[Spatial distribution of rare species: statistical approach]

Many species are locally rare (have low occurrences in a given region). The method is proposed for the analysis of spatial distribution of such species. The procedure is based on the comparison of actual mean distances between records with Monte-Carlo-simulated mean distances expected for random occurrence pattern. The method was applied to two datasets: benthic macrofauna from the Barents and Kara Seas (Kucheruk, Kotov, 2002) and the Black Sea interstitial ciliates (original data). For both datasets, the number of rare species positively correlates with number of common species per site and with the total number of species. Furthermore (and irrespectively of total diversity pattern), rare species usually were locally clumped in their distribution: each of the species was mostly found at sites that were close together. This tendency, however, was significant for the macrofauna species but not for ciliates.