Download Student Exploration Sheet: Growing Plants

Name: ______________________________________
Date: ________________________
Student Exploration: Rainfall and Bird Beaks
(vocabulary terms at the end of the worksheet)
Vocabulary: adaptation, beak depth, directional selection, drought, evolution, natural selection,
range, stabilizing selection
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
During the voyage of the HMS Beagle (1831–1836), the young Charles Darwin collected several
species of finches from the Galápagos Islands. Two of Darwin’s finches are shown below.
1. Which species do you think is best adapted to a diet of small, delicate
seeds? Explain why you think so.
_______________________________________________________
_______________________________________________________
2. Which species do you think is best adapted to a diet of large, toughto-crack seeds? Explain.
_______________________________________________________
_______________________________________________________
Gizmo Warm-up
Darwin’s finches are one of many types of animals on the
Galápagos Islands that have unique adaptations, or traits that
help an organism survive in its environment. The Rainfall and
Bird Beaks Gizmo™ allows you to explore how rainfall influences
the range of beak shapes found in a single finch species.
1. The beak depth of a finch is the distance from the top of the beak to the bottom, as shown.
A. What is the current average beak depth in the Gizmo? ________________________
B. Select the BAR CHART tab. Do all the finches have the same beak depth? _______
2. Click Play (
) and let the simulation play for five years with average rainfall (12.5 cm/yr).
Select the GRAPH tab and view the Finches vs time and Beak depth vs time graphs.
A. How does the finch population change? __________________________________
B. Does the beak depth change significantly? ________________________________
Activity A:
Normal years
Get the Gizmo ready:
 Click Reset (
).
Introduction: The Galápagos Islands are very dry, with an average rainfall on some islands of
about 12 centimeters per year. The amount of rainfall has a large impact on the abundance and
types of seeds that are available to be eaten by finches. In the process of natural selection,
only the finches that are best adapted to the available seed types survive and have offspring.
Question: How is the finch population affected by a period of average rainfall?
1. Observe: With the Rain sliders set to 12.5 cm, click Play, and then Pause (
) after one
year has passed. Select the TABLE tab and look at the Month and Finches columns.
A. How did the finch population change over the course of one year? ______________
___________________________________________________________________
B. The finches have their young during the rainy season. Based on the table, which part
of the year do you think is the rainy season? _______________________________
2. Analyze: Click Reset, and choose the BAR CHART. The bars represent the numbers of
finches that have different beak depths. The range of beak depths is equal to the difference
between the largest and smallest beaks.
A. What is the average beak depth of the current finch population? ________________
B. What is the range in beak depths in the population? __________________________
C. Do most of the finches have beak depths near the lower extreme, the middle, or the
higher extreme of the range? ____________________________________________
3. Experiment: Click Play, and observe the bar chart as the simulation plays for five years.
A. What is the average beak depth now? ____________________________________
B. What is the current range of beak depths? _________________________________
C. Based on what you have seen, are finches with very small, medium, or very large
beaks most likely to survive in times of normal rainfall? Justify your answer.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
Activity B:
Drought
Get the Gizmo ready:
 Click Reset.
Introduction: In years of extreme drought, Galápagos plants don’t produce new seeds. The
small, delicate seeds get eaten up quickly, leaving behind only the largest, toughest seeds.
Question: How does drought affect the finch population and average beak depth?
1. Form hypothesis: What type of beak do you think will be best for finding food in a drought?
_________________________________________________________________________
2. Predict: Select the BAR CHART tab. On the left side below, sketch the current bar chart and
list the average beak depth and range of beak depths. On the right side, sketch what you
think the chart will look like after five years of drought. Explain your predicted graph.
Initial beak depths
Beak depths after 5 years (predicted)
Initial number of finches: ___________
Explanation: ________________________
Initial average depth: _________
___________________________________
Initial range of beak depths: _________
___________________________________
3. Experiment: Use the sliders to set the Rain to 2.5 centimeters for each of the five years in
the simulation. Click Play, and wait for five years. Observe the beak of the finch.
A. How does the beak depth change over time? _______________________________
B. What is the final average beak depth? ____________________________________
C. What is the final range of beak depths? ___________________________________
(Activity B continued on next page)
Activity B (continued from previous page)
4. Describe: Compare the final bar chart to the initial bar chart. How have the finches been
affected by drought? Describe at least two changes that you notice.
_________________________________________________________________________
_________________________________________________________________________
5. Analyze: Was the increase in the average beak depth caused by an increase in largebeaked finches or a decline in small-beaked finches? Explain your answer.
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
6. Draw conclusions: What do you think caused the changes in the finch population and
average beak size during the drought?
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
7. Interpret: Directional selection occurs when individuals at one end of a range are more
likely to survive than intermediate individuals or individuals at the opposite end of the range.
Stabilizing selection occurs when intermediate individuals are the most likely to survive.
Is directional selection, stabilizing selection, or both operating in this example? Explain.
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
8. Think and discuss: Evolution is the process by which populations of organisms can change
over time. How is directional selection related to evolution?
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
Activity C:
Get the Gizmo ready:
Rainy days
 Click Reset.
Introduction: In years of abundant rainfall, there can be 25 centimeters or more of rain. In
these years, plants produce an enormous number and variety of seeds.
Question: How does plentiful rainfall affect the finch population and average beak depth?
1. Form hypothesis: What beak shape do you think will be best for finding food in a period of
abundant rainfall? __________________________________________________________
2. Predict: Select the BAR CHART tab. On the left side below, sketch the current bar chart and
list the average beak depth and range of beak depths. On the right side, sketch what you
think the chart will look like after five years of abundant rain. Explain your predicted graph.
Initial beak depths
Beak depths after 5 years (predicted)
Initial number of finches: ___________
Explanation: ________________________
Initial average depth: _________
___________________________________
Initial range of beak depths: _________
___________________________________
3. Experiment: Click Reset. Use the sliders to set the Rain to 25 cm for each of the five years
in the simulation. Click Play, and wait for five years. Observe the beak of the finch.
A. How does the beak depth change over time? _______________________________
B. What is the final average beak depth? ____________________________________
C. What is the final range of beak depths? ___________________________________
(Activity C continued on next page)
Activity C (continued from previous page)
4. Describe: Compare the final bar chart to the initial bar chart. How have the finches been
affected by abundant rain? Describe at least two changes that you notice.
_________________________________________________________________________
_________________________________________________________________________
5. Analyze: Was the decrease in the average beak depth caused by an increase in smallbeaked finches or a decline in large-beaked finches? Explain your answer.
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
6. Draw conclusions: What do you think caused the changes in finch population and average
beak size during the period of abundant rain?
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
7. Extend your thinking: Most scientists think that a small group of finches colonized the
Galápagos Islands thousands of years ago. They would have been the only seed-eating
birds on the islands. Suppose one island was very dry and another had plentiful rainfall.
A. How would the finch populations on these islands change over time? ____________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
B. What might happen to the finch populations after millions of years? ______________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
Answer the Assessment Questions (5) on the website. On the sheet below put a CIRCLE AROUND
YOUR ENTIRE ANSWER. Then click Check Your Answers at the bottom of the website and put a
SQUARE AROUND THE ENTIRE CORRECT ANSWER even if it’s the same as your answer.
1.
The finch population of a remote island is 1000 finches on average. Choose the statement that best
describes the climate during the five years shown in the graph below.
A. A year of drought followed by four years of average or above-average rain
B. A year of above-average rainfall followed by four years of drought
C. Five years of drought
D. A year of average rain followed by four years of above-average rain
2.
A. Year 1
B. Year 2
C. Year 3
D. Year 4
In the graph below, which year most likely had the lowest rainfall?
3.
A population of Galapagos finches were monitored over a five-year period. Based on the graph below,
what can you conclude about the weather during these five years?
A. Rainfall was close to average throughout.
B. Three years of drought were followed by two years of above-average rain.
C. Three years of excessive rainfall were followed by two years of drought.
D. There were five straight years of excessive rainfall.
4.
A new kind of seed plant has been found on a remote island. This plant has larger, harder seeds than
those found on the Galapagos Islands. Which of the following finch adaptations would be likely to arise on this
new island?
A. Larger beaks
B. Smaller beaks
C. Longer legs
D. Shorter legs
5.
Which of the following statements best describes the response of finches to drought on the Galapagos
Islands?
A. During drought, individual finches saw that large, hard seeds were the only available food. To crack these
harder seeds, individual finches grew their beaks larger, resulting in an increased average beak depth.
B. During drought, finches struggled to open harder seeds. All the scraping and pecking wore down their beaks,
resulting in a reduced average beak depth.
C. During drought, only finches with larger-than-average beaks were able to crack the hard seeds that were
available. These finches survived while smaller-beaked finches died, resulting in an increased average beak depth
in the population.
D. During drought, finches with smaller beaks (and smaller bodies) had an advantage. With reduced food supplies,
larger finches (with larger beaks) were more likely to starve. The result was a decrease in average beak depth.
Vocabulary: Rainfall and Bird Beaks
Vocabulary

