CH 55 & 56 – Energy flow in Ecosystems

1. CH 55 & 56 – Energy flow in Ecosystems

2. Overview: Ecosystems • An ecosystem consists of all the organisms living in a community, as well as the abiotic (non-living) factors with which they interact • Ecosystems range from a small, such as an aquarium, to a large, such as a lake or forest

3. Figure 55.2

4. Ecosystem dynamics involve two main processes: energy flow and chemical cycling • Energy flows through ecosystems • Matter cycles within them • Physical laws govern energy flow and chemical cycling in ecosystems • Conservation of Energy (first law of thermodynamics) • Energy enters from solar radiation and is lost as heat • Conservation of matter - Chemical elements are continually recycled within ecosystems • Ecosystems are open systems, absorbing energy and mass and releasing heat and waste products

5. Energy, Mass, and Trophic Levels • Autotrophs build molecules themselves using photosynthesis or chemosynthesis as an energy source • Heterotrophs depend on the biosynthetic output of other organisms

6. Energy and nutrients pass from primary producers (autotrophs) to primary consumers (herbivores) to secondary consumers (omnivores & carnivores) to tertiary consumers (carnivores that feed on other carnivores) • Detritivores,or decomposers, are consumers that derive their energy from detritus • Prokaryotes and fungi are important detritivores • Decomposition connects all trophic levels

7. Figure 55.4 Sun Key Chemical cycling Energy flow Heat Primary producers Primaryconsumers Detritus Microorganismsand otherdetritivores Secondary andtertiary consumers Arrows represent energy flow so they go from prey TO predator

8. Concept 55.3: Energy transfer between trophic levels is typically only 10% efficient • Net Primary Production (NPP) is the amount of new biomass added in a given time period • Only NPP is available to consumers • Ecosystems vary greatly in NPP and contribution to the total NPP on Earth • Limited by light, nutrients and other abiotic factors • Secondary is the amount of chemical energy in food converted to new biomass

9. Production Efficiency • When a caterpillar feeds on a leaf, only about one-sixth of the leaf’s energy is used for secondary production • An organism’s production efficiency is the fraction of energy stored in food that is not used for respiration

10. Figure 55.10 Plant materialeaten by caterpillar 200 J 67 J Cellularrespiration 100 J Feces 33 J Not assimilated Assimilated Growth (new biomass;secondary production)

11. Interesting Energy production facts: • Birds and mammals have efficiencies in the range of 13% because of the high cost of endothermy • Fishes have production efficiencies of around 10% • Insects and microorganisms have efficiencies of 40% or more

12. Trophic Efficiency and Ecological Pyramids • Trophic efficiency is the percentage of production transferred from one trophic level to the next • It is usually about 10%, with a range of 5% to 20% • Trophic efficiency is multiplied over the length of a food chain

13. Approximately 0.1% of chemical energy fixed by photosynthesis reaches a tertiary consumer • A pyramid of net production represents the loss of energy at each level Tertiaryconsumers 10 J Secondaryconsumers 100 J Primaryconsumers 1,000 J Primaryproducers 10,000 J 1,000,000 J of sunlight

14. In a biomass pyramid, each level represents the dry mass of all organisms in each level • Most biomass pyramids show a sharp decrease at successively higher trophic levels

15. Role of Humans in Energy flow: • Dynamics of energy flow in ecosystems have important implications for the human population • Eating meat is a relatively inefficient in terms of utilizing photosynthetic production • Worldwide agriculture could feed many more people if humans ate only plant material • Fossil fuels used to Produce foods

16. Biological and geochemical processes cycle nutrients and water in ecosystems • Life depends on recycling chemical elements • Nutrient cycles in ecosystems involve biotic and abiotic components and are often called biogeochemical cycles

17. Biogeochemical Cycles • Gaseous carbon, oxygen, sulfur, and nitrogen occur in the atmosphere and cycle globally • Less mobile elements include phosphorus, potassium, and calcium • These elements cycle locally in terrestrial systems but more broadly when dissolved in aquatic systems

18. Figure 55.13 Reservoir A Organic materialsavailable asnutrients Reservoir BOrganicmaterialsunavailableas nutrients Fossilization Peat Livingorganisms,detritus Coal Oil Respiration,decomposition,excretion Burning offossil fuels Assimilation,photosynthesis Reservoir DInorganic materialsunavailableas nutrients Reservoir CInorganic materialsavailable asnutrients Weathering,erosion Atmosphere Mineralsin rocks Water Soil Formation ofsedimentaryrock

19. In studying cycling of water, carbon, nitrogen, and phosphorus, ecologists focus on four factors • Each chemical’s biological importance • Forms in which each chemical is available or used by organisms • Major reservoirs for each chemical • Key processes driving movement of each chemical through its cycle

20. The Carbon Cycle • Carbon-based organic molecules are essential to all organisms • Photosynthetic organisms convert CO2 to organic molecules that are used by heterotrophs • Carbon reservoirs include fossil fuels, soils and sediments, solutes in oceans, plant and animal biomass, the atmosphere, and sedimentary rocks • CO2 is taken up and released through photosynthesis and respiration • Volcanoes and the burning of fossil fuels also contribute CO2 to the atmosphere

21. Figure 55.14b CO2 inatmosphere Photosynthesis Photo-synthesis Cellularrespiration Burningof fossilfuels andwood Phyto-plankton Consumers Consumers Decomposition

22. Figure 55.UN03

23. The Nitrogen Cycle • Nitrogen is a component of amino acids, proteins, and nucleic acids • The main reservoir of nitrogen is the atmosphere (N2), though this nitrogen must be converted to NH4+ or NO3– for uptake by plants, via nitrogen fixation by bacteria

24. Figure 55.14c N2 inatmosphere Reactive Ngases Industrialfixation Denitrification N fertilizers Fixation Runoff Dissolvedorganic N NO3– Terrestrialcycling N2 NO3– NH4+ Aquaticcycling Denitri-fication Decompositionandsedimentation Assimilation Decom-position NO3– Uptakeof aminoacids Fixationin root nodules Ammonification Nitrification NH3 NO2– NH4+

25. The Phosphorus Cycle • Phosphorus is a major constituent of nucleic acids, phospholipids, and ATP • Phosphate (PO43–) is the most important inorganic form of phosphorus • The largest reservoirs are sedimentary rocks of marine origin, the oceans, and organisms • Phosphate binds with soil particles, and movement is often localized

26. Wind-blowndust Geologicuplift Weatheringof rocks Runoff Consumption Decomposition Plantuptakeof PO43– Dissolved PO43– Plankton Leaching Uptake Sedimentation Decomposition