Tuesday, February 3, 2009

What Are Food Webs & Food Chains

Vegetation forms the lowest level of most food chains.


All living things are part of food chains and food webs. Food chains and food webs describe the relationships between different species of plants and animals. Food webs are more complex than food chains.


Definition of a Food Chain


A predator is typically high in a food chain.


A food chain describes the eating relationship between a series of plants and animals. For example, a food chain might state that a grasshopper eats grass, a frog eats the grasshopper, a snake eats the frog, and a hawk eats the snake. Food chains follow a single linear path.


Definition of a Food Web








Food chains connect to form food webs. Food webs have many different paths and show how different species connect. For example, while a food chain might show a snake eating a frog, a food web would also show that lizards, birds, hedgehogs, and sharp-toothed fish also eat frogs.


Levels of a Food Chain


In food chains, each organism has a different level. Producers are the first level of the food chain; these are organisms such as plants that can make their own food. Consumers are the next level of the food chain. Consumers get their energy by eating other plants or animals. A food chain can have several levels of consumers. Decomposers are the final level of the food chain. Decomposers, such as fungi and bacteria, break down dead plants and animals and return their raw materials to the environment.


Predators and Prey


Predators are a type of consumer that survive by eating other animals, called prey. Some animals can be both predator and prey: for example, a snake eating a frog is a predator, while the same snake is prey when it is eaten by the hawk.


Interconnectedness


Food webs show the interconnectedness between species. If something happens to one element of a food web, all other elements can be affected. For example, if acid rain causes phytoplankton in a lake to die, the insects that eat the phytoplankton have less food to eat, and they begin to die. Fish, birds, frogs and salamanders that eat the insects then have less food. The effects continue throughout the food web.


Energy Transfer


At each level of a food chain or food web, energy transfers from one species to another. However, at each level, energy is used up or lost as heat and less energy is available to pass on. Species high in the food chain or food web need more food in order to get enough energy to survive.

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