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biodiversity
- the distribution and abundance of life on earth, same thing as species diversity
- Ecologists look for patterns seeking to explain this
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3 kinds of Natural Selection
- directional
- stabilizing (normalizing)
- disruptive
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Directional Selection
- for one extreme and against other extreme
- results in change in mean (average) phenotype
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Stabilizing (normalizing) Selection
- favors the mean, against both extremes
- keeps population phenotype distribution where it is
- examples: many components of fitness; birth weights, egg #'s in bird nests
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David Lack and clutch size experiment in birds
- egg # and egg survival trade off because of food limitation (quantity vs quality)
- 1. average - medium egg #, pretty high survival, fledgling # high
- 2. above average - high egg #, low survival, fledgling # medium, (too low quantity)
- 3. below average - low egg #, high survival, fledgling # medium, (too low quality)
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Disruptive Selection
- against mean, for both extremes (opposite of stabilizing)
- end up with bimodal distribution, average may not change, but there will be two different bell shapes with different means
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Coho salmon
- females build nests, males fertilize eggs, first two to get there fertilize the most
- biggest male wards off other big males (hooknose) (largest mean)
- small males hide nearby ready to sneak in (jack) the smallest is usually quickest and can sneak into tight places
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