Collembolan communities of the Ubsu-Nur Basin and adjacent mountains (Russia, Tuva)

摘要

Collembolan communities were investigated in different mountain soils of tundra, forest and steppe belts on the southern macroslope of the Eastern Tannu-Ola Mountain Range as well as in some dry and psammophytic steppes in the arid Ubsu-Nur Basin of the Tuva Republic. The fauna of these areas is unique with many species new to science and some species shared with the Mongolian fauna. A total of 95 springtail species were recorded in the 16 sites studied. Of this number 81 species inhabited sites along altitudinal gradients. Specifically, 38, 50 and 49 species were recorded in alpine tundra, mountain forests and mountain steppes, respectively. In plain steppes 34 species (23 in dry and 23 in psammophytic steppes) were noted. The highest density was found in high altitude pine-larch forest, in the zone of maximum annual precipitation. Along the altitudinal gradient, with increasing aridity from the alpine tundra to steppe sites, dominance structure, spectrum of life forms and spatial distribution of collembolan communities changed markedly. Furthermore, levels of diversity and density decreased while Lexis's aggregation index increased gradually with increasing aridity both in forest and steppe sites. In dry larch forests euedaphic forms were dominant. Collembolan communities of the dry and psammophytic plain steppes of Southern Tuva were characterised by the superdominance of one or two specific species. Decreasing collembolan diversity and density were observed with increasing distance from the latitudinally oriented Tannu-Ola Range, which trapped precipitation (dry plain steppe) and also with penetration into the depth of the sand massif (psammophytic steppe). In Tuva steppes, collembolan populations, especially xerophilous or psammophilous species (Folsomides aridoviator Brachystomella parvula, Isotomodella psammophila and Xenylla spp.) were most numerous in the summer due to increased precipitation during this period. Patchy distribution of Collembola in steppes is associated with favourable microhabitats (i.e. rhizospheres of certain plants).