Proportions of active ciliate taxa in soils

 Active and total soil ciliate populations were analyzed by a non-destructive method for 25 collections. Total numbers ranged from a few individuals in soils under stressed conditions to 750 g^–1 dry soil. Active ciliates were <15% (mainly r-selected colpodids) and 40–60% of the total ciliate population under stress conditions, respectively. About 55% (18–86%) of ciliates, both in active and total populations, were colpodids, and about half of these belonged to five taxa: Colpoda inflata, Colpoda steini, Cyrtolophosis elongata, Cyclidium mucicola, and Platyophyra vorax. Only about 5% of the 572 presently known soil ciliate species furnished most of the individuals. A hierarchical approach is suggested to explain the high diversity in the less abundant 95% species, and is extended to explain species distribution in stressed habitats. This study analyzed only mineral soils and found, in a comparison of agroecosystem soils and the adjacent woodlands they were derived from, that the former contained more active individuals and species of ciliates. Received: 15 June 2000