Biodiversity of Plant Pathogenic Fungi - Kerala Forest Research ...

index. Consequently, a number of indices that are independent of the number of samples
taken have been developed to estimate species richness. Those indices are based on the
relationship between S and n, the total number of individuals in the collection of samples.
The two well-known species-richness indices, the Margalef index (1988) and Menhinick
index (1964), make specific assumptions concerning the relationship between S and n (S
= k n 0.5 , where k is a constant). In the present study, both Margalef index and Menhinick
index of species richness were worked out for each forest ecosystem, which ranged from
2.5605 to 5.665242 and 4.089955- 21.085314 respectively (Table 4). Among the eight
forest ecosystems investigated, moist-deciduous forests and forest plantations exhibited
maximum species richness and dry deciduous forests showed the least species richness
value (Table 4).
Species diversity indices
Diversity is a measure of the complexity of structure in an ecological community. It
comprises two distinct attributes: species richness and species evenness. Simpson (1949)
proposed the first index of diversity used in ecology. The index varies from 0 to 1 and is
referred to as dominance measure because it is influenced strongly by the abundance of
the most common species. Originally Simpson’s index ( λ ) was restricted to ecological
units in which all members of the unit (in the present case community) could be
enumerated. As it is impossible to count all members, Simpson developed an unbiased
estimator (D) of diversity based on a sample of N individuals. In the current study,
Simpson’s index was worked out for each forest ecosystem which ranged from
0.0228204041 to 0.1118367347.
The Shannon index of diversity (H’) (Shannon and Weaver, 1949) is currently the most
popular index in community ecology. H’ is a measure of the average degree of
uncertainty in predicting the specific identity of an individual chosen at random from a
collection of S species and N individuals. Average uncertainty will increases as the
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