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Species diversity

• Species diversity: variation in types of organisms present in a community

• Components of species diversity– species richness: number of species present– heterogeneity or equitability of species: how

equally distributed in the community are the abundances of individual species

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Measurement of species diversity

• Species diversity indices: Table 5B.1, p. 178

• Species richness– number of species in the community– simplest estimate– count only resident species, not accidentals– gives all species same “importance”, regardless of

number of individuals present

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Measurement of species diversity

• Heterogeneity of species in the community– attempt to overcome problem of considering common

and rare species as having same “importance” in the community

– uses relative abundance

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Measurement of species diversity

• Heterogeneity of species in the community– e.g., two communities with two species and the same

total number of individuals could be comprised of two extremes:

Community 1 Community 2

Species A 99 50

Species B 1 50

– heterogeneity increases in a community when there are more species and when the species are equally abundant (heterogeneous)

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Measurement of species diversity

• Shannon-Wiener function– measurement of species diversity using

• species richness (number of species)• relative abundance (heterogeneity)

H’ = - (pi)[ln(pi)]where H’ = Shannon-wiener index of species

diversity

s = number of species in the community

pi = proportion of total abundance represented by the ith species

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Measurement of species diversity

Community 1 Community 2

N pi ln(pi) pi[ln(pi)] N pi ln(pi) pi[ln(pi)]

Species A 99 0.99 -0.010 -0.010 50 0.50 -0.693 -0.347

Species B 1 0.01 -4.605 -0.046 50 0.50 -0.693 -0.347

Total 100 -0.056 100 -0.694

H’ 0.056 0.694

Shannon-Weiner species diversity calculations for the two 2-species communities:

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Measurement of species diversity

• Shannon-Wiener index– values range from near zero to ???

• higher index values indicate higher species diversity• index has no units, has value only when comparing

communities

– increasing the number of species (s) increases H’– increasing the equitability (heterogeneity) of the

species in the community increases H’

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Measurement of species diversity

• Evenness– measurement of equitability among species in the

community

E = H’ / Hmax where E = Pielou’s index of evenness

H’ = calculated Shannon-wiener index

Hmax = ln(s) = species diversity under maximum equitability

conditions

s = number of species in the community

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Measurement of species diversity

• Evenness– values range from 0 to 1– for the two 2-species communities example:

Community 1 Community 2

s 2 2

H’ 0.056 0.694

Hmax 0.693 0.693

E 0.081 1.000

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Measurement of species diversity

• Simpson’s index– measurement of dominance and diversity

• uses number of species and relative abundance of species• if two individuals are sampled at random within a community,

the probability that the two will belong to the same species is

I = ni (ni-1) / N (N-1) where ni = number of individuals of the ith

species N = total number of individuals

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Measurement of species diversity

• Simpson’s index– the quantity I is a measure of dominance or the

concentration of N individuals among s species

Ds = 1 - I

Ds = 1 – [ni (ni-1) / N (N-1)]

where Ds = Simpson’s dominance index

ni = number of individuals of the ith species N = total number of individuals

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Measurement of community similarity

• Jaccard’s coefficient of community similarity

CCJ = c / (s1 + s2 + sn – c)

CCJ = c / Swhere CCJ = Jaccard’s coefficient of community

s1 = number of species in community 1

s2 = number of species in community 2

sn = number of species in communities n

c = number of species common in all communities

S = total number of species found in all communities

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Experiment 2

• Comparative species diversity – small nekton community associated with salt marshes

in the Galveston Bay system– objectives

• compare species diversity and species composition at one site (Hance Bayou) between two collection times: October 2010 and September 1999

– Shannon Weiner diversity– Pielou evenness,– Jaccard’s coefficient of similarity– Simpson’s dominance

• compare fish size (age class) among the three sites• compare differences in biotic indices among sites to

differences in physical and chemical environment

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Experiment 2

• Comparative species diversity – variables

• water quality– salinity– temperature– pH– total dissolved solids (TDS)

• physical environment– wind direction and speed– tide level– structures

• biological environment

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You are here!

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3Virginia Point

2 Hance Bayou

I-45

1 Christmas Bay

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Site 3: Virginia Point

Site 2: Hance Bayou

Site 1: Christmas Bay

N

West Galveston Bay

Gulf of Mexico

FM3005

Stewart Rd.

Sportsman's Rd.

8-mileRd.

I-45

To Houston

Galveston

61st St.

BIOL 4233 and 5533Field Trip for Expt 2

Comparative Species DiversityDate: Monday, 10/04/10

Meet at 8:00 am sharp at the Bright Light bait store just west of

the San Luis Pass bridge

San Luis Pass bridge$2 toll each way

Bright LightBait Store

SeawallBlvd.

Map is notto scale!

Flashing light

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