Which of the following is NOT responsible for increase in the biodiversity of an ecosystem?

The correct answer is D. The question asks which factor does not raise biodiversity, and the other three are standard drivers in ecology.

• A) Productivity: The productivity-diversity relationship is usually hump-shaped. Moderately productive systems with enough energy to support more species tend to be richer than very poor ones, so productivity is treated as a driver of diversity.
• B) Intermediate disturbance: Connell's Intermediate Disturbance Hypothesis (1978) says moderate, periodic disturbance prevents competitive exclusion by dominant species and keeps more species coexisting. Very low or very high disturbance reduces diversity.
• C) Age of the ecosystem: Older, stable ecosystems have had more evolutionary and colonisation time, which is the basis of the time hypothesis. This is why tropical rainforests are among the richest.
• D) Less number of nutrition levels: This is the odd one out. A greater number of trophic levels creates more feeding niches and a more complex food web, which supports more species. A simpler web with fewer levels offers fewer niches. So fewer levels does not increase diversity.

This links to the syllabus under ecology and biodiversity, and to Mains questions on conservation, where habitat complexity and disturbance regimes matter for policy.

Trap: Candidates often pick A or B because they sound like energy or disturbance arguments. Read the negative carefully and check which factor is actually linked to richer communities.