Depauperate Small Mammal Assemblage in Wolin National Park (Poland): Effects of Insular Isolation, Topography, and Vegetation

Terrestrial small mammal species typically assemble according to plant communities, but multiple factors, including large-scale geographic patterns, influence their assemblage structure. Despite their ecological significance, small mammals are often underrepresented in biodiversity assessments, and many Polish national parks lack comprehensive surveys. This is also the case for Wolin National Park (WNP), Poland’s only national park on a coastal marine island, which is known for its unique bat fauna. Here, we surveyed small mammals in WNP using live and pitfall trapping, identifying only nine species—the lowest richness among the five regional national parks (which host 11–13 species based on trapping data alone). Rarefaction analysis indicated a very low probability of detecting additional species with further sampling. This unexpectedly low richness is likely linked to insular isolation and the park’s location at the edge of the regional distributions of three species. Cluster analysis revealed a key pattern in WNP’s small mammal assemblages: a division between two distinct landscape units—moraine hills and the alluvial delta—where Apodemus flavicollis and Apodemus agrarius were the predominant species, respectively. This division had a greater influence on assemblage clustering than local vegetation.