Species-Area Relationship
1. Alexander Von Humboldt has observed that within a region, species richness increases with increased explored area, but only upto a limit.
2. The relationship between species richness and area for a number of taxa like angiospermic plants, freshwater fishes and birds is found to be a rectangular hyperbola.
3. On a log scale, the relationship becomes linear (straight line) and is described by the equation:
log S = log C + Z log A, where
S = Species Richness
Z = Slope of the line (regression coefficient)
A = Area and C = Y - intercept
4. Ecologists have found that the value of Z-line ranges between 0.1 and 0.2 irrespective of the taxonomic group of the region.
5. But in very large areas, like a continent, the Z value ranges between 0.6 and 1.2 and indicate species richness.

Ecologist Paul Ehrlich gave 'rivet popper hypothesis' to understand the contribution of the species richness. He compared each species with rivet in the body of an airplane.
(i) This hypothesis explain that ecosystem to be an airplane and the species to be the rivets joining all parts together.
(ii) If every passenger traveling in the airplane start taking rivets home(causing a species to become extinct), initially it may not affect flight safety (proper functioning of ecosystem), but over a period of time the plane become weak and dangerous (Species become endangered and then extinct).

Effects of habitat fragmentation on Biodiversity:
1.Fragmentation creates barriers that limit the potential of species to disperse and colonise new areas.
2. Species get divided into smaller populations which are unable to sustain.
3.Migratory birds lose their seasonal habitats.
4.It Increases edge areas thus making the species more vulnerable to predators as well as wind and fire.
Thus there is loss of biodiversity because a large number of animals, e.g. elephant, lions, bears, and large cats require big territories to move around and live in. Likewise some birds reproduce successfully only in deep forests. 

Types of extinction processes:
Natural extinction: With the change in environmental conditions, some species disappear and others, which are more adapted to changed conditions, take their place. Tihs loss of species which occurred in the geological past at a very slow rate is called natural or background extinction.
Mass extinction.  There have been several periods in the earth's geological history when large number of species became extinct because of catastrophes. Mass extinctions occurred in million of years.
Anthropogenic extinction. An increasing number of species is disappearing from the face of the earth due to human activities. this man-made mass extinction represents a very serve depletion of biodiversity, particularly because it is occurring within a short period of time.

Uses of biodiversity.
1. As source of food and improved varieties.
2. As source of drugs and medicines.
3. Aesthetic and cultural benefits.
Examples of aesthetic rewards include ecotourism, bird watching, wildlife, pet keeping, gardening, etc. Throughout human history, people have related biodiversity to the very existence of human race through cultural and religious beliefs.
4. Biodiversity is essential for the maintenance and sustainable utilization of goods and services from ecological system as well as from individual species.

Functions of biosphere reserves.
1. Conservation. To ensure the conservation of landscape, ecosystems, species and genetic resources. It also encourages traditional resource use.
2. Development. to promote economic development which is culturally, socially and ecologically sustainable.
3. Scientific research, monitoring, and education. The aim is to provide support for research, monitoring, education, and information exchange related to local, national and global issues of conservation and development.

(i) DDT is a non-biodegradable insecticide which, through agricultural run off, reaches water bodies and enters the food chains. During this process, the concentrations of DDT goes on increasing at each trophic level.The fishes are finally consumed by man, raising DDT concentration in the human beings.
(ii) The phenomenon of increase in the concentration of harmful non-biodegradable substances at successive trophic levels is known as biomagnification.
(iii) Arun's teacher explained to Arun the reasons of biomagnification of non-biodegradable substances and their harmful effects in humans.

Earth's rich biodiversity is vital for the very survival of mankind. The reasons for conserving biodiversity are narrowly utilitarian, broadly utilitarian and ethical. Besides the direct benefits (food, fibre, firewood, pharamaceuticals, etc.), there are many indirect benefits we receives through ecosystem services such as pollination, pest control, climate moderation and flood control. Each and every living being has some intrinsic value. We derive countless economic benefits from the living things. Living things play a major role in many ecosystems. All the species in the ecosystem are interlinked. When a species becomes extinct, the plant and animal species associated with it in an obligatory way also becomes extinct. When a host fish species becomes extinct, its unique assemblage of parasites also meets the same fate. Another example is the case of coevolved plant-pollinator mutualism where extinction of one leads to extinction of the other.

(i) Construction of such a highway will result in the fragmentation of the habitat and this will disrupt its continuity. The organisms will be confined to smaller area. The fragmentation reduces the amount of functional habitat, the species richness, taxon diversity and may also reduce the ecosystem functioning. Fragmentation also disrupts complex interactions amongst species. It results in annihilation of species and risk of their local extinction and thereby decreased biodiversity.
(ii) The forests are useful to mankind in many ways. They provide us oxygen and help in bringing rain. They are the source of constructional material, industrial products and products of medicinal importance and also firewood. They act as the habitat of a wide variety of flora and fauna, and keep the environment healthy.
(iii) Values exhibited by Kalpna-awareness, love for nature, environmental censciousness, vision to foresee the disaster in the future.