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Energy Efficiency and Adaptatio1

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Energy Efficiency and Adaptation In measuring flow of energy through ecosystems, ecologists use several measures of efficiency with which energy is "converted" into biomass In ecological anthropology, however, most common measures of energy efficiency focus on subsistence choices: 1. Output/input ratio = energy acquired/energy expended = E a /E e 2. Net return rate = (E a -E e )/Time spent in acquiring energy (i.e., net energy/labor time) In a moment, I'll give some reasons why the return rate measure is superior, but first let's consider general criticisms of what critics have called "calorific obsession" (Vayda & McCay 1975) with energy in human ecology These critics argue a) that food contains other nutrients besides energy; b) that many populations do not face energy scarcity; and c) that other goals may be more important than efficiently obtaining energy Three replies to these criticisms: 1. Although other nutrients are important, energy
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Unformatted text preview: is the most general (widely applicable) and convenient (easily calculated) measure of food value; and in fact, majority of documented cases of severe nutritional scarcity (both chronic and acute) have pinpointed calories as limiting factor 2. Other goals are important, but in most pre-industrial populations, acquisition of food energy seems to be single most time-consuming activity 3. If we use rate measure, increased efficiency will often be advantageous even when energy is not in short supply To expand on this last point, theory suggests that increasing one's energy return rate is adaptive in 3 general situations (see also Hames 1989 reading): 1) food energy is scarce relative to demand ("energy-limited") 2) time for other activities is scarce relative to demand ("time-limited") 3) energy acquisition involves greater risk (e.g., of accident or attack) than many other activities...
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