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.