CYCLE 6. What are the consequences over time of natural selection?

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1 CYCLE 6 What are the consequences over time of natural selection? 268

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3 CYCLE 6 What are the consequences over time of natural selection? OVERVIEW You have spent these five cycles determining what an ecosystem is, how plants and animals acquire and use energy, what happens to the energy and matter (carbon) in an ecosystem, and what happens to a community and a population over time. You have determined several facts: 1. An ecosystem consists of all the organisms living in a region as well as all the abiotic factors with which they interact. 2. Plants and animals use food for energy and for building blocks. 3. Energy enters Earth ecosystems from the Sun, flows through ecosystems, ending up as heat that is released to the environment. Matter continuously cycles within Earth ecosystems due to the action of producers, consumers, and decomposers. 4. The efficiency of transfer of matter and energy between organisms is low and in most ecosystems producers have the largest biomass and the top consumers have the smallest biomass. Now we are going to look at how the struggle to obtain food can affect organisms within a population. ACTIVITY 1 How does the flow of energy and matter influence organisms within a population? PURPOSE You have seen that photosynthesis, predation and decomposition are a process whereby organisms obtain energy and matter. This exercise will demonstrate how this transfer relates to the process of changes in populations over time. INITIAL IDEAS On your own: Attempt to answer the following questions: Why do we see so much diversity in individual members of animal and plant populations? Think for example about the different personalities of individual horses, smells of individual dogs, traits of individual humans or the sounds of individual birds. 270

4 CYCLE 6 ACTIVITY 1 What is natural selection? EXERCISE 1 Bird feeding exercise * YOU WILL NEED large area beans and rice (for food) one scale per team four large tubs with water (feeding area) one container to hold feeding mechanism per team one cup (offspring stomach) per student one feeding mechanism per student: - solid cooking spoon - medium-slot cooking spoon - large slot cooking spoon BACKGROUND Pretend that you are a member of a population of birds. The birds feed along the lakes of an island to which they arrived from the mainland. The ancestral population had bills in the shape of a spoon (like present-day spoon bills), though sexual recombination and mutation the population now has a great deal of genetic variation. We will focus on the individual variation seen in the beak of these birds. The birds feed by capturing prey from the water and carrying it in their beaks to feed their offspring (like seabirds do). Hence, they have to be able to capture and transport prey to their offspring. Offspring that are fed the most prey survive the best. All birds have a spoon-shaped bill, however there is difference in the presence and absence of grooves in the bill and in the number and size of the groove. Below is a partial list of foods that these birds normally eat: cereal (e.g. Cheerios) solid cat food marshmallows raisins dried beans * This exercise modified from Kathleen M. Fisher s at San Diego State University ( 271

5 CYCLE 6 ACTIVITY 1 Based on the list, hypothesize what kind of food would be best captured and transported according to the type of beak that the individual possesses. (Examine each type of beak to develop your hypotheses.) Explain your answer (you can add food items not listed on the previous list). 1. Spoon with grooves: 2. Spoon with numerous, medium-size grooves: 3. Spoon with few, large-sized grooves: Group Discussion With your group, discuss with your group members? How can genetics (heritable traits) explain the observable differences in the shapes of the bird beaks? Write down below and on the whiteboard the group s ideas regarding natural selection and a ranking performance of eating dried beans (from best to worst). Class Discussion Your instructor will now lead a short whole-class discussion about the ideas from each table. Be prepared to explain your table s ideas and to write down ideas comments from other tables that you find interesting or useful. 272

