Basin approach to the study of the spatial organization of ground beetles (a case of the Ivolga river basin - lake Baikal basin)

The ground beetles fauna of the Ivolga river basin is typical for the transitional forest steppe zone between the Siberian taiga and the Mongolian steppe, which formed at the junction of the Khamar-Daban ridge and the Selenga Middle Mountains. It was identified 148 species of ground beetles from 32 genera. Based on the basin concept, we have studied the spatial organization of ground beetles in the Ivolga river basin (Selenga river - Lake Baikal basin system) in Western Transbaikal, identified the landscape complexes of ground beetles from the source to the mouth of the river and from the watershed to the flood of the river. In the first case, zoning of the Ivolga River basin was carried out on the basis of local faunas of ground beetles and faunistic relations between them. We have revealed five landscape complexes of ground beetles at the level of natural boundaries: Upper Ivolga meadow-march-forest, Mukha meadow-march, Lower Ivolga meadow-steppe halophytic, Bolshaya Rechka forest-steppe and Tapkhar steppe. The ground beetles fauna of the Upper Ivolga natural boundary is the richest (102 species), and forest species prevail in it, which are confined to the upper reaches of Ivolga River on the southern slope of the Khamar-Daban ridge. A relic of deciduous forests Carabus smaragdinus (Fischer von Waldheim, 1823) lives under the conditions of increased humidity. The species composition of ground beetles of the Mukha natural boundary is poor (34 species), it is a transitional fauna between the Upper Ivolga and the Lower Ivolga natural boundaries. Meadow and swamp species of ground beetles prevail on the banks of the Mukha Marsh. In the Lower Ivolga natural boundary steppe, meadow and halophytic species of ground beetles (76 species) are widespread, in the Bolshaya Rechka (53 species) and Tapkhar (55 species) natural boundaries - steppe species, which probably penetrated from Mongolia along the Selenga migration corridor. In the second case, we have revealed the catena change of ground beetle complexes from the watershed to the river floodplain on the north and south catenas. The ground beetles complexes in the eluvial position (EL) of both catenas in pine dry forests are characterized by poor species composition of the ground beetles (16-17 species), low number (a couple hundred copies of beetles) and low catch of beetles per season (0,1-0,2 copies / trap / day). The highest number and high catchability (4109 copies, 3,3 copies / trap / day) of ground beetles was registered in the complex of the transit position (T) of the southern catena in the hollow deposit. A relatively rich species composition (34 species) was found in the complex of ground beetles of the accumulation (A) position of the southern catena in the cheegrass steppe on the solonetz soil. Steppe species and halophilic ground beetle species, especially those from the genera Harpalus and Poecilus, prevail in the structure of dominance in almost all positions of catenas. Arid forest steppe complexes of ground beetles are formed in the conditions of dry climate, lack of soil moisture and salinization in the Ivolga river basin.