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Background Information: Darwin’s Finches When Charles Darwin stepped ashore on the Galapagos Islands in September 1835, it was the start of five weeks that would change the world of science, although he did not know it at the time. Among other finds, he observed and collected the variety of small birds that inhabited the islands, but he did not realize their significance, and failed to keep good records of his specimens and where they were collected. It was not until he was back in London, puzzling over the birds, that the realization that they were all different, but closely related, species of finch led him toward formulating the principle of natural selection. Vocabulary Specimen – an individual animal, plant, piece of a mineral, etc., used as an example of its species or type for scientific study or display. Paucity – the presence of something only in small quantities or amounts; scarcity. Archipelago – chain of islands Figure 1: Drawings of different heads and beaks of finches that Darwin found on the Galapagos Islands In his memoir, The Voyage of the Beagle, Darwin noted, almost as if in awe, "One might really fancy that, from an original paucity of birds in this archipelago, one species had been taken and modified for different ends." Indeed, the Galapagos have been called a living laboratory where speciation can be seen at work. A few million years ago, one species of finch migrated to the rocky Galapagos from the mainland of Central or South America. From this one migrant species would come many -- at least 13 species of finch evolving from the single ancestor. This process in which one species gives rise to multiple species that exploit different niches is called adaptive radiation. The ecological niches exert the selection pressures that push the populations in various directions. On various islands, finch species have become adapted for different diets: seeds, insects, flowers, the blood of seabirds, and leaves. The ancestral finch was a ground-dwelling, seed-eating finch. After the burst of speciation in the Galapagos, a total of 14 species would exist: three species of ground-dwelling seed-eaters; three others living on cactuses and eating seeds; one living in trees and eating seeds; and 7 species of treedwelling insect-eaters. Scientists long after Darwin spent years trying to understand the process that had created so many types of finches that differed mainly in the size and shape of their beaks. Text from http://www.pbs.org/wgbh/evolution/library/01/6/l_016_02.html Speciation – changes in related organisms to the point where they are different enough to be considered separate species. Niche – the specific resources a species consumes and the habitats it lives in. Selection pressures – environmental forces such as lack of food or extreme temperatures that result in the survival of only certain organisms with traits that let them survive. Background Information: Bird Beaks Did you ever wonder why there are so many types of bird beaks or bills? The most important function of a bird bill is feeding, and it is shaped according to what a bird eats. The bill is one of the characteristics used to identify birds. You can learn about bird behavior by looking at the bill and thinking about what it eats. Then you may think about where it lives, and so on. Below are some common bill shapes and a description of the food they are especially adapted to eat. A cone shaped bill is found in many birds such as finches and grosbeaks. It is a strong beak used for cracking seeds. Thin, slender, pointed beaks are found mainly in insect eaters. They are used to pick insects off leaves, twigs, and bark. This warbler is a good example. Woodpeckers have strong beaks which taper to the tip, forming a chisel for pecking holes in trees for food or nests. Most feed on insects which live under the bark. Hummingbirds have long, tubular bills that resemble straws, which they use to sip nectar from flowers. Mergansers, specialized for eating fish, have sharp tooth-like structures on the edge of the bill to hold fish tightly. Hawks, owls, and other birds of prey which catch and kill live prey have sharp, "hooked" beaks. These are used to bite the skull or neck and also to tear the body into pieces small enough to swallow. The edges of a Mallard's bill are fringed to strain plants, seeds, and small animals from mud and water. Beaks which are flat and wide at the base are found in birds which catch insects in flight, such as flycatchers. These birds also often have "whiskers," which are actually modified feathers, at the corners of the mouth, which effectively widens the mouth opening, allowing more effective capture of prey. From: http://fsc.fernbank.edu/Birding/bird_beaks.htm Name: __________________________________________________ Date: _________________ Period: _____ Clipbirds Lab: Background Information Questions 1. What did Darwin realize about the Galapagos Finches that led him to formulate the principle of Natural Selection? 