Brainstorm a definition of a species based on your knowledge from the previous lesson.
Overview
Purpose: The purpose of this activity is to understand how new species can form from old species through the mechanisms of evolution covered so far in the unit (mutation, genetic drift, changes in environmental conditions, and natural selection).
Connection to previous activities: Students refer to the mechanisms of mutation (introduced in the last activity), genetic drift (from the activity before that), changes in environmental conditions and natural selection (from two previous activities), to develop the explanations for the outcomes in this activity.
Learning Performances
• Analyze data from a computer investigation applying concepts of statistics and probability to explain why adaptations for reproductive isolation can help reinforce specialized adaptations for survival for different niches within different gene pools in a population. [Emphasis is on analyzing shifts in numerical distribution of traits in a histogram and using these shifts as evidence to support explanations.]
Scientific Principles Discovered in This Activity:
• New species emerge from old species (a group of organisms that is capable of interbreeding only between each other to produce fertile offspring).
• Speciation can occur when specialization for survival in different niches is available to a population; this specialization opportunity can tend to reinforce adaptations that lead to greater reproductive isolation between those populations.
• Speciation can occur when geographic isolation leads to separate populations that through mutation and genetic drift, develop genes and corresponding traits that make descendent from each population less reproductively compatible with each other over time.
Description of the Lesson
The class revisits their definition of a species and discusses whether genetic drift alone could account for why new species emerge.
They then use a computer model of plants in an ecosystem to explore how speciation always could also emerge from a single population over time under certain conditions.
Through discussion, the teacher helps build consensus about why speciation might occur when mutation initiates the pathway to speciation, but natural selection and adaptation are the driving mechanisms that continue to reinforce the emergence of this outcome.
In the homework, they study examples of how speciation has been created in laboratory conditions with human intervention and contrast the mechanisms at work in real world ecosystems when new species emerge. And they read Darwin’s finches on the Galapagos Islands as a real-world example of adaptive radiation.
Standards
Next Generation Science Standards
Computational Thinking in STEM
- Data Practices
- Analyzing Data
- Manipulating Data
- Visualizing Data
- Modeling and Simulation Practices
- Using Computational Models to Find and Test Solutions
- Using Computational Models to Understand a Concept
- Computational Problem Solving Practices
- Troubleshooting and Debugging
- Systems Thinking Practices
- Investigating a Complex System as a Whole
- Thinking in Levels
- Understanding the Relationships within a System
Credits
Unit designed/developed by Dabholkar, S., Hall K., Woods P., & Bain C.
Acknowledgement
CODAP is developed and built by The Concord Consortium at https://codap.concord.org/
Lesson 7 is based on the lesson Evolution in Action: The Galápagos Finches Authored by Paul Strode for Howard Hughes Medical Institute based on data collected by Peter and Rosemary Grant, Princeton University.
This work is supported by the National Science Foundation (grants CNS-1138461, CNS-1441041 and DRL-1020101) and the Spencer Foundation (grant 201600069). Any opinions, findings, conclusions, and/or recommendations are those of the investigators and do not necessarily reflect the views of the funding organizations.
Activities
- 1. Introduction
- 2. Predict
- 3. Looking at Flowering Time
- 4. Looking at Metal Tolerance
- 5. Predict
- 6. Test Your Predictions
- 7. Discoveries and Insights
Student Directions and Resources
The purpose of this activity is to understand how new species can form from old species through the mechanisms of evolution covered so far in the unit (mutation, genetic drift, changes in environmental conditions, and natural selection).
1. Introduction
Purpose
What are other ways that new species can form?
Brainstorm
Last lesson you looked at species formation over time based on geographic separation. Is this the only way that new species can form?
Question 1.1
Question 1.2
Besides geographic isolation, what other type of scenario could lead to new species being formed?
2. Predict
Your teacher will play this video for the class, but it is provided here for reference.
Question 2.1
What does the difference in color of the soil represent?
Question 2.2
How does the model show when flowering is occurring?
Question 2.3
What should occur when you change time-steps from days to years?
Question 2.4
The video discussed a scenario where neither flowering time or metal tolerance are allowed to change. What do you think would happen if flowering time was allowed to change, but metal tolerance was not? Briefly explain your prediction.
Question 2.5
What do you think would happen if metal tolerance was allowed to change, but flowering time was not? Briefly explain your prediction.
3. Looking at Flowering Time
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Set the initial values to:
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Press SETUP. and Press GO/STOP to run the model.
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You can switch the VISUALIZE-TIME-STEPS to “years” or “days”. Years runs faster, but days lets you see the actual difference (if any) in flowering times between plants.
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Run, the model for at least a hundred years.
