Identification key
Encyclopedia
In biology
, an identification key is a printed or computer-aided device that aids the identification
of biological entities, such as plant
s, animal
s, fossil
s, microorganism
s, and pollen
grains. Identification keys are also used in many other scientific and technical fields to identify various kinds of entities, such as disease
s, soil type
s, mineral
s, or archaeological
and anthropological
artifacts.
Traditionally identification keys have most commonly taken the form of single-access key
s. These work by offering a fixed sequence of identification steps, each with multiple alternatives, the choice of which determines the next step. If each step has only two alternatives, the key is said to be dichotomous, else it is polytomous. Modern multi-access
or interactive keys allow the user to freely choose the identification steps and their order.
At each step, the user must answer a question about one or more features (characters) of the entity to be identified. For example, a step in a botanical
key may ask about the color of flowers, or the disposition of the leaves along the stems. A key for insect
identification may ask about the number of bristle
s on the rear leg.
, medical diagnosis, pest
control, forensics, etc.. Therefore, identification keys must be constructed with great care in order to minimize the incidence of such errors.
Whenever possible, the character used at each identification step should be diagnostic; that is, each alternative should be common to all members of a group of entities, and unique to that group. It should also be differential, meaning that the alternatives should separate the corresponding subgroups from each other. However, characters which are neither differential nor diagnostic may be included to increase comprehension (especially characters that are common to the group, but not unique).
Whenever possible, redundant characters should be used at each step. For example, if a group is to be split into two subgroups, one characterized by six black spots and the other by four brown stripes, the user should be queried about all three characters (number, shape, and color of the markings) — even though any single one of them would be sufficient in theory. This redundancy improves the reliability of identification, provides a consistency check against user errors, and allows the user to proceed even if some of the characters could not be observed. In this case, the characters should be ordered according to their reliability and convenience. Further error tolerance can be achieved by using reticulation
.
The terminology
used in the identification steps should be consistent in meaning and should be uniformly used. The use of alternative terms for the same concept to achieve more "lively prose" should be avoided. Positive statements should be used in preference to negative statements. The wording of the alternatives should be completely parallel sentences; alternatives like "flowers red, size 10-40 cm" versus "flowers yellow" should be avoided.
Geographic distribution characters should be used with caution. Species that have not been observed in a region may still occasionally occur there. Also, the organism
may have been transported, particularly to locations near ports and airports, or it may have changed its range (e. g., due to global warming
). For Europe
and, probably, North Africa
a Palaearctic key is advisable.
Rarity is not a viable character. An identification may be correct even though a species is very rare.
. Many keys contain brief descriptions to allow more certain identification, but these should not be assumed sufficient for verification.
Comparison with a monographic description is often difficult in practice, as many monographs are expensive, out of print, written in foreign languages, or hard to obtain. Monographs are often several decades old, so that often the species names used in the key do not match those used in the monograph.
Another alternative is comparison with authoritatively identified specimens in natural history museums or other relevant repositories. Authoritatively identified images are becoming more common on the internet. To qualify, the image must be labeled with a voucher specimen number, the name of the scientist who identified the photographed specimen, and the name of the public institution where the specimen is housed (so that interested parties can re-examine the specimen themselves).
Biology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...
, an identification key is a printed or computer-aided device that aids the identification
Identification (biology)
Identification in biology is the process of assigning a pre-existing individual or class name to an individual organism. Identification of organisms to individual names may be based on individualistic natural body features Identification in biology is the process of assigning a pre-existing...
of biological entities, such as plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
s, animal
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
s, fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s, microorganism
Microorganism
A microorganism or microbe is a microscopic organism that comprises either a single cell , cell clusters, or no cell at all...
s, and pollen
Pollen
Pollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants or from the male cone to the...
grains. Identification keys are also used in many other scientific and technical fields to identify various kinds of entities, such as disease
Disease
A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...
s, soil type
Soil type
In terms of soil texture, soil type usually refers to the different sizes of mineral particles in a particular sample. Soil is made up in part of finely ground rock particles, grouped according to size as sand, silt and clay...
s, mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...
s, or archaeological
Archaeology
Archaeology, or archeology , is the study of human society, primarily through the recovery and analysis of the material culture and environmental data that they have left behind, which includes artifacts, architecture, biofacts and cultural landscapes...
and anthropological
Anthropology
Anthropology is the study of humanity. It has origins in the humanities, the natural sciences, and the social sciences. The term "anthropology" is from the Greek anthrōpos , "man", understood to mean mankind or humanity, and -logia , "discourse" or "study", and was first used in 1501 by German...
artifacts.
