Biodiversity:

The 1992 United Nations Earth Summit in Rio de Janeiro defined “biodiversity” as “the variability among living organisms from all sources, including, ‘inter alia’, terrestrial, marine, and other aquatic ecosystems, and the ecological complexes of which they are part: this includes diversity within species, between species and of ecosystems”. The term biodiversity refers to the totality of genes, species, and ecosystems of a region. We know that all the species cannot occur at one place. A species can occur on a site is determined by the environmental conditions of the site and the range of tolerance of the species. Therefore, we find different types of plants and animals at different sites. Taking into consideration the total habitats of plants and animals, one can arrive at the inference that the living world abounds with enormous biodiversity. Biodiversity found on Earth today is the result of 4 billion years of evolution. The origin of life is not well known to science, though limited evidence suggests that life may already have been well-established only a few 100 million years after the formation of the Earth. Until approximately 600 million years ago, all life consisted of bacteria and similar single-celled organisms.

Diversity is a characteristic of life everywhere on Earth, from the ocean floor to inside the human gut, from the global to the microscopic level. Biologically-rich and unique habitats are being destroyed, fragmented, and degraded due to problems caused by increasing human population, resource consumption and pollution. Biodiversity loss is now one of the world’s most pressing crises. The primary reason for the concern is the realisation that biological diversity is being lost even before its size is known. Loss of biodiversity would check the evolutionary capability of biota to cope up with environmental changes. How to check the loss of species and erosion of gene pool is one of the major challenges to science. In this chapter, we shall study about the amazing biological diversity on Earth, and the dependence of human population on biodiversity for food and other necessities.

Biodiversity: Plants in India Angiosperms 17500 Gymnosperms 64 Pteridophytes 1100 Bryophytes 2850 Lichens 2000 Fungi 14500 Algae 6500 Bacteria 850

Biodiversity: Animals in India

Mammalia 390

Anes 1232

2.1. Levels of biodiversity

Biological diversity includes three hierarchical levels: (i) Genetic diversity,

(ii) Species diversity, and

(iii) Community and ecosystem diversity.

These levels of biodiversity are interrelated, yet distinct enough to be studied separately to understand the interconnections that support life on earth.

2.2.Genetic Diversity

We know that each species, varying from bacteria to higher plants and animals, stores an immense amount of genetic information. For example, the number of genes is about 450-700 in Mycoplasma, 4000 in Escherichia coli, 13000 in

Drosophila melanogaster, 32000-50000 in Oryza sativa, and 35000 to 45000 in Homo sapiens sapiens.

Genetic diversity refers to the variation of genes within species; the differences could be in alleles (different variants of same genes), in entire genes (the traits determining particular characteristics) or in chromosomal structures. The genetic diversity enables a population to adapt to its environment and to respond to natural selection. If a species has more genetic diversity, it can adapt better to the changed environmental conditions. Lower diversity in a species leads to uniformity, as is the case with large monocultures of genetically similar crop plants. This has advantage when increased crop production is a consideration, but can be a problem when an insect or a fungal disease attacks the field and poses a threat to the whole crop.

2.3. Species Diversity

Species are distinct units of diversity, each playing a specific role in an ecosystem. Therefore, loss of species has consequences for the ecosystem as a whole. Species diversity refers to the variety of species within a region.

Simplest measure of species diversity is species richness, i.e., the number of species per unit area. The number of species increases with the area of the site. Generally, greater the species richness, greater is the species diversity. However, number of individuals among the species may also vary, resulting into differences in evenness, or equitability, and consequently in diversity

2.4 Community and Ecosystem Diversity

Diversity at the level of community and ecosystem has three perspectives. Alpha diversity (within-community diversity) refers to the diversity of organisms sharing the

same community/habitat. A combination of species richness and equitability/evenness is used to represent diversity within a community or habitat. Species frequently change when habitat or community changes. The rate of replacement of species along a gradient of habitats or communities is called beta diversity (between - community diversity). There are differences in species

composition of communities along environmental gradients, e.g., altitudinal gradient, moisture gradient, etc. Higher the heterogeneity in the habitats in a region or greater

keystone species. Studies in temperate grasslands have shown that diverse communities are functionally more productive and stable, even under environmental stresses such as prolonged dry conditions.

