(4)

The major causes of biodiversity loss (accelerated rates of species extinctions) is largely due to 'The Evil Quartet' which includes over-exploitation, co-extinction, alien species invasion and habitat loss and fragmentation.

(4)

(1)

Tropical regions show greatest level of species richness because of the following reasons:
(I) Tropical latitudes have remained relatively undisturbed for millions of years and thus, had a long evolutionary time for species diversification.
(II) Tropical environments are less seasonal, relatively more constant and predictable. Such constant environments promote niche specialisation and lead to a greater species diversity.
(III) There is more solar energy available in the tropics, which contributes to higher productivity; this in turn might contribute indirectly to greater diversity.

(2)

(1)

The Rivet popper hypothesis was proposed by Stanford ecologist Paul Ehrlich as an analogy. He compared the rivets in an airplane to species within a genus. According to him, in an airplane (ecosystem), all parts are joined together using thousands of rivets (species). If every passenger travelling in it starts popping a rivet (causing a species to become extinct), it may not affect flight safety (proper functioning of the ecosystem) initially, but as more and more rivets are removed, the plane becomes dangerously weak over a period of time. Loss of rivets on the wings (species that drive major ecosystem functions) is obviously a more serious threat to flight safety than loss of a few rivets on the seats or windows inside the plane.

(4)

Keystone species are those species which has significant and disproportionately large influence on the community structure and characteristics. It has often considerably low abundance and biomass as compared to dominant species. Removal of such species causes serious disruption in structure and function of community.

(1)

There are four major causes of biodiversity losses which are collectively called as the evil quartet. These are habitat loss and fragmentation, over-exploitation, alien species invasion and co-extinctions. However, other factors are also intensifying extinctions like disturbance and degradation, pollution, intensive agriculture and forestry.

(3)

Habitat loss and fragmentation is the most important cause driving animals and plants to extinction. The most dramatic examples of habitat loss come from Amazon tropical rain forest.

(3)

There are four major causes (The Evil Quartet) of biodiversity losses: habitat loss and fragmentation, over exploitation, alien species invasion and co-extinctions.

(4)