BIOL_3500_Chapter 6

BIOL 3500: Ecology


Chapter 6: Evolution and Ecology

Overview

  • Evolution can be understood as:

    • Genetic change over time

    • Descent with modification

Key Terminology

  • Genotype vs. Phenotype

    • Genotype: The genetic constitution of an individual.

    • Phenotype: The observable characteristics resulting from the genotype.

  • Genes vs. Alleles

    • Genes: Units of heredity made up of DNA that influence traits.

    • Alleles: Different forms of a gene.


Mechanisms of Evolution

Natural Selection, Genetic Drift, and Gene Flow

  • Natural selection, genetic drift, and gene flow can cause allele frequencies in a population to change over time.

Mutations and Recombination

  • Mutations: Can lead to the formation of new alleles, essential for evolution.

  • Recombination: Produces different genotypes within a population, significant for evolution.

Differences in Mechanisms

  • Discuss how mutations and recombination differ in their contributions to evolution.


Types of Natural Selection

1. Directional Selection

  • Example: Finches’ beak size adaptations during droughts.

  • More birds with larger beaks survived due to food accessibility.

2. Stabilizing Selection

  • Example: Galls from plants; optimal gall diameter increases reproductive success.

  • After selection, average size of galls stabilizes around a mean.

3. Disruptive Selection

  • Example: Different survival rates based on lower mandible width in birds.

  • Causes two or more contrasting phenotypes to be favored over the average.


Effects of Natural Selection

  • Natural selection can lead to fixation where all individuals in a population have the favored allele (allele frequency = 100%).

  • Example: Andean geese evolved specialized hemoglobin for high-altitude advantage.


Genetic Drift

  • Concept: Random processes can affect allele frequencies, especially in small populations.

  • Impact: Affects large vs. small populations differently due to chance events determining allele passage.


Gene Flow

  • Definition: Movement of alleles between populations via individuals or gametes.

  • Effects of Gene Flow:

    • Populations become more genetically similar.

    • New alleles can be introduced into populations.


Adaptive Evolution

  • Examine which processes/mechanisms consistently cause adaptive evolution.

  • Adaptations and Exaptations: Definitions and measurement methods.


Constraints on Natural Selection

  • Natural selection does not lead to perfect organism-environment matches due to:

    • Constant environmental changes

    • Lack of genetic variation: Without beneficial alleles, adaptive evolution cannot occur.

    • Evolutionary history: Natural selection operates on existing traits (phylogenetic constraints).

    • Ecological trade-offs: One advantageous trait may reduce another's efficacy.


Long-term Patterns of Evolution

  • Shaped by large-scale processes such as:

    • Speciation

    • Mass extinction

    • Adaptive radiation

Ecological Mechanisms

  • Explore ecological mechanisms that underpin these long-term evolutionary patterns.

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