Classification & Taxonomic Tools (DP IB Environmental Systems & Societies (ESS))

Classification

• There are millions of different species that currently exist on Earth

  • Biologists and ecologists can manage and organise this enormous diversity of species by putting similar species together into groups

• This process is known as classification

  • It involved organising and categorising species based on their similarities and differences

  • Species are grouped into a hierarchy of different categories according to the biological characteristics that they share

  • Classifying species in this way allows us to quickly identify them and predict their characteristics

The hierarchical classification system—the higher ranks contain more organisms with less similarity between them and the lower ranks contain fewer organisms with more similarity between them

• The first step to classifying a species is to put it into a group known as a genus

  • A genus is a category in the classification hierarchy that includes one or more species that are closely related and share common characteristics

• Every species gets a two-part name in the following format: the name of the genus, then the name of the species

  • The genus name is always written first and with a capital letter

  • The species name does not have a capital letter

  • Both genus and species should be either italicised or underlined.

• For example, humans are called Homo sapiens, where Homo is the genus and sapiens is the species

  • This could also be written as Homo sapiens

  • Although a genus usually contains more than one species, we are the only species in our genus that exists today

  • However, in the past, there were other species within the Homo genus, such as Homo neanderthalensis (Neanderthals) and Homo erectus, among others

• An example of a well-known genus is the genus Canis

  • This genus includes several species of canids or members of the dog family, including:

    • Canis lupus (Grey wolf)

    • Canis familiaris (Domestic dog)

    • Canis latrans (Coyote)

    • Canis aureus (Golden jackal)

    • Canis simensis (Ethiopian wolf)

    • Canis mesomelas (Black-backed jackal)

    • Canis anthus (African golden wolf)

    • Canis adustus (Side-striped jackal)

    • Canis lupaster (African wolf)

  • These species share common characteristics, such as similar body structures, behaviours and genetic traits

  • While they may have distinct features and habitats, they are all grouped together under the genus Canis due to their close evolutionary relationship and shared ancestry

Taxonomic Tools

• Taxonomists use various tools to identify an organism and to help them decide how to classify it

  • Identification in this context means determining which species an individual organism belongs to

Comparison of specimens with reference collections

• Taxonomists can compare unknown specimens with well-documented reference collections

  • These reference collections contain a large number of similar organisms that have already been identified and classified

  • This method involves physically comparing the specimen to known samples

  • It relies on the taxonomist's expertise and the quality of the reference collection

    • For example, a botanist could identify an unknown plant specimen by visually comparing it with a large collection of known plant species at a botanical garden

  • Today there are apps that identify unknown species by comparing a photo to thousands of photos of different species in an online database (a virtual reference collection)

DNA surveys

• DNA surveys involve analysing an organism's DNA to determine its species

  • This method compares the DNA sequence of the specimen with known sequences from a very large number of species, stored in very large computer databases

  • It provides precise and reliable identification, especially for closely related species

    • For example, in a wildlife conservation project, researchers could use DNA surveys to distinguish between similar-looking species of butterflies

Dichotomous keys

• Dichotomous keys are tools used to identify organisms based on their characteristics

  • The keys consist of a series of paired statements or questions with two possible answers

  • Each pair offers two choices, leading the user to another pair of statements or questions, eventually resulting in the identification of the organism

• Below is an example of a dichotomous key that can be used to identify eight species in the Serengeti ecosystem:

Serengeti Dichotomous Key

• There are limitations to using a dichotomous identification key:

  • Limited scope:

    • Dichotomous keys are typically designed to identify a limited number of species and may not be comprehensive enough to identify all organisms in a given ecosystem

  • Inaccuracies:

    • Dichotomous keys are only as accurate as the information provided

    • If the key is not designed properly or lacks important distinguishing characteristics, the identification may be inaccurate

  • Variability:

    • Organisms can exhibit variability in their physical characteristics, which can make it difficult to accurately identify them using a dichotomous key

  • Time-consuming:

    • Using a dichotomous key can be a time-consuming process, especially for beginners who are not familiar with the organisms in question

  • Expertise required:

    • Dichotomous keys require a certain level of expertise and familiarity with the organisms in question

    • Beginners may find it difficult to use the key without assistance from an expert

  • Limited to physical characteristics:

    • Dichotomous keys are limited to the physical characteristics of organisms and may not take into account other important factors, such as behaviour or habitat, which can be important in identifying certain species