Traditionally identification keys have most commonly taken the form of single-access key
Single-access key
A 'key' in Biology is a modeling method used for categorizing species using logical choices. A single-access key is a key where the sequence and structure of identification steps is fixed by the author of the key...
s. These work by offering a fixed sequence of identification steps, each with multiple alternatives, the choice of which determines the next step. If each step has only two alternatives, the key is said to be dichotomous, else it is polytomous. Modern multi-access
Multi-access key
In biology or medicine, a multi-access key is an identification key which overcomes the problem of the more traditional single-access keys of requiring a fixed sequence of identification steps. A multi-access key enables the user to freely choose the set and characteristics that are convenient to...
or interactive keys allow the user to freely choose the identification steps and their order.
At each step, the user must answer a question about one or more features (characters) of the entity to be identified. For example, a step in a botanical
Botany
Botany, plant science, or plant biology is a branch of biology that involves the scientific study of plant life. Traditionally, botany also included the study of fungi, algae and viruses...
key may ask about the color of flowers, or the disposition of the leaves along the stems. A key for insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
identification may ask about the number of bristle
Bristle
A bristle is a stiff hair or feather. Also used are synthetic materials such as nylon in items such as brooms and sweepers. Bristles are often used to make brushes for cleaning uses, as they are strongly abrasive; common examples include the toothbrush and toilet brush...
s on the rear leg.
Principles of good key design
Identification errors may have serious consequences in both pure and applied disciplines, including ecologyEcology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
, medical diagnosis, pest
Pest (animal)
A pest is an animal which is detrimental to humans or human concerns. It is a loosely defined term, often overlapping with the related terms vermin, weeds, parasites and pathogens...
control, forensics, etc.. Therefore, identification keys must be constructed with great care in order to minimize the incidence of such errors.
Whenever possible, the character used at each identification step should be diagnostic; that is, each alternative should be common to all members of a group of entities, and unique to that group. It should also be differential, meaning that the alternatives should separate the corresponding subgroups from each other. However, characters which are neither differential nor diagnostic may be included to increase comprehension (especially characters that are common to the group, but not unique).
Whenever possible, redundant characters should be used at each step. For example, if a group is to be split into two subgroups, one characterized by six black spots and the other by four brown stripes, the user should be queried about all three characters (number, shape, and color of the markings) — even though any single one of them would be sufficient in theory. This redundancy improves the reliability of identification, provides a consistency check against user errors, and allows the user to proceed even if some of the characters could not be observed. In this case, the characters should be ordered according to their reliability and convenience. Further error tolerance can be achieved by using reticulation
Reticulation (single-access key)
In biology, a reticulation of a single-access identification key connects different branches of the identification tree to improve error tolerance and identification success...
.
The terminology
Terminology
Terminology is the study of terms and their use. Terms are words and compound words that in specific contexts are given specific meanings, meanings that may deviate from the meaning the same words have in other contexts and in everyday language. The discipline Terminology studies among other...
used in the identification steps should be consistent in meaning and should be uniformly used. The use of alternative terms for the same concept to achieve more "lively prose" should be avoided. Positive statements should be used in preference to negative statements. The wording of the alternatives should be completely parallel sentences; alternatives like "flowers red, size 10-40 cm" versus "flowers yellow" should be avoided.
Geographic distribution characters should be used with caution. Species that have not been observed in a region may still occasionally occur there. Also, the organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
may have been transported, particularly to locations near ports and airports, or it may have changed its range (e. g., due to global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...
