An Attempt to Assess Alpha Diversity and Sample Size: Using the Ostracod Assemblages off Kumamoto Port, Japan

Authors: Seishiro Higashi* and Gengo Tanaka

DOI: 10.23880/ijoac-16000350

Volume 9, Issue 2

Abstract

Micropalaeontologists often encounter select the appropriate number of individuals per sample based on the study objectives and consider the trade-offs between analysing more samples with fewer individuals and analysing a larger sample size with fewer samples. The relationship between a number of individuals and Shannon’s index using rarefaction is useful for finding this compromise. However, previous methods of calculating the Shannon index using rarefaction have not discussed how to determine the number of individuals required for sampling. Here, we present a new empirical relationship between the specimen number and alpha diversity using the extant ostracod assemblage of Kumamoto Port, Kyushu, Japan. If we define a gradient of 0.002 or less as the rarefaction curve being sufficiently flat, then when Shannon’s index calculated from the number of individuals extracted is plotted in the area below the line with a gradient of 0.002, we can consider that a sufficient number of individuals have been picked up. In the case of Kumamoto Port, the maximum number of individuals required was calculated to be 229, a result consistent with the number of individuals required to extract microfossils, which has been statistically estimated so far. However, since the explanatory coefficient between the number of individuals and Shannon’s index is extremely high, even when a gradient of 0.005, it can be said that 116 individuals are sufficient for Kumamoto Port. This study presented a new method for determining the number of individuals required to estimate species diversity from rarefaction curves.

Keywords: Inner Bay; Number of Individuals; Ostracoda; Rarefaction; Species Diversity

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