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VOCABULARY Gene pool – all genes available in a population Allele frequency – how many times one allele is present compared to all the other alleles for the same gene Evolution – change in allelic frequency Genetic drift – loss of some alleles in a population Genetic equilibrium – allelic frequencies remain constant; no evolution Speciation – formation of a new species from an existing species HOW COULD IT HAPPEN? Lets use Darwin’s Finches as out Example Start with a group of finches in Ecuador. A small group makes its way to the Galapagos Islands, possibly blown in a storm or on a land raft. The finches can’t get back to the mainland – they don’t like open water. Darwin found 14 different species of finches, none identical to the ones on the mainland. Galapagos Of relatively recent volcanic origin most of animal species on the Galápagos live nowhere else in world, but they resemble species living on South American mainland. 500 miles west of mainland Darwin’s Finches Differences in beaks associated with eating different foods adaptations to foods available on islands Warbler finch Cactus finch Woodpecker finch Sharp-beaked finch Small insectivorous tree finch Large insectivorous tree finch Small ground finch Cactus eater Insect eaters Seed eaters Vegetarian tree finch Bud eater Medium ground finch Large ground finch 1. Founding Fathers and Mothers Only one type of finch on mainland Small group arrives in Galapagos on Island A Can’t return to mainland Doesn’t like open water Survive and reproduce 2. Separation of Populations Birds from Island A cross to Island B Two populations isolated from each other ecological isolation Don’t like to cross open behavioral isolation water Same species, but isolation means can’t blend gene pools Ecological Behavioral Geographic geographic isolation 3. Changes in the Gene Pool Island B has different vegetation (large, thickshelled seeds) than Island A (small, thinshelled seeds) Birds on Island B with larger, heavier beaks can open seeds better (natural variation, mutation) Birds with large beaks survive better; smaller beaks disappear 4. Reproductive Isolation A few birds from Island A go to Island B Birds like mates to have same size beaks No mating between two groups (reproductive isolation) No mixing of gene pools – two separate species 5. Sharing the Same Island Three possibilities: Coexist – different niches Extinction – of least-adapted species Further evolution of second group – if enough variation, could have beak change to fit new environment Correlation of species to food source Seed eaters Flower eaters Insect eaters Darwin’s finches Finches with beak differences that allowed them to… successfully compete successfully feed successfully reproduce ○ pass successful traits onto their offspring http://www.hhmi.org/biointeractive/originspecies-beak-finch