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Ch54 - Chapter 54 Ecosystems Lecture Outline Overview...

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Chapter 54 Ecosystems Lecture Outline Overview: Ecosystems, Energy, and Matter An ecosystem consists of all the organisms living in a community as well as all the abiotic factors with which they interact. The dynamics of an ecosystem involve two processes that cannot be fully described by population or community processes and phenomena: energy flow and chemical cycling. Energy enters most ecosystems in the form of sunlight. It is converted to chemical energy by autotrophs, passed to heterotrophs in the organic compounds of food, and dissipated as heat. Chemical elements are cycled among abiotic and biotic components of the ecosystem. Energy, unlike matter, cannot be recycled. An ecosystem must be powered by a continuous influx of energy from an external source, usually the sun. Energy flows through ecosystems, while matter cycles within them. Concept 54.1 Ecosystem ecology emphasizes energy flow and chemical cycling Ecosystem ecologists view ecosystems as transformers of energy and processors of matter. We can follow the transformation of energy by grouping the species in a community into trophic levels of feeding relationships. Ecosystems obey physical laws. The law of conservation of energy states that energy cannot be created or destroyed but only transformed. Plants and other photosynthetic organisms convert solar energy to chemical energy, but the total amount of energy does not change. The total amount of energy stored in organic molecules plus the amounts reflected and dissipated as heat must equal the total solar energy intercepted by the plant. The second law of thermodynamics states that some energy is lost as heat in any conversion process. We can measure the efficiency of ecological energy conversions. Chemical elements are continually recycled. A carbon or nitrogen atom moves from one trophic level to another and eventually to the decomposers and back again. Trophic relationships determine the routes of energy flow and chemical cycling in ecosystems. Autotrophs, the primary producers of the ecosystem, ultimately support all other organisms. Most autotrophs are photosynthetic plants, algae or bacteria that use light energy to synthesize sugars and other organic compounds. Chemosynthetic prokaryotes are the primary producers in deep-sea hydrothermal vents. Heterotrophs are at trophic levels above the primary producers and depend on their photosynthetic output.
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Herbivores that eat primary producers are called primary consumers. Carnivores that eat herbivores are called secondary consumers. Carnivores that eat secondary producers are called tertiary consumers. Another important group of heterotrophs is the detritivores, or decomposers.
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