Chapter 14 - The Origin of Species

Key Concepts

• Darwin's Observations: On the Galápagos Islands, Darwin noted unique species, leading to insights about speciation and biological diversity.
• Microevolution: Change in the gene pool of a population across generations.
• Speciation: Process where one species splits into two or more, increasing biological diversity.

Defining Species

• Species Definition:
  • Traditionally from Latin, meaning 'kind' or 'appearance'.
  • Biological species concept: a group capable of interbreeding and producing fertile offspring.
• Reproductive Isolation:
  • Prevents gene flow between species, maintaining species boundaries.
  • Hybrids occasionally result from distinct species interbreeding (e.g., grolar bears from grizzly and polar bears).
• Challenges in Definition:
  • Fossils and asexual organisms challenge the biological species concept.
  • Alternative concepts include:
    • Morphological: Based on physical traits, useful for fossils and asexual organisms.
    • Ecological: Defined by ecological roles (niches).
    • Phylogenetic: Smallest group sharing a common ancestor, emphasizing genetic lineage.

Reproductive Barriers

• Prezygotic Barriers: Prevent mating or fertilization.
  • Types: Habitat, temporal, behavioral, mechanical, and gametic isolation.
• Postzygotic Barriers: After hybrid zygote formation.
  • Types: Reduced hybrid viability, reduced hybrid fertility, and hybrid breakdown.

Mechanisms of Speciation

• Allopatric Speciation:
  • Geographic isolation leads to new species.
  • Examples include physical barriers like mountain ranges or lakes.
• Sympatric Speciation:
  • Occurs within the same geographic area.
  • Often involves polyploidy in plants or habitat differentiation and sexual selection.

Speciation on Islands

• Isolated Islands:
  • Often sites of diverse, unique species due to adaptive radiation.
  • The Galápagos Islands are a prime example with Darwin's finches.

Hybrid Zones

• Study of Reproductive Isolation:
  • Regions where closely related species meet and produce hybrid offspring.
• Outcomes:
  • Reinforcement: Natural selection strengthens barriers.
  • Fusion: Weak barriers may result in merging of species.

Tempo of Speciation

• Models of Speciation:
  • Punctuated Equilibria: Rapid change followed by periods of stasis.
  • Gradualism: Slow, steady evolutionary changes.
• Time Intervals: Speciation events can range from thousands to millions of years.

These notes cover the core themes of Chapter 14 from "Campbell Biology: Concepts and Connections," focusing on the origin and diversification of species, mechanisms of speciation, and the challenges in defining species.