Biosphere & Three Levels of Biodiversity

14.1 The Biosphere — Earth's Thin Living Skin

Imagine you could squeeze the entire earth into a perfect ball the size of a football. The thin film of dampness on its skin — the layer where water, air, soil and life meet — is the biosphere^?. Every plant you have ever seen, every animal that has crossed your path, every microbe inside your gut and every fish in the deep sea live within this slender envelope. The biosphere is a tiny portion of the planet by mass — yet it is the only place in the known universe where life is found. This chapter is the closing chapter of Fundamentals of Physical Geography, and it asks a single, urgent question: how can we recognise, value and protect the variety of life that fills this living skin?

You have already met the geomorphic processes — particularly weathering and the depth of the weathering mantle in different climatic zones (recall Figure 5.2 in Chapter 5). That weathering mantle is the foundation upon which the diversity of vegetation, and therefore the diversity of all life, is built. The fundamental drivers of weathering variations are the input of solar energy and water. Wherever the supply of both is generous, the spectrum of biodiversity widens; wherever they are scarce, life thins.

14.2 Biodiversity — Defining the Variety of Life

The word biodiversity^? is itself a combination of two parts — Bio (life) and Diversity (variety). In simple language, biodiversity is the number and variety of organisms found within a specified geographic region. It refers to the varieties of plants, animals and micro-organisms, the genes they carry and the ecosystems they form. More technically, biodiversity is the variability among living organisms on the earth, including the variability within and between species and within and between ecosystems. It is, in short, our living wealth — the dividend of hundreds of millions of years of evolutionary history.

Biodiversity is also a system in constant evolution, both from the viewpoint of the species and of the individual organism. The average half-life of a species is estimated at between one and four million years — and 99 per cent of all species that ever lived on the earth are today extinct. Importantly, biodiversity is not distributed evenly. It is consistently richer in the tropics; as one moves toward the polar regions, larger and larger populations of fewer and fewer species are found. The basic cause is the same combination — abundant solar energy and abundant water in the tropics, and their scarcity at the poles.

14.3 The Three Levels of Biodiversity

Biodiversity is conventionally discussed at three nested levels: (i) Genetic diversity, (ii) Species diversity, and (iii) Ecosystem diversity. The smallest level sits inside the larger; the differences inside one species build into the variety between species, which together build into the variety of ecosystems.

(i) Genetic Diversity

Genes^? are the basic building blocks of every life form. Genetic biodiversity refers to the variation of genes within a single species. Groups of individual organisms that share certain similarities in their physical characteristics are called a species — and yet within that species, no two individuals are identical. Human beings, for example, all belong to the species Homo sapiens, but we differ in height, skin colour, eye colour, blood type, physical appearance and a thousand other traits. This is genetic diversity at work. It is essential for the healthy breeding of a population and is the very raw material of evolution — for natural selection can only act when there is variation to select from.

(ii) Species Diversity

Species diversity^? refers to the variety of species. It relates to the number of species in a defined area and can be measured through three components — richness (the count of different species), abundance (how many individuals of each), and types (which kinds are represented). Some areas are far richer in species than others. Areas that are exceptionally rich in species and at the same time facing serious threat are called hotspots of diversity — and we will study them in detail in the next part of this chapter.

(iii) Ecosystem Diversity

You have already studied ecosystems in earlier chapters. The broad differences between ecosystem types and the diversity of habitats and ecological processes occurring within each ecosystem type together form ecosystem diversity^?. Forests, deserts, wetlands, mountains, oceans, grasslands, mangroves, coral reefs, alpine meadows — every distinct combination of climate, soil, water and community is a separate kind of ecosystem.

The "boundaries" of communities (which ecologists call associations of species) and of ecosystems are not very rigidly defined; one type grades into another along environmental gradients. The demarcation of an ecosystem boundary is therefore difficult and complex — yet the diversity of types is itself a treasure to be preserved.

14.4 Importance of Biodiversity

Why does it matter that the earth holds so many species? Biodiversity has contributed in many ways to the development of human culture, and in turn, human communities have played a major role in shaping the diversity of nature at the genetic, species and ecological levels. Biodiversity plays the following roles — ecological, economic and scientific — and we may add to these its ethical, cultural and aesthetic value.

