Ecosystems. Physical Laws Law of Conservation of Energy - Energy can not be created or destroyed, only transformed. Chapter 55: Ecosystems. Fig. 55.

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1 Chapter 55: Ecosystems 1 Ecosystems consist of the living organisms in a community as well as the abiotic factors Microecosystem Two important considerations: Energy Flow Chemical cycling Fig Physical Laws Law of Conservation of Energy - Energy can not be created or destroyed, only transformed 2nd Law of Thermodynamics - Energy transfers cause energy to be transferred to a less useful form (usually heat) Law of Conservation of Mass - matter cannot be created or destroyed Sun Key Heat Primary producers Chemical cycling Energy flow Primary Detritus Fig Secondary and tertiary Microorganisms and other detritivores 3

2 Tropic Relationships Producers - autotrophs Primary - eat producers Secondary - eat primary Tertiary - eat secondary Detritivores - that get energy from detritus 4 Importance of Decomposers Food (birds eat earthworms) Recycling of materials: Make vital chemical elements available to producers Transfer chemical elements in inorganic forms to abiotic reservoirs like soil, water, and air Producers take these inorganic elements and recycle them into organic compounds 5 Physical and Chemical Factors Primary production - amount of light energy converted to chemical energy by autotrophs during a given time period Global Energy Budget Only a small fraction of the solar energy that makes it to the earth s surface comes into contact with photosynthesizing organisms and is a usable wavelength (about 1%) 6

3 Gross and Net Primary Production Gross Primary Production (GPP) - the amount of light energy that is converted to chemical energy by photosynthesis per unit time Net Primary Productivity - equals GPP minus the energy used by the primary producers for respiration NPP = GPP - R Can be expressed in terms of energy (J/m 2 / yr) or in terms of biomass (g/m 2 /yr) 7 Limitations to Productivity in Aquatic Ecosystems Light photic vs. aphotic zone Nutrients limiting nutrient - element that must be added in order for production to increase (usually nitrogen or phosphorus) RESULTS Phytoplankton density (millions of cells per ml) Ammonium enriched Phosphate enriched Unenriched control A B C D E F G Collection site Fig Eutrophication process by which nutrients become highly concentrated leading to increased growth of organisms (like algae) Cultural Eutrophication - origin from human sources (usually agricultural runoff and sewage) Fig

4 Temperature and Moisture Measured as evapotranspiration Actual evapotranspiration - annual amount of water transpired by plants and evaporated from the landscape Fig Net annual primary production (above ground, dry g/m 2. yr) 1,400 1,200 1, Mean annual precipitation (cm) 10 Tropic Levels and Energy Secondary Production - amount of chemical energy in food that is converted into their own new biomass during a given time period Production efficiency - the fraction of energy stored in food that is not used for respiration Plant material eaten by caterpillar 200 J Feces 100 J 33 J 67 J Cellular respiration Not assimilated Growth (new biomass; secondary production) Assimilated Fig Tropic Efficiency Percentage of production transferred from one trophic level to the next Tertiary 10 J Secondary 100 J Primary 1,000 J Fig Primary producers 10,000 J 1,000,000 J of sunlight 12

5 Green World Hypothesis terrestrial herbivores consume relitivly small amounts of plant biomass because they are kept in check by various factors Factors: Plants have defenses against herbivores Nutrients Abiotic factors Intraspecific competition Interspecific interactions 13 Biogeochemical Cycles nutrient circuits that involve both biotic and abiotic components of the ecosystem General Model Reservoir A Organic materials available as nutrients Living organisms, detritus Fossilization Reservoir B Organic materials unavailable as nutrients Peat Coal Respiration, decomposition, excretion Oil Burning of fossil fuels Fig Reservoir D Inorganic materials unavailable as nutrients Minerals in rocks Assimilation, photosynthesis Weathering, erosion Formation of sedimentary rock Reservoir C Inorganic materials available as nutrients Atmosphere Water Soil 14 General Scheme of Biogeochemical Cycles Key role of decomposers Decomposition increases with increases in evapotranspiration Consumers Producers Nutrients available to producers Abiotic reservoir Decomposers Fig Geologic processes 15

6 Agriculture and Nitrogen Cycling Nutrients not recycled in agricultural applications Nutrients taken away as crop biomass Natural store of nutrients will eventually be exhausted 16