Co-extinction as extinction of one invariably leads to extinction of the other.

Alexander von Humbolt / Rectangular hyperbola which on log scale appears as linear straight line.

Equator has tropical environment and hence harbour more species e.g. Columbia near the equator has 1400 species of birds, while New York at 41⁰ N has 105 Species.

Categories of threatened species;
1. Critically endangered (plant. Berberis salvanius. animal. Sus nilghiriensis)
2. Endangered (plant. Bentinckia nicobarica, Animal. Red panda.)
3. vulnerable (plant. Cupressus cashmerianan Animal. Antilope cervicapra)

Classification of extinction process
1. Natural extinction. It is due to change in environmental condition. It is very slow rate.
2.Mass extinction. Mass extinction occurs due to catastrophes. In this case large number of species became extinct in millions of years.
3. Anthropogenic Extinction. Extinction of species due to man's activities. It is occurring in a short period of time. 

Sacred Groves are the tracts of forests where all the trees and wildlife within were venerated and given total protection.
(i) These are the last refuges for a large number of rare and threatened plants.

The two major causes other than anthropogenic causes of the loss of biodiversity are
(i) Alien species invasions When alien species are introduced unintentionally or deliberately in a habitat, some of them can cause decline or extinction of indigenous species.
(ii) Co-extinctions when a species becomes extinct, the plant and animal species associated with it, in an obligatory way, also become extinct.

The first Earth Summit was held in Rio de Janerio in 1992.
its objectives were:
(i) Conservation of biodiversity, and 
(ii) Sustainable utilisation of the benefits from biodiversity

A harmful organism, that is harmful for one/more populations/species, can be made extinct; the food chain should not be affected. For example, the virus causing small pox has been controlled world over.

Since plants cannot move away from their predators (herbivores) and harsh environmental conditions, many of them have become extinct. But animals can move away from the harmful/unfavourable environments or their predators and evolution of favourable characters has thus taken place in them.

When Nile perch a large predator fish was introduced in lake Victoria, it started feeding on native fish, cichlid fish. As a result, cichlid fish become extinct and Nile perch, not finding any food for itself, died too.

Biodiversity must be conserved as it plays an important role in many ecosystem services.
(i) Spiritually or philosophically, we have to realise that every species has an intrinsic value, though it may not be of any economic value to us currently.
(ii) Morally, we have a duty to care for the well-being of the species and pass on our biological legacy in good order to future generations.

Hot spots are the regions with very high levels of species richess and high degree of endemism and need maximum production.
e.g. Western Ghats and himalayas.