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Diversity indices

Diversity indices. BCB242. F M Weitz. Introduction. Measurement of species diversity. Species richness vs. species diversity. Can we know the exact number of species living in a habitat?. Samples are partial measures of the total number of species of habitat.

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Diversity indices

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  1. Diversity indices BCB242 F M Weitz

  2. Introduction • Measurement of species diversity • Species richness vs. species diversity • Can we know the exact number of species living in a habitat? • Samples are partial measures of the total number of species of habitat • Comparative measures for different localities: Selected groups of plants or animals, e.g.. woody higher plants, spiders or butterflies

  3. Groups for study may be selected for different reasons TYPES OF DIVERSITY How and why does species vary across the Cape Floristic region? What controls the different diversity components, and how do these interact to explain how species are packed into a landscape?

  4. TYPES OF DIVERSITY (cont.) Alpha (α) diversity – the diversity of species within a community or habitat` Beta (ß) diversity – a measure of the rate and extent of change in species along a gradient, from one habitat to others Gamma (γ) diversity – the richness in species of a range of habitats in a geographic area (e.g. island); it is a consequence of the α diversity of the habitats together with the extent of the ß diversity between them

  5. Estimating Species richness Why do we need species inventories/ lists for a particular habitat? Is a complete census feasible for a community? Two questions need to addressed? • Sufficient sampling • How can we estimate the total species number Smax for a community?

  6. Alpha (α) diversity indices Both species richness and evenness of a dataset may be summarized with a single number – diversity index Indices may tend to biased in favour of species number or equitability and thus may simply reflect a change in one of these quantities.

  7. Diversity indices: (Selected) Shannon function (H) – to characterise species in a community Simpson-Yule index (D) Berger-Parker dominance index McIntosh diversity measure

  8. B A COLOUR A B RED 18 41 LILAC 14 3 YELLOW 4 2 ORANGE 6 3 LIGHT GREEN 5 4 DARK BLUE 4 2 BLACK 9 7 APPLE GREEN 3 2 LIGHT BLUE 2 1 TOTAL 65 65 Species Richness - S Same Number Species – 9 Same Number individuals - 65 Different Distribution of individuals amongst species (M. Gibbons)

  9. Species Density Botanists Number of Species Observed Total Number of Individuals Counted Determining Species Richness Numerical Species Richness Sample-based Samples taken: all individuals within identified & counted Individual-based Individuals sampled sequentially (M. Gibbons)

  10. Species-Area or Accumulation Curves Asymptote considered to represent the number of species occurring in the community Issues of Sample Area or Number (M. Gibbons)

  11. (M. Gibbons)

  12. (M. Gibbons)

  13. There are a number of ways of determining this: Randomised 999 times Rarefaction Curves The absolute number of species likely to be found in the pool is obtained when the curve flattens out DEPENDS ON THE QUESTION BEING ASKED (M. Gibbons)

  14. Diversity indices: (Selected) Shannon function (H) – to characterise species in a community Simpson-Yule index (D) Berger-Parker dominance index McIntosh diversity measure

  15. ∑ H’ = - pi ln(pi) Shannon Index (H’ ) pi = Proportion of the ith species H tends to increase with the number of species in the sample

  16. Berger-Parker dominance index d = Nmax NT The ratio of the number of individuals in the sample belonging to the most abundant species For the sample data Nmax = 77; NT = 89; d = 77/89 = 0.865

  17. Species Abundance Curves Students to prepare a short essay on the different types of species abundance curves and their use in Ecology Examinable but not assessed!

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