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Frequency Dependent Selection
The fitness of a phenotype depends on how common it is in the population
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Based on the graph, predict the frequency of left-mouthed individuals in the next census.
A) Left-mouthed individuals will decrease in frequency
- Left- vs. Right- mouthed frequency fluctuates.
- This is because the most common phenotype frequency hits tipping point where it is no longer most successful
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Coevolution
The joint evolution of two or more interacting species in which pressure from each species acts as a selective agent on the other
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What type of selection is speed an example of?
- Speed is under strong directional selection pressure in the cheetah population and the gazelle populations
- Slow gazelles were more likely to get eaten = lower relative fitness
- Slow cheetahs are less likely to eat = lower relative fitness
- Cheetahs and gazelles exert selective pressures on each other
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What conditions would be necessary for two or more populations to coevolve?
- Geographical overlap of the species
- Reciprocal effects on phenotypic traits as a result of differential survival/reproduction
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What does reciprocal mean in reciprocal effects on phenotypic traits?
- Each species acts as a selective pressure on the phenotype of the others (fast gazelles = selective pressure on cheetahs to be fast and vice versa)
- Effects on fitness: A given phenotype of species A is more fit in the presence of species B
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Which of the following best describes the results presented?
C) Where squirrels are present, pinecones are rounder and have fewer seeds/cone
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Which of the following best describes the results presented?
A) Squirrels that live with pines have larger jaw muscles than those that live without pines, on average
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Which of the following best describes the results presented?
D) 2 of the above are correct
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Which of the following best describes the results presented?
E) Two of the above are correct
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Based on the data presented __________ are in a coevolutionary relationship.
D) Crossbills and pines
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