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Food webs and trophic levels


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Food chains, food webs, trophic levels and energy transfer

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Food webs and trophic levels

  1. 1. Trophic Levels, Energy transfer and Pyramids
  2. 2. Vocabulary  Trophic Levels – is the position an organism occupies in a food chain. It refers to food or feeding.  Apex predator – top level predators with few or no predators of their own.  Detritavore – feeds on dead organisms, helps with decomposition  Review Vocab – carnivore, omnivore, herbivore, scavenger, decomposer
  3. 3. Food Chain
  4. 4. Food Chains The energy flow from one trophic level to the other is know as a food chain Producers are at the first TROPHIC LEVEL Primary Consumers are the SECOND TROPHIC LEVEL Secondary consumers are at the THIRD TROPHIC LEVEL Tertiary consumers are at the FOURTH TROPHIC LEVEL In some ecosystems you can go out to Quaternary consumers
  5. 5. Trophic Levels (feeding levels) 3 2 1
  6. 6. Food Web Most organisms eat more than JUST one organism When more organisms are involved it is know as a FOOD WEB Food webs are more complex and involve lots of organisms
  7. 7. Food webs
  8. 8. Trophic Level Producer, primary consumer, secondary consumer, tertiary consumer Grass 1st Producer Mouse 2nd Primary consumer Grasshopper 2nd Primary consumer Frog 3rd Secondary consumer Owl 3rd and 4th Secondary and tertiary consumer Hawk 3rd Secondary consumer
  9. 9. Terrestrial Food Web
  10. 10. Aquatic Food web
  11. 11. Transfer Between Ecosystems  If an organism that lives in a terrestrial ecosystem consumes an organism in an aquatic (or aquatic to terrestrial) energy is transferred between the two.  Ex. Bear eats a fish (energy from aquatic to terrestrial) or fish eats a caterpillar (energy from terrestrial to aquatic)
  12. 12. Transfer of Energy When a lion eats a zebra, it does not get all of the energy from the zebra. Energy lost is usually in form of heat Energy lost from chain “link” to “link” is significant!
  13. 13. from grass to sheep, loss is about 90%! 10% Original Energy! 1% Original Energy! 100% Energy Available HEAT 90% HEAT 90%
  14. 14. Energy lost from one trophic level (energy level) to the next level can be represented by a pyramid PRODUCERS 1° CONSUMERS 2° CONSUMERS 3° CONSUMERS 4⁰° CONSUMERS
  15. 15. ♦ Each level above only gets 10% of the energy from below − Ex: 10,000 J of producers (plants) only give 10% of energy to primary consumers > 1,000 J to primary consumers (snails, minnows, dragonflies) > 100 J to secondary consumers (small fish) > 10 J to tertiary consumers (big fish) > 1 J to quaternary consumers (fish hawk)
  16. 16. ENERGY PYRAMID 10,000 J10,000 J 1,000 J1,000 J 100 J100 J 10 J10 J 1 J1 J
  17. 17. Energy Pyramid
  18. 18. Three hundred trout are needed to support one man for a year. The trout, in turn, must consume 90,000 frogs, that must consume 27 million grasshoppers that live off of 1,000 tons of grass. -- G. Tyler Miller, Jr., American Chemist (1971)
  19. 19. Usually no more than 5 trophic levels since 6th level would have very little energy to keep it alive
  20. 20. Ecological Pyramid • Which level has the most energy? • Which level has the most organisms? • Which level has the least organisms? • Which level has the least energy?
  21. 21. Pyramid of Numbers • Shows the numbers of individual organisms at each trophic level in an ecosystem. tertiary consumers secondary consumers primary consumers producers 5 5000 500,000 5,000,0005,000,000producers • A vast number of producers are required to support even a few top level consumers.
  22. 22. Biomass pyramid • Biomass is a measure of the total dry mass of organisms in a given area. tertiary consumers secondary consumers primary consumers producers 75 g/m2 150g/m2 675g/m2 2000g/m2producers 2000g/m2