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Types of Natural Selection Directional Selection • One extreme of a specific trait is more advantageous than both the other extreme and the average trait. • It pays to be different!! • Examples: – Peppered Moth – Bacteria that are genetically resistant to some antibiotics. Video http://www.pbs.o rg/wgbh/evolutio n/library/10/4/l_ 104_03.html Stabilizing Selection • Tends to eliminate individuals on both ends of the genetic spectrum. • It pays to be average!! • Occurs when the environment changes little and most species are well-adapted. • Often mistaken for no selection Example: Birth Weight Diversifying (Disruptive) Selection • Environmental conditions favor individuals at both extremes of the genetic spectrum and eliminate or sharply reduce individuals with intermediate genes. • It pays to be extreme!! • Examples: – Green vs. Brown Anole – Darwin’s Finches Darwin’s Finches Each finch species is specialized for a particular lifestyle (structure of their beaks) An adaptation to their specific diets seed eaters, cactus eaters, insect eaters, fruit eaters) and different from finches on the South American mainland. 14 species of Galapagos finches decended from a single ancestorone or a small population of finches that originally colonized the Galapagos. Types of Species Evolution Convergent Evolution • Two different species who live in the same type of habitat evolve to have similar traits. • Example: Sharks and dolphins – Dolphins are mammals, Sharks are fish. – So how did they convergently evolve? • They look the same and act in similar manners because they both live in the ocean, so they’ll need similar traits! CONVERGENT EVOLUTION Convergent Evolution Divergent Evolution • Two populations of the same species who live in different places evolve to become different… • Example: Birds – Now we have penguins & puffins!! – So how do they divergently evolve? • Penguins live where it’s cold and where there’s lots of water. There’s more food for them in the water, so they evolved to “fly” underwater. • Puffins live where it’s slightly warmer. There’s lots of food sources outside of the water, so they continued to fly normally. Again… Darwin and the birdies Adaptive Radiation process by which ancestral species evolve into a number of diff species Divergent Evolution Divergent Evolution Coevolution • Two species that interact closely may become adapted to one another He is fast! I have to run faster!! Yummy…. Rabbit for dinner! • Example: a wolf and a rabbit Why does he want to eat me? I am sooo cute! I will run faster then… – How are they related in an ecosystem? – So how do they co-evolve? • If the rabbit evolves to be faster, the wolf will have to keep up, so it must also evolve to be faster. Animal/Plant Coevolution The gracefully curved bill of the ‘I’iwi enables it to sip nectar from flowers of the lobelia. The ‘I’iwi bill fits perfectly into the long tubular lobelia flowers. Coevolution in Plants Acacia Tree & Ant * Tree has large hollow thorns that provide a protected nesting site for stinging ants. Ants attack any animal and clear away vegetation surrounding the tree which helps the tree get the sunlight it needs. Caterpillars & Plants •Plants may have poisonous chemicals that prevent insects from eating them. •Some caterpillars have the ability to resist these poisons. •They can feed on plants that other insects can’t •As the plant adapted by producing poisonous chemicals, the caterpillar adapted by resisting them. Coevolution