Author Results: Z.Wikar


The Positive Response of Small Terrestrial and Semi-Aquatic Mammals to Beaver Damming

Ecosystem engineers, such as the Eurasian beaver, Castor fiber, transform habitats, thereby creating favourable conditions for other species and increasing biodiversity. Multiple studies have revealed that beaver ponds are valuable habitats for invertebrates and vertebrates, including other mammals, but the impact of watercourse damming on the fauna of small terrestrial rodents and shrews has not yet been documented. We aimed at testing the hypothesis that the presence of beaver dams and consequent flooding enriches the small mammal assemblage both quantitatively and qualitatively. We live-trapped small mammals at nine beaver-modified sites on 300 metre transects alongside dammed watercourses, starting from the dam through to the pond to the sections with unmodified lotic conditions. The abundance and species richness of trapped small mammals were highest near the dams and declined with distance. Additionally, five out of 12 trapped species significantly decreased their abundance with distance from the dam and none revealed the opposite trend. Four species were more abundant on plots subjected to damming (especially Sorex minutus and Micromys minutus), while none were present solely on undammed plots. Among the semi-aquatic species, two water shrews benefited from beavers’ activity in different ways. Neomys milleri occurred only in flooded sections, while N. fodiens preferred unmodified sections, but was the most numerous closer to the dams, following the already known patterns of competitive displacement observed in Central Europe. An important factor affecting small mammals, the herbaceous layer cover, appeared to be interdependent with damming. We provide the first unequivocal evidence that beaver dams facilitate the abundance and diversity of small mammals, presumably due to increased food abundance, availability of shelters and habitat connectivity. Beaver-created wetlands may act as potential refuges for the species most susceptible to the consequences of anthropogenic climate change, while revealing a critically low range-shift capacity.