). For Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
and, probably, North Africa
North Africa
North Africa or Northern Africa is the northernmost region of the African continent, linked by the Sahara to Sub-Saharan Africa. Geopolitically, the United Nations definition of Northern Africa includes eight countries or territories; Algeria, Egypt, Libya, Morocco, South Sudan, Sudan, Tunisia, and...
a Palaearctic key is advisable.
Rarity is not a viable character. An identification may be correct even though a species is very rare.
Common problems in key usage
Key users must overcome many practical problems, such as:- Variant forms: The key may identify only some forms of the species, such as adult males (or, more rarely, females). Keys for larvae identification may consider only the final instarInstarAn instar is a developmental stage of arthropods, such as insects, between each molt , until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or...
. (This is not the case, however, of keys used in forensic identification of fly larvaeForensic entomologyForensic entomology is the application and study of insect and other arthropod biology to criminal matters. It is primarily associated with death investigations; however, it may also be used to detect drugs and poisons, determine the location of an incident, and find the presence and time of the...
.)
- Incomplete coverage: Species and groups that are difficult to identify or that have been poorly characterized may have been left out of the key, or may be mentioned only in introductory text.
- Lighting and magnification: Very few keys give details of how the specimen was viewed (the magnification, lighting system, angle of view etc.). This can cause problems. The author may, for instance refer to tiny bristles, hairs or chaetaChaetaA chaeta or cheta is a chitinous bristle or seta found on an insect, arthropod or annelid worms such as the earthworm, although the term is also frequently used to describe similar structures in other invertebrates. The plural form is chaetae or chetae.In the Polychaeta, they are located on the...
e--but how tiny?
- Language: Very few keys are multilingual. Translations of a key may be incorrect or misleading. Many keys contain vague words that do not translate..
- Obsolescence: Older keys may not include more recently described species. They may also use outdated species names, which must then be mapped to the current ones.
Verifying identifications
The identification obtained from a key should be viewed as only a suggestion of the species's real identity. Full identification requires comparison of the specimen with some authoritative source, such as a full and accurate description of the species, preferably in a monographMonograph
A monograph is a work of writing upon a single subject, usually by a single author.It is often a scholarly essay or learned treatise, and may be released in the manner of a book or journal article. It is by definition a single document that forms a complete text in itself...
. Many keys contain brief descriptions to allow more certain identification, but these should not be assumed sufficient for verification.
Comparison with a monographic description is often difficult in practice, as many monographs are expensive, out of print, written in foreign languages, or hard to obtain. Monographs are often several decades old, so that often the species names used in the key do not match those used in the monograph.
Another alternative is comparison with authoritatively identified specimens in natural history museums or other relevant repositories. Authoritatively identified images are becoming more common on the internet. To qualify, the image must be labeled with a voucher specimen number, the name of the scientist who identified the photographed specimen, and the name of the public institution where the specimen is housed (so that interested parties can re-examine the specimen themselves).
External links
- Xper2 - Interactive identification and descriptive data management software
- Identification key webservice
- Principles of interactive keys
- Programs for interactive identification and information retrieval
- Lucid - Interactive Identification and Diagnostics key software
- Visual Generic Identification to Grasses of Louisiana
- Discover Life - Interactive Guides and free online guide development space
- Bioimages Comments on Royal Entomological Society of London Keys
See also
- Cryptic species complexCryptic species complexIn biology, a cryptic species complex is a group of species which satisfy the biological definition of species—that is, they are reproductively isolated from each other—but whose morphology is very similar ....
- Scientific classification
- Single-access keySingle-access keyA 'key' in Biology is a modeling method used for categorizing species using logical choices. A single-access key is a key where the sequence and structure of identification steps is fixed by the author of the key...
- Multi-access keyMulti-access keyIn biology or medicine, a multi-access key is an identification key which overcomes the problem of the more traditional single-access keys of requiring a fixed sequence of identification steps. A multi-access key enables the user to freely choose the set and characteristics that are convenient to...