Coevolution: A Simulation
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Studying Living Organisms

Coevolution: A Simulation

William Sumner
Woodrow Wilson Biology Institute
1995

Target age or
ability group:
Introductory biology students.
Class time
required:
10-15 minutes.
Materials and equipment:
Artificial/real flowers (I use a minimum of three) Straws/coffee stirrers (cut to varying lengths) Test tubes/small plastic bottles of varying lengths (test tubes should not have been used previously) Juice/water
Summary of activity: Coevolution is the term used to identify the process in nature in which two or more species interact so intimately that their evolutionary fitness depends on each other. Nature abounds with numerous examples such as the milkweed, monarchs and their mimics. Perhaps the best known examples of coevolution involve flowering plants and their pollinators/seed dispersers. In this activity, various materials are used to simulate flowering plants, nectar and nectaries, and the mouth parts of pollinating insects.

Teacher preparation:

1. Prepare at least three test tubes/small bottles of varying lengths (to represent the nectaries in a flower) by trimming the length of three different flowers so that the flower sits directly on top of the container. The distance from the flower to the bottom of the container should be different in each container.

2. Cut a small hole in the base of each flower.

3. Cut a straw/coffee stirrer (representing the tongue of an insect) so that each tube has one straw/stirrer that matches the distance from the bottom of the flower to the bottom of the container.

4. Remove flowers and straws and pour juice/water (representing nectar) into each container.

5. Place flowers back into containers. Shield container so that only the flower is visible. A block of Styrofoam with holes cut to match the lengths of the containers works well.

Student Involvement

1. Give one of each of the three different length straws to three different students.

2. Have student come up to the flower set-ups and ask them to suck "nectar" (the juice/water) from the "nectaries" of the flowers by placing their straw through the hole in the bottom of the flower and into the liquid. Straw must reach the bottom of the container and the top of the straw should be nearly level with the location of the anthers.

Discussion

1. Was it possible to use only one of the three straws on all three different flowers? Explain.






2. Why was it specified that the top of the straw must be level with the anthers of the flower?






3. How does this activity illustrate the coevolution of different species?






4. Give some actual examples of coevolution in nature.






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