Bio190-Ecosystems - Ecosystems - Themes I. Energy Flow...

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Ecosystems - Themes I. Energy Flow & Trophic Relationships 0. Primary Production i. Secondary Production b. Chemical Cycling 0. Decomposition connects all trophic levels c. 1. Introduction – Definitions 0. Ecosystem = all the organisms living in a community plus abiotic factors with which they interact 1. Ecosystem approach focuses on 2 key processes: energy flow and chemical (nutrient) cycling 2. We study these processes by grouping the species in a community into trophic levels of feeding relationships a. Trophic relationships determine the routes of energy flow in an ecosystem 3. Primary producers = photosynthetic plants or algae. 0. They use light energy to synthesize sugars and other organic compounds. 1. Bottom of the ‘food chain’ 2. Heterotrophs are at trophic levels above primary producers and depend on their photosynthetic output 4. Primary consumers = herbivores that eat primary producers 5. Secondary consumers = carnivores that eat herbivores 6. Tertiary consumers = carnivores that eat secondary producers 7. Detritivores & Decomposers = heterotrophs that get energy from detritus (nonliving organic material) 3. They are crucial in matter recycling b. Decomposition connects all trophic levels 8. All organic matter that makes up the living organisms gets recycled back into the ecosystem 9. Decomposers are a major link from the consumers back to primary producers, which assimilate matter into organic molecules
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10. Decomposers secrete enzymes that digest organic matter and absorb the breakdown products and release nutrient elements back into the ecosystem 11. Principal decomposers = fungi and bacteria c. Laws of physics and chemistry apply to ecosystems 4. Conservation of energy 0. All energy from its solar origin to its release as heat by organisms can be traced through the ecosystem 5. Second Law of Thermodynamics 1. Deals with efficiency of the energy conversions 2. Transfer of energy between trophic levels involves losses 2. Primary production 12. Primary production = amount of light energy converted to chemical energy in a given time period by autotrophs 13. Ecosystem energy budget starts with primary production a. The Global Energy Budget 14. 6. Much of this radiation lands on the water and land that either reflect or absorb it 7. Of the visible light that reaches photosynthetic organisms, only ~1% is converted to chemical energy 15. Primary producers —> 170 billion tons of organic material per year ! b. Gross and Net Primary Production 16. Gross primary production (GPP) = total primary production (= amount of light directly converted into chemical energy) 17. Net primary production (NPP) = GPP minus energy used by the primary producers for respiration (R): 0. NPP = GPP – R 18. Primary production is expressed as energy per unit area per unit time, or as biomass of vegetation added per unit area per unit time ( Standing crop
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This note was uploaded on 04/14/2008 for the course BIOL 190 taught by Professor Kemp during the Fall '07 term at San Diego.

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Bio190-Ecosystems - Ecosystems - Themes I. Energy Flow...

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