gray areas — species

There are lots of cases where it's unclear if a population is one species or two.

• Ring species
• Species complex
• Species flock
• Hybrid
  • Klepton
  • Chimera (virus)
• Subspecies
  • These have a clear taxonomic ranking:   Species ⇒ Subspecies ⇒ Variety ⇒ Subvariety ⇒ Form [2] ⇒ Subform (some of these are exclusively used in botany)
  • Cultivar and cultivar group
  • Strain
  • Breed
  • Race
  • Landrace   [2]
  • Serotype,   biovars,   and morphovars
  • Ecotype
• Genetic isolate / Reproductive isolation
  • Population fragmentation
  • Metapopulation
  • Genetic dynamics:
    • Small population size
    • Founder effect
    • Population bottleneck
    • Genetic rescue,   rescue effect,   and evolutionary rescue. (are these distinct concepts, or are they actually the same?)
    • Inbreeding depression
    • Drift load
    • Genetic purging

Concepts:

• The above concepts are closely tied up with speciation, so the above are usually not a static situation.
• Trinomial nomenclature
• Quasipecies model
• Intergradation

These support the idea that the species / subspecies distinction is fuzzy:

• Species problem
• Taxonomic inflation

See also

• History of the study of species

Even more general concepts:

• Lumpers and splitters