Changes in the Ground Beetle and Darkling Beetle Communities (Coleoptera: Carabidae, Tenebrionidae) in the Mountain Hollows of the Tuva and Altai Republics over 60 Years: A Trend or a Fluctuation?

We have studied the communities of soil-surface Coleoptera (Carabidae et Tenebrionidae) in the mountain hollows of Altai (Kurai and Chuya) and Tuva (Ulug-Khem and Ubsu-Nur; the arid western sector and the more humid eastern sector have been studied in the latter). Collections were made in the same habitats at intervals of about 60 years: in 1962–1963 and in 2018–2020. Climate change patterns over this period have been analyzed. In general, the climate of the characterized steppe hollows retains sharply continental features, with negative mean annual temperatures, moisture deficit, and a high frequency of fluctuations of all parameters. The average annual temperatures and the annual precipitation (during the last 10–20 years) have increased in all regions. These changes are most sharply pronounced in the Ulug-Khem hollow, creating the background for a reduction in aridity of environmental conditions. Over 60 years, the number of beetles of the studied taxa has changed several times, sometimes by more than an order of magnitude. At the same time, the number of representatives of the more xerophilic Tenebrionidae family decreased, while the number of the more mesophilic Carabidae increased. The proportions of tenebrionids in different habitats in 2018–2020 decreased significantly in comparison to the 1960s in almost all cases. More beetle species with a more northern or broader (polyzonal and/or trans-palaearctic) distribution are becoming more common in the Tuva hollows. Such species are found in both humid and arid regions. These changes in species compositions and soil-dwelling beetle communities may reflect mitigating climatic conditions due to some increase in precipitation in the studied region. The mean values of the indices of species diversity and evenness do not differ in general for the previous and current states of ecosystems. There are also no reliable differences for total species richness and total abundance. However, there are noticeable interannual differences for some diversity indices calculated for the Altai ecosystems in 2018 and 2020. This may indicate that differences between the overall diversity indices of ground beetle communities in dry and wet years overlap the long-term trend caused by climate change, and populations of species with different life strategies respond quickly to these changes without losing the overall structural complexity of the animal population.