Ecosystem 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 Concept • Organisms physical environment • Organisms 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 system • Spatial concept: defined boundaries, often difficult to define
Focus of Ecosystem Ecology • Ecosystem ecology: focus on the exchange of energy and matter • Inputs: exchanges from surrounding environment • Outputs: exchanges from inside the ecosystem to the surrounding environment • Closed ecosystem: no inputs • Open ecosystems: with inputs
Three 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 inorganic • Consumers: feed on living tissue • Decomposers: break down dead material • Abiotic • Soil, sediments, particulate matter, dissolved organic matter, litter • Energy source driven from sunlight
Energy 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 work • Kinetic energy (KE): energy in motion, performing work at the expense of PE • Work : 1) storage of energy or 2) ordering of matter
First 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 ways • However, 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 state • Photosynthesis products (sugar) store more energy than the reactants that combined to form the products
Entropy • 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 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.
Heat PE I PE II KE
Primary 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 processes • NPP stored at organic matter • NPP = GPP – R • Standing Crop biomass (g/m2 or cal/m2) • NPP accumulates over a given time as biomass in a given area • Instantaneous versus NPP is a rate
Energy Allocation • Annual Plants: begin above ground life cycle in spring • Photosynthates to leaves leaves photosynthesis • At flowering photosynthates reproduction • Perennial: maintain vegetative structure over years • Similar allocation to annuals early • Before allocation switch to reproduction, allocation to roots. Roots can be reserves of food • Reserves flowering and fruits • Trees and woody shrubs • Early life, leaves >1/2 biomass; later leaves=1-5% biomass • Energy goes toward support and maintenance • Evergreens • Year round photosynthesis in leaves • Don’t draw upon reserves of roots in spring year round photosynthesis.
Energy Allocation • Reproduction and vegetative growth • Vegetative growth first, reproduction secondary • Above-ground vs. below-ground biomass • Low 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 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 season • PP function of the rate of photosynthesis and total surface area of the leaf
P= primary production (tn/ha) B= biomass (tn/ha) R= PAR solar radiation (kcal/m2/yr)
Nutrient Limitation in Oceans • Vertical separation between zones of PP and decomposition and nutrient release • Aquatic ecosystems • Surface = photosynthesis occurs via phytoplankton • Deeper water= nutrients recycle due to death a • N, P, and iron limited in the area of primary productivity • Requires upwelling of nutrient rich water to enhance primary productivity (Fig 23.6)
PP Varies with Time • Seasonal variations in PP • Wet tropics: little variation • Cold or distinct wet and dry seasons: variation due to dormancy • Year to year • Climatic: wet and dry years • Herbivory • Fire • Age of ecosystem: • Early stages biomass is in leaf area, later biomass in woody tissue • GPP goes to maintenance, less towards growth as ecosystem ages
PP 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 PP • Climatic factors then can control 2° production
Consumers 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 • Poikilotherms • Assimilation efficiency of 30% • 79% of their assimilation in metabolism, converting greater portion of assimilated energy into biomass.
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 Production Efficiencies
PP, Decomposers, & Climate • Decomposers limited by amount of food energy • Therefore limited by PP • Decomposers also strongly influenced by climate. • Low temps and water limit microbial populations • This then limits decomposition