Global changes are causing a massive loss of biological diversity, with an estimated of up to 25% of species threatened by extinction worldwide. Changes in the ranges of various organisms are also alarming. The habitats of many species are expanding northward or to higher altitudes due to climate warming. This could lead to problems for resident species, either due to competition for resources (food, habitats) or due to the introduction of pathogens by newly arrived species. The Greater white-toothed shrew (Crocidura russula) is a widespread species of insectivores that is find in northern Africa, from Morocco to Tunisia, and in southern and western Europe to the western-central regions of Switzerland and Germany. It occurs from sea level to elevations of 1,200 m, although it can reach up to 2,000 m in Mediterranean landscapes. It also occurs on some Mediterranean and Atlantic islands and has recently been reported as a rapidly spreading species in Ireland from 2007 and recently as a new species for Great Britain. The eastern known distribution limit of C. russula on mainland Europe was described to have moved from East Germany to the west part of Czech Republic in Karlovy Vary region in 2022. However, the proper distribution of this species in Czech Republic is still unknown. Crocidura russula has been reported to be a competitor with resident shrew species resulting in local extinctions. This species is an invasive species in Ireland, spreading rapidly to the detriment of S. minutus. In continental Europe, C. russula has been reported to spread in several regions at the expense of C. suaveolens in Bavaria, Germany, or C. leucodon in Switzerland and north-western Germany. Therefore, the impact of C. russula on resident species in Czech Republic should be monitored carefully. The aim of the thesis will be to determine the current distribution and the habitat of C. russula. The student will address the following questions and tasks: (1) what is the current range of C. russula in Karlovy Vary region? The student will perform bibliographic research (Crocidura russula, range expansion of animals due to climate changes, competitive behaviour of C. russula with resident shrew species); participate in the sampling of shrews in the Karlovy Vary region in 2023 and 2024 to determine the range and expansion of C. russula and the sympatric occurrence with other shrew species; when necessary, confirmed the field identification of captured specimens by genetic analysis of the Cyt b gene) (2) determined the biotopes of C. russula in this region. The study will be conducted in collaboration with the Museum Karlovy Vary within the project of regional collaboration of Czech Academy of Sciences R200932301 (2023-2025).