Measuring Species Diversity

1. Measuring Species Diversity

2. Think about what’s ahead . . . Starter exercise • Discuss in pairs the title of this section. • What do you think it is about? • Do you know anything about it already? • What might we be discussing during this section?

3. What is species diversity? • Species diversity comprises the number of different species in an ecosystem (the species richness) and the proportion of each species in the ecosystem (the relative abundance).

4. How do you measure it? • You can measure species diversity by measuring species richness or species evenness.

5. Species richness • The number of different species in an ecosystem.

6. Species evenness • Relative abundance – the proportion of each species in the ecosystem.

7. So what does that tell us? • A community where a dominant species is abundant has less species diversity than one with the same species richness but where the abundance of species is more evenly distributed.

8. Measuring species diversity • When carrying out a practical investigation into the species diversity of a local area, you can use a species diversity index.

9. Species diversity index (1) • Scientists have developed a variety of mathematical equations (or indices) that incorporate both species richness and evenness into a single measure of species diversity (eg the Shannon–Wiener index and Simpson’s index).

10. Species diversity index (2) • Different diversity indices assign different weightings to species richness and evenness, so the most useful index to choose depends on the circumstances.

11. Habitat fragmentation • Habitat fragmentation is the fragmentation in an organism’s habitat. • Work in pairs to discuss this concept – what is it? How does it happen? Could we reduce it?

12. Task Using your new knowledge create a diagram showing two communities. Highlight the one with the higher species diversity. (You don’t need to draw organisms, colour or shape can be used to distinguish between species.)