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Energy through Ecosystems

Energy through Ecosystems. A2 Chapter 12. By the end of this session I will:. (d) define the terms producer, consumer decomposer and trophic level ;   (e) describe how energy is transferred though ecosystems; (f) outline how energy transfers between trophic levels can be measured;

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Energy through Ecosystems

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  1. Energy through Ecosystems A2 Chapter 12

  2. By the end of this session I will: • (d) define the terms producer, consumer decomposer and trophic level;   • (e) describe how energy is transferred though ecosystems; • (f) outline how energy transfers between trophic levels can be measured; • (g) discuss the efficiency of energy transfers between trophic levels;   • (h) explain how human activities can manipulate the flow of energy through ecosystems (HSW6b);

  3. The first one is down to you guys 2 MINUTES (d) define the terms producer, consumer decomposer and trophic level; GIVE EXAMPLES

  4. Basic processes to consider!

  5. Food chain • Passage of food energy through ecosystem trophic levels in a linear path • A trophic, or feeding, level consists of all organisms feeding at the same energy level

  6. How can we calculate the amount of energy at each trophic level? Consumers (heterotrophs) Producers (autotrophs)

  7. What limits the length of the food chain?

  8. What limits length of food chain? • H1: Energetics • Availability of energy limits to 5-7 levels • Depends on: NPP energy needed by consumers average ecological efficiency • H2: Dynamic stability Longer chains less stable because: Fluctuations at lower trophic levels magnified at higher levels ---> extinction of top predators.

  9. A food web is a branching food chain with complex trophic interactions • Species may play a role at more than one trophic level • Food webs can be simplified by isolating a portion of a community that interacts very little with the rest of the community

  10. How heterotrophs use food energy Energy loss in an ecosystem Biomass available at the next trophic level • About one order of magnitude of available energy is lost from one trophic level to the next • Reason why food chains generally consist of only 3 or 4 steps Cayuga Lake In NY

  11. Primary productivity • Gross Primary Productivity (GPP): • total amount of photosynthetic energy captured in a given period of time. • Net Primary Productivity (NPP): • the amount of plant biomass (energy) after cell respiration has occurred in plant tissues. NPP = GPP – Plant respiration plant growth/ total photosynthesis/ unit area/ unit area/unit time unit time

  12. Photosynthesis: • Light energy captured by pigments • Used to build bonds forming various complex molecules – anabolic processes • Carbon dioxide absorbed/oxygen waste product • Autotrophs: ‘self feeders’ – algae, certain bacteria, plants • Only certain wavelengths of light effective

  13. 1. Pigments capture energy from sunlight • Water is split, O2 released • 2. Using energy to make ATP and NADPH • 3. Using ATP and NADPH to power the synthesis of carbohydrates from CO2 Light-dependent reactions + + + 6 CO2 6 H2O Light energy C6H12O6 6 O2 carbon dioxide water glucose oxygen Light-independent reactions The Calvin cycle

  14. Absorption spectra of chlorophylls and carotenoids

  15. Global O2 from photosynthesis • 80% comes from marine cyanobacteria. • Synechococcus • Synechocystis • 20% comes from terrestrial systems. • 5% of this comes from tropical rainforests.

  16. Primary productivity – marine ecosystems

  17. Global variation in estimatedNPP Figure 9

  18. Secondary Productivity • Secondary productivity – the rate at which consumers convert the chemical energy of the food they eat into their own new biomass • Involves heterotrophs • Essentially reverse of photosynthesis - May occur with or without oxygen • Aerobic – most efficient • Anaerobic  fermentative pathways (in anoxic environment) • ATP immediate cellular energy form

  19. Challenges We Face • To feed 9+ billion people in 2050, global food production must increase by 70% -- 80% to come from yield increases and 20% from area expansion • Developing countries must almost double production – with little possibility of land expansion in many countries • Yield growth rate for cereals declining: 3.2% in 1960 to 1% in 2050 • Land area (per cap.) declining: from 4.3 ha in 1961 to 1.5 ha in 2050 • Climate change likely to add greater and unpredictable stresses • Increased demand for better variety, quality and safety of agricultural products

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