This lesson will provide a definition of a food web, as well as describe its parts and discuss examples of different types. It will also explain the transfer of energy through a food web.
Definition of a Food Web
All life needs energy. Whether living organisms make energy themselves or get it from the food they hunt, they need it to maintain and repair their bodies. Reproduction, hunting, growth, cell division, and metabolism are all processes that require energy.
The sun is the ultimate source of energy for life on Earth. Without it, nothing would be able to survive. As a result, living things have evolved special ways to harness the energy of the sun and use it for their own well-being. They have also developed special relationships and interactions that allow energy to be transferred. Once the energy has been captured, it gets passed around through the various organisms in a particular area. This transfer of energy is called a food web.
In their simplest form, food webs are made of food chains. Food chains show a direct transfer of energy between organisms. A chain might involve a mouse eating some seeds on the forest floor. Then, a snake comes along and eats the mouse. A while later, an owl eats the snake. With each step, some of the energy from the sun, which is trapped within the seeds, is getting passed on.
Food chains do not accurately portray the transfer of energy in an ecosystem. This is because there are often multiple organisms that can be eaten, and many that can do the eating. For example, the aforementioned mouse might eat seeds, but it also might eat some berries, or maybe even some grass. The mouse might be eaten by a snake, or the owl, or even a fox. The snake could be eaten be the owl, but also might get eaten by a fox or a coyote in the forest. Since each organism can eat multiple things and be eaten by multiple things, a food web is a much more realistic schematic of the transfer of energy within an ecosystem.
Producers
Often considered the bottom of the food chain, producers are the organisms that make their own food and serve as the foundation for all food chains and webs. Producers are organisms such as plants, algae, and even some bacteria. They make their own energy by converting sunlight into sugars through a process called photosynthesis. They use the sunlight as an energy source to convert carbon dioxide in the air into glucose (a simple sugar that can easily be broken down for energy). The producers then store this sugar and use it for energy later on.
In marine ecosystems, the producers are dominated by algae, plant-like organisms. Algae can be microscopic, like diatoms, or they can be quite large, like the giant kelp found off the coast of California. Either way, the oceans are the prime spot on the planet for producers. Since water covers 72 percent of the planet, it only makes sense that most of the oxygen on the earth comes from the oceans. In fact, the diatoms alone make about 30 percent of it!
Rainforests are another ecosystem that has many producers. Even though rainforests only cover about six percent of the earth's surface, they produce about 40 percent of the oxygen because of all the plants that live there. Since rainforests and the oceans are so plentiful in terms of the number of producers, there are many food webs that exist in each of these ecosystems. The plants and algae provide energy for many creatures living in these areas.