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From Eggs to Butterflies: How Does a Population Grow?
Teaching Suggestions

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Introduction

Background
A female monarch butterfly can lay hundreds of eggs. If every egg survived, the monarch population could grow to a billion butterflies in only four generations. Use this slideshow to explore the essential question:

Essential Question
What limiting factors keep the monarch population from growing exponentially?

Purpose:

  • To explore population dynamics: the reproductive potential of monarch butterflies and the limiting factors that keep the population from growing exponentially.
  • To invite students to record limiting factors that may impact the size of the population as they follow the migration live this spring.

Objectives:
After reading the slideshow and completing follow-up activities, students will be able to:

  1. Define the phrase "reproductive potential" and explain how it relates to monarch butterflies.
  2. Identify and describe the limiting factors that keep the monarch population from reaching unsustainable levels.

Slideshow
Activities

1. Build background knowledge by reading aloud “How Much is a Million?” by David M. Schwartz. Use the book to help students conceptualize immense numbers and understand exponential growth.

2. Explore the mathematics of monarch population growth. Place students in small groups. Provide each group with a copy of the handout, From One to One Billion Butterflies. Examine the graphs that use a simplified model to explore the complex concepts of population growth and the reproductive potential of monarchs.

  • Invite students to describe what each graph shows and to summarize how the graphs help them understand the growth potential of monarch populations.
  • Encourage students to write story problems for the class to solve using the data on the graphs.

3. Revisit key concepts described in the slideshow. Write these two phrases on chart paper: “reproductive potential” and “limiting factors.” Challenge students to define each word and phrase. Have them explain how these words relate to monarch butterflies using details described in the slideshow. Reread the final page of the slideshow together. Discuss how limiting factors keep populations from reaching unsustainable levels.

Here are some Guiding Questions to facilitate discussion:

  • What factors might influence the number of eggs monarchs lay?
  • Which factors might impact survival at each phase of the life cycle?
    • egg
    • larval
    • chrysalis
    • adult
  • What limiting factors might impact survival during each stage of the annual cycle:
    • spring migration?
    • fall migration?
    • the breeding season?
    • the overwintering season?

4. Chart the limiting factors throughout the four phases of the monarch’s annual cycle. Distribute the Monarch Annual Cycle handout and have students think about what challenges monarchs face during each stage of their annual cycle. As students track the migration, have them record limiting factors that may impact population growth and decline on the chart. Display the chart and add ideas throughout each season.

 

How Much is a Million?
by David M. Schwartz

 

From One to One Billion Butterflies

 

Monarch Annual Cycle
Limiting Factors at Each Stage

 

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