Species diversity: rarefaction, evenness and indices

1. Species diversity:rarefaction, evenness and indices

2. Problem 1: Accounting for sample size Are these two communities equally diverse?

3. Problem 2: Accounting for abundance Are these two communities equally diverse?

4. Resampling techniques • Can be used to estimate a statistic or parameter for a different sample size • Can be used to estimate a statistic or parameter under the null hypothesis of no treatment effect

5. Smartie diversity! • Suppose we found 5 colours represented in a sample of 10 smarties. Is this the same diversity (species richness) as in your sample?

6. .477

7. 1 P= = 0.001 999 .477

8. Problem 2: Accounting for abundance Are these two communities equally diverse?

9. 3 Ways to include abundance in species diversity • Plot the distribution of individuals amongst species. • Summarize both abundance and species richness in a single index. • Examine the evenness of the distribution of individuals amongst species

10. Log-series distribution “Most species are rare” Most species are represented by only a couple of individuals (i.e. rare). Only a few highly-abundant (i.e. common) species. Number of species Log abundance class per species

11. Log-normal Most species are do NOT have abundances of only a few individuals, but rather have intermediate abundances (on a log scale! Still low) Number of species Log normal Log abundance class per species

12. 2003 class mite data Essentially number of species Log2 abundance class PRIMER “Geometric class plot”

13. 2. Summarize everything in one index Some indices output by PRIMER (formulas in Krebs and Magurran) • Simpson’s (1-lambda, or 1-D in Krebs) • Shannon-Wiener • Alpha (a parameter from log series) • Margalef d

14. Shannon-Wiener = sum(-Proportion spA * ln (prop spA)+ (-Proportion spB*ln(prop spB)...)

15. Which index? Read Krebs and Magurran and consider: - Sensitivity to differences in sample size. - Do you want differences in rare or abundant species to be emphasized? - Do you want differences in species richness or evenness to be emphasized? - How does log-normal vs. log-series affect? - Performance in other studies (what works?).

16. 3. Measure evenness separately Pielou’s J: Comparison of actual Shannon-Wiener with Shannon-Wiener if species had equal proportion (log S). Question: Why would Shannon-Wiener = logS if species equally abundant?

17. 3. Measure evenness separately • Pielou’s J: • J = Shannon-Wiener / logS • Close to 1: very even distribution of abundances amongst species • Close to 0: very uneven