Chapter 14 - The Origin of Species

Overview

• Focuses on the origin of species, a fundamental aspect of biological diversity.
• Exploration of speciation, defining species, reproductive barriers, and speciation models.

Key Concepts

1. Defining Species

• Species Definition: Derived from Latin meaning "kind" or "appearance".
• Biological Species Concept: Species are groups that can interbreed and produce fertile offspring.
• Reproductive Isolation: Prevents gene flow between species, maintaining distinct species boundaries.
• Hybrids: Offspring from the interbreeding of distinct species.

2. Speciation and Biological Diversity

• Speciation: Process by which one species splits into two or more distinct species.
  • Each speciation event increases biodiversity.
• Microevolution: Changes in the gene pool from generation to generation.

3. Concepts for Defining Species

• Morphological Species Concept: Based on physical traits.
• Ecological Species Concept: Defined by ecological niche and roles in the environment.
• Phylogenetic Species Concept: Smallest group sharing a common ancestor.

4. Reproductive Barriers

• Prezygotic Barriers: Prevent mating or fertilization between species.
  • Habitat, Temporal, Behavioral, Mechanical, and Gametic Isolation.
• Postzygotic Barriers: Affect hybrid offspring viability and fertility.
  • Reduced hybrid viability, fertility, and hybrid breakdown.

5. Mechanisms of Speciation

• Allopatric Speciation: Geographic isolation leads to speciation.
  • Caused by physical barriers like mountains or lakes.
• Sympatric Speciation: Occurs without geographic isolation, often through polyploidy.
  • Common in plants, can result from self-fertilization or hybridization.

6. Isolated Islands and Speciation

• Islands often serve as showcases for speciation and adaptive radiation.
• Adaptive Radiation: Evolution of various species from a common ancestor.
  • Example: Galápagos finches.

7. Hybrid Zones

• Regions where different species meet and produce hybrids.
• Reinforcement: Strengthening of barriers when hybrids are less fit.
• Fusion: Weak barriers may lead to species merging.

8. Tempo of Speciation

• Punctuated Equilibria Model: Species undergo rapid changes during speciation, followed by little change.
• Gradualism Model: Species evolve through small, gradual changes over long periods.

Conclusion

• Speciation is a complex process contributing to the diversity of life.
• Different models and concepts help understand how species form and maintain boundaries.
• Islands and hybrid zones provide valuable insights into speciation dynamics.