Fedyn, I. | Search bioRxiv

bioRxiv2026

Ecosystem engineer restores trophic interactions: beavers alter landscape of risks and resources for megafauna

Ecosystem engineers hold potential to modify the environment and resource availability. The recovery of the Eurasian beaver reintroduces both a novel trophic component, as herbivore and prey, and an ecological driver that alters landscape of resources and risks. Together, the species comeback may trigger cascading effects on the ecosystem and shape relationships among megafauna, with contrasting effects on different trophic groups. We studied 30 beaver sites and paired reference sites in forests across Poland to assess how beaver presence affects habitat use and interactions among ungulates, large carnivores and mesocarnivores. With the same species composition and species richness, the number of detections of animals was lower at beaver sites, whereas detection duration was longer there. Structural equation modelling showed that beaver affects mammal community via a combination of direct and indirect pathways. The species presence had a positive direct effect on large carnivores, partly offsetting the negative indirect pathway mediated through reduced ungulate presence. These effects extended indirectly further to mesocarnivores, detection of which was positively related with increasing number of detections of ungulates and large carnivores. Beaver effects on habitat were spatially structured: canopy openness and deadwood abundance declined with increasing distance to water. Ungulates showed spatially diversified response at beaver sites, with the number of detections increasing away from the water, whereas large carnivores were detected most frequently near the water. Ungulates also changed seasonally their behaviour along water-land gradient, indicating a trade-off between resource acquisition and perceived predation risk. Our results show that beaver engineering reorganizes ecosystem through spatial and temporal changes in habitat use, behaviour and trophic interactions among large and medium-sized mammals. Beaver recovery may therefore restore ecological complexity by generating fine-scale mosaics of resources and risk that propagate across multiple trophic levels.

ecology↗

bioRxiv2024

Ecosystem engineers cause biodiversity spill-over: beavers affect breeding bird assemblages on both wetlands and adjacent terrestrial habitats

The influence of ecosystem engineers on habitats and communities is commonly acknowledged in a site-bounded context, i.e. in places directly affected by the presence of the focal species. However, the spatial extent of the effects of such engineering is poorly understood, raising the question as to what impact they have on ecosystems situated beyond the species direct influence. Beavers Castor spp., iconic ecosystem engineers, are capable of significantly transforming aquatic ecosystems. Their presence boosts biodiversity in near-water habitats, but as a result of cascading processes, beavers may affect terrestrial habitats situated beyond the range of their immediate activity. Our study investigates the breeding bird assemblage along a spatial gradient from the water to the forest interior on central European watercourses modified and unmodified by beavers. The results show that beaver sites are characterized by a higher species richness and abundance of breeding birds than unmodified watercourses. Such sites also host a different species pool, as 27% of the recorded bird species occurred exclusively on the beaver sites. The effect of the beavers presence on the bird assemblage caused this to spill over from the wetlands to adjacent terrestrial habitats located up to 100 m from the waters edge, where the species richness and abundance was higher and the species composition was substantially modified. We also found a positive correlation between the total area of beaver wetland and the numbers of bird species and individuals recorded. Our study indicates that beaver activity has major consequences for ecosystem functioning that extend beyond the wetland, spilling over on to adjacent terrestrial ecosystems. These findings add to the general understanding of the spatial context of the ecosystem engineering concept, as the changes brought about by engineers have an influence beyond the area of their immediate occurrence. Our work also has implications for landscape planning and management, where existing beaver sites with terrestrial buffer zones may constitute a network of biodiversity hot-spots. Highlights* Beavers create hot-spots of bird richness and abundance in temperate forests * The beavers impact spills over beyond wetlands on to terrestrial ecosystems * Bird richness, number and composition is changed up to 100 m from beaver sites * The area of a beaver wetland positively correlates with bird richness and numbers * The beaver is an umbrella species for the riparian forest bird community

ecology↗