The variation of testacean assemblages (Rhizopoda) along the complete base-richness gradient in fens:: A case study from the Western Carpathians

Most recent ecological Studies of testate amoebae were conducted in acid Sphagnum-dominated mires. Little data exists about the variation in testacean assemblages along the complete gradient from extremely poor acid fens to strongly calcareous spring fens. This so called poor-rich gradient is the most important gradient for the majority of mire biota and can display a time dimension as well. In order to fill this gap we studied modern testacean assemblages in spring fens in the Western Carpathians (Czech Republic and Slovakia). The DCA of all testacean assemblages revealed two major factors controlling species variation, the poor-rich gradient and the microhabitat-type: waterlogged bare sediments versus bryophytes. Sampled sediments of poor acidic fens have species composition similar to that of bryophyte tufts from mineral-richer fens. The ordination of the subset of samples taken from bryophyte tufts shows the clear poor-rich gradient on the first axis and moisture gradient causing variation of "acid" samples along the second axis. Based of DCA results, testacean assemblages were divided into six major types for which the diagnostic species were determined using phi-coefficient. Nearly all types are dominated by Euglyphidae, Centropyxidae, Cyclopyxidae and Difflugiidae were characteristic for calcareous habitats. Species richness did not correlate with the poor-rich gradient. The species variation in testate amoebae assemblages is better predicted by both the species composition of the vegetation as a whole and by the composition of bryophyte tuft than by long-term averages of water chemistry variables. The autecology of many species living in acid Sphagnum fens corresponds well with published data with several exceptions. On the other hand, the study of the complete poor-rich gradient revealed different species optima reported from higher pH Sphagnum fens, and thus it changed our view on the indicative value of some species.