Quick Lab: Competition and Predation

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Competition and Predation
How can you model competition among organisms as resources become limited?
Background A forest may be home to many deer, rabbits, and a variety of birds, insects, and
other animals. How many of these animals can live in the forest? The answer depends on the
size of the forest and other factors. As populations increase, the organisms compete for food,
water, space, and other needs. Their numbers are limited by the amount of resources that their
environment can provide. In this investigation, you will model competition between organisms.
Then you will identify patterns of behavior among organisms that are competing for limited
resources.
Materials (per pair)
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plastic spoons
plastic beads
plastic cups
Procedure
□1.
In this activity, you represent an organism competing for a limited resource. The
limited resource you are competing for is beads. You need at least eight beads to survive.
Your goal is to collect at least eight beads.
□2.
□3.
Spread ten beads per person on a flat surface.
Each of you will use one plastic spoon to capture the beads. Note: You may use
only the spoon to collect beads. You may not use your free hand.
□4.
Investigate how organisms may compete for biotic factors by following these
instructions: When your teacher indicates, you will have 30 seconds to collect at least
eight beads. Put beads in your cup as you capture them. After 30 seconds, record the
number of beads in your cup.
□5.
Return all beads to the flat surface. Remove half of the beads, and repeat Steps
2 through 4.
Analyze and Interpret Data
1. Use Models Develop an explanation for how organisms and populations in an ecosystem
depend on, and may compete for, resources in their environment by answering the following
questions.
a. In this activity, you represent an organism competing for a limited resource. If you
represent a predator, what do the beads represent? How is this factor a limiting
resource?
b. How does this activity model competition among organisms for this biotic factor?
Populations and Biodiversity Quick Lab • Copyright © by Pearson Education, Inc., or its affiliates. All Rights Reserved.
c. What was the effect of a decrease in food availability in this model?
d. Suppose two members of your group now represent a population of organisms that are
not predators for the same food source. In terms of competition between populations,
predict how their presence might change the results of this model?
2. Interpret Data What is the relationship between predators and the amount of available
resources, such as food, in an ecosystem?
3. Construct Explanations Identify a pattern between the availability of food and levels of
competition that you observed in this activity. Describe the pattern using a cause and effect
statement such as, “When food supplies…then competition…” Then, explain how that
pattern could be used to predict similar interactions among organisms in different
ecosystems.
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Extend Your Inquiry
Conduct Research Projects For each ecosystem listed below, describe two examples of
predator/prey relationships. Apply the patterns you observed in this activity to those
relationships by explaining how the availability of prey affects levels of competition. Use
classroom, library, or Internet resources to help you.
1. Marine ecosystem
2. Freshwater ecosystem
Populations and Biodiversity Quick Lab • Copyright © by Pearson Education, Inc., or its affiliates. All Rights Reserved.
3. Terrestrial ecosystem
Populations and Biodiversity Quick Lab • Copyright © by Pearson Education, Inc., or its affiliates. All Rights Reserved.
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