Science.7
Natural Selection:
Environmental Influence / Name ______
Date ______
Essential Questions
  1. How do variations enhance survival of organisms?
/ Vocabulary
structure, function, generation, survival, organism, population, species, adaptation, trait, characteristic, natural selection / Objectives
  1. Identify major structures in organisms.
  2. Differentiate between population, species and organism.
  3. Identify characteristics within species that have been caused by natural selection.

Problem: How does environmental influence affect adaptations and natural selection?

Introduction: A hurricane occurs on a small island. When the hurricane’s winds die down, a small lizard crawls out of her hiding place in the branches of a mangrove tree (pictured on the left). Her home is now part of a tangled mat of vegetation (plants) floating on the surface of the ocean. She shares the mat with insects and slugs, as well as other lizards from her own species. After a week, ocean currents push the mat onto the shore of a small island. The hungry lizards creep ashore in search of food.

In this activity, you will be given a description of the island on which the lizard landed. You will be asked to suggest how the founding population may adapt over time to their new environment and how this will affect future generations of offspring of the lizard species.

  1. What is an adaptation? ______
  2. What is natural selection? ______

Procedure:

  1. Examine the drawing of a lizard from the founding population to the right. 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.

  1. Read the description of the island assigned to your group. Based on the characteristics of the island, identify existing external features in the founding population that may be adaptive. These traits will tend to increase the survival rate of the lizards that have them.

List the external features that may be adaptive below:
______
______

  1. Make a drawing of an offspring in a future generation of this lizard species. 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 Offspring in Future Generations

Analyze and Conclude:

  1. Describe a new behavior or internal structure that might increase the chances of survival of the new population of lizards.

______
______

  1. Cause and Effect: How are the external structures you described for your future offspring related to the conditions on your assigned island?

______
______

  1. Predict: Suppose that lizard-eating birds live on the island. 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 the population of lizards and why?

______
______

Adapted from Ecosystems and Speciation by Pearson Education, Inc.