Comprehensive Study Notes on Diversity in the Living World and Taxonomic Hierarchy
Biodiversity and the Diversity of Living Organisms
The variety and count of all organisms existing on the Earth are defined as Biodiversity.
Currently, the number of species that have been scientifically documented and described ranges between and million.
The identification of new organisms is a continuous process occurring both in newly explored regions and in previously studied areas.
Systematics and Its Foundations
Systematics is defined as the scientific study of the various kinds of organisms, their inherent diversities, and the evolutionary relationships existing among them.
The term is rooted in the Latin word ‘systema’, which translates to the systematic arrangement of organisms.
Carolus Linnaeus utilized the title Systema Naturae for his seminal publication.
The original scope of systematics has evolved over time to encompass identification, nomenclature, and classification.
A core component of systematics is the consideration of evolutionary relationships between organisms.
Taxonomy and the Modern Basis of Classification
Taxonomy is the process of classifying all living organisms into different categories known as taxa based on their specific characteristics.
Modern taxonomic studies rely on several essential factors for accuracy:
External and internal structures of the organism.
The structure of the cell.
Developmental processes.
Ecological information regarding the organism.
The fundamental processes basic to taxonomy include characterisation, identification, classification, and nomenclature.
Processes of Taxonomy
Characterisation: This involves developing an understanding of an organism's specific characters, including its external and internal structures, the structure of its cells, its development process, and its ecological context.
Identification: Nomenclature or naming can only occur after an organism is described accurately. Identification is the process of determining exactly what organism a specific name is attached to.
Classification: This is the process of grouping organisms into convenient categories, or taxa, based on easily observable characters. Classification makes the study of millions of organisms possible and manageable.
Nomenclature (Naming): This provides standardized names to organisms so that a specific organism is universally recognized by the same name throughout the world.
Standardisation of Nomenclature
Standardisation is necessary because local names for plants and animals vary significantly across different regions and languages, even within a single country.
Scientific names ensure that every organism has only one unique name and that no specific name is reused for any other known organism.
Governing International Organizations:
ICBN: The International Code for Botanical Nomenclature provides the principles and criteria for naming plants.
ICZN: The International Code of Zoological Nomenclature was evolved by animal taxonomists to govern the naming of animals.
Binomial Nomenclature and Universal Rules
Biologists use universally accepted principles for scientific naming, specifically the system of Binomial Nomenclature established by Carolus Linnaeus.
Components of a Name:
The first component is the Generic name (Genus).
The second component is the specific epithet (Species).
Universal Rules of Nomenclature:
Biological names are usually in Latin and are written in italics. They are Latinised regardless of their linguistic origin.
When handwritten, both the genus and the specific epithet must be separately underlined. When printed, they must be in italics to indicate their Latin origin.
The genus name begins with a capital letter.
The specific epithet begins with a lowercase letter.
Example: Mangifera indica.
Author Citation:
The name of the author who first described the species appears after the specific epithet in an abbreviated form.
Example: Mangifera indica Linn. indicates that Linnaeus was the first to describe this species.
Human Classification:
Human beings belong to the species sapiens and the genus Homo. The correct scientific name is Homo sapiens.
The Taxonomic Hierarchy
Classification is a hierarchical process where each step represents a specific rank or category.
A taxonomic category is a single part of the overall arrangement, and the collection of all categories is the taxonomic hierarchy.
Each unit of classification is referred to as a rank and is scientifically termed a taxon (plural: taxa).
The common categories, in order from most specific to most general, are: Species, Genus, Family, Order, Class, Phylum or Division (for plants), and Kingdom.
Species
Species is the lowest or most basic category in the taxonomic hierarchy.
Ernst Mayr, known as the "Darwin of the 20th century," defined species as a group of closely related organisms that are genetically distinct and capable of interbreeding to produce fertile offspring.
Examples include:
Mangifera indica (Mango)
Solanum tuberosum (Potato)
Panthera leo (Lion)
A single genus may contain one or more specific epithets representing different organisms that share morphological similarities. For example, Panthera includes leo (lion) and tigris (tiger), while Solanum includes tuberosum, nigrum, and melongena.
Genus
A genus comprises a group of related species that resemble one another more than they resemble species of other genera.
Examples:
Potato, tomato, and brinjal are different species belonging to the genus Solanum.
Lion (Panthera leo), leopard (P. pardus), and tiger (P. tigris) share common features and belong to the genus Panthera.
The genus Felis includes cats.
Family
Similar genera are grouped into a family. Families exhibit fewer similarities compared to the genus and species levels.
Examples:
The genera Solanum, Petunia, and Datura are all placed in the family Solanaceae.
The genus Panthera and the genus Felis (cats) are grouped together in the family Felidae.
Dogs are classified under the family Canidae.
Order
An order is a group of related families that share a few common characters.
Examples:
Plant families like Convolvulaceae and Solanaceae are grouped in the order Polymoniales, primarily based on floral characteristics.
The animal order Carnivora includes families such as Felidae and Canidae.
Class
A class consists of related orders sharing common characters.
Examples:
The order Primata (monkeys, gorillas, and gibbons) is grouped into the class Mammalia.
The order Carnivora (tigers, cats, and dogs) is also included in the class Mammalia.
Phylum and Division
A phylum is a group of related classes with common features.
In the classification of plants, the term "Division" is used as the equivalent category to Phylum.
Kingdom
The Kingdom is the highest category in the classification system.
All animals across various phyla are assigned to Kingdom Animalia.
All plants across various divisions are assigned to Kingdom Plantae.
Hierarchical Trends and Relationships
As the hierarchy progresses from species upward to the kingdom, the number of common characteristics among the members decreases.
Conversely, the lower the taxa, the greater the number of characteristics that the members within that taxon share with one another.
Questions & Discussion
Q) Why are living organisms classified?
Because there are millions of living organisms, it is nearly impossible to study each one individually. Classification is necessary to devise a means to make this study possible. It is the process by which organisms are grouped into convenient categories based on easily observable characters.
Q) Why should the names of living organisms be standardised?
There are millions of plants and animals globally, known locally by different names that vary from place to place and country to country. Standardisation (nomenclature) ensures that a particular organism is recognized by the same unique name worldwide, preventing confusion and ensuring no name is used for more than one species.