IALS Evolution: Activity 96 “Battling Beaks”

Absent Work

Key Words: Mutation, Speciation

Getting Started:

1. What kinds of evidence do scientists have for natural selection?

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2. Your classmates conducted a simulation of their own, using forks and cereal to represent a population of wild birds (fork birds) feeding. The fork bird population consists of birds with either 1-tined, 2-tined, or 4-tined beaks, who are all part of the same species. Considering that these fork birds feed on cereal, do you think that all three fork bird types will be equally successful at gathering food? Why or why not?

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3. Read the Introduction and Challenge for Activity 96, “Battling Beaks” on page F-33 of your Student Book.

Procedure:

1. Read “The Fork bird Model” and Procedure Steps 1-7 on pages F-34 through F-35 of your Student Book. Your classmates performed this experiment. Watch the video link below to see part of the experiment being performed.

http://www.youtube.com/watch?v=-lKDoTq2DWs

2. Notice that the two fork birds that “survive,” by eating the most cereal, each determine the type of beak that their offspring will have by tossing a number cube. Since tossing a 3, 5, or 6 makes the offspring have the same beak as the parent, it is most likely that the surviving fork bird will reproduce a new fork bird just like itself. Therefore, the type of beak (1-tines, 2-tined, or 4-tined) that thrives in the population will be the one with the most success at gathering food.

3. Look at the sample group and class data below.

Table 1: Sample Group Forkbird Population Data
Generation / 1-Tined Forkbirds / 2-Tined Forkbirds / 4-Tined Forkbirds
Initial / 0 / 4 / 0
1 / 0 / 4 / 0
2 / 1 / 2 / 1
3 / 1 / 1 / 2
4 / 0 / 1 / 3
5 / 0 / 0 / 4
6 / 0 / 0 / 4
7 / 0 / 0 / 4
8 / 1 / 1 / 2
9 / 0 / 1 / 3
10 / 0 / 0 / 4
Table 2: Sample Class Forkbird Population Data
Generation / 1-Tined Forkbirds / 2-Tined Forkbirds / 4-Tined Forkbirds
Initial / 0 / 32 / 0
1 / 3 / 22 / 7
2 / 5 / 14 / 13
3 / 4 / 6 / 22
4 / 3 / 7 / 22
5 / 3 / 5 / 24
6 / 2 / 3 / 27
7 / 1 / 2 / 29
8 / 2 / 4 / 26
9 / 0 / 3 / 29
10 / 1 / 2 / 29

4. Create a graph of the class totals of each type of fork bird over many generations. You can plot the data for all three types of fork birds on a single graph. Be sure to title your graph, label your axes, and provide a key.

Graph:

Follow-Up:

1. What is the source of the physical variation in the fork bird population?

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2. How does (inheritable) variation arise in any population?

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3. Why must variation be present in the population in order to simulate natural selection?

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4. If a fork bird broke one of its tines (or if a real bird chipped its beak), and then reproduced, what would its offspring look like?

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Analysis Questions:

1. Which type of fork bird was the most successful? Explain how the class data support this conclusion.

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2. a. Look at your graph of the class results. Describe what happened to the number of each type of fork bird over many generations.

b. In the fork bird model, mutations at reproduction were much more common than they are in real life. Imagine that the number of mutations was lowered, so that the vast majority of offspring had beaks similar to those of their parents. Predict what you think would have happened to the numbers of each type of fork bird in future generations.

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3. How did the fork bird activity simulate the process of natural selection?

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4. The fork birds that you studied are a single species. Although they look slightly different, they are part of a single, interbreeding population. Imagine that a change in the food supply occurred.

a. As a result of heavy rains, the major source of fork bird food is now soft berries, like blueberries. After many, many generations, how many types of fork birds do you think will be in the population? Explain your reasoning.

b. As a result of a drought, the major source of fork bird food is now sunflower seeds. After many, many generations, how many types of fork birds do you think will be in the population? Explain your reasoning.

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5. Did this activity model Darwin’s or Lamark’s Theory of Evolution?

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6. What are the strengths and weaknesses of this activity as a model for evolution?

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7. Reflection: The cheetah, an extremely fast and efficient hunter, is an endangered species. The few cheetahs alive today show very little variation. How does this help to explain why cheetahs are on the verge of becoming extinct?

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