Read the passage carefully and give the answers to the next five questions: Does the number of species in a community really matter to the functioning of the ecosystem? This is a question for which ecologists have not been able to give a definitive answer. For many decades, ecologists believed that communities with more species, generally, tend to be more stable than those with less species. According to the International Union for Conservation of Nature and Natural Resources (IUCN) (2004), the total number of plant and animal species described so far is more than 1.5 million.

Which of the following is not a characterstic of a stable biological community?

All the species are equally important in a stable community and absence of any one leads to its unstability.

The correct answer is Option (3) – All the species are equally important in a stable community and absence of any one leads to its unstability.

A stable community should not show too much variation in productivity from year to year; it must be either resistant or resilient to occasional disturbances (natural or man-made), and it must also be resistant to invasions by alien species. We don’t know how these attributes are linked to species richness in a community, but David Tilman’s long-term ecosystem experiments using outdoor plots provide some tentative answers. Tilman found that plots with more species showed less year-to-year variation in total biomass. He also showed that in his experiments, increased diversity contributed to higher productivity. Although, we may not understand completely how species richness contributes to the well-being of an ecosystem, we know enough to realise that rich biodiversity is not only essential for ecosystem health but imperative for the very survival of the human race on this planet. 

While all species contribute to biodiversity and ecosystem functions, not all species are equally critical for ecosystem stability. Keystone species, ecosystem engineers, and foundation species play vital roles, and their absence can lead to instability. However, many ecosystems have redundancy built into their structure, allowing them to remain stable despite the loss of some species.