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How Changes in Population Lead to the Formation of

Natural selection worksheet illustrating directional, disruptive, and stabilizing selection through body‐size vs. population graphs. Includes questions on comparing variables and identifying selection types from the models.

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    Selection and Speciation How can changes in a population result in the formation of a new species? Why? J Have vou ever wondered how the great diversity of life on Earth has come about or how a single new species forms? Environmental pressures may cause populations to change overtime or evolve. This is because an organism's abilitv to live to adulthood in its current environment will determine its reproductive success and abilitv to pass on its genes. But changes withm a population can occur without creating a new species. At what point do scientists start thinking of a new name for a species? Model 1 - Three Types of Selection DirccuMid Sdcuion Diirupuvt SefcciMMi S a i i h E i r iri I faiL-* l i l u d * i M i - hi i,.’ 1 - 5 ■ - - ; ■ i : <, n | r » & M W 1. What variables do die graphs in Model 1 com] Bodr sise and number of people. 2. What are die three types of selection illustrated in the graphs in Model 1? Directional., disruptive. and intermediate. Selection and Speciation How can changes in a population result in the formation of a new species? Why? J Have vou ever wondered how the great diversity of life on Earth has come about or how a single new species forms? Environmental pressures may cause populations to change overtime or evolve. This is because an organism's abilitv to live to adulthood in its current environment will determine its reproductive success and abilitv to pass on its genes. But changes withm a population can occur without creating a new species. At what point do scientists start thinking of a new name for a species? Model 1 - Three Types of Selection DirccuMid Sdcuion Diirupuvt SefcciMMi S a i i h E i r iri I faiL-* l i l u d * i M i - hi i,.’ 1 - 5 ■ - - ; ■ i : <, n | r » & M W 1. What variables do die graphs in Model 1 com] Bodr sise and number of people. 2. What are die three types of selection illustrated in the graphs in Model 1? Directional., disruptive. and intermediate.

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    3. According to the graphs in Model 1, there is variation in the bodv mass in the original i. describe how this variation is possible. vour Different alleles can occur within a population because of mutations. 4. Refer to graph A of Model 1. j. H o w is the population that has experienced selection different from the original population? The individuals in the new population have a larger bodv size then the individuals in the original population. A Fitness is defined as the relative ability of anindividual for population} to survive, reproduce, and pass on genes. Which individuals in the original population appear to display better fitness? Those with a larger bodv mass because the species has evolved to favor it. t. As a group, propose some characteristics of theenvironment that could lead to the population changes illustrated in graph A. The climate could become colder so those with more bodv mass could keep warmer. 5. Refer to graph E of Model la. H o w is the population that has experienced selection different from tite original population? i Which individuals in the original population appear to displav better fitness? Thev are different because the individuals of the new p opulation are either larger or smaller than the individuals o f the old population because o f disruptive selection. t. As a group, propose some characteristics of theenvironment that could lead to the population changes illustrated in graph B. The environment could select against people with the middle bodv size since thev probablv are not useful to the environment. 6. Refer to graph C of Model 1. j. H o w is the ion that has ex- selection different from the origi Those with the middle bodv mass are more ideal. h. Which individuals in the original population appear to displav better fitness? The middle bodv mass. f og: 3. According to the graphs in Model 1, there is variation in the bodv mass in the original i. describe how this variation is possible. vour Different alleles can occur within a population because of mutations. 4. Refer to graph A of Model 1. j. H o w is the population that has experienced selection different from the original population? The individuals in the new population have a larger bodv size then the individuals in the original population. A Fitness is defined as the relative ability of anindividual for population} to survive, reproduce, and pass on genes. Which individuals in the original population appear to display better fitness? Those with a larger bodv mass because the species has evolved to favor it. t. As a group, propose some characteristics of theenvironment that could lead to the population changes illustrated in graph A. The climate could become colder so those with more bodv mass could keep warmer. 5. Refer to graph E of Model la. H o w is the population that has experienced selection different from tite original population? i Which individuals in the original population appear to displav better fitness? Thev are different because the individuals of the new p opulation are either larger or smaller than the individuals o f the old population because o f disruptive selection. t. As a group, propose some characteristics of theenvironment that could lead to the population changes illustrated in graph B. The environment could select against people with the middle bodv size since thev probablv are not useful to the environment. 6. Refer to graph C of Model 1. j. H o w is the ion that has ex- selection different from the origi Those with the middle bodv mass are more ideal. h. Which individuals in the original population appear to displav better fitness? The middle bodv mass. f og:

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    b. Human babies with very high or very low birth weights have a higher mortality rate. Babies with an intermediate weight will be selected for (stabilizing;. c A population of seed-cracker finches feeds on seedsavailable in two sizes, small or large. Finches with either large or small beaks will be selected for. Disruptive; d. Overfishing occurs in two rivers in British Columbia, Canada, where larger salmon ate preferentially caught Smaller fish will be selected for since the bigger fish are caught and killed. Directional; c. As a group, propose some characteristics o f theenvironment that could lead to the population changes illustrated m graph C. Small amounts of food could be available and the environment could be changing. As a group, define the following terms in grammatically correct sentences. Each definition should contain the following words: population, selection, fitness, and environment. j. Directional selection One extreme of a phenotype is selected for compared to the middle and other extreme because of the environmental conditions. This means that the population is most likely going to mainly consist of the extreme because it has more fitness. & Disruptive selection Both extremes of a phenotype are selected for compared to the middle because of the environmental conditions. This means that the population is most likely going to mainly consist of the extremes because they have more fitness. f. Stabilizing selection The intermediate of a phenotype is selected for compared to the extremes because of the environmental conditions. This means that the population is most likely going to mainly consist of the intermediate type because it has more fitness. 8. In each of the following examples, describe the likely outcome due to the environmental pressure and state the type of selection. Justify your choice. j. Finches with a small beak cannot crack open seeds. A population with a larger beak will be selected for because die smaller beak cannot get food.(Directional', A Human babies with yen' high or very low birth weights have a higher mortality rate. Babies with an intermediate weight will be selected for (stabilizing). y. A population of seed-cracker finches feeds o n seedsavailable in two sizes, small or large. Finches with either large or small beaks will b e selected for. Disruptive j d. Overfishing occurs in two nvers in British Columbia, Canada, where larger salmon are preferentially caught Smaller fish will be selected for since the bigger fish are caught and killed. (Directional)

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