Labs & Activities › Natural selection lab

Natural Selection Lab: Predators and Camouflage

Students become predators hunting colored paper “prey” on different backgrounds. Over several generations, the colors that are harder to see become more common. Then the environment changes.

• 45–60 minutes
• Groups of 3–4
• Paper and forceps
• Biology BIO.4.4, BIO.4.5
• Foundations FB.5.4

Question

How does the environment affect which traits become common in a population over generations?

Background

Individuals in a population vary. Some traits help an individual survive and reproduce in a particular environment. More offspring are born than can survive, so individuals compete, and the ones with helpful traits are more likely to leave offspring. This is natural selection. Over many generations, helpful traits become more common in the population. The environment does not create the variation. It selects among the variation that already exists.

Real example: on Kauai, a fly finds male crickets by their chirping and lays parasitic maggots on them. Silent male crickets survived and reproduced more often, and silent males now make up most of the male crickets.

• natural selection
• adaptation
• genetic variation
• competition
• overproduction
• reproductive success
• fitness
• population

Materials (per group)

• Two backgrounds, for example newspaper and a solid green sheet or fabric (about 40 by 40 cm)
• 100 paper dots from a hole punch, 20 each of five colors (red, yellow, green, blue, brown)
• Forceps (the predator’s beak) or fingers, a timer, and a small cup for captured prey
• Data table and calculator

Procedure

1. Predict which colors will survive best on Background A (for example, newspaper) and which will be removed first.
2. Generation 1. Spread the 100 dots evenly on Background A. Record 20 of each color as the starting counts.
3. One group member is the predator. With eyes on the background, pick up dots one at a time as fast as possible until 40 dots are captured. Count the dots left (survivors) of each color.
4. Reproduction. The population returns to 100 dots in the same proportions as the survivors. For each color: (survivors of that color ÷ total survivors) × 100, rounded to the nearest whole number. Add or remove one dot so the total is exactly 100.
5. Record the new counts as the start of the next generation and repeat steps 3 and 4. Continue to Generation 5.
6. Change the environment. Switch to Background B (for example, solid green) and run two or three more generations starting from your Generation 5 counts. Add rows to your table on paper if needed.

Data

Enter the number of dots of each color at the start of each generation.

Analysis

1. Which color increased the most on Background A? Which decreased the most? Use numbers from your table.
2. Explain why, using the words variation, adaptation, and reproductive success.
3. What happened to the colors when you changed the background? What does this show about adaptations and the environment?
4. Did the predator cause new colors to appear? Explain what natural selection acts on.
5. Compare this model with the Kauai crickets: what plays the role of variation, the selection pressure, and reproduction?
6. Name two ways this model is not like real populations.