Lesson 9. Adaptive Radiation in the Galapagos

Sugat Dabholkar
Biology, Environmental Science
45-50 minutes
High School
v2

Overview

  • A new trait might grant individual(s) a competitive advantage for survival and/or reproduction in an environment (an adaptation), or a competitive disadvantage, or neither.
  • Advantageous traits tend to accumulate in populations over many generations yielding a population progressively better adapted to survive and reproduce in that environment over time.

Standards

Next Generation Science Standards
  • Life Science
    • [HS-LS4] Biological Evolution: Unity and Diversity
  • NGSS Practice
    • Analyzing Data
    • Communicating Information
    • Constructing Explanations, Designing Solutions
    • Asking Questions, Defining Problems
    • Using Models
    • Arguing from Evidence
    • Conducting Investigations
Computational Thinking in STEM
  • Data Practices
    • Analyzing Data
    • Collecting Data
    • Creating Data
    • Manipulating Data
    • Visualizing Data
  • Modeling and Simulation Practices
    • Using Computational Models to Find and Test Solutions
    • Using Computational Models to Understand a Concept
  • Systems Thinking Practices
    • Investigating a Complex System as a Whole
    • Thinking in Levels
    • Understanding the Relationships within a System

Acknowledgement

CODAP is developed and built by The Concord Consortium at https://codap.concord.org/  

This lesson 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. How Do Species Emerge?
  • 2. Introduction to Galapagos Finches
  • 3. Intro to CODAP
  • 4. What Causes Change in Finches?
  • 5. More Finch Data
  • 6. How Can Speciation Occur?

Student Directions and Resources


The purpose of this activity is to discover how the combination of mutations, natural selection, and environmental change generate progressively better-suited adaptations.

1. How Do Species Emerge?


Purpose  
How do new species emerge?

Brainstorm
You know that many species that were alive in the past have gone extinct.  Many of the species that are alive today did not exist at one point in the past.  

 


Question 1.1

Explain how natural selection could help to explain how new species might emerge. Think back to some of the earlier concepts you went over.



Question 1.2

Can evolution occur without natural selection?

  Yes
  No


2. Introduction to Galapagos Finches


There are 13 species of finch on the islands, but they are at once both so similar and so diverse that they have provided a fertile ground for exploring evolution since Darwin’s 1835 visit.  Darwin himself did not realize their role in explaining evolution until after ornithologists revealed the abundance of speciation to him.

The finches are proposed to have arrived on the volcanic islands from the South American mainland and are now considered part of the tanager family rather than the finch family.  There are four genera recognized in the group, and the species occupy overlapping but distinct ecological niches. In the genus Geospiza, there are six species.  In good times, they often eat the same foods, but in times of scarcity, each species has a specialized niche – large seeds, cactus fruits, etc. – on which they rely.  Their mating behaviors, such as times and songs, differ greatly, maintaining the distinct species.  The ecology of the different islands influences which species live on each island, and especially which species co-exist on an island.  Gene flow between islands occurs with occasional immigrants depending on storms and the distance between islands.

For several decades, scientists have gone to the Galapagos islands to study the physical characteristics of the finches there.  They recorded data on many traits including beak dimensions and weight.  In this lesson you will explore some of that data to understand the processes underlying speciation and adaptive radiation.


Question 2.1

What do you think separates species from each other?  In other words, what does it mean to be a 'different species' than another organism?



Question 2.2

How would you go about trying to distinguish one species from another?



Question 2.3

Why do you think the data the scientists collected might be useful for studying differences between species?

3. Intro to CODAP


Below is a data analysis tool called CODAP created by educators at the Concord Consortium. Using this computational tool, you will be able to delve deeply into the finch data mentioned on the previous page. When the page loads you will see the basic finch dataset with columns for sex, weight (g), beak length (mm), beak depth (mm). In CODAP we are able to interact dynamically with the data, allowing us to make connections and draw conclusions. We will use this set to answer several questions about these Galapagos finches.


Question 3.1

Use CODAP to fill out the following data table.

You can see the value of a data point by hovering your mouse over the point.  Use this to find the minimum and maximum beak lengths.

Clicking on the data point will highlight the row in the data table.

Clicking on a graph will cause a toolbar to appear next to it.  You can find and display useful information about the data in a graph using the ruler menu in that toolbar. Click the check boxes for median, mean, and standard deviation to display them on the graph.  You can find their values by hovering your mouse over the display.



Question 3.2

If you click and drag to surround points on a graph, they will be selected on all current graphs. You can use this to hide points that you don't want to see. Sometimes CODAP responds slowly and will have a slight delay, so you may need to wait for it to catch up.

Click and drag to select all of the male finches.  Then, on the histogram of beak length, use the eye menu to the right of the graph to hide unselected points.  For clarity, you can also change the title of the graph to "Males" by clicking on the current title in the blue bar at the top of the graph.

