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This educational unit explores the concept of natural selection and its effect on the survival of species in changing environments. Students will learn about genetic variation, adaptation, and the four phases of natural selection through interactive activities and case studies.
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Learning Intention: 8.LS4.4 Develop a scientific explanation about how natural selection effects the survival of a species in changing environments. Science Standard 12 8th Grade Terms to Investigate natural selection, species, and environment Cross Cutting Concepts CCC 02: Cause and Effect, CCC 06: Structure and Function CCC 07: Stability and Change Success Criteria/I Can Statement By the end of this unit I will be able to say... ...I can explain the connection between natural selection and species survival.
Phenotype Variation in Populations • Variation refers to a variety or diversity of traits • (different kinds) within any given population. Two causes of variation 1) Diversity of genetic traits from sexual reproduction. 2) Diversity of genetic traits that result from mutations. Adapt or Die • Environments always change, sooner or later. • Organisms must adapt to these changes or die. • If too many individuals die, then the species goes extinct. • Those that survive pass on their DNA to their offspring. When an environmental change occurs, a variety of traits within a population provides the species a chance that at least some individuals will survive the changed conditions.
Four Phases of Natural Selection Bunny Rabbits Overproduction Too many offspring are born. Phase 1 Genetic Variation in a Population Offspring are born with a variety of traits. Some offspring are better suited to survive than others. Genetic Variation in a Population Offspring are born with a variety of traits. Some offspring are better suited to survive than others. Phase 2 Struggle to Survive Offspring compete for limited resources. Many die or are eaten. Phase 3 Successful Reproduction The well-adapted offspring survive to breed with each other. Phase 4
Genotype Variation in Populations • The Galapagos Islands are located in the Pacific Ocean about 600 miles west of Ecuador (see picture below). • Each island has a slightly different ecosystem, and these finches adapted accordingly. This lead to significant variation in the shapes and sizes of their beaks. • At some point in the past, a small population of Finches (birds) were blown from South American to these islands. Galapagos Islands Consists of 18 larger islands and 3 smaller islands. South American Finch South American Finch
Over time the finches developed different beak shapes and sizes in order to eat the local food (structural adaptations). Food Source Only Seeds Food Source Seeds & Bugs Food Source Only Bugs Moderately wide beak for cracking seeds and sharp point for insects Very wide beak for only eating seeds narrow-pointed beak for insects Natural Selection: On each island, Finches with the most effective beaks dominated while those with less effective beaks died out.
Activity Let’s see how beak variations in a population of birds enables some to adapt to a specific environment. A bird species is brought to an island with just 2 food sources. We will simulate their two food sources Worms Seeds Popcorn Kernels Pieces of Yarn
Activity For this activity we will simulate the beaks with these 4 items Large/wide Beak Medium Beak Plastic Spoons Plastic Forks Small Beak Large/thin beak Popsicle Sticks Plastic Knives
Activity You will be given simulated bird beaks and bird food. You will have only a brief amount of time to eat your food. You will record your data using info from these 2 tables.
Activity Instructions Each group of four students will have the following items: 1) A plate with food: yarn(worms) & popcorn kernels (seeds) 2) Pair of plastic spoons: (Large/wide beak) 3) Pair of plastic forks: (Medium beak) 4) Pair of plastic knives: (Small beak) 5) Pair of popsicle sticks: (Large/thin beak) 6) Four bowls (one for each student) Step 1: Select a bird beak type. Step 2: When signaled by the teacher, use your beak to “eat” for 45 seconds. Place your “eaten” food in your bowl. Step 3: Determine the number of calories that you “ate.” Step 4: Determine if your bird survived and/or reproduced. NOTE: Record details in your science journal.
Activity Results Medium Beak Large/wide Beak Small Beak Small Beak Was your bird’s phenotype well suited for survival in this ecosystem? (Explain why or why not)
8.LS4.3 Analyze...anatomical evidence that demonstrates that specific phenotypes in a population can increase survival rates. (1) What anatomical (phenotype) differences did these finches have? (2) Which phenotype was best suited for this island environment? (3) Which phenotype was the least suited for this environment? (4) How did phenotype variations enable this species to survive? 8.LS4.4 Develop an explanation about how natural selection effects the survival of species in changing environments. (5) Describe how the Finches went through the four phases of natural selection. Phase 1-Overproduction: Phase 2-Offspring Variation: Phase 3-Struggle to Survive: Phase 4-Reproduction:
