Species diversity Species diversity variation in types of

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 1

Measurement of species diversity • Species diversity indices: Table 5 B. 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 2

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 3

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: Species A Species B Community 1 99 1 Community 2 50 50 – heterogeneity increases in a community when there are more species and when the species are equally abundant (heterogeneous) 4

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 5

Measurement of species diversity Shannon-Weiner species diversity calculations for the two 2 -species communities: Community 1 Community 2 N pi ln(pi) pi[ln(pi)] Species A 99 0. 99 -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 -0. 056 100 Total H’ 100 0. 056 -0. 694 6

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’ 7

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 8

Measurement of species diversity • Evenness – values range from 0 to 1 – for the two 2 -species communities example: s H’ Hmax E Community 1 2 0. 056 0. 693 0. 081 Community 2 2 0. 694 0. 693 1. 000 9

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 10

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 11

Measurement of community similarity • Jaccard’s coefficient of community similarity CCJ = c / (s 1 + s 2 + sn – c) CCJ = c / S where CCJ = Jaccard’s coefficient of community s 1 = number of species in community 1 s 2 = 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 12

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 13

Experiment 2 • Comparative species diversity – variables • water quality – – salinity temperature p. H total dissolved solids (TDS) • physical environment – wind direction and speed – tide level – structures • biological environment 14

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I-45 Virginia Point 3 2 1 Hance Bayou Christmas Bay 16

BIOL 4233 and 5533 Field Trip for Expt 2 Comparative Species Diversity Date: Monday, 10/04/10 Meet at 8: 00 am sharp at the Bright Light bait store just west of the San Luis Pass bridge N Site 3: Virginia Point I-45 To Houston Map is not to scale! West Galveston Bay Galveston Site 2: Hance Bayou Bright Light Bait Store Sportsman's Rd. 61 st St. 8 -mile Stewart Rd. Seawall Blvd. Site 1: Christmas Bay FM 3005 Flashing light Gulf of Mexico San Luis Pass bridge $2 toll each way 17

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