What is the mean beak length for male finches?



Question 3.3

In order to visually compare two or more subgroups, it can be helpful to have multiple graphs.  Sometimes the points on a new graph will not look the same as those on other graphs. You can change the appearance of the points on any graph using the paintbrush menu to the right of the graph.

In the upper left corner, click the "Graph" button to create a new blank graph. Drag the "Weight" column header from the table to the x-axis of the new graph to create a second histogram and title it "Females".  Using the same method as before, hide all of the points on the new plot that aren't from female finches.  Drag the "Weight" column header to the x-axis of the original graph to replace "Beak Length".

What differences do you notice in the graph of male finches vs. the graph of female finches? Be sure to mention characteristics like shape of the graph and median values.



Question 3.4

Another way to compare subgroups is to put categorical data on the y-axis.  Close one of the two histograms and use the eye menu to show all points on the remaining graph.  If you want, you can change the title for clarity.  Then, drag the "Sex" column header to the y-axis of the histogram.

How does the group of finches of unknown sex compare to the male and female finches?



Question 3.5

Drag the "Beak Length" column header to the y-axis of the histogram to turn it into a scatter plot.  If you still want an idea of how the male, female, and unknown sex finches compare, you can drag the "Sex" column header to the middle of the plot to change the color of each point to match the sex of the finch.

Based on this plot, what seems to be the relationship between weight and beak length in these finches?



Question 3.6

The data above comes from only one species of finch. Why do you think there is variation in the beak lengths and weights of these finches? Think back to some of the earlier lessons when you saw a graph like this.

4. What Causes Change in Finches?


The scientist that have collected this data have done so for over 40 years now, the first bar graph that you saw in section one contains finch data from 1973 -1981. Lets see what we can find if we look deeper into the data.

In this data set, "Last Year" is the record of the last year an individual finch was seen by the researchers.  This typically means that the individual finch died during that year.

Use the methods you learned in the last activity to compare the finches that died during 1977 with the finches that survived 1977 and answer the questions below.


Question 4.1

What differences do you see between the group of finches that only lived until 1977 and the finches that lived to 1978 and beyond? Please discuss the position (i.e. mean, median) and shape (i.e. standard deviation, range) of the beak depth distributions in your response, along with any other information you think is relevant.



Question 4.2

The medium ground finch (Geospiza fortis) has a short, blunt beak which is adapted to picking up seeds from the ground. In 1976, seeds on the island were diverse and plentiful. During a drought in 1977, seeds became much harder to find. Once the finches had eaten all the small and medium-sized seeds, they had to turn to larger, spiny seeds that are hard to crack open. In your group come up with a reasonable hypothesis as to why there might be changes in how beak depths are distributed before and after 1977. Think about connecting past ideas like competition and natural selection. Be as specific as you can.



Question 4.3
During the drought, the beak depth with the greatest fitness increased, but the amount of variation in the trait did not.  This is an example of directional selection.  Directional selection is often the result of a change in environmental conditions.  How does this compare to the stabilizing selection you saw in the previous lesson?

 

5. More Finch Data


This CODAP frame has a much larger data set than those you have explored in the previous activities.  To help you gain a better understanding of the finches in the Galapagos, there are many more physical traits to explore.  Use the skills you developed in the previous activities to use CODAP to look at several traits and compare them across species and locations.

Not all of the traits were measured on each individual, so some traits will have more complete information than others.  We will focus on a trait that has a lot of data points, beak height.


Question 5.1

Generally speaking, how are the different finch species similar or different?

For example, which species have similar ranges of beak height?  Which species have different ranges of beak height?



Question 5.2

Generally speaking, how are the finches on different islands similar or different?  

For example, you might think about whether the islands all have the same species, or whether the islands all have similar distributions of beak height.



Question 5.3

Generally speaking, are members of the same species on different islands different from each other? Give examples to support your answer.



Question 5.4

Look at the histogram of beak heights for all finches.  There appear to be several peaks in it.  Are there multiple species or islands represented in each peak?  What does this suggest about the niches present in this ecosystem and the species that are in a peak together?



Question 5.5

Do the answers to any of these questions change if you look at another trait with many data points, like wing length or N-UBkL (another measure of upper beak length)?  How?

6. How Can Speciation Occur?



Question 6.1

Scientists think the finches on the Galapagos are descended from finches that traveled from the mainland at some time in the past.  One possibility is that one type of finch arrived at the islands and split into new species over time.  Another possibility is that several species arrived at the islands.  Which do you think is more likely?  Why?



Question 6.2

Do you think the environments on each island are similar? How might they be different?  It may be helpful to think about this in terms of ecological niches, and to think back to what you saw in the previous activity.



Question 6.3

Why do you think there are so many different species of finch on such a small group of islands?  How might differences between the islands and their niches have affected the number of species?



Question 6.4

Come up with a story that describes the how the different species of finches could have developed in the Galapagos islands.