Global soil ciliate (Protozoa, ciliophora) diversity: a probability-based approach using large sample collections from Africa, Australia and Antarctica

Large sample collections from Africa (92 samples), Australia (157) and Antarctica (90) were investigated for soil ciliates using the non-flooded Petri dish method, which re-activates the ciliates' resting cysts from air-dried samples. Species were determined from life and by silver impregnation. The African samples were the richest, containing 507 species (240 undescribed, = 47%), followed by the Australian (361 species, 154 = 43% undescribed) and the Antarctic (95 species, 14 = 15% undescribed) samples. The percentage of new species/sample was consistently low, viz. 4-8% on average, indicating that new species were considerably undersampled relative to described ones, very probably due to methodological shortcomings, i.e. usually only cysts of the more euryoecious species could be reactivated. Thus, a probability theory-based statistical approach was applied to the data sets to compensate for the underestimated number of undescribed species. This procedure indicated that, depending on the region, 70-80% of the soil ciliates are still unknown and global soil ciliate diversity amounts to at least 1330-2000 species. Several indicators, especially the constant rate at which new species have been found during a 20-year period of intensive research, suggest that this estimate is conservative.