Biodiversity

• The term biological diversity was used first by Arthur Harris (1916), an American botanist in his article “The Variable Desert” published in a science magazine called, The Scientific Monthly as part of a statement: “The bare statement that the region contains a flora rich in genera and species and of diverse geographic origin or affinity is entirely inadequate as a description of its real biological diversity”. The term, “biodiversity” was first coined by Walter G. Rosen in 1985. 
• Sum total of all the variety of living organisms on earth constitute biodiversity. Biological diversity is usually considered at three different levels – a) genetic diversity i.e. at genetic level , b) species diversity i.e. at the level of species, and c) ecosystem diversity i.e. at the level of ecosystem.

Genetic diversity 

• It refers to the variety of genes contained within species of plants, animals and micro-organisms. New genetic variation in individuals occurs by gene and chromosomal mutation, and in organisms with sexual reproduction may be spread across the population by recombination. For instance, two brothers differ in their structure, although their parents are the same. The differences could be in alleles (different variants of the same gene), in entire gene (the traits determining particular characteristics) or in chromosomal structure. 
• The amount of genetic variation (gene pool) present in an inter-breeding population is shaped or decided by the process of natural selection. Selection leads to certain genetic attributes being preferred and results in changes in the frequency of genes within this pool. This forms the basis of adaptation among the living organisms. India has high genetic diversity and is regarded as a Vavilov’s centre of high crop genetic diversity – so named after the Russian agro-botanist N I Vavilov, who identified eight such centres of origin of cultivated plants around the world in the 1950s.

Species diversity 

• Species diversity refers to the variety of species within a geographical area. Species diversity can be measured in terms of:

1. 1. Species richness – refers to the number of various species in a defined area
   2. Species abundance – refers to the relative numbers among species. For example,the number of species of plants, animals and microorganisms may be more in an areathan that recorded in another area.
   3. Taxonomic or phylogenetic diversity – refers to the genetic relationships betweendifferent groups of species.

• Kinds of species that are present in an area is also important. When taxonomically unrelatedspecies are present in an area, the area represents greater species diversity as comparedto an area represented by taxonomically related species.
• Species diversity is not evenly distributed across the globe. The overall richness of species is concentrated in equatorial regions and tends to decrease as one moves from equatorial to polar regions. In addition, biodiversity in land ecosystems generally decreases with increasing altitude.
• The other factors that influence biodiversity are amount of rainfall and nutrient level in soil. In marine ecosystems, species richness tends to be much higher in continental shelves.

Ecosystem diversity

• It refers to the presence of different types of ecosystems. For instance, the tropical south India with rich species diversity will have altogether different structure compared to the desert ecosystem which has far less number of plant and animal species. Likewise, the marine ecosystem although has many types of fishes, yet it differs from the freshwater ecosystem of rivers and lakes in terms of its characteristics. So such variations at ecosystemlevel are termed as ecosystem diversity. 
• As stated above, ecosystem diversity encompasses the broad differences betweenecosystem, and the diversity of the habitats and ecological processes occurring withineach ecosystem type.

Hot spots of biodiversity 

• Biodiversity is not uniformly distributed across the geographical regions of the earth. Certain regions of the world are very rich in biodiversity. We call such areas as “mega diversity zones”. We also refer to them as “hot-spots”. For example, India accounts for only 2.4 % of the land area of the world; but it contributes approximately 8% species to the global diversity due to existence of such pockets.
• The term ‘biodiversity hotspot’ was coined by Norman Myers (1988). He recognized 10 tropical forests as “hotspots” on the basis of extraordinary level of plant endemism and high level of habitat loss, without any quantitative criteria for the designation of “hotspot” status. Two years later, he added eight more hotspots, and the number of hotspots in the world increased to 18 (Myers 1990). 
• Subsequently, the Conservation International in association with Myers made the first systematic update of the hotspots, and introduced the following two strict quantitative criteria, for a region to qualify as a hotspot: 
  • It must contain at least 1,500 species of vascular plants (> 0.5% of the world’s total) as endemics; 
  • It has to have lost ≥ 70% of its original native habitat. 
• According to Conservation International, at present, there are 36 biodiversity rich areas in the world that have been qualified as hotspots, which represent just 2.5% of earth’s land surface, but support over 50% of the world’s endemic plant species, and nearly 43% of bird, mammal, reptile and amphibian species as endemics.

Biodiversity Hotspots in the World

Biodiversity Hotspots in India 

• India, the seventh largest country in the world by geographical area (constitutes 2.4% of the total geographical area of the world) with varied physiographic divisions, climatic regimes, and ecological habitats exhibits a rich floral diversity, and harbours nearly 8% of the globally known flora, of which 28% of floral elements are endemic to the country.
• India is one of the 17 mega diversity countries in the world. According to a recent estimation the country harbours a total of 18,800 taxa of angiosperms, 82 taxa of Gymnosperms, 1307 taxa of Pteridophytes, 2786 taxa of Bryophytes, besides 15447 taxa of Fungi, 7434 taxa of Algae, 2917 taxa of Lichens and 1239 species of microbes (Viruses and Bacteria), which represent 8% of total recorded plant species (including algae, fungi, lichens, viruses and bacteria) of the world. India has four biodiversity hotspots namely 
  • Himalaya: Includes the entire Indian Himalayan region [Jammu and Kashmir, HimachalPradesh, Uttarakhand, northern part of West Bengal (Darjeeling), Sikkim, northern part of Assam and Arunachal Pradesh] and that falling in Pakistan, Tibet, Nepal, Bhutan, China and Myanmar. 
  • Indo-Burma: Myanmar, Thailand, Vietnam, Laos, Cambodia and southern China; alsoincluded the entire northeastern India (Mizoram, Manipur, Nagaland, Meghalaya, andTripura), and Andaman group of Islands, Bangladesh and Malaysia.
  • Sundaland: Indonesia, Malaysia, Singapore, Brunei and Philippines; also included Nicobargroup of Islands. 
  • Western Ghats and Sri Lanka: Includes the entire Western Ghats [Tamil Nadu, Kerala,Karnataka, Goa, Maharashtra and Gujarat] and Sri Lanka.