Which species has a greater impact on the stability of a community?

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

Which of the following statements are true?
$I$. Species diversity provides stability to the ecosystem.
$II$. Communities with more species tend to be more stable than those with fewer species.
$III$. Ecosystems with higher biodiversity are more productive than ecosystems with lower biodiversity.
$IV$. Biodiversity is not essential for the maintenance and health of the ecosystem.
Choose the correct option.

According to the Rivet Popper Hypothesis,rivets represent $........$.

What characteristics make a community stable?

Who helps in maintaining species diversity in a biological community?