In
this lesson you will study examples of actual food webs to become
familiar with the organization of these diagrams and develop an
understanding of the information about an ecosystem that they contain.
In the second part of these lessons you will create your own food webs
in an exercise that will help you appreciates just how complicated even
simple food webs can be. Select your lesson from the list below to
begin. Take notes as you read this information and answer the questions
listed in each lesson. Email me your answers.
Lesson One: Biodiversity And Food Webs The first lesson uses a web site sponsored by the American Museum of Natural History. A
visit to their web site is worth some extra time. Here you will find a
great deal of useful information on a wide variety of topics. Go to the
Museum's Center for Biodiversity and Conservation and find the "What Is Biodiversity" link. Read the information on this page and answer the following two questions. - What is biodiversity? Use your own words to paraphrase the information you read.
- Describe two specific examples that illustrate why biodivesity has direct benefits to humans. Again, use your own words!
Now click on the food web link to begin you study of sea otters and their ecological community. Read
the introductory material and study the first food web diagram (A, the
food web with otters). Answer the following questions. - How many first, second, third, and fourth level consumers are in this food web? Name them.
- Are there any consumers at levels higher than the fourth level? Name them if there are any.
- Why is the sea otter considered to be a "keystone" species? Use your own words!
- Why
is the relationship between the sea otter and the sea urchin so
important to other organisms in this community. Give specific examples.
Now study the second food web diagram (B, without otters) and read the accompanying text. Answer the following questions. - Why did sea otter populations decline almost to extinction?
- What
was the effect of the absences of the otters on the other organisms in
the community? Which ones declined and which ones increased?
- Once
otters became protected species, these communities have begun to
recover. However, there are several factors that are slowing this
recovery and once again causing the otter populations to decline.
Discuss three specific factors that are now contributing to the sea
otter decline.
Go back to the top of this page.
Lesson Two: Build Your First Food Web
A few points to remember as you work with this program.
- In the upper right hand corner select Lesson Food Web. This is not critical, but it helps if everyone uses the same setting.
- Begin each lesson by clicking on "All Off" to clear previous work; it just makes life easier for you.
- Be sure you click on Reset before running new models of your food web. This is important.
Being
by clicking on " All Off" and running the program with on plant A, then
only plant B, and finally only plant C. Take notes on the population
growth curves for each. Remember to click on Reset between each of
these runs.
Now try combinations of two species of plants,
e.g. plants B and C, and A and B. Note that the plants interact with
one another. Keep this in mind as you add various consumers.
Finally,
and your challenge is to create a food web that includes all three
plant species and all three herbivore species. Start simple and
gradually work your way to the complete food web. You don't have to
start with all three plants at once. You can add them one at a time or
in any other combination you wish. The goal is to produce a food web
that reliably runs without any of the species going extinct.
Once you have achieved this goal, print out or sketch the food web and the growth curves and answer the following questions.
- Briefly
describe the interaction among the three plant species. Does one tend
to dominate over the others? Do the numbers of one species influence
the numbers of the others?
- Once you add the herbivores, does the answer to the previous question change? Explain.
- Are
the herbivores more likely to go extinct if they are eating a single
plant species or if they eat a variety? Explain and give an example.
- Do either of the herbivores play the role of a "keystone" species in your food web? Explain.
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Lesson Three: Adding The Omnivores To Your Food Web
Once you have accomplished this, print out or sketch the food web and the growth curves and answer the following questions.
- Does adding the omnivores make creating a stable community easier or harder? Explain.
- Is there a "keystone" species in your new food web? Explain.
- Did your omnivores act as first or second level consumers or both? Explain and give examples.
Got to the top of this page.
Lesson Four: Finally Adding The Top Predator To Your Food Web
Once you have accomplished this, print out or sketch the food web and the growth curves and answer the following questions.
- Is
there now a "keystone" species in your new food web? Is it the same
species that may have been a keystone species in the previous food webs
you created? Explain.
- Test the hypothesis that one of the
species in your food web is a "keystone" species by eliminating it from
your community and rerunning the program. Describe the results and
print out the altered food web diagram and the growth curves (if you
didn't think there was a keystone species, think again)
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Birch's Biology Class Pages.
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