gray areas — species

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

• Groups of subspecies
  • Ring species
  • Species complex
  • Species flock
  • Viral quasispecies
• Taxonomy
  • The ranks below species are:   Species ⇒ Subspecies ⇒ Variety ⇒ Subvariety ⇒ Form [2] ⇒ Subform (some are only used in botany)
  • Infraspecific naming
  • Trinomial nomenclature
• Subspecies
  • Cultivar and cultivar group
  • Strain
  • Breed
  • Race
  • Landrace   [2]
  • Forma specialis
  • Methods for grouping species or subspecies:   [2] (explanation of 'x-type')
    • Biovar (biotype) — Members of any species can be grouped in terms of:     biochemistry or physiology
    • Morphovar (morphotype, or morph) — morphology
    • Pathovar (pathotype) — pathogenicity to a host
    • Serovar (serotype) — reactivity between its surface antigens and an antiserum
    • Ecovar (ecotype) — phenotypical features that result from environmental factors (such as elevation, climate, or predation)
    • Phagovar (phagotype) — reactions to a bacteriophage
    • Chemovar (chemotype) — production of (or amount of) a chemical
• Genetic isolate / Reproductive isolation
  • 'Parapatric' — Species whose ranges do not significantly overlap but are immediately adjacent to each other.
  • 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
• Hybrid,   hybrid swarm,   hybrid speciation
  • F1/F2/... hybrid,   second-generation hybrids,
  • Category:Hybrid animals and Hybrid plants
  • 'Nothospecies', 'nothogenus', 'nothotaxa', etc
• TODO: Soft polytomy vs. hard polytomy, expand on this
• TODO: Explore multi-species hybrids
• Chimera,   graft-chimera

Concepts:

• The above concepts are very closely related to speciation. As such, the above are usually a dynamic rather than static situation.
• Quasipecies model
• Intergradation and cline

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