Food Chains and Webs
Food chains and food webs describe the feeding relationships in an ecosystem. Every population needs energy to survive. That energy comes from the sun. Everything in the food chain or food web relies on the sun for that energy and obtains it throughout the chain. A person can feel the sun warning the skin. A field mouse and a hawk can feel it, too. Neither of them can directly use the sun's energy; however, they must have it in order to breathe, keep their hearts beating, and to stay alive.
The energy of the sun is stored in food, and the energy in food is passed from one organism to another in a food chain. A food chain is a path that energy takes from producers to consumers to decomposers.
One of the first organisms in the food chain is the plant. During photosynthesis the plant captures the sun's energy. It then stores that energy in foods or sugars that the plant makes for itself. Next, a grasshopper may eat the plant and energy is released for the grasshopper to use or to be stored in the tissue of the grasshopper. Some of the energy is lost as heat. After that a lizard may eat the grasshopper releasing energy to the lizard that was being stored in the grasshopper. The food chain becomes the avenue by which energy is passed from one organism to another in the ecosystem.
When animals die they become food for the organisms like crickets, worms, ants, and other bugs. They also become a food source for microscopic organisms like bacteria. The food chain becomes the path of energy as it moves from one organism to another.
Because an organism eats more than one kind of food, and animals are eaten by more than one kind of organism, there becomes a relationship between all of the species in a community. This relationship is called a food web. It reveals how populations must compete for the food so that they are able to receive the needed energy. A food web is a map of overlapping food chains.
Food webs begin with producers; the living organisms that use the sun's energy to make their own food, and include, grass, trees, and plants. Organisms that cannot make their own food are called consumers, which get energy from the producers. As they store energy from the sun, they are eaten and the stored energy is released into the organism that eats it. Consumers are grouped by the kind of food they eat.
There are herbivores and there are carnivores in the food web. Herbivores are those organisms that only eat the producers. The herbivores will not eat animals, but only plants, algae, grass and flowers. The carnivores are animals that will eat other animals. There are carnivores on land and in the sea. The most frightening carnivore is the great white shark. When an animal eats both meat and plants they are called omnivores. Humans and bears are omnivores.
Living things that hunt other living things are called predators. And the hunted are called the prey. The relationship between predator and prey is a key part of both the food chain and the food web. There are also those meat eaters that do not hunt for meat like the predator, but eat it as it scavenges for it. They are called scavengers. They feed on the remains of dead animals they find.
Every food chain and food web ends with decomposers. Decomposers are worms, insects, bacteria, and fungi. These organisms break down dead matter into substances that can be used by the producers. The decomposed matter returns to the soil for the process to begin all over again. The food chain continues. In doing so, all organisms are receiving the energy needed to survive, and the ecosystem is able to sustain itself.