2. What did Darwin say about the Finches in his memoir, The Voyage of the Beagle? After writing down the quote, put his statement in your own words. 3. What different diets are the Galapagos Finches adapted to eat? 4. Compare the beaks shown in Figure 1 of the article Background Information: Darwin’s Finches to the beaks shown in the article Background Information: Bird Beaks to identify what kinds of food you think that the four Finches shown the drawings of Darwin’s Finches eat: 5. What kind of variation do you think was in the original population of Finches that first migrated to the Galapagos Islands from mainland South America? What evidence makes you think this? 6. ON THE BACK: Choose one Finch from the four in the drawing of Darwin’s Finches. Based on your understanding of Natural Selection, draw a diagram and explain how that particular species of Finch might have evolved from the original population of Finches that first migrated to the Galapagos Islands from mainland South America: (HINT: If you’re stuck, use the same format as your Natural Selection Explanation Cartoon homework) Name: ___________________________________________ Date: ________________ Period: _____ Clipbirds Evolution is the result of natural selection acting upon variation within a population. Organisms with adaptive traits in an environment they are adapted to have an advantage over individuals with different traits. However, it is important to remember that adaptations are only advantageous within the environment they are adapted for, and may not help an organism survive in other environments. For example, a cat’s long tail may help with balance on a tree branch, but be a problem in a house with frequently closing doors. The same is true for specialized beaks on birds. The beak may be an adaptation in certain circumstances, but in others, it may not help the bird survive. Today, you will model a population of imaginary birds, Clipbirds, that lives happily in a faraway fictional place called Clipland. In this population of Clipbirds, there is variation in the beak sizes. There are Clipbirds with big, medium, and small beaks. One day, out of nowhere, tectonic forces pushed a new mountain range into existence. The population of Clipbirds became divided into two smaller populations, east and west. The birds of different beak sizes usually do just fine, but it takes more food energy to maintain the larger beak size than the smaller sizes. There are multiple types of food that Clipbirds eat, each having a different nutritional value. Megacalories Needed for Clipbirds Food Values in Megacalories Jewels 10 Lima Beans Popcorn To Survive To Reproduce Bigbeak 80 160 5 Mediumbeak 50 100 2 Smallbeak 25 50 You will model the Clipbirds over four seasons of changing environmental conditions. If you do not eat enough food to survive, you must turn in your beak and sit down. If you manage to eat enough to survive, you will continue on in the next season. If you manage to eat enough to survive and reproduce, you may choose someone who is sitting out to represent your offspring (with a matching beak). Over four seasons of changing environmental conditions, we will see if there is any natural selection happening in Clipland, and if there will be any evolution in the two separate Clipbird populations. HYPOTHESIS: Which birds do you think will be best adapted to the different food types? Why? __________________________________________________________________________________________ __________________________________________________________________________________________ __________________________________________________________________________________________ HYPOTHESIS: If the food that is available in West Clipland becomes different from the food available in East Clipland, do you think there will be any evolution in the two different Clipbird populations? __________________________________________________________________________________________ INDIVIDUAL RESULTS: Observations of Competition and Adaptations: Your Beak Type: ____________________ Megacalories Needed for Survival: ___________ Megacalories Needed for Reproduction: __________ 1st Season Food Eaten # Eaten 2nd Season Megacalories # Eaten 3rd Season Megacalories # Eaten 4th Season Megacalories # Eaten Megacalories Jewels X 10 = X 10 = X 10 = X 10 = Lima Beans X5= X5= X5= X5= Popcorn X2= X2= X2= X2= Total = Total = Total = Total = CLASS RESULTS: Clipbird Populations West Clipland 1st Season 2nd Season East Clipland 3rd Season 4th Season 1st Season Bigbeak Bigbeak Mediumbeak Mediumbeak Smallbeak Smallbeak 2nd Season 3rd Season 4th Season