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Lec17_Darwin

Lec17_Darwin - • Typically 130mm of rain in 1977 only...

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Geospiza fortis Medium Ground Finch Peter and Rosemary Grant Researchers at Princeton, began studying the finches in the 70’s Evidence of Evolution Example of microevolution: change w/in a population over generations Evolution of beak depth by natural selection Darwin’s finches - medium ground finch
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Darwin’s finches Galapagos South America Darwin observed on Beagle 1831-1836 noticed: different bills and diets Grassquit colonized islands from SA 2.3 mya
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Darwin’s finches there is variation in types of seeds eaten by different species
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Researchers captured, measured, weighed, and banded individuals Variation in beak depth Variation in beak depth is heritable: midparent: average beak depth of mother and father Medium Ground Finch
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Over 20 months 84% disappeared before breeding variation in who survives to reproduce population of Medium Ground Finch crashes
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Unformatted text preview: • Typically 130mm of rain, in 1977 only 24mm • Number and type of seeds decreased • remaining seeds were larger and harder Selective pressure: drought Tribulus seeds Result: evolution of greater beak depth • mean beak depth of finches hatched in 1976: 8.9 mm • mean beak depth of finches hatched in 1978: 9.7 mm • 8.9% increase in one generation! • fossils: usually 1% change in million yrs Evidence of Evolution fig 22.12 see fig. 2.11 Example of microevolution: change w/in a population over generations • variation in bill size in population • larger bill - can get tough seeds • smaller bill - small seeds • weather conditions affected what seeds were available • selective advantage for large bills in dry years (limited resources) • large-billed birds have more offspring in those years heritable character!...
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