Life on Earth - Ecosystem Energy
All living things use energy to do everything. Ecologists trace the flow of energy through ecosystems to identify nutritional relationships. The ultimate source of energy for nearly all living things is the sun.
Producers: Energy Storers
Plants have the ability to capture sunlight in a process called photosynthesis. This process takes the sun's energy and uses it to form chemical bonds in sugar molecules. The energy is stored in the molecules and can be released when the molecule's bonds are broken. Storing matter and energy in this form makes it possible for other organisms to use plants as food. Because plants capture and store energy in this way, they are referred to as producers.
Consumers: Energy Users
Plants use the energy they store during photosynthesis to complete their own life processes. Other organisms rely on plants as their energy source. Those organisms which eat plants for food are called primary consumers. Some organisms rely on plant-eating animals as the source of their energy and are called secondary consumers because they are getting their energy "second-hand."
Ecologists who trace energy and matter flow in ecosystems have identified a number of interesting things. Energy flows from one organism to another as each organism is eaten by the next. These relationships are called food chains. For example, a plant may capture the sun's energy then become food for a deer which may then be eaten by a bear. Each organism forms a link in the chain.
In an ecosystem many food chains will overlap to form a web through which energy moves. Examine the food web below and count the number of overlapping food chains.
The food webs in an ecosystem depend on both the abiotic and biotic parts of the ecosystem. In the photograph above, you see pictures of two different ecosystems. Based on what you see, try to imagine the food chains and webs you might find in each area. Write your ideas down and share them with friends or your family to see if they think your ideas are realistic. If you have the opportunity to visit real ecosystems, try to draw food chains that you observe. Try to assemble the chains into a web if you can.
Another interesting item ecologists noticed is that a great deal of energy is lost as heat to the environment as it moves through a food chain. In fact, approximately 90% of the energy available at one level in a food chain is lost as it moves to the next level. An energy pyramid is usually drawn to represent the energy loss. Each level of the pyramid is drawn with a rectangle representing the amount of energy available at that level. Notice that smaller rectangles represent less energy being available at that level.