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

(N/A) Ecologists believe that communities with more species tend to be more stable than those with fewer species.
$A$ stable community shows the following characteristics: $(i)$ It does not show too much variation in year-to-year productivity. (ii) It must be resistant or resilient to occasional disturbances (man-made or natural). (iii) It must be resistant to invasion by alien species.
David Tilman,through his long-term ecosystem experiments using outdoor plots,provided concrete evidence of the link between species richness and a stable community. According to him,more species-diverse communities show almost constant productivity in total biomass and contribute to higher productivity.
Rivet Popper Hypothesis: Rich biodiversity is not only important for ecosystem health but is also essential for the survival of humans on Earth.
Since all species on Earth are interlinked through various types of relationships,the loss of even a few species can have a destabilizing effect.
Paul Ehrlich,a Stanford ecologist,explained the importance of diversity using the 'Rivet Popper Hypothesis'.
According to this hypothesis,an ecosystem is like an aeroplane,and 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) initially. However,as more and more rivets are removed,the plane becomes dangerously weak over time.
Moreover,which rivet is removed is also crucial; for example,the loss of a rivet on the wings (key species that drive major ecosystem functions) is a more serious threat than the loss of rivets on seats or windows inside the plane.