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Teacher Information!

This PowerPoint guide explains trophic levels, energy flow, and the factors influencing primary productivity in ecosystems. It also discusses the importance of biomass and the role of cellulose in the food chain.

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Teacher Information!

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  1. Teacher Information! • Necessary materials: • PowerPoint Guide • If teacher has internet access, the following YouTube video would be a good tool at Slide 12 • “Trophic Level Cascades Complete” at http://www.youtube.com/watch?v=yg5ieYKvYI8

  2. Ecosystem Productivity Principles of Ecology

  3. Students will be able to… • Discuss trophic levels and energy flow in ecosystems

  4. Food chains • Definitions reviewed: • Producers autotrophs make up the base of an ecosystem • Consumers  eat other living organisms • Detrivores/decomposers  consume dead organisms and fecal wastes

  5. Primary productivity • The rate at which producers capture & store energy in their tissues • Gross = total • Net = after respiration • The most productive ecosystems in the world  estuaries, swamps, marshes, tropical rain forest

  6. Net primary production per unit area of the world’s common ecosystems

  7. Factors influencing primary productivity • Climate & nutrients • Morphology & size of organism • Rainfall • Temperature • Season • Soil (mineral & nutrient availability)

  8. Pathways of energy flow • Energy from primary productivity can flow through 2 categories of food webs • Grazing food webs • Producer  Primary consumer  Secondary consumer  tertiary consumer… • Detrital food webs • Energy flows from producers to detrivores & decomposers

  9. Trophic levels • Feeding levels with respect to primary source of energy • Producers & consumers each occupy a different trophic level • Energy is lost at each level

  10. Biomass • The total weight of all living organisms • Biomass at each trophic level  biomass pyramid 1.5 Biomass pyramid (grams/m2) Top carnivores 11 Primary carnivores 37 Herbivores 809 Detrivores/ decomposers Producers 5

  11. Energy flow pyramid • The amount of energy in each trophic level can also be estimated and plotted in a pyramid Energy flow pyramid (kcal/m2/year) 21 Top carnivores 383 Primary carnivores 3,368 Herbivores Detrivores/decomposers 20,810 Producers 5,060

  12. Why do energy and biomass decrease at higher trophic levels? • Not all biomass is consumed from one trophic level to next • Not all that is consumed is turned into biomass • Shorter food chain/web = less loss of energy • Supports idea that vegetarianism is the best way to feed a large population…

  13. Vegetarianism • Results in a decrease of human position on food chain • This won’t solve world hunger • Only 25% of earth’s land can be farmed • We need ruminants

  14. The “Cellulose Dichotomy” • Cellulose  most abundant, naturally-occuring organic molecule on earth • Humans can’t digest it • Ruminants can digest it • Cattle, sheep, goats • Deer, bison, antelope, moose, elk • “Hind-gut fermentors” can digest cellulose • Horses, rabbits, some rodents cellulose

  15. Review • Discuss trophic levels and energy flow in ecosystems

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