A simple approach to estimate similarity in ecosystem analysis

A simple rank similarity index is proposed to use in estimation of ecological community similarities. The analysis of similarities is based on hypergeometric probabilities of the coincidence of dominant species in the samples. When 4 dominant species are ranked in samples, two sets of ranks can be compared in 133 different ways. In the case of total similarity rank similarity index M=10 and for dissimilarity M=0. Critical levels of M are given for total amount of species from 10 to 300. The proposed approach useful in rapid similarity analysis of planktonic communities.