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Open-Ended Inquiry • Skills Lab
Additional Lab 8
Ecosystems and Speciation
Problem
How does a founding population adapt to new environmental conditions?
Introduction
When the hurricane’s winds died down, a small lizard crawled out of her hiding place
in the branches of a mangrove tree. Her home was now part of a tangled mat of
vegetation floating on the surface of the ocean. She shared the mat with insects and
slugs, as well as other lizards from her own species. After a week, ocean currents
pushed the mat onto the shore of a small, isolated island. The hungry lizards crept
ashore in search of food.
In this lab, your teacher will give you a description of the island on which the
lizards landed. You will be asked to suggest how the descendants of the founding
population may adapt over time to their new environment.
Skills Focus
Infer, Predict, Apply Concepts
Materials
• colored pencils
Pre-Lab Questions
1. Review What is an adaptation?
2. Infer What are the most likely sources of new genetic variation in the
descendants of the founding population of lizards?
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3. Compare and Contrast Explain the difference between genetic drift and
natural selection.
Procedure
1. Examine the drawing of a lizard from the founding population. This small
lizard feeds on insects. In the founding population, skin color varies from
yellow to green to brown. Some lizards have longer bodies than others, and
some have limbs that are slightly longer in proportion to their bodies. All
the lizards have the same size feet, but some individuals have larger toe
pads. The toe pads help the lizard stick to narrow and vertical surfaces. The
flap of skin on the lizard’s throat (a dewlap) is extended during social
interactions with other members of the species.
2. Read the description of the island assigned to your group. Based on the
characteristics of the island, identify existing phenotypes in the founding
population that may be adaptive. These traits will tend to increase the
fitness of the lizards who have them.
Adaptive phenotypes:
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3. Make a drawing of a descendant lizard. Your drawing should reflect how your
lizard population has changed over time in response to its new environment.
Label specific traits on the drawing and note how they have changed.
Drawing of Descendant Lizard
4. Describe a new trait, introduced through mutation, which might be adaptive for
your population of lizards.
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Analyze and Conclude
1. Relate Cause and Effect How were the traits you described for your
descendant lizard related to the conditions on your assigned island?
2. Apply Concepts Use what you know about natural selection to explain
how the relocation of the lizards to a new ecosystem could affect the
frequency of phenotypes in the population.
3. Design an Experiment How might you test whether the lizards on your
island have evolved into a new species distinct from the mainland species
that first colonized the island?
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4. Predict Suppose 10 percent of the mainland population of lizards are yellow.
The other 90 percent are green or brown. Of 10 lizards that colonize an island, 6
of them are yellow. Will the frequency of yellow skin among the descendants of
these lizards be the same as the frequency in the mainland population? Explain
your answer.
5. Predict Suppose that lizard-eating birds live on the island colonized by the
lizards described in Question 4. Because the island is covered with trees and
bushes, yellow lizards are easier to spot than green or brown lizards. What will
happen to the frequency of yellow skin in this population of lizards, and why?
6. Form a Hypothesis Lizards from the family Iguanidae are found only in North
and South America, except for two species that live on the Polynesian islands of
Fiji and Tonga. The Polynesian species are not found anywhere else in the world.
How might their ancestors have migrated across the Pacific Ocean?
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Extend Your Inquiry
The most famous example of rapid speciation following colonization of a new
environment is the finches on the Galápagos Islands. Research another example
of rapid speciation following colonization of a new environment. Possible
examples include tortoises on the Galápagos, fruit flies and honeycreepers on
Hawaii, or anolis lizards in the Lesser Antilles chain of the Caribbean. As part
of your response, include an explanation for why rapid speciation often occurs
on volcanic islands.
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