The Energy Cycle in an Ecosystem

by Mara Dolph, Demand Media

http://everydaylife.globalpost.com/energy-cycle-ecosystem-29423.html

Energy is something that every living thing needs and must obtain to stay alive. Some organisms absorb it, others consume it. But the term “cycle” when referring to energy is a misnomer. A cycle is an event or series of events that return to the beginning and repeat over and over again. While most things in nature are cyclical, energy isn’t. Energy in an ecosystem is actually lost as it moves, usually as heat, and most of it doesn’t return to the beginning. Therefore, the better word to use to describe energy in an ecosystem is “flow.”

The Food Chain

Because energy is lost as it moves, there needs to be a constant source of it to keep life on this planet going. In most cases, that source is the sun. In all but the deepest parts of the ocean, the sun powers life. Harnessing its energy is the job of the first level of the food chain — the primary producers, or plants. Plants use the sun’s energy to break apart carbon dioxide and water and use the components to make their own food from photosynthesis. Its very efficient, but not completely. Some energy is lost in the process.

Primary Consumers

Plants introduce new energy into ecosystems every day. While they make food for their own use, they are also adapted to have a certain amount of it taken away every day. Plants pass the energy they absorb on to the primary consumers, also known as herbivores. Because consumers can’t make their own food like plants do, they still have to eat. While plants are efficient producers, the animal consumers are not. A lot of energy is lost when herbivores eat plant material, most of it as heat. Of course, some animals are more efficient than others, but none are completely so.

Secondary Consumers

As the energy that was first absorbed by the plants makes its way through the food chain, it will eventually either be lost as heat, or taken by a secondary consumer — a carnivore. While herbivores eat plants, carnivores eat the herbivores, so some of the energy remaining in the herbivore will be passed on to the carnivore, and again, a lot will be lost as heat in the transfer. Sometimes, the secondary consumers may be themselves eaten by a tertiary consumer, with the same result. By this time, there is very little original energy remaining, and top predators have to work very hard to get enough of it to survive.

The Last Phase

Once the energy reaches the top predators it is either lost as heat or stored in the animal’s tissue as fat until the animal dies. Once this happens, it gets passed on to either scavengers or bacteria. This is the only time that it could be considered cyclical, because a very small amount of it does eventually return to the soil to benefit microbes and other soil dwellers. Even here, however, energy is lost as heat, because decomposition generates quite a bit of it. What gets recycled are the nutrients. The energy exists to be used up.