Biology · Biodiversity and Conservation · NEET
Two things. First, plots with more species showed less year-to-year variation in total biomass, meaning they were more stable. Second, increased diversity led to higher productivity (more biomass produced). NCERT calls these 'tentative answers' because ecologists still do not fully know how species richness links to ecosystem health.
Tilman did not use a lab. He grew plant communities in real outdoor field plots and watched them for many years (long-term). Some plots had few species, some had many. By comparing them over time, he could see how diversity affected stability and productivity. For NEET, remember the exact phrase 'outdoor plots' because it is used in matching questions.
A stable community does not show too much variation in productivity from year to year. It should be either resistant or resilient to occasional disturbances (natural or man-made), and it should be resistant to invasions by alien species. Tilman's finding of low biomass variation in species-rich plots supports this idea of stability.
No. Tilman gave real experimental data from outdoor plots showing diversity increases stability and productivity. The rivet popper hypothesis is an analogy given by Paul Ehrlich (airplane = ecosystem, rivets = species) to explain why losing species is dangerous. NEET often puts Tilman and Ehrlich in the same match-the-column question, so keep them separate.
It increased productivity. Tilman showed that in his experiments, increased diversity contributed to higher productivity. Students often flip this. Remember: more species means MORE productivity and LESS variation in biomass.
Match List I with List II. List I: A. Robert May, B. Alexander von Humboldt, C. Paul Ehrlich, D. David Tilman. List II: I. Species-Area relationship, II. Long term ecosystem experiment using outdoor plots, III. Global species diversity at about 7 million, IV. Rivet popper hypothesis. Choose the correct answer.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
David Tilman is an ecologist known for long-term ecosystem experiments using outdoor field plots that studied how species diversity affects ecosystem stability and productivity.
One, plots with more species had less year-to-year variation in total biomass (more stability). Two, increased diversity gave higher productivity.
Tilman gave real experimental evidence from outdoor plots. Ehrlich gave the rivet popper hypothesis, which is only an analogy (airplane and rivets). NEET tests both in match-the-column questions.
It supports the idea that rich biodiversity is essential for ecosystem health and stability, which is the base for why we must conserve biodiversity.
Class 12 Biology, Chapter 'Biodiversity and Conservation', under 'The importance of Species Diversity to the Ecosystem'.
