# Explain why a habitat with a high species richness does not necessarily have a high biodiversity index.

> OCR A-Level Biology A (H420) — 4.2 Biodiversity · Explain · 4 marks

> Ecologists studying two woodland sites recorded the same number of species at each site. However, when they calculated the Simpson's Diversity Index for each site, the values were markedly different.

## Mark scheme (4 marks)

1. Species richness only measures the number of different species present, not their relative abundance
2. A diversity index also takes into account the abundance / proportion of individuals belonging to each species
3. If one species dominates (high proportion of individuals), the diversity index will be low even if many species are present
4. A high diversity index requires both high species richness AND an even distribution of individuals among those species

## Key terms

- [species richness](https://www.gradenine.co.uk/glossary/species-richness)
- [biodiversity index](https://www.gradenine.co.uk/glossary/biodiversity-index)

## Related

- [Revision notes for OCR A-Level Biology A (H420)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-a-habitat-with-a-401f515d) · Published by Druglandscape Ltd.