Aquatic ecology and Biodiversity

Practical 8- Study of indices of organisms
Experiment No. 8
The number of species and their abundance by one or a few species in their environment is referred to as diversity. Diversity indicates the degree of complexity of community structure. It is a function of two elements-the number of species (richness) and the equitability (evenness) with which individuals are distributed among species. Diversity index is used for assessing the degree of environmental pollution. E.g.the diversity is generally lowest in polluted waters, and also it provides useful information on the succession of community structure.
Species diversity indices:
Species diversity is a measure of species richness. Shannon-Wiener’s index of general diversity (H) (Shannon & Wiener’s, 1949):

Where : Pi is the proportion of individual in the i^th species
Pi=ni/N ni is the number of individuals for each species
N is the total number of individual organisms
Also

3.321928

H1= ----------- (N log10N- Σ^S_i=1 ni log ni)

N

Note : H1 increases as both the number of species and the equitability of species abundance increase.
Diversity index as a measure of ‘Species richness’ (d) (Margalef, 1951):
d= (S-1)/log_cN
Where : S is the number of species
N is the number of total individuals.
Note : If all the individuals in a sample (population) belong to one species then ‘d’ becomes zero.
Diversity index as a measure of ‘Species Eveness’ (J1) (Pielou’w, 1966):

H1

J1=H1/log2S=J1= -----------

3.3219long ₁₀ S

Where H is the Shannon index,
S is the number of species
Index of dominance (c) (hulburt’s index):
C= Σ(n_i/N)²
Where :
ni is the number of individuals for each species, number of individuals
biomass, production and so forth.
N is the total number of individuals.
Index of similarity (s) (similarity index):
It is the measure of comparing experimental stations belonging to different biotopes for obtaining an integrated picture of the biotopes. It is calculated by the following equation.
S = (2c/a+b) x 100
Where c is the number of species common at any two stations
a is the number of species at one station
b is the number of species at the other station.