Environmental Studies

Module 4. Biodiversity and its conservation

Lesson 12
INTRODUCTION TO BIODIVERSITY

12.1 The Concept of Biodiversity

The term biodiversity is a relatively new term. It is a contraction of ‘biological diversity’. Simply stated, biodiversity is the variety of life on earth and its myriad of processes. It includes all life forms – from the unicellular fungi, protozoa and bacteria to complex multicellular organisms such as plants, birds, fishes and mammals. According to the World Resources Institute – “Biodiversity is the variety of the world’s organisms, including their genetic diversity and the assemblage they form. It is the blanket term for natural biological wealth that under girds human life and well-being. The breadth of the concept reflects the inter-relatedness of genes, species and ecosystems. Because genes are the components of species, and species are the components of ecosystems. Therefore, altering the make-up of any level of this hierarchy can change the others – species are central to the concept of biodiversity’.

Since biodiversity covers a wide range of concepts and can be examined at different levels; therefore, it has now become customary to study the concept of biodiversity at three hierarchical levels.

12.1.1 Genetic diversity

Within any given species, there can be several varieties, strains or races which slightly differ from each other in one or more characteristics such as size, shape, resistance against diseases, pests, insects, etc., and resilience to survive under adverse environmental conditions. Such diversity in the genetic make-up of a species is termed as the ‘genetic diversity’. In other words ‘genetic diversity’, is the variety of building blocks found within individuals of a species. The species having large number of varieties, strains or races are considered as rich and more diverse in its genetic organization. The differences between individual organisms arise from variation in the genetic material possessed by all organisms and passed on to successive generations (heritable variation), and from environmental influence on the growth and development of each individual organism. Heritable variation serves as the raw material for both, evolution by natural selection and by artificial selection, and is ultimately the basis for all biodiversity.

Opportunities for evolutionary change, the survival of species and the formation of new species are in part a function of the amount of genetic diversity in populations. The various applications of biotechnology, such as crop or animal breed improvement, depend on the identification of genetic material that give rise to desirable traits and the incorporation of this genetic material in appropriate organisms.

12.1.2 Species diversity

In practice, most attention is generally given to ‘species diversity’. It refers to the number of different kinds of organisms found at a particular place, and how it varies from place to place and even seasonally at the same place. In terms of species diversity, it must be noted that merely counting the number of species is not enough to describe biological diversity. Diversity has to do with the relative chance of seeing species as much as it has to do with the actual number present. A community in which each species has the same number of individuals as all others would be the most diverse; whereas, a community with one species making up most of the individuals would be least diverse. Further, species that are very different from each other contribute more to overall diversity than species which are similar to each other.

12.1.3 Ecosystems diversity

Ecosystem diversity is generally assessed in terms of the global or continental distribution of broadly-defined ecosystem types, or in terms of the species diversity within ecosystems. It is the distinctive assemblage of species that live together in the same area and interact with their physical environment in unique ways. A system having the component species present in nearly equal abundance is considered as more diverse than one having extremes of high and low abundance.

12.1.4 Landscape diversity

Sometimes, the phrase ‘landscape diversity’ is used on a broad regional scale. It refers to size and distribution of several ecosystems and their interaction across a given land surface.

12.2 The Bio Geographic Zones of India

India is recognized to be uniquely rich in biodiversity. Here, almost all the bio geographic zones of the world are represented. According to a recent classification done by the Wild-life Institute of India, the country’s biological wealth can be seen as representing about ten broad bio geographical zones (Fig. 12.2). Each of these ten bio geographic zones has characteristic biota, and broadly represents similar climatic conditions and constitutes the habitat for diverse species of fauna and flora.

12.2.1 Trans-Himalayan zone

The Trans-Himalayan zone, spreads over an area of about 1,86,000 sq.km. With its sparse mountain vegetation type it has the richest wild sheep and goat community in the world. The snow leopard is found here, as is the migratory black-necked crane.

