Introduction

In taxonomy, the species rank refers to a low-level category which is hierarchically intermediate between the ranks of subspecies and genus. Contrary to widespread opinion, the species rank is not qualitatively different from other ranks.

The term species refers to taxa that are defined based on the species rank. Species are assigned a two-part name (e.g. Columba livia), with the first name representing the name of the affiliated genus, thus implicating a phylogenetic assumption. Species are represented by a name-bearing type specimen or by a set of type specimens in scientific collections, providing a primary source of reference.

The theoretical concept of delimiting species-group taxa (i.e. species and genera) via temporal thresholds is illustrated for an exemplary timetree that comprises eight arbitrary taxa:

References

Agapow P, Bininda-Emons ORP, Crandall KA, Gittleman JL, Mace GM, Marshall JC, and Purvis A (2004), The impact of species concept on biodiversity studies, Q. Rev. Biol. 79, 161-179. (abstract)

Aldhebiani AY (2018), Species concept and speciation, Saudi J. Biol. Sci. 25, 437-440. (pdf)

Aleixo A (2023) On species concepts, species delimitation criteria, taxonomy committees, and biases: a response to Lima (2022a), Ornithol. Res. 31, 62-70. (free pdf)

Allmon WD (20017), Species, lineages, splitting, and divergence: why shall we still need ‘anagenesis’ and ‘cladogenesis’, Biol. J. Linn. Soc. 120, 474-479.  (pdf)

Avise JC, and Walker D (2000), Abandon all species concepts? A response, Conserv. Genet. 1, 77-80. (pdf)

Baetu TM (2012), Defining species: a multi-level approach, Acta Biotheor. 60, 239-255. (abstract)

Baker RJ, and Bradley RD (2006), Speciation in mammals and the genetic species concept, J. Mammal. 87, 643-662. (pdf)

Balakrishnan R (2005), Species concepts, species boundaries and species identification: a view from the Tropics, Syst. Biol. 54, 689-693. (pdf)

Barley AJ, Brown JM, and Thomson RC (2017), Impact of model violations on the inference of species boundaries under the multispecies coalescent, Syst. Biol. 67, 269-284. (free pdf)

Barraclough TG (2019), The evolutionary biology of species, Oxford University Press. (link) 

Cadena CD, and Zapata F (2021), The genomic revolution and species delimitation in birds (and other organisms): why phenotypes should not be overlooked, Ornithology 138, 1-18. (free pdf)

Christoffersen ML (1995), Cladistic taxonomy, phylogenetic systematics, and evolutionary ranking, Syst. Biol. 44, 440-454. (abstract)

Darwin C (1859), On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life, London. (pdf)

de Queiroz K (1997), The Linnaean hierarchy and the evolutionalization of taxonomy, with emphasis on the problem of nomenclature, Aliso 15, 125-144. (pdf)

de Queiroz K (1998), The general lineage concept of species, species criteria, and the process of speciation, In: “Endless forms. Species and speciation” (Howard DJ, and Berlocher SH, eds), pp. 57-75, Oxford University Press, Oxford, UK. (pdf)

de Queiroz K (2007), Species concepts and species delimitation, Syst. Biol. 56, 879-886. (pdf)

de Queiroz K (2011), Branches in the lines of descent: Charles Darwin and the evolution of the species concept, Biol. J. Linn. Soc. 103, 19-35. (pdf)

Fišer C, Robinson CT, and Malard F (2018), Cryptic species as a window into the paradigm shift of the species concept, Mol. Ecol. 27, 613-635. (pdf)

Fujita MK, Leaché AD, Burbrink FT, McGuire JA, and Moritz C (2012), Coalescent-based species delimitation in an integrative taxonomy, Trends Ecol. Evol. 27, 480-488. (abstract)

Garnett ST, and Christidis L (2017), Taxonomy anarchy hampers conservation, Nature 546, 25-27. (pdf)

Giribet G, Hormiga G,and Edgecombe GD (2016), The meaning of categorical ranks in evolutionary biology, Org. Divers. Evol. 16, 427-430. (abstract)

Gourbière S, and Mallet J (2009), Are species real? The shape of the species boundary with exponential failure, reinforcement, and the missing “snow ball”, Evolution 64, 1-24. (pdf)

