CHAPTER 55 - CHAPTER 55: ECOSYSTEMS Overview: Observing...

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CHAPTER 55: ECOSYSTEMS Overview: Observing Ecosystems An ecosystem consists of all the organisms living in a community, as well as the abiotic factors with which they interact Ecosystems range from a microcosm, such as an aquarium, to a large area such as a lake or forest Regardless of an ecosystem’s size, its dynamics involve two main processes: energy flow and chemical cycling Energy flows through ecosystems while matter cycles within them Energy flows through an ecosystem, entering as light and exiting as heat Concept 55.1: Physical laws govern energy flow and chemical cycling in ecosystems Ecologists study the transformations of energy and matter within their system Conservation of Energy Laws of physics and chemistry apply to ecosystems, particularly energy flow The first law of thermodynamics states that energy cannot be created or destroyed, only transformed Energy enters an ecosystem as solar radiation , is conserved, and is lost from organisms as heat The second law of thermodynamics states that every exchange of energy increases the entropy of the universe In an ecosystem, energy conversions are not completely efficient, and some energy is always lost as heat The law of conservation of mass states Chemical elements are continually recycled within ecosystems In a forest ecosystem, Ecosystems are open systems, Energy, Mass, and Trophic Levels Autotrophs build molecules themselves using photosynthesis or chemosynthesis as an energy source; heterotrophs depend on the biosynthetic output of other organisms Energy and nutrients pass from primary producers (autotrophs) to primary consumers (herbivores) to secondary consumers (carnivores) to tertiary consumers (carnivores that feed on other carnivores) Detritivores, or decomposers , are consumers that derive their energy from detritus , nonliving organic matter
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Prokaryotes and fungi are important detritivores Decomposition connects all trophic levels PICTURE 1: Fungus breaking down dead tree cycle – blue – nutrient Red – heat each step loose energy not a lot of chemical energy lost Concept 55.2: Energy and other limiting factors control primary production in ecosystems Primary production – an ecosystem is the amount of light energy converted to chemical energy by autotrophs during a given time period Ecosystem Energy Budgets The extent of photosynthetic production sets the spending limit for an ecosystem’s energy budget The Global Energy Budget The amount of solar radiation reaching the Earth’s surface limits photosynthetic output of ecosystems Only a small fraction of solar energy actually strikes photosynthetic organisms, and even less is of a usable wavelength Gross and Net Primary Production Total primary production is known as the ecosystem’s gross primary production (GPP) Net primary production (NPP) is GPP minus energy used by primary producers for respiration Only NPP is available to consumers
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CHAPTER 55 - CHAPTER 55: ECOSYSTEMS Overview: Observing...

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