Levels of Biodiversity

Diversity is the hallmark of life on Earth -- from microorganisms and algae to fungi, plants and animals, living things show remarkable variation in size, shape, mode of nutrition, habitat, reproduction and length of life cycle. Biodiversity captures this variety at every scale: it is the totality of genes, species and ecosystems found within a region -- spanning the genetic differences among individuals of a species, the richness of plant and animal species across local to global scales, and the range of terrestrial and aquatic ecosystem types present in an area (the sense in which bodies such as IUCN, UNEP and WRI use the term). The word itself was coined by Walter Rosen in 1982 and later popularised by the sociologist Edward Wilson to describe this combined diversity across every level of biological organisation. The biodiversity seen today is the outcome of over 3.5 billion years of evolutionary history, shaped mainly by natural processes and, increasingly, by human activity.

Diversity in the living world can be studied at several interrelated, hierarchical levels, ranging from the molecular to the ecosystem level. Three major levels are usually distinguished: genetic diversity, species diversity and ecological (ecosystem) diversity.

Genetic diversity is the intraspecific diversity -- variation in the number and type of genes and chromosomes present within a species, including variation between individuals of the same population and between different populations of the species. Such variation, for example in allelic genes, creates individual differences within a species, improves its chances of persisting through changing environmental conditions, and lets the best-adapted individuals survive -- it is the raw material natural selection acts on. Subspecies and races are everyday examples; India alone has roughly 1,000 varieties of mangoes and about 50,000 varieties of rice and wheat. The medicinal plant Rauwolfia serpentina, which secretes the active compound reserpine, shows the same idea at the individual-plant level -- its potency and chemical concentration vary from one Himalayan location to another purely because of genetic diversity within the species. A healthy breeding population depends on this kind of genetic variability.

Species diversity is the interspecific diversity -- the number of plant and animal species present in a region -- and has two components: species richness (the variety of species present) and species evenness (how individuals are distributed among those species). Not every region is equally rich: amphibian diversity, for instance, is markedly higher in the Western Ghats than in the Eastern Ghats, and an undisturbed natural tropical forest carries far greater species richness than a monoculture timber plantation raised on the same land. India is one of only around 15 nations recognised as especially rich in species diversity. …