Main Trends in Vertebrate Population Dynamics in the Clay Semi-desert of the Trans-Volga Region since the Mid-18th Century

摘要

The main natural changes related to the climate variations and the economic activities over the past 250 years in the area of the clay semi-desert along the interfluve between the Volga River and the Ural River have been considered. The authors define four climate periods based on humidity in the region: the mid-18th century to the 1820s, the 1830s to the 1950s, the 1960s to the end of the 1980s, and the 1990s to the 2010s. For each period, the area features related to humidity and human economic activities, which are followed by altering life for plants and animals in the region, are described. It is proven that only the existence and patterns of aquatic and waterfront communities are directly dependent on the climatogenic factors. Most changes in wildlife of the other communities reflect the impact of regional economic activities representing different stages and types, while the climate variations only adjust them. The ravine forests that existed in lake depressions until the 19th century could ensure the presence of a ravine-woodland complex in the regional fauna. After clearing these forests, a part of the ravine-woodland species complex completely disappeared from the region, some part became synanthropes, while others, once extinct from the region, then recolonized with the occurrence of polydominant woody-shrub thickets in lake depressions and afforested plains. A shift from a steppe vegetation formation to a desert formation across the plain occurred because of overgrazing during the dry season. Therefore, some steppe animal species also became extinct in the region, while the desert animals occupied the niches left vacant. Plowing of the flatlands caused the occurrence of wildlife species using the arable fields in the region as feeding habitats. Anthropogenic activities of various kinds contributed to the arrival of the range-shifting species.