Spatial and biotopic distribution of rare animal species in the tributaries of the Irpin River basin (Northern Ukraine)

The conservation of biodiversity in transformed riverine systems is one of the key challenges in modern ecology, particularly under conditions of urbanization, agricultural expansion, and climate change.This study aimed to assess the spatial patterns of rare animal species distribution within small river systems using the Irpin River basin as a case study, and to identify the ecological factors that determine their presence. Between 2020 and 2025, faunal inventories were conducted in 18 tributaries of the Irpin River, revealing 45 species listed in the Red Data Book of Ukraine. Most of these species were associated with aquatic (21 species), forest (12 species), and wetland (9 species) habitats.The highest richness of rare species was recorded in fish farming ponds (e.g., Nivka, Bobrytsia) and in mosaically structured landscapes of the Unava, Bucha, and Kudelia river valleys, where forested, wetland, meadow, and shrub habitats coexist. In contrast, the lowest numbers of species (1–6 species) were found at sites dominated by homogeneous biotopes or extensive urban landscapes. One of the most striking patterns was the concentration of rare species in the valleys of the Irpin’s right-bank tributaries.It was found that even under urbanized and agricultural conditions, stable assemblages of rare species can persist if remnants of natural habitats or artificially created cascade ponds (fish farms) are present. The highest species richness was consistently associated with river valleys maintaining complex spatial and biotopic structures.The results highlight the crucial role of small rivers as biodiversity hotspots and as structural components of ecological networks. The data obtained may serve as a foundation for the designation of new protected areas and for the planning of conservation actions aimed at preserving key habitats and ecological corridors in regionssubject to high anthropogenic pressure.