A network of food energy interchange
| A "food chain" can be defined as a simple, linear relationship of food sources in a given environment. But in most situations, biologists see examples in nature where the interchange of food sources does not follow such a simple arrangement. Instead, an organism may be observed to hunt, kill and consume smaller animals, feed on a larger animal in a group the next day, or eat plants (such as fruits or leaves) many days later. In other words, many animals eat different kinds of animals and plants, not just one exclusive food source. In this way, an organism is not limited to one food source and can acquire the energy and nutrients it needs from multiple sources. Evolutionary theory predicts that if a species simply consumes one food source, and that food source disappears, the reliant species either has to adapt to eating a new source, or become extinct. To avoid this situation, many animals (and humans) consume plants and animals from more than one trophic level. As a result, a "food web" can be set up, where energy is transferred between trophic levels. |
Credit: USGS
For more info: http://www.geog.ucsb.edu/~dylan/mtpe/biosphere/topics/en/foodweb.html