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Lecture 18

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BIOL 373

How Does Energy Flow Through the Global Ecosystem? Solar energy drives ecosystem processes • Solar energy enters ecosystems by way of plants and other photosynthetic organisms. • Only about 5 percent of the solar energy that arrives on Earth is captured by photosynthesis; remaining energy is either radiated back into the atmosphere as heat or taken up by the evaporation of water. • Gross primary productivity (GDP) is the rate at which energy is incorporated into the bodies of photosynthetic organisms. • The accumulated energy is called gross primary production. • Primary producer use some of this accumulated energy for their own metabolism; the rest is stored in their bodies or used for their growth and reproduction. • The energy available to organisms that eat primary producer, called net primary production (NPP), is gross primary production minus the energy expended by the primary producers during their metabolism. • Only the energy of an organism’s net production is available to other organisms that consume it. • The geographic distribution of the energy assimilated by primary producers reflects the distribution of land masses, temperature, and moisture on Earth. • Production in aquatic ecosystems in limited by light, which decreases rapidly with depth; by nutrients, which sink and must be replaced by upwelling of water; and by temperature. Human activities modify flows of energy • Some human activities decrease net global primary productivity (e.g. conversion of forests). What Services Do Ecosystem Provide?
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