6 CYCLE 6 ACTIVITY 1 EXERCISE A Beans are the only prey available in the lake because they outcompeted all other prey species. If birds having a certain beak shape fail to consume beans and, therefore, die they won t be able to produce offspring. The genetic traits of the parent birds will not be passed on to the younger generations. Predict on your own: Which beak will offer the most success to the individuals who possess it? Which beak will offer the least success to the individuals who possess it? Explain your reasoning. STEP 1 Divide yourselves in 3 teams which all should have about the same number of students. STEP 2 Each group of students represents a group of individual birds having the same beak shape (feeding mechanism). Each member of the group should get one of the feeding mechanisms (beak), which has to be of the same type for the entire group, and a mouth (cup). STEP 3 You and your group will try to get food using your beak during 5 rounds of play. You will be competing with the other groups of birds to capture and transport beans to the offspring. The food is found in a tub filled with water (lake) at one end of the classroom while the offspring is found at another end, in a safe place away from predators. When the teacher gives the signal, you will try to capture and transport beans as fast as you can until STOP is called. You will hve about 1 minute to capture food during each round. Rules of the hunt: a. Food must be lifted with the feeding mechanism (beak) and placed into the offspring stomach (cup) in the opposite end of the classroom. b. You must drop the food into the offspring s stomach, which cannot be moved but should be held firmly in place with one hand. c.. You can steal food from another student if he/she is still trying to get into his/her mouth. Food being transported cannot be stolen. STEP 4 a. After the STOP signal is given: Discard all the water from the offspring s stomach and weigh the total amount of beans collected as a group and write it down on the board. (Weight of full cup wihout water minus weight of empty cup.) Write down the weight in grams. b. Return your food to the tub at the end of the classroom. c. Add up all the weights reported by each team to determine a class total. Divide the class total by the number of groups to determine the class average. d. The groups will be reconstructed based on how your group did compared to the average. If your group has more than the average you get another player. If your group has less than the average, you lose a player. Put your new number of players on the board in the column labeled survivors. 273 e. To begin the next round of play (the next generation), give the new members of your team feeding

7 CYCLE 6 ACTIVITY 1 mechanisms (beaks). This sympolizes the survival of babies having the same trait as their parents. STEP 5 You will follow this procedure until five generations (rounds of play) have passed. Note that the class total of beans found and number of groups may change each round. TABLE 6-1 SURVIVAL RATE OF GROUPS GEN. GENERATION GENERATION GENERATION GENERATION GENERATION NUMBER OF GROUP PLAYERS FOOD OFFSPRING FOOD OFFSPRING FOOD OFFSPRING FOOD OFFSPRING FOOD OFFSPRING (beak shape) WEIGHT SURVIVORS WEIGHT SURVIVORS WEIGHT SURVIVORS WEIGHT SURVISORS WEIGHT SURVIVORS solid spoon medium sized slots large sized slots TOTAL AVERAGE STEP 6 Fill in Table 6-3. First, copy the number of birds in each group from Table 6-2. Next, calculate the percentages of each beak shape in the total population over the five generations. To find the percent of the population having a particular beak shape for each generation, first: a. Add up the total number of players for each round. b. Divide by the total number of survivors from each group by the total number of people playing. TABLE 6-2 PERCENTAGE OF THE TOTAL POPULATION REPRESENTED BY GROUPS GEN 0 GENERATION 1 GENERATION 2 GENERATION 3 GENERATION 4 GENERATION 5 GROUP (beak shape) Offspring Surviving % Total Population Offspring Surviving % Total Population Offspring Surviving % Total Population Offspring Surviving % Total Population Offspring Surviving %Total Population Offspring Surviving % Total Population Solid spoon Medium sized slots Large sized slots TOTAL 274

8 CYCLE 6 ACTIVITY 1 STEP 7 Graph the results, showing how the percentages of beak shapes in the total population changed over time. Data for each group will be represented by a line. All beak shapes will be shown on the same graph. Be sure to label both the x and the y-axis. Excersise B Disaster has struck this population of birds! Sudden changes in the climate have altered the environment so that the beans have been wiped out and another prey species, smaller and quicker to reproduce has taken over: rice. Now the entire population of birds must eat rice to survive. If birds having a certain beak fail to obtain food and therefore die, they won t be able to produce offspring. The genetic traits of the parent birds will not be passed on to the younger generations. Predict on your own: Which beak will offer the most success to the individuals who possess it? Which beak will offer the least success to the individuals who possess it? Explain your reasoning. 275