12.2.2 Himalayan zone

The Himalayan zone extends from north-west region of Kashmir to the east upto NEFA (North East Frontier Area). It encompasses an area of about 3,47,000 sq.km and comprises of four biotic provinces--north-west, west, central and east Himalayas. Altitudinally there are three zones of vegetation in the Himalayan zone corresponding to three climatic belts. First, the sub-montane or lower region (tropical and subtropical), that extends from plain foot of the hill upto 5,000 to 6,000 ft. altitude, has vegetation dominated by trees of Acacia catechu, Cedrala toona, Eugenia jambolana, Albizzia procera, etc. Second, the temperate or montane zone (ranges between 5,500 to 12,000 ft. altitude) has vegetation dominated by Pinus excelsa, Cedrus deodara, Cedrela, Eugenia, etc. in the lower region, and confers such as Abies pindrow, Picea morinda, Juniperus, Taxus baccata, etc. in the upper regions. Third, the alpine zone (above 12,000 ft.) is the limit of tree growth (known as ‘timber or tree line’), where the shrubby growth of Betula utilis, Juniperus and Rhododendron is found in grassy areas. At about 15,000 ft. and above snow-line, plant growth is almost nil.

12.2.3 Desert zone

The desert zone comprises of three biotic provinces, viz. Kutch, Thar and Ladakh. The north-west Desert region (Kutch and Thar) spreads over an area of about 2,25,000 sq.km. and consists of parts of Gujarat, Rajasthan, Haryana and Delhi. The climate of this region is characterized by very hot and dry summer, and cold winter. Rainfall here is less than 700 mm. The north-west desert region has extensive grasslands. The plants are mostly Xerophytic, such as Acacia nelotica, Prosopis spicifera, etc.; and the ground vegetation is dominated by the species Calotropis, Eleusine, Panicum antidotale, etc. The Great Indian Bustard, a highly endangered species, is found in this north-west desert region. The Ladakh region, on the other hand, has sparse vegetation – it is a cold desert region.

12.2.4 Semi-Arid zone

Adjoining the north-west desert are the Semi-Arid areas comprising of Madhya Pradesh, Chattisgarh, parts of Orissa and Gujarat. It spreads over an area of about 5 lac sq.km. Depending upon the amount of rainfall, the forests in this region have developed into thorny, mixed decidiuous and sat type. The forest vegetation is mostly constituted by Tectona grandis, Diospyros melanoxylon and Butea monosperma. The thorny vegetation is dominated by Acacia leucophloea, Accacia catechu, etc.

12.2.5 Western ghats zone

The Western Ghats zone comprises the Malabar coast and Western Ghat mountains of India extending from Gujarat in the north to the Cape Camorin in the south. This zone encompasses an area of about 1.6 lac sq.km. Rainfall in this region is heavy. The vegetation is of four types – tropical moist evergreen forests, sub-tropical or temperate evergreen forests, mixed deciduous forests and the mangrove forests.

12.2.6 Deccan peninsular zone

The Deccan Penninsula zone comprises of five biotic provinces, viz. Deccan Plateau (South), Central Plateau, Eastern Plateau, Chhota Nagpur Plateau and Central Highlands. The zone spreads over an area of about 14 lac sq. km. It is a semi-arid region lying in the rain-shadow of the Western Ghats. Rainfall is about 100 mm. The zone has a centrally hilly plateau with forests of Boswellia serrata, Hardwickia Pinnata and Tectona grandis.

12.2.7 The gangetic plain

In the North, is the Gangetic Plain extending up to Himalayan foothills. This region comprising of Uttar Pradesh, Bihar and West Bengal is the most fertile region and encompasses an area of about 3.5 lac sq.km. The major climatic factors, the temperature and rainfall together are responsible for the distinctive type of vegetation in this zone. The rainfall varies from less than 700 mm in Western Uttar Pradesh to more than 1,500 mm in West Bengal. Vegetation is chiefly of tropical moist and dry deciduous forest type.

12.2.8 The north-east India

The North-East India is one of the richest flora regions in the country covering an area of about 1.6 lac sq.km. The region receives the heaviest rainfall, with Cherrapunji as much as more than 10,000 mm. The temperature and wetness are also very high, resulting in dense tropical evergreen forests. The important trees are Mesua ferrea, Michelia champaca, Dipterocarpus macrocarpus etc., and many Bamboo species. Many grass species and insectivorous plants like are also present. Beside this, the region has several wild relatives of cultivated plants such as banana, mango, citrus and pepper.

12.2.9 The Islands

The Islands of Lakshadweep in the Arabian Sea, and Andaman and Nicobar Islands in the Bay of Bengal have a wide range of coastal vegetation like mangroves, beech forests and in the interior some of the best preserved evergreen forests of tall trees. Rhizophora, Calophyllum and Dipterocarpus are some of the important species of Islands’ vegetation.

12.2.10 Coast

India has a coastline of about 7,516.5 km. Mangroves vegetation is the characteristic of estuarine tracks along the coast, for instance, at Pichavaram near Chennai and Ratna Giri in Maharashtra.