Species group

Species group

A species group is an informal taxonomic rank into which an assemblage of closely related species within a genus are grouped because of their morphological similarities[1][2] and their identity as a biological unit with a single monophyletic origin.[3]



The use of the term reduces the need to use a higher taxonomic category in cases with taxa that exhibit sufficient differentiation to be recognized as separate species but possess inadequate variation to be recognized as subgenera. Defining species groups is a convenient way of subdividing well-defined genera with a large number of recognized species. The use of species groups have enabled systematists to consolidate polytypic species species into nominal species which in turn can be grouped into the larger array of the species group.[3]


In regards to whether or not members of a species group share a range, sources differ. A source from Iowa State University Department of Agronomy says that members of a species group usually have partially overlapping ranges but do not interbreed with each other.[1] A Dictionary of Zoology (Oxford University Press 1999) describes a species group as complex of related species that exist allopatrically and explains that this "grouping can often be supported by experimental crosses in which only certain pairs of species will produce hybrids."[2] The examples given below may support both uses of the term "species group."

Arthropod examples

Vertebrate examples

  • Brachygobius, a small genus of gobies which are popular as aquarium fish, are informally divided by taxonomists into two species groups. The dwarf "Brachygobius nunus species group" contains Brachygobius nunus, Brachygobius aggregatus, and Brachygobius mekongensis while the bigger "Brachygobius doriae species group" contains the bigger species of Brachygobius doriae, Brachygobius sabanus, and Brachygobius xanthomelas.[10]
  • The chameleon Brookesia minima has been characterized as belonging to a species group with other "Madagascan Dwarf Chameleons" such as Brookesia dentata, Brookesia tuberculata, and other new or unidentified species such as a recently described chameleon from Tsingy de Bemaraha Strict Nature Reserve.[11]
  • Peromyscus, a genus of deer mice, has been divided into subgenera Peromyscus and Haplomylomys and these subgenera are subdivided further into thirteen species groups.[3]
  • Recent cytogenetic studies have shown that the Middle East Blind Mole Rat (Spalax ehrenbergi) may actually be a species group containing several cryptic species that can be distinguished by chromosome numbers.[12]

Other uses

The term "species group" is also used in a different way so as to describe the manner in which individual organisms group together. In this non-taxonomic context one can refer to "same-species groups" and "mixed-species groups." While same-species groups are the norm, examples of mixed-species groups abound. For example, zebra (Equus burchelli) and wildebeest (Connochaetes taurinus) can remain in association during periods of long distance migration across the Serengeti as a strategy for thwarting predators. Cercopithecus mitis and Cercopithecus ascanius, species of monkey in the Kakamega Forest of Kenya, can stay in close proximity and travel along exactly the same routes through the forest for periods of up to 12 hours. These mixed-species groups are cannot be explained by the coincidence of sharing the same habitat. Rather, they are created by the active behavioural choice of at least one of the species in question.[13]

See also


  1. ^ a b Iowa State University Department of Agronomy
  2. ^ a b Michael Allaby. "species group." A Dictionary of Zoology (Oxford University Press 1999)
  3. ^ a b c Molecular systematics of the Peromyscus boylii species group
  4. ^ Ranz JM, Maurin D, Chan YS, et al. (June 2007). "Principles of genome evolution in the Drosophila melanogaster species group". PLoS Biol. 5 (6): e152. doi:10.1371/journal.pbio.0050152. PMC 1885836. PMID 17550304. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1885836. 
  5. ^ World- Wide Distribution of Pestiferous Social Wasps(Vespidae)
  6. ^ Walter Reed Biosystematics Unit "Scorpion of the Day":Centruroides limbatus
  7. ^ Kaston, B. J. (1970). "Comparative biology of American black widow spiders". Transactions of the San Diego Society of Natural History 16 (3): 33–82. 
  8. ^ Anderson Tully Worldwide
  9. ^ Le Moult (E.) & Réal (P.), 1962-1963. Les Morpho d'Amérique du Sud et Centrale, Editions du cabinet entomologique E. Le Moult, Paris]]
  10. ^ Schäfer F (2005). Brackish Water Fishes. Aqualog. pp. 49–51. ISBN 3-936027-82-X. 
  11. ^ AdCham.com: Brookesia minima by E. Pollak
  12. ^ Sözen M, Matur F, Çolak E, Özkurt Ş, Karataş A (2006). "Some karyological records and a new chromosomal form for Spalax (Mammalia: Rodentia) in Turkey" (PDF). Folia Zool. 55 (3): 247–256. http://www.ivb.cz/folia/55/3/247-256.pdf. 
  13. ^ Tosh CR, Jackson AL, Ruxton GD (March 2007). "Individuals from different-looking animal species may group together to confuse shared predators: simulations with artificial neural networks". Proc. Biol. Sci. 274 (1611): 827–32. doi:10.1098/rspb.2006.3760. PMC 2093981. PMID 17251090. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2093981. 

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