Evolutionary Factors and Population Growth

  • Evolutionary Factors

    • Learning Outcomes:
    • Describe factors causing gene pool diversity changes.
    • Describe factors affecting population growth.

  • Recap

    • Hardy Weinberg Equilibrium: allele and genotype frequencies constant across generations.
    • Conditions for equilibrium:
    1. No migration
    2. No mating preferences
    3. No natural selection
    4. No mutations
    5. Large population
    • Disruption of any condition leads to evolution.

  • Factors Leading to Evolutionary Change

    1. Mutations:
    • Changes in DNA sequence; can be neutral, beneficial, or harmful.
    • Introduces variation.
    • Example: Sickle Cell (HBB gene mutation).
    1. Gene Flow:
    • Migration of alleles between populations.
    • Introduces or removes alleles.
    • Example: Grey Wolves.
    1. Genetic Drift:
    • Allele frequency changes due to random events in small populations.
    • Reduces genetic variation.
    • Bottleneck Effect:
      • Rapid population decreases lead to gene pool changes.
      • Example: Whooping Crane.
    • Founder Effect:
      • A few individuals create a new isolated population, limiting gene variation.
      • Example: Indigenous peoples migrating from Siberia.
    1. Non-Random Mating:
    • Preferred phenotypes lead to increased homozygosity.
    • Example: Devil’s Hole Pupfish.
    1. Natural Selection:
    • Some individuals better survive/reproduce in an environment.
    • Example: Antibiotic resistance.

  • Population Growth

    • Influenced by births, deaths, immigration, and emigration.
    • Carrying Capacity: Maximum sustainable population size.
    • Biotic Potential: Maximum reproductive rate under ideal conditions.
    • Factors include reproductive rate, maturity age, survivorship, and reproductive frequency.

  • Life Strategies

    • Two main life strategy types:
    1. r-selected Strategies:
      • Rapid reproduction, short lifespan, little parental care.
      • Example: bacteria, insects.
      • “J-shaped” growth curve.
    2. K-selected Strategies:
      • Reproduce near carrying capacity, long lifespan, high parental care.
      • Example: elephants, humans.
      • “S-shaped” growth curve.