9 Follow the same rules of Exercise A Steps 1-5 You will follow the procedures of Exercise A until five generations (rounds of play) have passed. Note that the class total of rice fed to offspring and number of groups may change each round. TABLE 6-3 SURVIVAL RATE OF GROUPS GEN. GENERATION GENERATION GENERATION GENERATION GENERATION NUMBER OF GROUP PLAYERS FOOD OFFSPRING FOOD OFFSPRING FOOD OFFSPRING FOOD OFFSPRING FOOD OFFSPRING (beak shape) WEIGHT SURVIVORS WEIGHT SURVIVORS WEIGHT SURVIVORS WEIGHT SURVISORS WEIGHT SURVIVORS solid spoon medium sized slots large sized slots TOTAL AVERAGE STEP 6 Fill in Table 6-4. First, copy the number of birds in each group from Table 6-2. Next, calculate the percentages of each beak shape in the total population over the five generations. To find the percent of the population having a particular beak shape for each generation, first: a. Add up the total number of players for each round. b. Divide by the total number of survivors from each group by the total number of people playing. TABLE 6-4 PERCENTAGE OF THE TOTAL POPULATION REPRESENTED BY GROUPS GEN 0 GENERATION 1 GENERATION 2 GENERATION 3 GENERATION 4 GENERATION 5 GROUP (beak shape) Offspring Surviving % Total Population Offspring Surviving % Total Population Offspring Surviving % Total Population Offspring Surviving % Total Population Offspring Surviving %Total Population Offspring Surviving % Total Population Solid spoon Medium sized slots Large sized slots TOTAL 276

10 STEP 7 Graph the results, showing how the percentages of beak shapes in the total population changed over time. Data for each group will be represented by a line. All beak shapes will be shown on the same graph. Be sure to label both the x and the y-axis. 277

11 CYCLE 6 ACTIVITY 1 SUMMARIZING QUESTIONS On your own: How did your predictions compare to the results? Explain. What determined how many baby birds will be born having a certain beak shape? Now, think of a very large time scale (that is, think about long periods of time and in terms of transfer of energy and matter), what determines how many baby birds having a particular beak shape will survive? Imagine that changes in the environment had made it so that only milkshakes remained. Predict how this might change the percentages of bird beak shapes seen in the population after five generations. Would these results differ from the results we got in this demonstration? Why or why not? 278

12 CYCLE 6 ACTIVITY 1 Remember that each beak type represents a sub-set of the entire population of imaginary birds. These beak types represent individual variations in beak types in a single species. It is important to note that even if a beak type died out during the simulation the population as a whole survived by hunting beans. However, the overall genetic variation in the population was reduced. How does genetic diversity (having a lot of genetic variation) allow a species to better survive in a changing environment? Predict how the outcome of your bird experiment would have been different if the beak types were not inherited from one generation to the next. Group Discussion WIth your group, discuss with your group members: How can genetics (heritable traits) explain the observable differences in the shapes of the bird beaks? Write down on the white board the group s ideas regarding natural selection and a ranking performance of eathing dried beans (from best to worst. Class Discussion Your instructor will now lead a short whole-class discussion about the ideas from each table. Be prepared to explain your table s ideas and to write down ideas and comments from other tables that you find interesting or useful. 279

13 CYCLE 6 ACTIVITY 1 280

14 CYCLE 6 ACTIVITY 1 HOMEWORK ACTIVITY 1: HOMEWORK Name Date Natural Selection Natural selection is the differential success in the reproduction of different phenotypes which are the traits (physical, biochemical, behavioral, etc.) of an organism resulting from the interaction of organisms with their environment. For natural selection to occur, there has to be individual variability in a population and this variability has to be inherited (genetic variation). Individuals with a phenotype favorable for the conditions in which they live will leave more descendants than other individuals. Through time, the population will have a larger proportion of individuals with the genetic material and consequent phenotype most favorable for the local conditions. IDEA 1 Different variations of a trait may exist in a population. Evidence/examples: IDEA 2 Organisms can pass some traits to their offspring (some of the traits of an organism are heritable). Evidence/examples: IDEA 3 Organisms may make more offspring than the environment can support. Evidence/examples: 281

