Food Chains & Food Webs
What was your last meal? Perhaps it included bread, bananas or bamboo shoots. Or maybe it was beefsteak, chicken or fish. If it was food from the first list, you might be a vegetarian or herbivore, eating just plants and their parts. The second list is the food of a carnivore or flesh eater, who feeds on animal parts, especially meat. Knowing who eats what allows us to study food chains and food webs, of people and in nature.
SIMPLE FOOD CHAINS
A gazelle grazes on the African plains. Suddenly a leopard pounces, kills and begins to feast. This is a simple food chain with three links: grass to gazelle to leopard. The gazelle eats grass to obtain nutrients for growth and to keep its body healthy, as well as energy to power its muscles and life processes. The leopard eats the gazelle for the same reason, to obtain nutrients and energy. In this way, we can imagine that nutrients and energy pass along a food chain from one link to the next.
PLANTS TO ANIMALS
Food chains start with the Sun. The Sun provides energy for plants. The plants get their energy by trapping sunlight in their leaves, in the process known as photosynthesis. Plants obtain nutrients in the form of simple minerals in the soil, which their roots take up. The next link in a food chain is usually a plant-eating animal or herbivore. After this come carnivores, animals that eat other animals.
HOW LONG ARE FOOD CHAINS?
Food chains can include plants and animals of all sizes, and the chains can have more than three links. For example, seeds are eaten by a mouse, which is caught by a weasel. Then the weasel is killed and consumed by a hawk, This is a four-link chain: seeds to mouse to weasel to hawk.
Food chains are often longest in the sea. They can have six or seven links. The chains start with the microscopic plants floating in plankton, which are eaten by tiny animals. These are consumed by small fish, which are eaten by slightly bigger fish and so on.
LOSSES ALONG THE CHAIN
In one sense, food chains do not go on forever. At each link an animal stores some of the energy it eats, in its own flesh and other body parts. This is the energy passed on to the next link when the animal is killed and eaten. But the animal has also used much of the energy it took in, to power its muscles and life processes. This used energy cannot be passed on to the next link. So the amount of energy gradually decreases along the chain, and the food chains have a limited length.
At the end of many food chains, there is a top carnivore—a big, fierce hunting animal. Examples include hawks and eagles in the air, leopards, and tigers on land and sharks and killer whales in the sea. Top carnivores hunt other creatures but are not hunted themselves. However, these creatures do not live forever. And when they die, they are eaten too. Their flesh and bodies are consumed by another group, known as detritivores. These include maggots, worms and grubs, moulds and other fungi, micro-organisms such as bacteria and anything else that causes rot and decay.
LOTS OF FOOD CHAINS
Detritivores consume anything that is dying or dead. They consume not just dead animals, but also plants such as trees and grasses. Some of these detritivores then become food for other animals, in yet more food chains. For example, grubs eat the decaying wood of a tree, and the birds eat the grubs. Also, some of the nutrients from dying or dead things rot into the soil. New plants then use these nutrients to grow and start yet more food chains. So in this sense, food chains never end.
MORE AND MORE LINKS
Food chains soon become complicated. A bird might peck at many different foods, including seeds and fruits, a caterpillar that has just eaten a leaf, a dragonfly that has feasted on sap-sucking aphids and some maggots in rotting meat. So the bird has eaten many different food items including plants, herbivores, carnivores, and detritivores. The bird is known as an omnivore, which means it eats anything.
In the natural world, very few animals eat just one kind of food. So food chains join and have many branches and connections, forming a food web. This is often drawn as a pyramid shape. Plants are put on the bottom. In the next layer are the herbivores, then the carnivores. The narrow uppermost point contains the top carnivores. The detritivores might be placed at the side of the main pyramid.
SIMPLE AND COMPLEX
Food webs vary greatly. In places where life is hard, like the icy Arctic, there are few kinds of animals and plants. So the food webs are fairly simple, with perhaps only 20 branches. Where millions of living things thrive, such as in a rainforest, food chains are incredibly complicated, with thousands of links. It is very difficult for scientists to find them all.
WHY STUDY FOOD CHAINS?
If a creature becomes very rare, then knowing what it eats, or what eats it, could help to prevent it dying out. Also, food webs are an important part of finding out about the balance of nature. This is the science of ecology. It studies how living things fit together, like a gigantic jigsaw puzzle, and how people are damaging so much of the natural world.
Humans are parts of food chains and food webs. Most of us are omnivores, eating a wide variety of plant and animal products. Studying the food chains that humans are part of can help farmers to grow better crops and raise more animals, and show us how to eat healthy foods.