Food Chains
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A food chain is used to show how each animal within an ecosystem gets its food. Each link in the chain is food for the next living organism. When a plant is eaten by an animal, energy is transferred from the plant to the animal. That animal is then eaten by another animal, which gains energy from that food. And another animal eats THAT one, and so on. The African plains are home to many wild animals. One of these is the zebra. Zebras eat grass. We can illustrate this using an arrow which represents the grass going into the zebra once the zebra has eaten it. Lions inhabit the grasslands, and they eat zebras. We add the lion to the chain and the zebra goes into it. Now we have a basic food chain that shows the passage of food and the energy it contains from one organism to the next. It finishes with the lion, because no larger animals hunt lions. We can make more food chains, each beginning with a plant and finishing with a carnivore. Food chains can be drawn for both land and marine environments. For example, on land, trees and shrubs are eaten by a juvenile giraffe, which is then eaten by a lion. Grass is eaten by a grasshopper. The grasshopper is eaten by a toad, which in turn is eaten by a snake that’s then eaten by an eagle. An example of a marine food chain is when a shrimp eats seagrass, sardines eat the shrimp, and snapper eat the sardines. Food chains don’t only show us what eats what, they can also help us to understand what might happen if the balance within an ecosystem changes. Let’s return to the food chain on the African savannah. If, for example, disease wiped out all the lions, what effect would this have on the ecosystem? Given that the zebras aren’t being eaten by the lions anymore, it’s likely that the zebra population would increase in the short-term. Over a longer period, the increasing number of zebras would require more and more grass. As a consequence of overpopulation, they risk eating all the available grass, and once all the grass is gone, the zebras will die off too. In an ecosystem, every plant and animal is dependent on the other plants and animals for their survival. A healthy ecosystem is delicately balanced and, as strange as it sounds, zebras need to be eaten by lions to ensure their continued existence.

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