Spider (Arachnida: Aranei) Communities in Mountain-Hollow Steppes of Southeastern Altai and Tuva

Spider communities in the intermontane hollows of southeastern Altai and Tuva have been studied for the first time using the catena approach. It is revealed that their abundance is very low and their taxonomical composition is very poor. The catenas of the Chuya hollow are dominated by subarid species, while polyzonal species prevail in the Kurai hollow in the valley of the large Chuya River. As in the Chuya hollow, the driest conditions of the catena in the Tannu-Ola mountain range (Ubsu-Nur hollow, western sector) have determined the predominance of subarid faunal elements in Tuva. For the same reason, these two catenas are characterized by the largest proportion of representatives of Central Palaearctic fauna. The catenas near lakes Khadyn (Ulug-Khem hollow) and Tore-Khol (Ubsu-Nur hollow, eastern sector), where the accumulative positions have a high humidity, are dominated by subboreal humid species. West Palaearctic species prevail on the catenas of the Kurai steppe and near Lake Khadyn, while there are no dominant species with some certain longitudinal type of range on the catena near Lake Tore-Khol. The dynamic density of spiders is usually highest at the lower catena positions. Under extremely arid conditions, the maximum dynamic density in the Chuya and Ubsu-Nur (Tannu-Ola) hollows is recorded at the uppermost catena positions. In the mountain hollows of southeastern Altai and Tuva, wolf spiders (Lycosidae) and gnaphosids (Gnaphosidae) are most abundant and diverse in spider communities. Specific spider faunas are formed in isolated conditions of separate hollows. The similarity by the community structure is observed only between the transitive and accumulative positions on the catena in the Kurai hollow.