15 CYCLE 6 ACTIVITY 1 HOMEWORK IDEA 4 Individuals with traits that are best suited to particular environmental conditions (advantageous traits) are more likely to survive and leave offspring. Evidence/examples: IDEA 5 Over time, populations will develop a larger proportion of individuals with traits that are most advantageous for the particular living conditions. Evidence/examples: 282

16 CYCLE 6 ACTIVITY 2 ACTIVITY 2 How does natural selection affect populations over time? PURPOSE You have seen that natural selection is the process whereby the environment favors the survival and reproduction of individuals with heritable traits that are most favorable for the local conditions. This activity will demonstrate how individual variations in a species over time can lead to large morphological changes in their descendants. INITIAL IDEAS On your own: Think about the population of birds in the simulation performed in Cycle 6, Activity 1. If a person had observed the population before the game started (Time 1) and then come back many, many bird generations later (Time 2), what would that person notice about the bird population at time 2 relative to the bird population at time 1? What term would you employ to describe the process witnessed by that person? Why? Your instructor has placed on the screen a photograph of a modern whale. Read the following statements. Whales are fish. They swim and spend all their lives in the water, just like fish. No way. Whales are mammals. Just like cats and us, they breathe air and have a similar body structure. Actually, whales are fish, but as they evolved they have been able to breathe air. In addition, their body structure is actually more similar to fish than to mammals. Alejandro Rene John 283

17 CYCLE 6 ACTIVITY 2 With whom do you agree? Why? What evidence would convince you that whales are fish? What evidence would convince you that whales are mammals? Group Discussion Share your thoughts with your group members and together write down on the white board the group s ideas regarding what whales are and how they transitioned from their ancestor s form to their modern form. Class Discussion Your instructor will now lead a short whole-class discussion about the initial ideas from each table. Be prepared to explain your table s ideas and to write down ideas and comments from other tables that you find interesting or useful. 284

18 CYCLE 6 ACTIVITY 2 EXERCISE 1 EXERCISE 1 What evidence exists for evolution by means of natural selection? * YOU WILL NEED computer with access to the web STEP 1 On your own: Type the following URL that would take you to the Whale Kiosk: edu/~ensiweb/lessons/whalekiosk.html, which was developed by Lara Sox-Harris at San Jose State University. Click on Go to Whale Site. Click on Enter. Click on Click Screen (under Whale Evolution ANATOMY). Click on Start. Click on skip animation. Perform the following exercises on the website: a) be an anatomist b) explore the fossil record c) compare with the molecular evidence STEP 2 Answer the following questions, complete the diagrams and fill-in the charts. Anatomical Evidence Place an X under the organism whose structure is more similar to the one found in a whale. STRUCTURE FISH CAT EARS EYES LUNGS FORELIMBS JAWS MAMMARY GLANDS * From: ENSI (Evolution & the Nature of Science Institutes) < Permission to copy granted by ENSI. 285

19 CYCLE 6 ACTIVITY 2 EXERCISE 1 Indicate in the diagram who is more closely related and who is more distantly related to whales. WHALE Fossil Evidence Why do scientists consider that the closest relatives of whales are artiodactyls (even-toed ungulates) and not mesonychids? (If you are unsure about what the names mean, go back to section Explore the fossil record of the website.) Molecular Evidence Write down the number of differences in the nucleotide sequence between whales and the organism indicated in each column. SEQUENCE SEAL COW HORSE A B C D E F G H TOTAL # OF DIFFERENCES 286

20 CYCLE 6 ACTIVITY 2 EXERCISE 1 Indicate in the diagram who is more closely related and who is more distantly related to whales. WHALE Are whales fish or mammals? Why? Who are the closest living relatives of whales? Why? Group Discussion Share your thoughts with your group members and together write down on the white board the group s ideas. Class Discussion Your instructor will now lead a short whole-class discussion about the answers from each table. Be prepared to explain your table s ideas and to write down ideas and comments from other tables that you find interesting or useful. Now that you have figured out what whales are and who their closest relatives are, you will explore the changes that took place in the transition from a terrestrial to a fully-aquatic mammal. 287

