What is the importance of species diversity to the ecosystem and various hypothesis related to it?

Ecologists believed that communities with more species tend to be more stable than those with less species.

A stable community show following characteristics : (i) It does not show too much of variations in the year to year productivity. (ii) It must be either resistant to resilient to occassional disturbances [manmade or natural]. (iii) It must be resistant to invasion by alien species.

David Tilman through his long-term ecosystem experiments using outdoor plots provided some concrete evidences of link between species richness and stable community. According to him more species diverse communities show almost constant productivity in total biomass and also contributes to higher productivity.

Rivet Popper Hypothesis : Rich biodiversity is not only important for ecosystem health but is also essential for survival of humans on the earth.

Since all species on earth are interlinked through various types of relationships and a loss of few species can have a destabilising effect.

Paul Ehrlich (a Stanford ecologist) explain the importance of diversity by an analogy of 'rivet popper hypothesis'.

According to this hypothesis, ecosystem is like an aeroplane, all its parts are joined together using thousands of rivets (species).

If every passenger, travelling in it, starts popping a rivet to take home (causing a species to become extinct), it may not affect flight safety (proper functioning of the ecosystem), but as more and more rivets are removed the plane becomes dangerously weak over a period of time.

Moreover, which rivet is removed is also crucial eg. loss of rivet on the wings (key species that drive major ecosystem functions) is a more serious threat than loss of rivets on seats or windows inside the plane.