On the Mathematical Significance of the Similarity Index of Ochiai as a Measure for Biogeographical Habitats

Abstract

A recent survey of similarity indices by Hubalek has shown that the index due to Ochiai is one of the few satisfying rather stringent conditions. It is shown that the Ochiai index has a geometrical interpretation that can be exploited to yield a critical value for separability of two habitats on the basis of their avifauna. This critical value is used to analyse data on bird habitats and is compared with the results of a null hypothesis test on the data. In addition, use is made of the indices of Jaccard and Sokal & Michener. When the null test is used at the 5% level, all three indices agree in separating the habitats. The presence of a critical value of the Ochiai index gives it an advantage. A table of critical values is given for various numbers of species.