Bio H - Ecology
Balance in an ecosystem
For this activity go to the following website: http://www.learner.org/courses/envsci/interactives/ecology/ecology.html
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Click on the lesson tab and select “food web”
Activity 1: Competition
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In the food web box there are various organisms that can be added to your ecosystem. Checking them will turn
them on and off in the ecosystem. For the consumers you can also check one or more food source for each species.
Turn on Plant A and B. Then click on the “Run” button.
a. Explain what happens to the population of the two species. Include a plausible explanation for why this
happened.
b. Now reset and turn on species B and C. Explain what happens here. Proposed a plausible explanation for how
the success of B differs so dramatically when combined with species C than it does with species A.
c. Why are we more likely to see competition between members of the same trophic level than we are members
of different trophic levels?
Now let’s examine competition between consumers.
Activity 2: Food Chain
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Now let’s examine a simple food chain. Turn on the following:
o Plant A
o Herbivore A (eats plant A)
o Omnivore A (eats herb A)
o Predator (eats omni A)
a. Sketch the results of your food chain on the graph and include a key. Notice that your data only covers the first
100 steps. We will add to this so do not continue your lines beyond 100 steps.
Bio H - Ecology
b. Explain the initial relationship between your plant and your herbivore.
Activity 3: Invasive species – DO NOT HIT RESET
Throughout history humans have introduced species to areas where they are not native, meaning they didn’t migrate
there naturally. The problem with this is that these species often have no natural predators in the population and yet
feed off species that are present.
a. Propose a way we could simulate the effect of an invasive species on your food chain.
b. Make the necessary changes to demonstrate the above on your food chain and continue the data run for
another 100 steps. Add the new data to your graph. Make sure you add your invasive species to your key.
c. Why are invasive species often the dominant species of their trophic level?
d. What happens to other members of the invasive species’ trophic level? Provide an explanation for each.
e. Without any predators, one might expect that the population of an invasive species will continue to rise,
however our data says otherwise. Explain why we don’t see continued growth of the invasive species.
Bio H - Ecology
Activity 4: Food web
Fortunately, in real life we don’t only have one thing that we can eat. Unfortunately, there is often more than one thing
trying to eat us too!
Using the simulator, try to create a successful food web where all your activated species are successfully sustained and
maintain a population above zero. (mousing over the line on the graph gives you the exact number of each species)
For each trial, sketch out the pyramid that you activated. Then, if it fails, indicate which species went extinct and how
you might adjust the food web to accommodate the mistake. Once you create a successful web, draw it below and
provide the final population of each species in the web.
Trial 1:
Trial 2:
Problem/solution:
Problem/solution:
Trial 3:
Trial 4:
Problem/solution::
Problem/solution::
Bio H - Ecology
Carrying Capacity: The carrying capacity of an ecosystem is the number of individuals that an ecosystem can support
successfully.
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How does the carrying capacity for each species change as more species are added into the food web? Explain.
2. In some rare instances, an ecosystem might be able to support a higher population of an herbivorous species
than it can of a particular producer species without violating our biomass laws. How is this possible?