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Diversity indices BCB242 F M Weitz. Introduction  Measurement of species diversity   Species richness vs. species diversity   Can we know the exact.

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Presentation on theme: "Diversity indices BCB242 F M Weitz. Introduction  Measurement of species diversity   Species richness vs. species diversity   Can we know the exact."— Presentation transcript:

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.) Beta (ß) diversity – a measure of the rate and extent of change in species along a gradient, from one habitat to others Alpha (α) diversity – the diversity of species within a community or habitat` 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 S max 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 Species Richness - S A B 65 TOTAL 12LIGHT BLUE 23APPLE GREEN 79BLACK 24DARK BLUE 45LIGHT GREEN 36ORANGE 24YELLOW 314LILAC 4118RED BACOLOUR Same Number Species – 9 Same Number individuals - 65 Different Distribution of individuals amongst species (M. Gibbons)

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

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

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13 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 There are a number of ways of determining this: (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 Shannon Index (H’ ) H’ = - p i ln(p i ) ∑ p i = Proportion of the ith species H tends to increase with the number of species in the sample SpeciesNo Proportion, plog e pp x log e p Albra nitida11/89 = Hydrobia ulvae77/89 = Cyathura carinata22/89 = Tubificoides7777/89 = Hediste diversicolor22/89 = Total

16 SpeciesNo Proportion, plog e pp x log e p Albra nitida9 Hydrobia ulvae3 Cyathura carinata27 Tubificoides24 Hediste diversicolor54 Total - SpeciesNo Proportion, plog e pp x log e p Albra nitida26 Hydrobia ulvae13 Cyathura carinata18 Tubificoides10 Hediste diversicolor36 Total -

17 Berger-Parker dominance index For the sample data N max = 77; N T = 89; d = 77/89 = SpeciesNo Proportion, plog e pp x log e p Albra nitida11/89 = Hydrobia ulvae77/89 = Cyathura carinata22/89 = Tubificoides7777/89 = Hediste diversicolor22/89 = Total d = Nmax N T The ratio of the number of individuals in the sample belonging to the most abundant species

18 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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