21 CYCLE 6 ACTIVITY 2 EXERCISE 2 EXERCISE 2 How do individual variations over time lead to large morphological changes in descendants? YOU WILL NEED whale fossil strips (5) glue sticks images of ancient and modern whales on the screen. STEP 1 On your own: Look at the image of a whale ancestor and a modern whale on the screen. Briefly describe the morphological changes that took place in the evolution of whales from their ancestor to the modern species. STEP 2 Look at the image of several extinct whales on the screen. Arrange them in chronological order of appearance. Explain your reasoning using the concept of natural selection. Group Discussion Share your thoughts with your group members and together write down on the white board the group s ideas. STEP 3 The following chart represents the Cenozoic Era, each of the five dotted lines in the chart points to a period of time in which a particular fossil whale appeared. Your instructor has provided you with five different strips, each of which depicts the skeleton and illustration of a fossil whale. Please attach each fossil strip next to the line that you consider indicates the period of time in which it appeared. Discuss and answer the following questions with your group members. What changes did you notice in the transition from the terrestrial to the marine environment? (Ignore the teeth.) 288

22 CYCLE 6 ACTIVITY 2 EXERCISE 2 TIME EPOCH FOSSIL FOUND Now Pleistocene (0-2 mya) Pliocene (2-5 mya) 10 mya Miocene (5-24 mya) 20 mya 30 mya Oligocene (24-34 mya) 40 mya Eocene (34-55 mya) 50 mya 60 mya Paleocene (55-65 mya) 289

23 CYCLE 6 ACTIVITY 2 EXERCISE 2 Class Discussion Your instructor will now lead a short whole-class discussion about your presentation board and the ideas from each table. Be prepared to explain your table s ideas and to write down ideas and comments from other tables that you find interesting or useful. 290

24 CYCLE 6 ACTIVITY 2 HOMEWORK ACTIVITY 2: HOMEWORK Name Date Your Ideas about Evolution The process of evolution by means of natural selection raises much interest for reasons completely unrelated to science. When you are a school teacher you will have to address issues derived from the teaching of evolution. Was Darwin Wrong?, by David Quammen, is a critical and essential article that will help you now to understand the concept of evolution and later to address its teaching in the schools. It is well-written and accessible to a non-specialist audience. Please read it carefully and answer the questions that follow. You can access the article online at: QUESTIONS Using the concept of natural selection, briefly explain the transition over time from ancestral to modern whale. From the homework readings and from your work in Cycles 5 and 6, what were the two most compelling pieces of evidence about evolution by means of natural selection? Why? 291

25 CYCLE 6 ACTIVITY 2 HOMEWORK In your opinion, what would be the most compelling piece of evidence for evolution by means of natural selection? Why? With which of the following statements do you agree? Why? a. Natural selection and evolution are random, unpredictable events. b. Natural selection and evolution are not random events, but rather are cumulative processes that result in selective survival and reproduction. Many scientists think that science and religion are perfectible compatible, addressing different questions about the world. Do you agree with them? Why? 292

26 CYCLE 6 BIG IDEAS Cycle 6 Big Ideas Look through Cycle 6 and list the big ideas and the evidence/example(s) that support the big ideas. Be thorough and complete. The big ideas should be in the form of a statement and should explain an important concept learned from the cycle. Headings and subheadings from the cycle cannot be used as your big ideas. Evidence and examples should be taken from class activities and/or homework. Include a reference to the cycle activity or homework that supports the big idea. Evidence / examples should be explained in detail. See Cycle 1 Big Ideas for example. Use the format below. CONCEPT 1 Evidence/Examples: CONCEPT 2 Evidence/Examples: 293

27 CYCLE 6 BIG IDEAS 294

Selection 10: Theory of Natural Selection

Selection 10: Theory of Natural Selection Darwin began his voyage thinking that species could not change His experience during the five-year journey altered his thinking Variation of similar species among