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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 and average phenotype
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Stabilizing (normalizing) Selection
- favors the mean, against both extremes (resists change)
- keeps population phenotype distribution where it is
- examples: many components of fitness; birth weights, egg #'s in birds 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 peaks
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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 the quickest and can sneak into tight places
- DISRUPTIVE SELECTION
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Ecology vs Evolution
- Ecology is the short-term, time frame of interactions between organisms and the environment
- Evolution is the long-term, resulting adaptations that occur over many generations
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gill rakers
- look like little teeth in a rake
- rakers filter food particles
- few rakers with space between them filter large particles
- many rakers cose together filter small particles
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pattern with food particle size and raker distance and number
- food particle size is negatively correlated with raker number (food size up, raker number down)
- food particle size is positively correlated with distance between rakers (food size up, distance between rakers up)
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structuralist vs functionalist approach
- functionalist - Does raker # evolve in response to diet or food availability?
- structuralist - Does animal move because of phenotype?
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JD McPhail's findings of correlation between lake area and # of rakers on 3 spine sticklebacks
- positive correlation - large lake, greater # of rakers
- small lake, fewer # of rakers
- Bimodal food distribution - larger food (benthos) live on bottom in shallow water, -smaller food (zooplankton) live in open water
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benthos
- larger food that lives on the bottom; insects, snails, isopod, amphipods
- small lakes have more of this
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zooplankton
- smaller food that lives in open water; copepods, cladocera, arthropods
- large lakes have more of this
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Darwin's theory of natural selection (short version)
- 1. Individuals within a population vary in phenotype (Vp > 0)
- 2. Some of this phenotypic variation is genetic, passed on from parent to offspring (h2)
- 3. Individuals produce more offspring than the environment can support thus there is a "struggle for existence" (the only exclusively Darwinian point)
- 4. Some individuals, due to phenotypes, survive/reproduce better than others (S)
- 5. Those favored phenotypes, if heritable (genetic) increase in frequency in the next generation (R)
- R = h2S
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microevolution
- change in the allele frequencies in a population over generations
- evolutionary change below the species level
- *short time scales over several generations
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quantitative trait
- a heritable feature that varies continuously over a range rather than in an either-or-fashon
- determined by many genes (polygenic) of small effect (like height in humans)
- will not follow patterns of Mendelian inheritance (monogenic traits)
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benthic fish
- eat benthos
- have few rakers with space between them
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limnetic fish
- eat zooplankton
- have many rakers close together
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How do we know raker number is a quantitative trait?
- cross a benthic with a limnetic --> get a hybrid intermediate
- cross hybrids and recover some of the parent phenotype that was lost in the hybrid generation
- *overall, hybrids do worse than either benthics or limnetics averaged over both environments
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