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BACKGROUND
A food chain, or food web, is a representation of the flow of energy through a community of plants and animals. Every participant in a food chain has an important role to play, and if one piece is added or removed, the ecosystem can develop serious problems.
Primary consumers are animals that consume the plants as food and extract nutrients, minerals, water and energy from the plant matter. Some animals feed exclusively on the plants themselves, including the leaves, shoots and root. Some animals also utilize the nectar, pollen, seeds and fruit of plants as well. Animals that consume mostly plants are known as herbivores.
Secondary consumers are animals that consume mostly other animals as food. These animals are considered carnivores. In some cases, secondary consumers feed off of living animals and are known as parasites.
Some animals may act both as primary and secondary consumers. These animals are known as omnivores because they eat both plant and animal matter.
The final step for any organism in the food chain is to eventually become food for the decomposers, in some for or another. Decomposers feed on dead plants and animals, or animal waste, and break the matter down into base materials such as water, nutrients, gasses and minerals. These materials are returned to the soil to begin the cycle anew.
Each stage in the food chain is important to the health of the ecosystem as a whole. When humans destroyed the major predators in North America such as wolves, snakes and raptors, their prey species populations exploded.
ADDITIONAL ACTIVITIES
Build a food chain pyramid. Draw a triangle, with one point facing up, and divide it into three sectors by drawing two horizontal lines. Select one organism from one of the following three categories: producers, primary consumers, or secondary consumers. Once you've selected your level, decide on what type of animal or plant you would like your organism to be. For example, let's say that you selected a secondary consumer and designated it as an osprey, a large cosmopolitan pied fish-eating raptor of lakes, rivers and coastlines.
Next, figure out what other organisms would complete a three-level food chain pyramid. Ospreys are secondary consumers and feed exclusively on fish. One fish species that osprey occasionally eat are carp. Carp are mostly herbivorous, thus considered primary consumers. Carp feed mostly on a wide variety of aquatic plants including Eurasian water milfoil. The milfoil is a plant that absorbs the sun's energy and other non-living elements from the environment. Thus, the milfoil is considered a producer.
Once you have determined three key characters in your food chain, lay the three species out in a pyramid format. Generally, the lower an organism is on the food chain (a healthy food chain), the greater its population in comparison to other food chain levels. Accordingly, we can place the Eurasian water milfoil on the lowest level, the carp on the second level, and the osprey on the upper level. Compare the three levels. The lower the level is on the food pyramid, the larger its size. The sizes diminish as the pyramid levels progress upwards.
Once the pyramid is completed, you will have a relatively accurate representation of producer, primary consumer, and secondary consumer populations in a certain environment. Try completing a pyramid using different food chain levels, numbers of levels, and different species
FOLLOW-UP
Have your student explain why everything goes together in this manner.
RESOURCES
Webquest Investigating Food Chains in Animal and Plant Communities
http://www.gecdsb.on.ca/sub/schools/elem/southwoo/Food%20Chain%20Webquest/index.htm
Aliens Explore Earth, Food Chains
http://www.alienexplorer.com/ecology/topic4.html
Food Chain Sites
http://www.oswego.org/staff/cchamber/resources/foodchain.cfm
The Open Door Web Site
http://www.saburchill.com/chapters/chap0006.html
Food Chains
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FoodChains.html
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