Natural Selection with the Bear-Eating Monster
For this activity, you are a Bear-Eating Monster!!! In your habitat, there are two kinds of bears: Happy Bears and Sad Bears. Happy Bears hold their hands up high. Sad Bears hold their hands down low. Which bear is which in the picture below?
Happy Bears taste sweet and are easy to catch.
Sad Bears taste bitter, are sneaky, and difficult to catch.
Because you eat bears to survive, you only eat Happy Bears if at all possible. How would this affect the bear population?
Answer some questions about what might happen to the bear population.
1) Over time, what do you think will happen to the population of Happy Bears?
2) Over time, what do you think will happen to the population of Sad Bears?
Now let’s do an experiment to see what really happens:
Purpose
The purpose of this experiment is to see what happens to the bear population when the Bear-Eating Monster only eats one kind of bear.
Materials
Happy Bears
Sad Bears
Paper Towel
Pencil
Graph Paper
Lab Sheet
Procedure—Part One—“Generation 1”
1. Get a “population” of bears from the lab station. Pour them out on your paper towel.
2. Count the total number of bears and record this number on the table.
3. Separate the bears into two groups: Happy Bears and Sad Bears. Count the number of each. Record these numbers on the table.
4. Check your numbers. The total number of bears should be equal to the number of Happy Bears plus the number of Sad Bears.
5. Eat three Happy Bears. If you have fewer than three, it’s okay. Eat all the Happy Bears you have—but NO MORE THAN THREE.
In every habitat, organisms reproduce. In this habitat, baby bears are born one time every year. The number of baby bears born is equal to the number of bears left after the Bear-Eating Monster has eaten its 3 bears for the year. The baby bears are called the “new generation.”
Procedure—Part Two—“Generation 2”
1. Get the “new generation” from your teacher. Add them to the bear population.
2. Count the total number of bears and record this number on the table for “Generation 2.”
3. Separate the bears into two groups: Happy Bears and Sad Bears. Count the number of each. Record these numbers on the table for “Generation 2.”
4. Check your numbers. The total number of bears should be equal to the number of Happy Bears plus the number of Sad Bears.
5. Eat three Happy Bears. If you have fewer than three, it’s okay. Eat all the Happy Bears you have—but NO MORE THAN THREE.
Repeat this two more times—for “Generation 3” and “Generation 4.” Make sure your numbers are all recorded in the chart.
Good work! You are a great Bear-Eating Monster!
Fill in the Percentage Table by calculating the percent of each type of bear. This is an alternate way of showing your results for the experiment.
If you can’t remember how to calculate percents, just take the number of one type of bear (Happy or Sad) and then divide it by the total number of bears--then multiply by 100. For example,
Number of Happy Bears x 100 = Percent of Happy Bears
Total Number of Bears
How would you calculate the percent of Sad Bears? Write how you would do that below. Have your teacher check this. J
Now do your calculations for each of the four generations and fill in the Percentage Table. You can do it! One way to check your work is to see if your percentages add up to 100 for each generation.
Graphing
To see what happens to the bears over time, a graph can be very helpful. The best type of graph to see this is a bar graph. You have made these in your math classes before.
· The vertical side should be labeled “Number of Bears.”
· The horizontal side should be labeled “Generations.”
· At each generation, graph the number of Happy Bears and the number of Sad Bears. It might be cool to do Happy Bears one color and Sad Bears another color.
· The title of the graph should be “Bear Population Over Time.”
Please use a ruler to draw straight lines. Ask your teacher for help in deciding how to put the numbers on the vertical side or how big to make each bar. J
Conclusion
Look at your charts and your graph. Examine them to see what happened to the bear population.
Now answer these questions:
1) What happened to the total bear population over time?
2) What happened to the population of Happy Bears over time?
3) Why do you think this happened?
4) What happened to the population of Sad Bears over time?
5) Why do you think this happened?
6) How do the results compare to what you said at the beginning of this activity (questions on the first page)?
Using What You Just Learned…
Natural Selection is a process that occurs over time in a population of organisms. In this process, organisms that have traits that increase their chances of survival are more successful. This means, they are more likely to live and carry on to future generations.
Using the Happy and Sad Bears activity you just finished, write a paragraph that tells me how the bears’ situation is an example of the process of natural selection. You can do it! You’re a good scientist!
Bear Population Table
Generation / Total Number of Bears / Number of HAPPY bears / Number of SAD bears1
How many baby bears were born?
2
How many baby bears were born?
3
How many baby bears were born?
4
Check your numbers! Make sure they are all filled in.
Bear Percentage Table
Generation / % Happy Bears / % Sad Bears1
2
3
4
Check your numbers! Each generation’s percentages should add up to 100.
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