Clipbirds: Natural Selection of Acquired Traits and Allopatric Speciation
Benjamin Nims
Maplewood Richmond Heights High School
I. MECHANICS
A. Title: An extended activity adapted from “Clipbirds,” developed by University of California, Berkeley
B. Time: 60 minutes (Activity may be completed in one class period. A discussion of the results may begin the next class period.)
C. Target Audience: General level Biology class, Sophomore/Junior standing
D. Resources: Students will need a journal or blank sheet of paper for an introductory activity. A computer and projector are required for the video clip, and brief PowerPoint presentation. Each student will need a copy of the Clipbird student worksheets. Each group of six students will need two large, two medium, two small binder clips, and one plastic cup per student. There should be an even number of groups, so plan accordingly for your class size. Each group will also need differing quantities of marbles, large beans (lima beans work well), and popcorn seeds. Each group will also need a medium sized box, large enough that all six people can fit around it.
E. Safety Concerns: Students will be working close together, competing for “food” with binder clips. There are no other safety issues.
II. ANTICIPATORY SET
A. Motivational Device to be Used
In order to get students thinking about the large diversity of life, begin with a brainstorming session. List on the chalkboard how many different “species” they can come up with. Examine the definition more closely by separating not only obvious differences (cat vs. dog), but more subtle ones as well (e.g. different types of finches).
The idea is not to focus too heavily on what is a species. Rather, how do new species arise?
B. Introduction to topic
The students will be given the journal question: “What are the four processes of natural selection?” They will then be shown a short, 6-minute video clip discussing natural selection. Students will know to look for four main points, and should be able to explain what each means after the video. A follow-up discussion will reinforce these concepts and ensure student understanding.
III OBJECTIVES AND PURPOSE
A. Concept: Natural selection consists of four processes
- Genetic variation
- Overproduction of offspring
- Struggle for existence
- Differential survival and reproduction
Natural selection is an important process in evolution, which explains how new species may arise. Geographical isolation can strengthen the role these processes play by changing environmental pressures both spatially and temporally.
B. Objectives
The student will be able to:
1. understand the process of natural selection and how it can occur in the natural world;
- identify that two key factors for evolutionary success are to survive and reproduce;
- analyze data over time and determine changes that occur, using inference to explain those changes;
4. model and explain how speciation can occur.
C. Purpose
The purpose of the Learning Cycle is to teach evolution and the process of natural selection. Evolution is at the core of biology and is a unifying concept in science. It holds great explanatory power for the diversity of life both past and present. Further, the role that natural selection plays in evolution is equally important. Natural selection is the process by which new species arise. This process requires understanding of ecology, animal behavior, population biology, and genetics. By closely analyzing the processes upon which natural selection acts, one can get a greater understanding of evolutionary theory.
IV. INSTRUCTIONAL INPUT
- Prior Knowledge
It is assumed that students have covered the concepts of basic ecology and genetics in previous units. The teacher may have to review the four processes of natural selection as are outlined in the video. This may be related to what students already know about evolution (e.g. “survival of the fittest”).
B. Problem Areas
This activity requires students to gather food with their “beaks.” As seasons pass and the quantity of food changes, certain beak sizes will be selected against. A degree of competitiveness amongst students may lead to cheating, which will reduce the success of the lesson. Students should be honest when carrying out the activity.
Certain details of the activity may need adjustment. These include the amount of time for each “feeding frenzy,” the caloric value of the different food available, and the amount of calories needed to survive and reproduce. Ideally, as environments change within the groups one should see a preference for a specific bill-size. The binder clips and the food used are crucial for this activity to work. Small binder clips should only be able to eat small food, medium clips should only be able to eat small and medium food, and large clips should be able to eat all food. Groups should not become too populated nor should they go extinct because no one could reproduce. Migrants to an extinct population may solve these problems.
C. Strategy
Overview
The purpose of this activity is to demonstrate how populations respond to different environmental pressures. Two populations, divided by a “geographical” barrier, similarly have to hunt for food in order to both survive and reproduce. There is variation in the type of food available, and over time food availability will change. This will lead to changes between subpopulations, imitating speciation.