(a) Ecological Role of Biodiversity

Species of many kinds perform some function or the other in an ecosystem — nothing in an ecosystem evolves and sustains without a reason. Every organism, while extracting what it needs, also contributes something useful to other organisms. Species capture and store energy through photosynthesis; they produce and decompose organic materials; they help to cycle water and nutrients through the ecosystem; they fix atmospheric gases such as nitrogen; and they help regulate the climate. These functions are vital not only for ecosystem function but for human survival itself.

(b) Economic Role of Biodiversity

For all humans, biodiversity is an important resource in their day-to-day life. One vital part of biodiversity is crop diversity, also called agro-biodiversity. Biodiversity is treated as a reservoir of resources to be drawn upon for the manufacture of food, pharmaceutical and cosmetic products. This concept of "biological resources" is partly responsible for the deterioration of biodiversity itself — and at the same time it is the origin of new conflicts dealing with rules of division and appropriation of natural resources. Important economic commodities that biodiversity supplies to humankind include food crops, livestock, forests, fish and medicinal resources.

(c) Scientific Role of Biodiversity

Biodiversity matters scientifically because each species can give us some clue as to how life evolved and how it will continue to evolve. Biodiversity also helps in understanding how life functions and the role of each species in sustaining ecosystems — of which we are also one species. This realisation must be drawn upon by every one of us, so that we live and let other species also live their lives.

(d) Ethical, Cultural and Aesthetic Role

It is our ethical responsibility to consider that each and every species, along with us, has an intrinsic right to exist. It is therefore morally wrong to voluntarily cause the extinction of any species. The level of biodiversity is a good indicator of the state of our relationships with other living species. The concept of biodiversity is, in fact, an integral part of many human cultures — sacred groves, totem animals, festival flowers, the peepul and banyan of Indian temple courtyards, the tiger of Indian heraldry, the lotus of national pride. Biodiversity also has an aesthetic and recreational dimension — the joy of birdwatching, the awe of a coral reef, the silence of a high-altitude meadow.

14.5 Why Some Regions Are Richer Than Others

Biodiversity is not painted evenly across the globe. The map of life shows three powerful patterns: the latitudinal gradient (more species near the equator), the altitudinal gradient (fewer species as you climb a mountain), and the area effect (larger regions hold more species). All three reflect the same underlying drivers — energy, water and time.

The same logic that makes the tropics species-rich also explains why the diversity of the deep ocean abyssal plains, the arctic tundra and the high alpine deserts is so thin. Where energy and water are scarce, only a few specialists survive, and they survive in tiny populations. Therefore biodiversity is not just biological — it is profoundly geographical.

14.6 Where India Stands

India occupies a special place on the world map of biodiversity. With only about 2.4 per cent of the world's land area, the country supports nearly 8 per cent of the recorded species — making it one of the seventeen mega-diverse nations of the world. Indian biodiversity ranges from the snow-capped Himalayas with their alpine meadows and the rare snow leopard, through the deserts of Rajasthan with the great Indian bustard, the deciduous forests of central India with their tigers and elephants, the evergreen rainforests of the Western Ghats with their lion-tailed macaques and Nilgiri tahr, the mangroves of the Sundarbans with the famous Royal Bengal tiger, the coral reefs of Lakshadweep and the Andaman and Nicobar islands, and the dolphins of the Ganga and Brahmaputra. Four of the world's biodiversity hotspots overlap with Indian territory — we will name them in the next part.

14.7 The Road Ahead

This first half of the chapter has set the stage. We have seen what biodiversity is, why it is unevenly distributed, what its three levels are, and why each of them matters ecologically, economically, scientifically and ethically. We have also seen that humans — having emerged within this living system — now hold extraordinary power over its future. In the second half of the chapter, we turn to the darker and more urgent half of the story: how biodiversity is being lost, where the world's hotspots lie, and what India and the world are doing — through national parks, biosphere reserves, gene banks and international treaties — to conserve the variety of life on which all of us depend.