Hart MW (2010), The species concept as an emergent property of population biology, Evolution 65, 613-613. (pdf)

Hendry AP, Vamosi SM, Latham SJ, Heilbuth JC, and Day T (2000), Questioning species realities, Conserv. Genet. 1, 67-76. (abstract)

Hill GE (2019), Reconciling the mitonuclear compatibility species concept with rampant mitochondrial introgression, Integr. Comp. Biol. 59, 912-924. (free pdf)

Isaac NJB, Mallet J, and Mace GM (2014), Taxonomic inflation: its influence on macroecology and conservation, Trends Ecol. Evol. 19, 464-469. (abstract)

Kunz W (2013) Do species exist? Principles of taxonomic classification, Wiley-Blackwell, Weinheim. (link)

Lambertz M, and Perry SF (2016), Again on the meaning of categorical ranks in modern evolutionary biology?, Org. Divers. Evol. 16, 723-735. (abstract)

Mallet J (2013), Concepts of species, In: “Encyclopedia of biodiversity” (Levin S, ed.), vol. 6, pp. 679-691, Academic Press, MA, USA. (pdf)

Mallet J (2020), Alternative views of biological species: reproductively isolated units or genotyping clusters?, Natl. Sci. Rev. 7, 1401-7. (pdf)

Mayr E (1963), Animal species and evolution, Belknap Press, Cambridge, MA. (link)

Mayr E (1996), What is a species, and what is not?, Philos. Sci. 63, 262-277. (preview)

Mishler BD (2010), Species are not uniquely real biological entities, In: “Contemporary debates in philosophy and biology” (Ajala FJ, and Arp R, eds), pp. 110-122, Wiley-Blackwell, Chichester, UK.

Nguyen JMT, and Ho SYW (2016), Mitochondrial rate variation among lineages of passerine birds, J. Avian Biol. 47, 690-696. (free reading)

Ottenburghs J (2019), Avian species concepts in the light of genomics, In: “Avian Genomics in Ecology and Evolution” (Kraus RHS, ed.),  pp. 211-234. Springer Nature, Switzerland. (abstract)

Pante E, Schoelinck C, and Puillandre N (2015), From integrative taxonomy to species description: one step beyond, Syst. Biol. 64, 152-160. (pdf)

Pavlinov IY (2013), The species problem, why again?, In: “The species problem” (Pavlinov I, ed.), chapter 1, eBook. (open access)

Roux C, Fraïsse C, Romigier J, Anciaux Y, Galtier N, and Bierne N (2016), Shedding light on the grey zone of speciation along a continuum of genomic divergence, PLoS Biol. 14, 1-22. (pdf)

Sangster G (2014), The application of species criteria in avian taxonomy and its implications for the debate over species concepts, Biol. Rev. 89, 199-214. (abstract)

Seifert B (2020), The gene and gene expression (GAGE) species concept: an universal approach for all eukaryotic organisms, Syst. Biol. 69, 1033-38. (free pdf)

Stankowski S, and Ravinet M (2021), Quantifying the use of species concepts, Curr. Biol. 31, R428-R429. (abstract)

Stanley SM (1978), Chronospecies‘ longevities, the oigin of genera, and the punctuational model of evolution, Paleobiology 4, 26-40. (abstract)

Vaux F, Trewick SA, and Morgan-Richards M (2016), Lineages, splits and divergence challenge whether the terms anagenesis and cladogenesis are necessary, Biol. J. Linn. Soc. 117, 165-176. (pdf)

Vaux F, Trewick SA, Morgan-Richards M (2017), Speciation through the looking-glass, Biol. J. Linn. Soc. 120, 480-488. (pdf)

Wilkins J (2006), Species, kinds, and evolution, Rep. Natl Center Sci. Edu. 26, 36-45. (pdf) 

Wu CI (2001), The genic view of the process of speciation, J. Evol. Biol. 14, 851-865. (pdf)

Zachos FE (2011) Linnaean ranks, temporal banding, and time-clipping: why not slaughter the sacred cow? Biol. J. Linn. Soc. 103, 732-734. (pdf)

Zachos FE (2016), Species concepts in biology, Springer Nature. (link)