Lecture Notes on Species Concepts

Importance of Species in Biology

• Species are a fundamental concept in biology.
• Darwin's work was largely focused on species, though not extensively on speciation.
• Example: Lazuli and Indigo Buntings, two species that can hybridize.

Challenges in Defining Species

• Common definition: Organisms that interbreed, but not strictly true.
  • Example: Horses and donkeys can interbreed to produce mules, which are sterile.
  • Interbreeding organisms can still be considered separate species.
• Difficulty in defining species boundaries.
• No universally agreed upon species definition.

Species Concepts

Biological Species Concept (BSC)

• Originated by Ernst Mayr.
• Defines species as groups of interbreeding natural populations, reproductively isolated from others.
• Challenges with asexually reproducing species.

Other Species Concepts

• Evolutionary Species Concept
• Phylogenetic Species Concept
  • Defined as an irreducible basal cluster of organisms distinct from others.
  • Represents the smallest monophyletic group in a phylogenetic tree.
• Genetic Species Concept
  • Proposed by Robert Baker and Robert Bradley.
  • Focuses on genetic isolation rather than reproductive isolation.
  • Defines a species by a distinct gene pool.

Examples of Species and Hybridization

• Ravens (Corvus corax) and different crow species hybridizing in Europe.
• Hybrid zones showing morphological and genetic variations between species.