2005_campbl54 - Movement of Stuff Through Ecosystems...

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1 Chapter 54: Ecosystems Movement of Stuff Through Ecosystems "An ecosystem consists of all the organisms living in a community as well as all the abiotic factors with which they interact." Ecosystems ± Note that the boundaries of ecosystems are typically not arbitrarily defined, but instead are defined in some meaningful way: A pond, a field, a forest, etc. ± Ecosystems are typically understood in terms of Energy flow through ecosystems Chemical cycling within (and through) ecosystems ± Note that both involve the movement of "stuff" through both biotic and abiotic components of the ecosystem ± “Ecosystems ecologists view ecosystems as energy machines and matter processors. By grouping the species in a community into trophic levels of feeding relationships, we can follow the transformation of energy in the whole ecosystem and map the movements of chemical elements as they are used by the biotic community.” (p. 1199, Campbel & Reece, 2002) detrivores Energy Flow ± Energy does not cycle through ecosystems but instead enters ecosystems and is used up within ecosystems ± Ultimately energy is lost from ecosystems primarily as waste heat, the most thermodynamically unavailable form of energy ± "Energy enters most ecosystems in the form of sunlight. It is then converted to chemical energy by autotrophic organisms, passed to heterotrophs in the organic compounds of food, and dissipated in the form of heat . . . Decomposers move energy out of dead things ± . . .The movements of energy and matter through ecosystems are related because both occur by the transfer of substances through feeding relationships. However, because energy, unlike matter, cannot be recycled, an ecosystem must be powered by a continuous influx of new energy from an external source (the sun). Thus, energy flows through ecosystems, while matter cycles within them.“ ± Note that energy flows through ecosystems mostly as bonds between carbon atoms and bonds between carbon and hydrogen atoms, e.g., as one finds in carbohydrates and lipids; consequently, within and between organisms the carbon cycle and the flow of energy are quite similar, at least until the two are decoupled in the course of cellular respiration (i.e., the separation of carbon atoms from their energy)
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2005_campbl54 - Movement of Stuff Through Ecosystems...

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