Pocket Mouse Example - Natural Selection

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Objective

SWBAT analyze and organize data to develop an explanation on how variation, selection and time drive the evolution of species.

Big Idea

Students use mathematical representations to support conclusions as they learn about how natural selection affected the pocket mouse population of the southwestern United States.

Warm-up

10 minutes

This lesson is from HHMI Biointeractive.  The teacher materials hold many teaching tips and the answer keys.  The student materials are also found in the resources.  Rather than walking you through these materials, this lesson demonstrates how I implement it in my classroom.

I begin by breaking students into pairs.  One of my goals through the year is to help students learn to work with a variety of different people.  To help lessen the stress of the project based nature of this course, I typically allow students to choose their groups (though I usually require that the current group is not an exact match to the prior group) so to ensure students work with different people it is important that I assign the groups for these smaller tasks. 

My favorite grouping strategy is to use "mirror groups".  My room is set up with 4 lab tables on opposite sides of the room with an aisle separating them.  A student's mirror is the person who sits in their seat but on the opposite side of the room.

Once the students are in their groups, I pass each group a set of images to analyze (pages 5-8 of the student materials) and give each student the Pocket Mouse Data Sheet to record their answers throughout the activity.  I use the Pocket Mouse Analysis PowerPoint to guide the activity.

Students begin by analyzing the images, counting the light colored and dark colored mice in each location and recording this information on their data sheet.  Students then determine the sequence of these images placing the oldest first and the most recent last.  Students also record this information on their data sheet.

Students go on to explain their reasoning behind the sequence they chose.  This video contains some students explaining the reasoning behind their choices.

Activity

30 minutes

I continue by showing students the following video that explains the history of the pocket mouse. As students watch the video, they should look for an explanation for the differences among the illustrations that will help them confirm that the order in which they arranged the illustrations is correct.

I also ask students to take some brief notes regarding the following questions:

  • Why are some mice light colored and some mice dark colored? 
  • Does fur color provide any selective advantage or disadvantage? 
  • What role does the rock pocket mouse play in the desert food web? 
  • What can explain the differences among the illustrations?

To ensure that students have enough time and information to accomplish all this, I show the video twice and have them compare information with the others at their tables in between viewings. 

Students go on to use what they learned from the video to verify or change their sequence of images and then complete the following data table (also found in the student data sheet).

 

ORDER OF ILLUSTRATIONS

FIRST

(oldest)

SECOND

THIRD

FOURTH

(most recent)

Location A

Number of mice with LIGHT FUR

 

 

 

 

Number of mice with DARK FUR

 

 

 

 

Location B

Number of mice with LIGHT FUR

 

 

 

 

Number of mice with DARK FUR

 

 

 

 

Once the data table is completed, students create a graph that illustrates the distribution of mice at locations A and B through time. 

Wrap-up

10 minutes

To end the lesson and allow students to synthesize all they have learned, students answer the following analysis questions (on data sheet):

1. Explain why a rock pocket mouse’s color influences its overall fitness. Remember that “fitness” is defined by an organism’s ability to survive and produce offspring. 
2. Explain the presence of dark-colored mice at location A. Why didn’t this phenotype become more common in the population? 
3. Write a scientific summary that describes changes in the rock pocket mouse populations at location B. Your summary should include:

    • a description of how the population has changed over time
    • an explanation of what caused the changes
    • a prediction that describes what the population will look like 100 years in the future.

Base your prediction on trends in the data you have organized. You can assume that environmental conditions do not change over the 100 years.

4. Use the data and what you have learned about evolution to explain how mutation is a random process, but natural selection is not random. 

 

The Perfect Student Examples and Student Example Answers (all 4 questions) provide an idea of the type of answers I was looking for from my classes.  I also wanted to share Examples - Not Quite as it shows the answers from students who did not quite acheive the level of detail needed to show understanding.