Species group
Encyclopedia
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 and their identity as a biological unit with a single monophyletic origin
.
species into nominal species
which in turn can be grouped into the larger array of the species group.
, 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. 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." The examples given below may support both uses of the term "species group."
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.
Taxonomic rank
In biological classification, rank is the level in a taxonomic hierarchy. Examples of taxonomic ranks are species, genus, family, and class. Each rank subsumes under it a number of less general categories...
into which an assemblage of closely related species within a genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
are grouped because of their morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
similarities and their identity as a biological unit with a single monophyletic origin
Monophyly
In common cladistic usage, a monophyletic group is a taxon which forms a clade, meaning that it contains all the descendants of the possibly hypothetical closest common ancestor of the members of the group. The term is synonymous with the uncommon term holophyly...
.
Use
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 speciesPolytypic
In zoology, polytypic refers to a taxonomic unit with more than one subgroup at the next lower level.-See also:*Linnaean taxonomy*monotypic*monotypic habitat...
species into nominal species
Biological classification
Biological classification, or scientific classification in biology, is a method to group and categorize organisms by biological type, such as genus or species. Biological classification is part of scientific taxonomy....
which in turn can be grouped into the larger array of the species group.
Range
In regards to whether or not members of a species group share a rangeRange (biology)
In biology, the range or distribution of a species is the geographical area within which that species can be found. Within that range, dispersion is variation in local density.The term is often qualified:...
, sources differ. A source from Iowa State University
Iowa State University
Iowa State University of Science and Technology, more commonly known as Iowa State University , is a public land-grant and space-grant research university located in Ames, Iowa, United States. Iowa State has produced astronauts, scientists, and Nobel and Pulitzer Prize winners, along with a host of...
Department of Agronomy
Agronomy
Agronomy is the science and technology of producing and using plants for food, fuel, feed, fiber, and reclamation. Agronomy encompasses work in the areas of plant genetics, plant physiology, meteorology, and soil science. Agronomy is the application of a combination of sciences like biology,...
says that members of a species group usually have partially overlapping ranges but do not interbreed with each other. A Dictionary of Zoology (Oxford University Press
Oxford University Press
Oxford University Press is the largest university press in the world. It is a department of the University of Oxford and is governed by a group of 15 academics appointed by the Vice-Chancellor known as the Delegates of the Press. They are headed by the Secretary to the Delegates, who serves as...
1999) describes a species group as complex of related species that exist allopatrically
Allopatric speciation
Allopatric speciation or geographic speciation is speciation that occurs when biological populations of the same species become isolated due to geographical changes such as mountain building or social changes such as emigration...
and explains that this "grouping can often be supported by experimental crosses in which only certain pairs of species will produce hybrids." The examples given below may support both uses of the term "species group."
Arthropod examples
- The fruit flyDrosophilidaeDrosophilidae is a diverse, cosmopolitan family of flies, which includes fruit flies. Another family of flies called Tephritidae also includes fruit flies. The best known species of Drosophilidae is Drosophila melanogaster, within the genus Drosophila, and this species Is used extensively for...
subgenus SophophoraSophophoraThe paraphyletic subgenus Sophophora of the genus Drosophila was first described by Alfred Sturtevant in 1939. It contains the best known drosophilid species, Drosophila melanogaster. Sophophora translates as carrier of wisdom...
contains the Drosophila melanogaster species groupDrosophila melanogaster species groupThe Drosophila melanogaster species group belongs to the subgenus Sophophora and contains 10 subgroups. The phylogeny in this species group is poorly known despite many studies covering many of the species subgroups. The most likely explanation is that the various subgroups diverted from each other...
which itself contains 12 subgroups. The Drosophila obscura species groupDrosophila obscura species groupThe Drosophila obscura species group belongs to the subgenus Sophophora and contains 6 subgroups:affinis, microlabis, obscura, pseudoobscura, subobscura, and sinobscura.-Species:affinis species subgroup...
belongs to the same subgenus and contains 6 subgroups. - In VespulaVespulaVespula is a small genus of social wasps, widely distributed in the Northern Hemisphere. Along with members of their sister genus Dolichovespula, they are collectively known by the common name yellowjackets in North America...
