Natural Selection and Populations
Natural Selection
Daphne Island
Scientific Investigation
As a scientist, you are assigned to complete a 10-year study to
record annual rainfall conditions, observe annual seed yield, and
estimate bird population numbers. Record and analyze your data
comparing how annual precipitation affects the two bird
populations, which have adapted differently to the available food
resources.
For the last 20 years, scientists have been researching a 100-acre
island called Daphne. These studies noted that the local plants yield two major types of seeds.
One type of seed is small and soft, while the other is large and hard. About 10 years ago, scientists
observed a bird species adaptable to eating the small seed types, but were unable to crack open
the larger seed types with their beaks. More recently, scientists watched individuals from a larger
beak species group eating the large seed types. Scientists concluded natural selection had
occurred when a genetic mutation of the small seed eating species resulted in producing the
variation of the larger-sized beaks in an individual bird, which then bred successfully with others.
This led to the spread of this adaptive trait, creating a subpopulation able to take advantage of the
larger sized seed resource.
What You Know:
• Bird Population A has small beaks and only eats the small seed type.
• Bird Population B has large beaks and only eats the large seed type.
• Annual precipitation varies.
• The annual yield of both seed types is directly dependent on annual precipitation.
• Dry conditions reduce the small seed yield, while wet conditions reduce the large seed yield.
• Other environmental factors limit the number of individuals to 300 for each subpopulation.
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Natural Selection
Daphne Island
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Procedure:
Step 1: Question.
Step 2: Relevance.
Step 3: Variables, if applicable.
Independent variable (also known as the manipulated variable)
Dependent variable (also known as the responding variable)
Control variable(s) or group, also known as constants.
Step 4: Hypothesis.
Is a hypothesis needed? If so, what is it?
How will the responding variable change when the manipulated variable changes?
Step 5: Materials.
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Step 6: Safety considerations.
Step 7: Procedure.
1.  Get the brown paper bag with the observation cards from your teacher.
2.  Randomly pull out one card for your first “Study Year.” Record the information from the
“Study Year” for Year 1 in your data table.
3.  Return the Observation Card to the bag, mix up the card set, and then pull out a card for the
next “Study Year.”
4.  Repeat the observation procedure for a total of 10 times to complete a 10-year study.
Step 8: Data Collection.
Use the table to record your data.
Year
Population A
(# of Birds)
Population B
(# of birds)
Small Seed
Yield
Large Seed Yield
Weather
1
2
3
4
5
6
7
8
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Natural Selection and Populations
Natural Selection
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Step 9: Data Analysis.
Create a graph based upon the data. Make a general statement about the results shown in graph.
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Natural Selection and Populations
Natural Selection
Daphne Island
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Step 10: Conclusion and scientific explanation.
Write a scientific explanation on what factors affected the survival of a population?
Claim:
Evidence:
Reasoning:
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