Procedure
Begin with a brief discussion about the diversity of life. Get students to begin thinking about different species and what makes them different. These should include obvious and subtle differences. Then begin the journal activity. Have students watch the 6-minute PBS video clip (http://www.pbs.org/wgbh/evolution/library/11/2/quicktime/e_s_4.html) about the four processes of natural selection. They should write down each process and provide a brief explanation. After the video discuss with the students each process and help reinforce what each means.
The second part introduces the concept of speciation in the Galapagos, as evidenced by Darwin’s finches. Use the short PowerPoint to illustrate this example. Explain that the Galapagos archipelago is a series of islands along the equator, 1,000 km off the coast of Ecuador. They are volcanic in origin, and have never been connected to the mainland. Reference may also be made to Darwin and his famous voyage to the islands. Next present the phylogeny of the Galapagos finches. Explain how these 14 different species are all related and have evolved from one common ancestor that arrived from Ecuador. Ask the students what makes each finch different. Students should return the obvious response of beak-size. Pose the open-ended question of how might these different species have arisen, and if it might relate to natural selection.
Distribute the Clipbird handout to each student. Have them read the first two pages and answer basic questions regarding food and reproduction. You may show the class the different kinds of “tootfruit:” marblefruit (marbles), big tootfruit (lima beans), and little tootfruit (popcorn seeds). Review students’ answers to the questions in the worksheet. Divide the students into an even number of groups. Group-size should be around 6 individuals. Groups on one half of the room should be “East Clipland,” and the other half will be called “West Clipland.” Some students may sit out the first season and can join when others “reproduce.” Distribute a “beak,” or binder clip, and a plastic cup to each individual. Each group should begin with two large beaks, two medium beaks, and two small beaks. Tell a marvelous story of the Clipbird, what it looks like, and how several populations have become isolated from one another.
Each season will consist of a different variety of food. Each group, depending on which side they are on, should get a box with the following food:
Season 1 |
Season 2 |
Season 3 |
|
East Clipland |
4 handfuls of popcorn |
1 handful of popcorn |
100 marbles |
West Clipland |
4 handfuls of popcorn |
6 handfuls of popcorn |
8 handfuls of popcorn |
A fourth season may be added to “strengthen” the results of selection. As is apparent by the food makeup on each side of Clipland, the populations should differ from both each other and from the starting point. Each season contains a “feeding frenzy.” Students will get 20-30 seconds to use their beaks to collect food and place it in their cup. Once time is up they will then record the type and amount of food they collected, calculate the calories obtained, and either die, live until the next season, or live and reproduce. If a student has enough calories to reproduce, their offspring should have the same-sized beak. Students should answer the questions on their handout after each season.
Record the size of each population after each season on the board. This will be a class data set of the populations over time. At the end of the activity, use the Excel file provided to demonstrate how the populations have changed over time. Your own class data may be substituted and the graph should change accordingly.
Finally, have the students complete the questions on their worksheet. Review their answers and connect it to the Galapagos finch example.
V. MODELING
VI. CHECKING FOR UNDERSTANDING
- Informal
Student lessons provide information blanks that allow the teacher to check the progress of students as they work. Class discussion should bring out the correct answers and allow students to demonstrate their level of understanding of natural selection and speciation.
- Formal
Student handouts will be graded based on their ability to follow directions, complete the worksheet, and answer the questions correctly based on class discussions.
VII. GUIDED PRACTICE
Throughout the activity the teacher should be guiding the class to the appropriate part, whether it is journal writing or carrying out a feeding frenzy. Students should be allowed to generate and share ideas, but kept on task. The teacher should relate the main points of natural selection back to the activity.
VIII. INDEPENDENT PRACTICE
Students will carry out the activity on their own. The instructor will act as a referee. Students should analyze their data and form conclusions based on the results of the activity.
IX. CLOSURE
To conclude, natural selection may lead to speciation given different environmental pressures and time. The activity will demonstrate this and the question about the Galapagos finch example may have a different answer now than when posed before the activity. Students should have an understanding of the four main points of natural selection and the importance of these pressures in the natural world.
X. REFERENCES
This activity was largely adapted from a lesson plan on the University of California – Berkeley website.
http://www.ucmp.berkeley.edu/education/lessons/clipbirds/
The movie link:
http://www.pbs.org/wgbh/evolution/library/11/2/quicktime/e_s_4.html
XI. NOTES
XII. APPENDED COMPONENTS