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Food Chain, Food Web, and Lake Michigan

Most biological energy here on Earth can be traced back to one single source: the sun. Plants and blue-green algae use photosynthesis to trap the electromagnetic wave energy generated by the sun, transforming it into chemical energy in the form of food for themselves and for other creatures that eat them.

Sounds simple so far, right? In an effort to simplify the way we think about creatures and their energy relationships, we often use food chains that show a very clear link between creatures and the things that eat them. Here is one example:

Rose bush > Beetle > Robin > Domestic Cat > Coyote

Organisms are connected by an arrow that points toward the creature consuming it.

While this kind of chain is great for visualizing how some creatures eat, it is not very realistic since most creatures eat a variety of foods. Most robins, for example, like to eat many kinds of insects, not just beetles.

Part 1:

Provide an example of a food chain in the area where you live.
Humans are parts of food chains and food webs, too. Where on a food web would you typically find humans (near the bottom with the producers, at the top with carnivores, or somewhere in between)?
What are some advantages of being part of a food web rather than a food chain?

Part 2:

Here is a food web for Lake Michigan:

http://www.glerl.noaa.gov/pubs/brochures/foodweb/LMfoodweb.pdf

To see this PDF, you'll need to download the free Adobe Reader .

In the Lake Michigan food web, is it possible to identify the most important producer? Why or why not?
What would happen if there was a change in the population size for any one of the producers (either an increase or a decrease)? How could these changes impact other producers and organisms on other trophic levels?
Provide at least two types of impacts that humans could have on this food web.
Read the description of the sea lamprey on page 2 of the food web. This species is described as non-native.
Propose a mechanism for how this fish was introduced to Lake Michigan.
What challenges could occur within a food web when a new predator like this is introduced into an ecosystem?
What natural population controls are missing for this species within this food web?
Do you think steps should be taken to eradicate this species from the food web? Explain why or why not? If so, what steps can be implemented?

Solution Preview

http://www.squidoo.com/thegreatlakesandsealampreys

What would happen if there was a change in the population size for any one of the producers (either an increase or a decrease)? How could these changes impact other producers and organisms on other trophic levels?
Provide at least two types of impacts that humans could have on this food web.

The questions above that refer to changes in population size of producers that result from an increase or decrease and how human impact could affect the food web are linked together as any change in the population emanating from human contact with either increases or decreases has immense impacts on the food web. Humans with their actions can dramatically alter the food web on trophic levels as well as with the producers. For example the spraying of chemicals such as pesticides affects producers as well as other trophic levels that rely on the producers. Initially this spraying may increase production from the producers by 'killing' the insects that feed on the producer on the trophic level, thus increasing output from the producer but the trophic levels that rely on the producer will eventually decrease in their numbers as well as those that rely on lower trophic levels such as the organisms that feed on the insects. The point in this summary that YOU must understand is that when human behavior occurs, a chain reaction is released that breaks the link in the food chain, which impacts organisms above and below that link that in the case of pesticides could threaten the entire chain as a result of the domino effect.

Another example that could cause extinction within a food chain or temporary increases ...

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