Q.How is biodiversity important for ecosystem functioning?

Does having more species in a community actually make the ecosystem work better — or is that just an intuition ecologists have never properly tested? The chapter's answer rests on two very different kinds of evidence: a real experiment, and a famous thought experiment.

The real evidence comes from the ecologist David Tilman's long-term outdoor-plot experiments. He found that plots planted with more species showed less year-to-year variation in total biomass — they were more stable — and that increased diversity also contributed to higher productivity. This is genuine, measured data, not a metaphor: more diverse plant communities really did behave more predictably and produce more, season after season.

What does 'stable' even mean for a community? The chapter is precise about it — a stable community (1) shouldn't show too much variation in productivity from year to year, (2) must be either resistant (largely unaffected by a disturbance) or resilient (bounces back quickly after one), and (3) must resist being taken over by invading alien species. None of this requires the community to be unchanging — it means it keeps functioning through the normal shocks nature throws at it. …