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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 2Species A 99 50Species 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

diversitys = number of species in the communitypi = 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 indexHmax = 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 2s 2 2H’ 0.056 0.694Hmax 0.693 0.693E 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 indexni = 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 1s2 = number of species in community 2sn = number of species in communities nc = number of species common in all

communitiesS = 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-mile

Rd.

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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