowering photosynthates reproduction
Perennial: maintain vegetative structure over yearsSimilar allocation to annuals earlyBefore allocation switch to reproduction, allocation to roots. Roots can be reserves of foodReserves flowering and fruits
Trees and woody shrubsEarly life, leaves >1/2 biomass; later leaves=1-5% biomassEnergy goes toward support and maintenance
EvergreensYear round photosynthesis in leavesDon’t draw upon reserves of roots in spring year round photosynthesis.
Energy AllocationEnergy AllocationReproduction and vegetative growth
Vegetative growth first, reproduction secondary
Above-ground vs. below-ground biomassLow light:
– Allocation of energy to leaves and stems at the expense of roots– High shoot-to-root ratio
Low water/nutrients:– Allocation of energy to roots at the expense of leaves and shoots– Low shoot to root ratio– Midwest prairies: shoot-to-root ratio of 1:3 due to low moisture
These are indicators of ecosystem conditions
Climatic InfluencesClimatic Influences
NPP increases with increasing temperature and rainfall
Temperature and rainfall influence photosynthesis via the area of the leaf that can be supported and the duration of the growing seasonPP function of the rate of photosynthesis and total surface area of the leaf
Nutrient Limitation in OceansNutrient Limitation in Oceans Vertical separation between zones of PP and
decomposition and nutrient release Aquatic ecosystems
Surface = photosynthesis occurs via phytoplanktonDeeper water= nutrients recycle due to death aN, P, and iron limited in the area of primary productivityRequires upwelling of nutrient rich water to enhance primary productivity (Fig 23.6)
PP Varies with TimePP Varies with Time Seasonal variations in PP
Wet tropics: little variationCold or distinct wet and dry seasons: variation due to dormancy
Year to yearClimatic: wet and dry yearsHerbivoryFire
Age of ecosystem:Early stages biomass is in leaf area, later biomass in woody tissueGPP goes to maintenance, less towards growth as ecosystem ages
PP Limits 2° ProductionPP Limits 2° Production 2° production:
Energy left over from maintenance and respiration goes into production, including growth of new tissue and the production of young
2° production limited by PPClimatic factors then can control 2° production
Consumers Vary in Efficiency of ProductionConsumers Vary in Efficiency of Production Not all consumers have the same efficiency of
transforming energy consumed into 2° production Homeotherms
High assimilation efficiency: 70 % but use 98% for metabolism low production efficiency
PoikilothermsAssimilation efficiency of 30%79% of their assimilation in metabolism, converting greater portion of assimilated energy into biomass.
Production EfficienciesProduction Efficiencies
Terms PP: Primary Production GPP: Gross Primary
Production NPP: Net Primary Production R: Respiration I: Ingestion W: Egestion; feces, urine, gas,
etc. A: Assimilation as food or
energy absorbed
Equations Photosynthetic efficiency
GPP/ solar radiation Assimilation efficiency, plants
GPP/light absorbed Respiration
GPP-NPP Effective PP
NPP/GPP Assimilation Efficiency, animals
A/I Ecological growth efficiency
P/I Production efficiency
P/A
PP, Decomposers, & ClimatePP, Decomposers, & Climate
Decomposers limited by amount of food energyTherefore limited by PP
Decomposers also strongly influenced by climate.
Low temps and water limit microbial populationsThis then limits decomposition