 Show Adaptation in Darwin's Finches In the Nutcracker Ground Finches of the Galapagos Islands, beak depth is correlated with body size and the mechanical force necessary to crack seeds. Beak depth varies according to drought conditions: plants in dry years produce fewer, harder seeds, and in wet years greater numbers of softer seeds. Only larger birds with deeper beak depths survive in drought years. The change is ±5% between extreme years. The graph shows a pattern of stabilizing natural selection, in which beak depth fluctuates around a mean of about 9.6mm. Consistent environmental differences in different habitats on different islands in the Galapagos, as well as the availability of different foods sources (seeds, cactus, insects, and fruit) promotes directional natural selection on resident finches for optimal beak morphology that maximizes survival under local conditions. This process has produced more than a dozen distinct species of finches, all unique to the archipelago. Name: ________________________________ Date: ___10/24/21____________ Student Exploration: Rainfall and Bird Beaks Vocabulary: adaptation, beak depth, directional selection, drought, evolution, natural selection, range, stabilizing selection Prior Knowledge Questions (Do these BEFORE using the Gizmo.) During the voyage of the HMS Beagle (1831–1836), the young Charles Darwin collected several species of finches from the Galápagos Islands. Two of Darwin’s finches are shown below. 1. Which species do you think is best adapted to a diet of small, delicate seeds? Explain why you think so. The Geospiza fortis because it has a smaller beak. 2. Which species do you think is best adapted to a diet of large, tough to-crack seeds? Explain. Geospiza magnirostris because it has a larger beak, making it easier to break the seeds open. Gizmo Warm-up Darwin’s finches are one of many types of animals on the Galápagos Islands that have unique adaptations, or traits that help an organism survive in its environment. The Rainfall and Bird Beaks Gizmo™ allows you to explore how rainfall influences the range of beak shapes found in a single finch species. 1. The beak depth of a finch is the distance from the top of the beak to the bottom, as shown. A. What is the current average beak depth in the Gizmo? 10.16 mm B. Select the HISTOGRAM tab. Do all the finches have the same beak depth? No 2. Click Play ( ) and let the simulation play for five years with average rainfall (10 inches/yr). Select the GRAPH tab and view the Finches vs time and Beak depth vs time graphs. A. How does the finch population change? It decreased B. Does the beak depth change significantly? Not by a lot, but it does go down. Activity A: Normal years Get the Gizmo ready: ∙ Click Reset ( ). Different finch species have beaks of different shapes and sizes. These different beak structures are evidence of ? different finch species adapting to different environments over many generations. different finch species with different beak structures coming to the Galapagos Islands from the mainland. different finch populations being evolutionarily unrelated. individual birds changing their beak characteristics so that they could feed efficiently. different finch species adapting to different environments over many generations. Which is the most likely explanation for the presence of 13 different finch species on the Galapagos Islands today? Many years ago a small population of a single bird species migrated to the islands and evolved into the 13 species that live on the islands today. Each of the 13 species has migrated to the islands at different times over the years. A single bird species migrated to one island at around the time of Charles Darwin's voyage to the Galapagos and then migrated to all 13 islands. Many years ago a small population of a single bird species migrated to the islands and evolved into the 13 species that live on the islands today Examine the phylogenetic tree of the 13 finch species below. Which of the following statements is a correct interpretation of the phylogenetic tree in the illustration? The sharp-beaked ground finch is more closely related to the small tree finch than either species is to the cactus finch. The warbler finch is the common ancestor to all the finch species that exist today in the Galapagos Islands. All the Galapagos finches are more closely related to one another than they are to the mainland finch species. The 13 finch species evolved in sequence; the warbler finch is the oldest species and the small ground finch is the most recent species to evolve. All the Galapagos finches are more closely related to one another than they are to the mainland finch species. The Grants witnessed strong selection during the droughts in 1977 and 1985. Compare the two droughts. Select all that are true. In both droughts, larger-beaked medium ground finches had the highest survival rates. Both droughts resulted in strong natural selection on medium ground finch populations Both droughts resulted in changes to available food, which favored the survival of some medium ground finches over others. Both droughts resulted in strong natural selection on medium ground finch populations Both droughts resulted in changes to available food, which favored the survival of some medium ground finches over others. In 1977, Daphne Major experienced a severe drought. The figure below shows the beak depths of the initial population of medium ground finches before the drought (gray bars), and of the drought survivors (black