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

Schematic DiagramSchematic Diagram

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.

PE I KE PE II

Heat

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

Terrestrial Ecosystem PPTerrestrial Ecosystem PP

P= primary production (tn/ha)B= biomass (tn/ha)R= PAR solar radiation (kcal/m2/yr)

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

Energy Metabolism of DeerEnergy Metabolism of Deer

Rainfall versus 2° ProductionRainfall versus 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

Decomposition versus ClimateDecomposition versus Climate