What is a food chain?

All living things depend on each other to live. The food chain shows how some animals eat other animals to survive. While being food for animals higher in the food chain, these animals may eat other animals or plants to survive. The food chain is a complex balance of life. If one animals source of food disappears, such as from over fishing or hunting, many other animals in the food chain are impacted and may die. Let's look at two examples of food chains, one in the water and the other on land.


In the Sea

All sea creatures rely on other sea creatures for food to survive. At the bottom of the food chain are the sea plants and plankton. Many types of fish and animals such as the snail, shrimp, jellyfish, and sea star eat the plankton.

The small animals and fish who eat plankton then become food for larger fish, such as the tuna and mackeral.

These fish are then eaten by larger fish and animals, such as the shark and dolphin.

And who eats the shark? Check out the menu at a seafood restaurant next time you are eating there. Don't be surprised if you find shark on the menu.


On Land

The food chain on land is just as complex as in the sea. Small animals eat plants or bugs. Larger animals then eat them, with even larger animals eating them. Who is at the top of the food chain? That's us! We humans eat many of the plants and animals on earth. That's why we rely so heavily on all plants and animals for our existance. A break in the food chain can impact everyone.

Here is a simple example of a food chain in the wild
The zebra eats grass for its food. And who eats the zebra? Larger predators like the lion eat the zebra.

Food chains, food webs and/or food networks describe the feeding relationships between species in a biotic community. Food webs graphically represent the transfer of material and energy from one species to another within an ecosystem. Typically a food web refers to a graph where only connections are recorded, and a food network or ecosystem network refers to a network where the connections are given weights representing the quantity of nutrients or energy being transferred.
As usually diagrammed, an organism is connected to another organism for which it is a source of food energy and material by an arrow representing the direction of biomass transfer. Organisms are grouped into trophic levels—from the Greek word for nourishment, trophikos—based on how many links they are removed from the primary producers. Primary producers, or autotrophs, are species capable of producing complex organic substances (essentially "food") from an energy source and inorganic materials. These organisms are typically photosynthetic plants, bacteria or algae, but in rare cases, like those organisms forming the base of deep-sea vent food webs, can be chemotrophic. All organisms that eat the autotrophs are called heterotrophs. They get their energy by eating the producers.

圖片參考：http://upload.wikimedia.org/wikipedia/commons/f/fc/Foodweb.png