Adaptation – a trait that is beneficial to an organism.

Beak depth – the distance from the top to the bottom of a
beak, as shown at right.

Directional selection – a process of natural selection in which phenotypes at one
extreme are favored over other phenotypes.
o

Drought – a period of much lower than normal rainfall.
o


Misconception alert: Evolution refers to changes in populations of organisms over
time, but does not imply how these changes have taken place. Natural selection
is considered by most biologists to be the primary mechanism of evolution.
Natural selection – the process by which favorable inherited traits become more
common over time.
o
Natural selection is the primary mechanism of biological evolution.
o
Natural selection assumes the following: (1) More organisms are born than can
survive and reproduce. (2) Organisms compete for limited resources and
survival. (3) There are variations between organisms, and these variations can
be inherited. (4) Some variations make an organism more likely to survive and
reproduce. Over time, favorable variations will spread throughout a population,
while unfavorable variations become less frequent.
Range – the difference between the greatest and least value in a data set.
o

During periods of drought on the Galápagos Islands, very few seeds are
produced.
Evolution – change in the inherited traits of a population of organisms that occurs over
many generations.
o

For example, directional selection is occurring if the finches with the largest
beaks are surviving and reproducing at higher rates than finches with averagesized or small beaks.
For example, if the greatest beak depth is 13.0 mm and the least beak depth is
9.0 mm, the range in beak depths is 4.0 mm. (13.0 mm – 9.0 mm = 4.0 mm)
Stabilizing selection – a process of natural selection in which intermediate phenotypes
are favored over phenotypes at the extremes.
o
For example, stabilizing selection is occurring if the finches with average-sized
beaks are surviving and reproducing at higher rates than finches with very large
or very small beaks.