, a genus of waspWaspThe term wasp is typically defined as any insect of the order Hymenoptera and suborder Apocrita that is neither a bee nor an ant. Almost every pest insect species has at least one wasp species that preys upon it or parasitizes it, making wasps critically important in natural control of their...
s, only a few species have a scavengingScavengerScavenging is both a carnivorous and herbivorous feeding behavior in which individual scavengers search out dead animal and dead plant biomass on which to feed. The eating of carrion from the same species is referred to as cannibalism. Scavengers play an important role in the ecosystem by...
habitHabit (biology)Habit, when used in the context of biology, refers to the instinctive actions of animals and the natural tendencies of plants.In zoology, this term most often refers to specific behavioral characteristics, even when directly related to physiology...
(as opposed to a strictly predatory habit) and thus are considered major pests. The most abundant and bothersome of these are the three species belonging to the "Vespula vulgaris species group" which includes the "common wasp" or "yellowjacket" (Vespula vulgaris), the "German wasp" or "European wasp" (Vespula germanica), and the "western wasp" or "western yellowjacket" (Vespula pensylvanicaVespula pensylvanicaVespula pensylvanica is a species of wasp in the genus Vespula.-Description:V. pensylvanica is a predatory species that feeds on a wide range of invertebrate taxa and this has great potential for negative impact on the native fauna in insular habitats...
). - The Central AmericaCentral AmericaCentral America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...
n bark scorpionCentruroidesCentruroides is a genus of scorpions belonging to the family Buthidae. Several North American species are known by the common vernacular name bark scorpion. Numerous species are extensively found throughout the southern United States, Central America, the Antilles and northern South America...
s Centruroides limbatusCentruroides limbatusCentruroides limbatus is a species of bark scorpion from Central America. Its specific name "limbatus" is from the Latin meaning "black-edged" and refers to the colored markings of this species.-Range:...
and Centruroides bicolorCentruroides bicolorCentruroides bicolor is a species of bark scorpion from Central America. Its specific name "bicolor" is from the Latin meaning "two colored" and refers to the markings of this species.-Range:...
belong to the "Gracilis species group". All of the species in this group are characterized by their long, narrow pedipalpPedipalpPedipalps , are the second pair of appendages of the prosoma in the subphylum Chelicerata. They are traditionally thought to be homologous with mandibles in Crustacea and insects, although more recent studies Pedipalps (commonly shortened to palps or palpi), are the second pair of appendages of the...
s and overall relatively large size. - The arachnidArachnidArachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although in some species the front pair may convert to a sensory function. The term is derived from the Greek words , meaning "spider".Almost all extant arachnids are terrestrial...
s to which the common nameCommon nameA common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
"Black widow spiderBlack widow spiderLatrodectus mactans, the Southern black widow, is a highly venomous species of spider in the genus Latrodectus. They are well known for the distinctive black and red coloring of the female of the species and for the fact that she will occasionally eat her mate after reproduction. The species is...
" is given are in a species group that includes the "southern black widow" (Latrodectus mactans), the "northern black widow" (Latrodectus variolusLatrodectus variolusLatrodectus variolus, the Northern black widow spider or Northern widow, is a venomous spider species of the Latrodectus genus in the Theridiidae family...
), and the "western black widow" (Latrodectus hesperusLatrodectus hesperusLatrodectus hesperus, the Western black widow spider or Western widow, is a venomous spider species found in western regions of North America. The female's body is 14–16 millimeters in length and is black, often with an hourglass shaped red mark on the lower abdomen. This "hourglass" mark can be...
'). - The Neotropical butterflyButterflyA butterfly is a mainly day-flying insect of the order Lepidoptera, which includes the butterflies and moths. Like other holometabolous insects, the butterfly's life cycle consists of four parts: egg, larva, pupa and adult. Most species are diurnal. Butterflies have large, often brightly coloured...
