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CH 55 & 56 – Energy flow in Ecosystems. Overview: Ecosystems An ecosystem consists of all the organisms living in a community, as well as the abiotic.

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Presentation on theme: "CH 55 & 56 – Energy flow in Ecosystems. Overview: Ecosystems An ecosystem consists of all the organisms living in a community, as well as the abiotic."— Presentation transcript:

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 Key Chemical cycling Energy flow Sun Heat Primary producers Primary consumers Secondary and tertiary consumers Detritus Microorganisms and other detritivores Figure 55.4 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 leafs energy is used for secondary production An organisms production efficiency is the fraction of energy stored in food that is not used for respiration

10 Plant material eaten by caterpillar Growth (new biomass; secondary production) Cellular respiration Assimilated Feces Not assimilated 100 J 33 J 67 J 200 J Figure 55.10

11 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 Interesting Energy production facts:

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 Tertiary consumers Secondary consumers Primary producers Primary consumers 1,000,000 J of sunlight 10,000 J 1,000 J 100 J 10 J

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 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 Role of Humans in Energy flow:

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 Reservoir A Organic materials available as nutrients Living organisms, detritus Reservoir B Organic materials unavailable as nutrients Reservoir D Inorganic materials unavailable as nutrients Reservoir C Inorganic materials available as nutrients Fossilization Burning of fossil fuels Assimilation, photosynthesis Weathering, erosion Formation of sedimentary rock Respiration, decomposition, excretion Peat Coal Oil Minerals in rocks Soil Atmosphere Water Figure 55.13

19 In studying cycling of water, carbon, nitrogen, and phosphorus, ecologists focus on four factors –Each chemicals 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 CO 2 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 CO 2 is taken up and released through photosynthesis and respiration Volcanoes and the burning of fossil fuels also contribute CO 2 to the atmosphere

21 CO 2 in atmosphere Photo- synthesis Burning of fossil fuels and wood Phyto- plankton Photosynthesis Cellular respiration Consumers Decomposition Figure 55.14b

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 (N 2 ), though this nitrogen must be converted to NH 4 + or NO 3 – for uptake by plants, via nitrogen fixation by bacteria

24 Fixation Denitrification N 2 in atmosphere Reactive N gases Industrial fixation N fertilizers Runoff NO 3 – NH 4 + Decomposition and sedimentation Aquatic cycling Dissolved organic N Terrestrial cycling Decom- position Denitri- fication NO 3 – NO 2 – N2N2 Assimilation Fixation in root nodules AmmonificationNitrification NH 4 + NH 3 Uptake of amino acids Figure 55.14c

25 The Phosphorus Cycle Phosphorus is a major constituent of nucleic acids, phospholipids, and ATP Phosphate (PO 4 3– ) 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 Geologic uplift Wind-blown dust Weathering of rocks Consumption Runoff Decomposition Leaching Sedimentation Plant uptake of PO 4 3– Dissolved PO 4 3– Plankton Uptake

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