Biodiversity describes the variety of living organisms of all kinds, the biota, that inhabit a particular area. Biodiversity involves three concepts: (i) genetic diversity; (ii) habitat diversity; and (iii) species diversity.

Genetic diversity: This refers to the total number of genetic characteristics of a single species or many species, subspecies, etc. Any organism is always ‘on the move’. It evolves, reaches its ‘prime’, evolves into superior forms or becomes extinct. Hence genetic diversity is an indicator of the evolution of the species. For example, the tiger, an animal in its evolutionary prime, has eight subspecies.

Habitat diversity: This is the diversity of habitats in any unit area. A ‘rich’ habitat, instead of being monotonous, has a variety of ‘niches’. These niches are specialized micro- habitats-a habitat within a habitat. The more diversified a habitat is, the more is the diversity of its species.

Species diversity: Species diversity can be divided into species richness, species evenness and species dominance. Merely counting the number of species is not enough to describe biological diversity. It has to do with the relative chance of seeing a species as it has to do with the actual number present. Hence the total number of species in an area is termed species richness; the relative abundance is species evenness and the most abundant as the dominant species.

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The enormous variety of species on Earth

The earth as a whole is a big ecosystem. It has an amazing variety of habitats and within those habitats, niches. The living organisms have evolved in such a way that they fit themselves into some part of the system. Some species have very specific requirements and they become extinct if they fail to get them. Some species adapt themselves to a variety of habitats and can survive a moderate spectrum of changes. In short, each organism is a link in a ‘chain’ -the ecosystem

Scientists have identified and described about 1.4 million species. But this is just the tip of the proverbial iceberg! Millions and millions of organisms await identification and classification. The earth’s most regions are the tropics. Tropical forests, where sunlight, water and nutrients are not limiting factors, teem with organisms. The tropical forests also provide a variety of very specialized microhabitats. Although tropical forests make up only 7% of the earth’s land area, they house almost half of its species.

A species endemic to a patch of forest may not be present in other forest just kilometres away. The Wroughton’s free-tailed bat is present only in the forest of Bhimgad and its surroundings, a roughly 2000 to 3000 sq. km area. A great majority of species are rare. Moreover, the more specialized an animal is, the more are its chances of extinction. As habitats get destroyed, the biodiversity too follows suit.

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Massive extinctions

There have been at least five major extinctions in the earth’s history. During each extinction, a percentage of living species died out. All the five major extinctions have been triggered by climatic changes-the earth’s tendency to change from time to time.

Scientists have the strong notion that we are in the midst of another massive extinction. The rate of extinction has been dramatic and unprecedented. This time around there is a difference-this is human-caused and can be stopped by timely action.

The most common reason for the loss of biodiversity is loss of habitat. Species become extinct when their habitats are destroyed: when forests are cut down, wetlands are polluted or drained and grasslands are converted to farmland. Overexploitation of resources also contributes towards the decline in biodiversity. Even seemingly inexhaustible resources like the fish from sea have been exploited to the point of no-return.

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Islands are particularly vulnerable to species extinction. As a result of their geographical isolation, many islands have many endemic and highly specialized species. Even an inadvertent introduction of a new species does incalculable damage to the ecosystem. The ground-dwelling and nesting birds of New Zealand have been threatened by rats which entered the islands along with the early settlers.

The concentration of many endangered species in small areas also makes them vulnerable. It is like the proverbial ‘all eggs in a basket’. When any natural calamity like floods or drought or disease hits them, the danger of extinction is correspondingly great.

Beyond the number of species that exist, it is important to conserve genetic diversity within each species. Populations that fall below certain ‘threshold levels’ do not survive, due to ‘inbreeding depression’. Inbreeding may lead to many genetic disorders and make the species vulnerable to many diseases. Hence we also need to have large tracts of contiguous forests for biodiversity to thrive. Ideally, in India, we would need to have every forest ‘networked’ by ‘corridors’.

The role of even the smallest organism

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Every organism in the web of the ecosystem contributes its mite towards the enhancement of the ecosystem, except perhaps a certain mischievous ape. No species is here without purpose. Species that may appear to be inconsequential outwardly may play very important roles in the ecosystem.

Soil nitrogen, a key element for agricultural productivity, depends on nitrogen-fixing bacteria, which live in symbiosis with leguminous plants. These bacteria fix enormous quantity of nitrogen in the soil.

The polymerase chain reaction technique, i.e., making millions of DNA copies was possible only because of a heat-stable enzyme discovered from a certain species of bacteria living in the hot springs of the Yellowstone National Park.