Morpho adonisMorpho adonisThe Adonis Morpho is a Neotropical butterfly.It is found in Surinam , French Guiana , Colombia, Ecuador , Brazil and Peru...
is in a species group with Morpho eugeniaMorpho EugeniaMorpho Eugenia is a 1992 novella by A. S. Byatt first published in complete form with The Conjugal Angel as Angels & Insects. It details the key events of the life of a Victorian naturalist, William Adamson, at first seemingly struggling to move up in class and settle down with a beautiful,...
and Morpho uraneis. Morpho marcus is also included in the group but might actually be the same species as Morpho adonis
Vertebrate examples
- BrachygobiusBrachygobiusBrachygobius is a small genus of gobies. They are popular aquarium fish where a number of species are sold as bumblebee gobies because their colours are similar to those of bumblebees.-Morphology:...
, a small genusGenusIn biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of gobiesGobyThe gobies form the family Gobiidae, which is one of the largest families of fish, with more than 2,000 species in more than 200 genera. Most are relatively small, typically less than 10 cm in length...
which are popular as aquariumAquariumAn aquarium is a vivarium consisting of at least one transparent side in which water-dwelling plants or animals are kept. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, marine mammals, turtles, and aquatic plants...
fishFishFish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
, are informally divided by taxonomists into two species groups. The dwarf "Brachygobius nunus species group" contains Brachygobius nunusBrachygobius nunusBrachygobius nunus is a species of bumblebee goby, a small genus of gobies that takes its common name from their round bodies, big heads, and their overall yellow to golden coloration interrupted by four brown to black vertical stripes reminiscent of the striped pattern of a bumblebee...
, Brachygobius aggregatus, and Brachygobius mekongensis while the bigger "Brachygobius doriae species group" contains the bigger species of Brachygobius doriae, Brachygobius sabanus, and Brachygobius xanthomelas. - The chameleonChameleonChameleons are a distinctive and highly specialized clade of lizards. They are distinguished by their parrot-like zygodactylous feet, their separately mobile and stereoscopic eyes, their very long, highly modified, and rapidly extrudable tongues, their swaying gait, the possession by many of a...
Brookesia minimaBrookesia minimaBrookesia minima, , is a diminutive chameleon "often said to be the smallest" or "probably the smallest" of the Chamaeleonidae.-Range:B...
has been characterized as belonging to a species group with other "Madagascan Dwarf Chameleons" such as Brookesia dentata, Brookesia tuberculataBrookesia tuberculataBrookesia tuberculata is a diminutive chameleon from far northern Madagascar.-Similar species:A 1999 paper in the Journal of Zoology disputed a 1995 paper which considered this species and B. peyrierasi to be the same species as B. minima...
, and other new or unidentified species such as a recently described chameleon from Tsingy de Bemaraha Strict Nature ReserveTsingy de Bemaraha Strict Nature ReserveTsingy de Bemaraha Strict Nature Reserve is a nature reserve located near the western coast of Madagascar in Melaky Region at . The area was listed as a UNESCO World Heritage Site in 1990 due to the unique geography, preserved mangrove forests, and wild bird and lemur populations...
. - PeromyscusPeromyscusThe genus Peromyscus contains the animal species commonly referred to as deer mice. This is a genus of New World mouse only distantly related to the common house mouse and laboratory mouse, Mus musculus...
, a genus of deer mice, has been divided into subgenera Peromyscus and Haplomylomys and these subgenera are subdivided further into thirteen species groups. - Recent cytogenetic studies have shown that the Middle East Blind Mole RatMiddle East Blind Mole RatThe Middle East Blind Mole Rat or Israel Mole Rat is a species of rodent in the Spalacidae family....
(Spalax ehrenbergi) may actually be a species group containing several cryptic species that can be distinguished by chromosome numbers.
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 SerengetiSerengeti
The Serengeti ecosystem is a geographical region in Africa. It is located in north Tanzania and extends to south-western Kenya between latitudes 1 and 3 S and longitudes 34 and 36 E. It spans some ....
as a strategy for thwarting predators. Cercopithecus mitis and Cercopithecus ascanius, species of monkey in the Kakamega Forest
Kakamega Forest
Kakamega Forest is situated in Western Province Kenya, north-west of the capital Nairobi, and near to the border with Uganda. It is said to be Kenya's last remnant of the ancient Guineo-Congolian rainforest that once spanned the continent....
of Kenya
Kenya
Kenya , officially known as the Republic of Kenya, is a country in East Africa that lies on the equator, with the Indian Ocean to its south-east...
, 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.