Statement I: Increased diversity in ecosystems leads to significant variations in productivity from year to year.
Statement II: David Tilman discovered that species diversity contributes to higher productivity in ecosystems.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Only statement II is correct.
A stable community should not show much variation in productivity from year to year. David Tilman studied this in long-term experiments on outdoor plots.
Statement I: Increased diversity in ecosystems leads to significant variations in productivity from year to year. — False. Tilman found the opposite. Plots with more species showed less year-to-year variation in total biomass. Greater diversity makes the community more stable, not more variable.
Statement II: David Tilman discovered that species diversity contributes to higher productivity in ecosystems. — True. In his experiments, increased diversity gave higher productivity.
NCERT Extract:
The Importance of Species Diversity to the Ecosystem – “… 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.”