bars). What do the data show? Select all that apply. The most common beak depth of the initial population (gray bars) was 8.8mm. A very small proportion of individuals with this beak depth survived the drought. More than half of the initial finch population died during the drought. The most common beak depth of the surviving population (black bars) was 10.3mm. Finches with larger beaks had a survival advantage in the 1977 drought. The most common beak depth of the initial population (gray bars) was 8.8mm. A very small proportion of individuals with this beak depth survived the drought. More than half of the initial finch population died during the drought. The most common beak depth of the surviving population (black bars) was 10.3mm. Finches with larger beaks had a survival advantage in the 1977 drought. Which experimental data from the film provides the best evidence that the cactus finch and the medium ground finch on Daphne Major are distinct species? Many more medium ground finches than cactus finches died in response to the drought. Cactus finch and medium ground finch males attempted to breed only with females of their own species. The cactus finch and medium ground finch feed on different types of food. Medium ground finch and cactus finch females have different markings and feather color. Cactus finch and medium ground finch males attempted to breed only with females of their own species How did the Grants test their hypothesis that differences in birds' songs can keep different species of finches from breeding with each other? They watched which birds were mating with each other and listened for the songs the birds were singing. They recorded birds singing on the island of Daphne Major for an entire breeding season to see which type of song was used more often by each species. They played the songs of medium ground finches and cactus finches through a loudspeaker at different times, when individuals from both species were present, to see which species responded to each song. They placed stuffed females of different finch species on branches to see which males would respond. They played the songs of medium ground finches and cactus finches through a loudspeaker at different times, when individuals from both species were present, to see which species responded to each song. Which statement best explains the evidence presented in the film for your answer to the last question? Males only came to the loudspeaker when the song of their own species was being played. The type of song used more often during the breeding season was also the song sung by the most abundant species. During mating, the birds were singing the songs of their own species. Males only came to the loudspeaker when the song of their own species was being played. Which observation or observations provide evidence that two populations are likely experiencing reproductive isolation and that there is little if any genetic exchange between them? The two populations live on different islands. One population breeds in late spring and the other population breeds in late summer. One population eats mostly small, soft seeds and the other population eats mostly large, hard seeds. The males of one population have different mating calls than the males of the other population. The females of the two populations look the same. The two populations live on different islands. One population breeds in late spring and the other population breeds in late summer. The males of one population have different mating calls than the males of the other population. Which statement or statements describes geographically isolated populations? The two populations live on different islands. One population breeds in late spring and the other population breeds in late summer. One population eats mostly small, soft seeds and the other population eats mostly large, hard seeds. The males of one population have different mating calls than the males of the other population. The females of the two populations look the same. The two populations live on different islands. How does drought affect beak depth?Beak depth varies according to drought conditions: plants in dry years produce fewer, harder seeds, and in wet years greater numbers of softer seeds. Only larger birds with deeper beak depths survive in drought years. The change is ±5% between extreme years.
How did the finch beak change during after the drought?The Grants found that the offspring of the birds that survived the 1977 drought tended to be larger, with bigger beaks. So the adaptation to a changed environment led to a larger-beaked finch population in the following generation.
What impact did the drought have on the finches of Daphne Major island?Recently they reported a change in the beak size of the medium ground finch on Daphne Major. In 1977 a drought reduced the number of small seeds available for the birds, forcing them to rely on larger seeds requiring considerable force to open.
What happened to the average beak depth of finches on the Galapagos Islands after the drought of 1977?Figure 18.1C. 1: Finches of Daphne Major: A drought on the Galápagos island of Daphne Major in 1977 reduced the number of small seeds available to finches, causing many of the small-beaked finches to die. This caused an increase in the finches' average beak size between 1976 and 1978.
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Describe the effect that the drought had on the average beak depth of the finches
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