Statement I: Communities with greater species diversity tend to be more stable than those with less species diversity.
Statement II: Species-rich communities are more resilient to disturbances and invasions by alien species.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Both statements I and II are correct.
A community is called stable when its productivity does not vary much from year to year, when it is resistant or resilient to occasional disturbances, and when it resists invasion by alien species. For many decades ecologists have held that communities with more species tend to be more stable. David Tilman’s long-term experiments supported this: plots with more species showed less year-to-year variation in total biomass.
Statement I: Communities with greater species diversity tend to be more stable than those with less species diversity. — True. This is the long-held view of ecologists, supported by Tilman’s plots.
Statement II: Species-rich communities are more resilient to disturbances and invasions by alien species. — True. Resistance or resilience to disturbances and to invasion by alien species is part of what stability means. Species-rich communities, being more stable, show these features.
So both statements are correct.
NCERT Extract:
The Importance of Species Diversity to the Ecosystem – “… For many decades, ecologists believed that communities with more species, generally, tend to be more stable than those with less species. … 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. … Tilman found that plots with more species showed less year-to-year variation in total biomass.”