2 q

which corresponds to eq. 6.35a. This index may be computed from numbers of individuals, or from measures of biomass or energy transfer. The higher is the probability that two organisms be conspecific, the smaller is the diversity of the sampling unit. For this reason, Greenberg (1956) proposed to measure species diversity as:

Diversity = 1 - concentration (6.41)

which is also the probability of interspecific encounter (Hurlbert, 1971). Pielou (1969) has shown that this index is an unbiased estimator of the diversity of the population from which the sample has been drawn. However, eq. 6.41 is more sensitive than H to changes in abundance of the few very abundant species, so that Hill (1973a) recommended to use instead:

Diversity = concentration 1 (6.42)

which is identical to eq. 6.35b. Hill (1973a) also showed that this index is linearly related to exp H (eq. 6.34b). Examples to the same effect are also given by Daget (1980).

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