Abstract
The Eurasian beaver (Castor fiber) has a greater impact on local ecosystems than other herbivores, and the affected area exceeds the range of its presence. Its activity may change or create new habitats by modifying the availability of the biotic and abiotic resources available not only to beavers, but also to other groups of animals. Our aim was to study how beaver activity affects the benthos composition in a small river and in a beaver pond. The way in which beavers function in the case of small rivers has received little attention. The study showed a lower density of benthos above the dam (beaver pond - 1467 ind./m2) compared to the river (3147 ind./m2). Below the dam, the diversity of Trichoptera and Coleoptera was greater, while Diptera were more abundant in the beaver pond. Betidae were a constant component in the benthos assemblages and were most abundant in the beaver pond. Collectors-gatherers and predators were the most numerous in the beaver pond. Decreasing percentages of collectors-gatherers were observed with an increased abundance of collectors-filterers and shredders in the river. All of the ratio values except the P/T FFG (Predators to total of all other groups) were lower in the beaver pond compared to the river. The % EPT (Ephemeroptera Plecoptera and Trichoptera) was also greater in the beaver pond. Small differences in the physicochemical properties of the water and organic matter content in the bottom sediments were found both above and below the beaver dam.
Highlights
The most characteristic indicator of the presence and activity of beavers are their dams, which may be constructed as a single threshold or as a cascade
The sampling sites were selected according to their location with respect to the beaver dam, four sampling sites were selected above the dam within the area of the beaver pond and four were selected below a beaver dam in a natural part of the river
*- significant differences using the t-test, FC/GC - Filtering Collectors to Gathering Collectors, SH/TC - Shredders to total Collectors, SC FC/SHR GC Scrapers + Filtering Collectors to Shredders + Gathering Collectors, P/T functional feeding groups (FFG) - Predators to total of all other groups, EPT – Ephemeroptera + Plecoptera + Trichoptera
Summary
The most characteristic indicator of the presence and activity of beavers are their dams, which may be constructed as a single threshold or as a cascade. They are primarily built on small streams or between ponds in places that have a relatively constant level of water where beavers have year-round access to the water resources. The main factor that motivates beavers in their construction activity is safety (Żurowski 1992), but in specific cases, the sound of the water stimulates them to build dams (Hartman and Rice 1963; Johnston 2017). In the southern part of Poland, beaver populations are relatively less numerous compared to other parts of the country, e.g., north-eastern Poland (GDOŚ 2015)
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