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Chapter 54 - CHAPTER 54 ECOSYSTEMS Introduction An...

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CHAPTER 54 - ECOSYSTEMS Introduction 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: energy flow and chemical cycling. A. The Ecosystem Approach to Ecology Ecosystem ecologists view ecosystems as energy machines and matter processors. We can follow the transformation of energy by grouping the species in a community into trophic levels of feeding relationships. 1. Trophic relationships determine the routes of energy flow and chemical cycling in an ecosystem The autotrophs are the primary producers , and are usually photosynthetic (plants or algae). They use light energy to synthesize sugars and other organic compounds. Heterotrophs are at trophic levels above the primary producers and depend on their photosynthetic output. 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 . They get energy from detritus , nonliving organic material, and play an important role in material cycling. 2. Decomposition connects all trophic levels The organisms that feed as detritivores often form a major link between the primary producers and the consumers in an ecosystem. The organic material that makes up the living organisms in an ecosystem gets recycled. An ecosystem’s main decomposers are fungi and prokaryotes, which secrete enzymes that digest organic material and then absorb the breakdown products. 3. The laws of physics and chemistry apply to ecosystems The law of conservation of energy applies to ecosystems. We can potentially trace all the energy from its solar input to its release as heat by organisms. The second law of thermodynamics allows us to measure the efficiency of the energy conversions. B. Primary Production in Ecosystems The amount of light energy converted to chemical energy by an ecosystem’s autotrophs in a given time period is called primary production.
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1. An ecosystem’s energy budget depends on primary production Most primary producers use light energy to synthesize organic molecules, which can be broken down to produce ATP; there is an energy budget in an ecosystem. The Global Energy Budget Every day, Earth is bombarded by large amounts of solar radiation. Much of this radiation lands on water and land that either reflect or absorb it. Of the visible light that reaches photosynthetic organisms, only about 1% is converted to chemical energy. Although this is a small amount, primary producers are capable of producing about 170 billion tons of organic material per year.
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