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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 number of species living in a habitat?. Samples are partial measures of the total number of species of habitat.

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slide1

Diversity indices

BCB242

F M Weitz

introduction
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
slide3

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?

slide4

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

slide5

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?
slide6

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.

slide7

Diversity indices:

(Selected)

Shannon function (H) – to characterise species in a community

Simpson-Yule index (D)

Berger-Parker dominance index

McIntosh diversity measure

slide8

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)

slide9

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)

slide10

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)

slide13

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)

slide14

Diversity indices:

(Selected)

Shannon function (H) – to characterise species in a community

Simpson-Yule index (D)

Berger-Parker dominance index

McIntosh diversity measure

slide15

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

slide17

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

slide18

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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