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Population Genetics and Communities, As overshooting becomes a possibility…

- - - - Equation:
        
        Gene pool:
        
        All of the alleles of every gene in a population make up the gene pool
        
        Allele frequency:
        
        Number of copies of an allele in a population divided by the total number of alleles for that gene in a population
        
        Genotype frequency
        
        Number of individuals with a particular genotype in a population divided by the total number of individuals in a population
        
        Predicts:
        
        an equilibrium-unchanging allele and genotype frequencies from generation to generation-if certain conditions exist in a population
        
        there must be:
        
        No new mutations
        
        No genetic drift.
        
        No migration
        
        No natural selection
        
        Random mating
        
        Provides a quantitative relationship between the allele and genotype frequencies
      - Assumptions:
        
        Microevolution
        
        Changes in a population’s gene pool from generation to generation
        
        Factors:
        
        Genetic Drift:
        
        Random loss of alleles
        
        Acts most strongly in small populations relative to large
        
        Bottleneck effect:
        
        Large population diminished suddenly
        
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        Mutation
        
        Some are apparent in phenotype
        
        Change in one of the nucleic acids
        
        Must be in gametes to be inherited
        
        Male pollen sperm
        
        Female ovule egg
        
        Polymorphism:
        
        multiple mutations in the long run means that a population is highly variable
        
        many phenotypes in a population
        
        Colorado Columbine, Aquilegia sp.
        
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        Natural selection:
        
        One allele selectively advantageous
        
        The overall vigor of the population grows
        
        Population size grows
        
        Artificial selection:
        
        Selection by humans
        
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        Increased frequency of desired trait
        
        Elimination of undesired traits
        
        Migration:
        
        Movement of alleles into and out of a population
        
        Can be impeded by:
        
        The environment
        
        Life history
        
        Results in:
        
        Gene Flow
        
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        Repercussions for:
        
        GMO
        
        climate change
        
        speciation
        
        Nonrandom Mating:
        
        Plants “choose” their mates
        
        Sexual Selection:
        
        Male-male competition
        
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        Female choice:
        
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    - - Directional Selection:
        
        x0≠x1
        var0=var1
      - Stabilizing selection:
        
        x0=x1
        var0>var1
      - Disruptive selection:
        
        x0=x1
        var0<var1
      - The net result of natural selection is a population that is better adapted to its environment and/or more successful at reproduction
      - Over the course of many generations, allele frequencies of many different genes may change through natural selection
      - Within a population there is allelic variation arising from various factors such as mutations causing differences in DNA sequences, Distinct alleles may encode proteins of differing functions
- - - - Study of the change in population size
        -- births and deaths in a population
      - Population size over time
        
        Population size (N)
        
        Exponential Growth:
        
        J-shaped curve
        
        Unlimited resources
        
        Logistic Growth:
        
        S-shaped curve
        
        Typical of a population that:
        
        Self regulates
        
        Has a carrying capacity (K)
        
        Reaching Carrying Capacity
        
        Overshoot K
        
        Result in die off
        
        EARTH CARRYING CAPACITY
        
        10 billion.
        
        Human population size:
        
        Growing Exponentially
        
        http://www.worldometers.info/world-population/
      - Growth Models:
        
        Exponential Growth:
        
        dN over dt equals r times N
        
        Logistic Growth:
        
        dN over dt equals r times N times the quantity one minus N divided by K
        
        r = intrinsic growth rate
        
        N = population size
        
        K = carrying capacity
      - Selected species:
        
        r-selected:
        
        Grow exponentially
        
        Disturbed areas
        
        Weedy
        
        Annuals
        
        Little investment in defense
        
        Many, small fruits
        
        K-selected:
        
        Fluctuate around carrying capacity
        
        Fairly stable habitats
        
        Perennials
        
        Invest in defenses
        
        Resource-intensive fruits
      - Plant strategies:
        
        Plants must make trade-offs due to environmental necessities
        
        Many strategies exist
        
        Grime’s model
        
        3 life stages
        
        C- competitors
        
        S- stress tolerators
        
        R- ruderals
    - - To predict if a population will grow or shrink, ecologists need to know birth and death rates for organisms at different ages as well as the current age and sex makeup of the population.
      - Life tables summarize birth and death rates for organisms at different stages of their lives.
      - (Handout)