Ecology of testate amoebae (Protozoa : Rhizopoda) on peatlands in western Russia with special attention to niche separation in closely related taxa

Testate amoebae (Protozoa: Rhizopoda) are frequently used as indicators of past environmental changes, and the interpretation of fossil assemblages de pends upon our knowledge of ecological affinities of taxa in modern environ ments. A variety of taxonomic approaches have been used in fossil studies, mostly involving grouping of closely related taxa. This paper presents data from peatlands in western Russia relating surface wetness parameters to sp ecies occurrence. Relationships between species abundance, water table dept h and soil moisture are modelled using weighted averaging, and species nich es are calculated as optima and tolerance for these parameters. Niche separ ation of closely related taxa is examined in detail and it is shown that th ere is often a gradient of hydrological preference within each group of tax a. Wet to dry gradients include those found in the Trigonopyxis arcula grou p (T. arcula var. major > T. arcula > T. minuta), the Assulina-Valkanovia g roup (A. seminulum > A. muscorum > V. elegans), and the Trinema lineare gro up (T. lineare var. truncatum/T. lineare > T. lineare var. terricola), all of which are associated with a large to small size gradient. In addition, s pined forms within the Euglypha and Placocista genera are shown to consiste ntly occur in wetter habitats than glabrous forms or those with shorter spi nes. It is concluded that palaeoecological studies should attempt the lowes t taxonomic divisions possible within these groups, to maximise the ecologi cal indicator value of the assemblages recorded.