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Analyze the FLOWER-TIMES graph.
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Record your data in your Observation section.
Question 3.1
Observations
Question 3.2
Were your predictions correct? Explain.
Question 3.3
What is the range of flower times?
Question 3.4
Let's look at why the flowering times show this pattern. Which type of individual would have the best chances of being pollinated by other flowers?
A plant with a flowering time much earlier than most of the population
A plant with a flowering time much later than most of the population
A plant with a flowering time similar to most of the population
A plant with a flowering time much later than most of the population
A plant with a flowering time similar to most of the population
Question 3.5
How does the shape of the FLOWER-TIME graph from this model run support this claim: "Any individual that flowers earlier than the average flower time or later than the average flower time, will have a lower chance of having offspring?"
Question 3.6
Do you think flowering time is under stabilizing selection or directional selection? Explain your choice.
Question 3.7
All of the plants are flowering in a very narrow range of flowering times, opening during a similar time of year. Do you think all of the plants are still part of the same species? Why or why not?
4. Looking at Metal Tolerance
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Set the initial values to:
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Press SETUP. and Press GO/STOP to run the model.
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You can switch the VISUALIZE-TIME-STEPS to “years” or “days”. Years runs faster, but days lets you see the actual difference (if any) in flowering times between plants.
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Run, the model for at least a hundred years.
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Analyze the FLOWER-TIMES graph.
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Record your data in your Observation section.
Question 4.1
Observations
Question 4.2
Were your predictions correct? Explain.
Question 4.3
What is the range of metal tolerance values?
Question 4.4
Metal tolerance is inherited from both parent plants. Knowing that all of the plants have the same flowering time, why do you think the plants mostly have similar metal tolerances, even when they are in the blue region?
Question 4.5
The plants in the left region and the plants in the right region tend to have different metal tolerances. Do you think they are still part of the same species? Why?
5. Predict
Purpose
Where do new species come from?
Predict
In the next model run you will allow both flower time mutations and metal tolerance mutations to occur in the offspring.
Question 5.1
What do you predict the outcome will be for the metal tolerance of the plants?
Question 5.2
What do you predict the outcome will be for the flower time of the plants?
6. Test Your Predictions
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Set the initial values to:
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Press SETUP. and Press GO/STOP to run the model.Keep the model running until the SIMULTANEOUS FLOWERING graph shows that the number of simultaneously flowering plants in the contaminated soil and in the regular soil, is very close to zero.
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Now make sure you have switched back VISUALIZE-TIME-STEPS to “days” mode and keep the model running.Below, record what you notice about when the flowers on the left side of the ecosystem are blooming versus the flowers on the right side of the ecosystem.
In the next set of questions you will try to explain why the flowers on the right have a different flower time than those on the left. To do this you may want to rerun this previous exploration in “days” mode, change labels, and study the model graphs. Feel free to conduct new experiments in this exploration to help you understand and explain why the initial plant population has “speciated”.
Question 6.1
Observations
Question 6.2
Why are the tolerance values in the two regions different, and why do you think there aren't there many plants in the population with a tolerance in between 10 and 90? Think back to the concepts of fitness, natural selection, and adaptation in response to different environments from the previous lessons.
Question 6.3
When the plants first reached the blue contaminated soil, the plants growing in that region increased their metal tolerance very quickly. Do you think this was a result of stabilizing selection or directional selection? Why?
Question 6.4
Now let's think about the differences in flowering times. If a plant with no metal tolerance, growing on the left side (clean soil) were to reproduce with a plant with metal tolerance growing on the right side (contaminated soil), their offspring would inherit genetic information from both parents. Why would this offspring plant be at a competitive disadvantage for survival compared to other plants growing either in the clean soil or in the contaminated soil?
Question 6.5
If a plant has to reproduce with another plant in order to have offspring, why would flowers in metal soil evolve a different average flower time than the flowers in the clean soil?
Question 6.6
| The type of selection acting on flowering times, where intermediate values are selected against and variation increases, is called disruptive selection. How is it similar to or different from stabilizing and directional selection? |  |
Question 6.7
How do the TOLERANCES and FLOWER TIMES graphs support the claim that: "The population of plants on the left side of the ecosystem no longer breed with the population of plants on the right side of the ecosystem"
Question 6.8
Do you think that the population of plants on the left side and the population of plants on the right side are still part of the same species? Why or why not?
7. Discoveries and Insights
Where do new species come from?
Question 7.1
What is the one big idea that you learned that helps you answer the question above?
Question 7.2
Do you think that the process you observed here will be similar for animal populations? Explain.
Question 7.3
How did this lesson inform or give new insights about what has happened in the Galapagos?
