The energy flow between levels

Although the previous example shows the available energy from one trophic level to the next, it is also useful to think of the food producers and consumers as part of a "biomass pyramid," in which the comparative masses of consumers and food can be represented simultaneously. Instead of energy, the approximate masses of the animals and plants involved are "stacked up" in pyramidal fashion, with the primary producers (plants) at the bottom, and the last (generally largest) carnivore in the "food chain" at the top. The poor energy-transfer efficiency from one trophic level to the next manifests itself by the end of the chain, where a mere one-hundredth of a percent of the "base" of the pyramid remains. In this example, if sharks were able to feed on zooplankton, the trophic levels in between the two would be "skipped over," and energy transfer would be made more efficient in that ecosystem. In the case of humans, entire fields of grain are planted and harvested for the purpose of feeding cattle, and the cattle in turn are raised for the production of meat products. However, between the stage of the primary producer (grain) to the cattle (herbivore), 90% of the energy supplied by the grain is lost in the raising of the cows. From the cattle to the humans, the same efficiency also holds; just 10% of the energy stored in the beef is passed on to people. But if the grain were directly fed to people, the amount of energy that would have been used (and wasted) by cattle would be used by people, essentially "saving" a great deal of available energy and biomass. This concept is particularly important in international food organizations, as world population continues to increase, and the difficulty of properly feeding everyone becomes more crucial. By "skipping over" levels of the biomass pyramid, less energy is wasted, and more available energy - food - becomes accessible to humans.

Credit: Dylan Prentiss, Department of Geography, University of California, Santa Barbara

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