Ecosystem diversity refers to the great variety of environments produced by the interplay of the living (animals and plants) and non-living world (earth forms, soil, rocks and water). Diversity of ecosystems is also important. There are ecosystems that occur in deserts, forests, wetlands, mountains, lakes, rivers, and agricultural landscapes. In each ecosystem, living creatures, including humans, form a community, interacting with one another and with the air, water, and soil around them. Diversity of ecosystems is also important. There are ecosystems that occur in deserts, forests, wetlands, mountains, lakes, rivers, and agricultural landscapes. In each ecosystem, living creatures, including humans, form a community, interacting with one another and with the air, water, and soil around them.

Source: http://mff.dsisd.net/Environment/Succession.htm

2.5 Important General Principles Associated with Ecological Succession

1. The physical environment determines which communities can exist in a particular place.

2. Succession is community controlled, i.e., succession is caused by modification of the surrounding physical environment by the existing community, i.e., a successional community will alter the environment so that the environment is

This tendency for the ecosystem to reach a stage where it stays in equilibrium is an example of Homeostasis – developing and maintaining stability.

5. High diversity produces stability.

Fig : Relationship of successional complexity to relative stability

Table Examples of factors which effect succession

2.6 Types of Ecological Succession

Ecological succession can be categorized variously like plant succession and animal succession, autotrophic succession and heterotrophic succession, aquatic, terrestrial or aerial succession etc based on the biological components and the places where the succession is happening. But basically succession is broadly categorized as primary and secondary succession.

1. Primary Succession begins on an area that has not been previously occupied by a community, e.g., newly exposed rock. There is no soil. Soil is a combination of broken down rock plus organic matter (humus* and small, living organisms). *Humus is accumulated, decomposed plant and animal material.

Primary succession takes place very slowly with a low rate of production of biological material.

2. Secondary Succession begins on an area where a community has previously

Bio-physical Factors Climate Water sources Weather Topography Soil composition Wildlife Natural Disturbances Volcanic activity Insects Fire Wind storms Flood Soil erosion Human-Made Disturbances Plowing and grazing

Tree harvesting Road building Soil erosion Introduced species Prescribed fire

Knowledge of local succession is necessary to start any eco-restoration process. We can’t select appropriate species for planting and sowing unless we have good idea about present biotic Successional stage of the area. Based on the biological community, succession is of two types:

(i) Plant Succession and (ii) Animal Succession

2.6.1 Plant Succession

The sequential change in vegetation and the animals associated with it, either in response to an environmental change or induced by the intrinsic properties of the organisms themselves. Classically the term refers to the colonization of a new physical environment by a series of vegetation communities until a final equilibrium state, the stable climax is achieved. The presence of the colonizers, the pioneer plant species, modifies the environment so that new species can join or replace the initial colonizers. Changes are rapid at first but slow to more or less imperceptible rate at the climax stage.

While making revegetation plan, one should efficiently ascertain the currently prevailing successional stage (Seral stage) of the area under consideration. Selection of such species, which exactly or near exactly synchronize with current successional stage, prove better in artificial regeneration i.e. sowing and planting. Selection of species of those seral stages, which are far away, may not prove better. However, by providing appropriate soil and moisture conservation activities and other inputs, we can try species of higher seral stages also but this may hold good up to some extent only. If area is passing through primary seral stage, planting of preclimax and climax species may prove failure. Species of adjacent seral stages always prove better.

2.6.2 Animal Succession

Once habitat is developed, animals automatically appearing establish there. If suitable condition prevails continuingly, they breed and build up their population. If prey base is available, later predators will reach there. Thus food chain would start to take shape in the area. Now animals will start playing their role in pollination dispersal etc. Micro-fauna will also develop there, which are good indicators of a functional healthy ecosystem.