Species interactions in beaver engineered habitats link land-water ecosystem processes

Beavers, as ecosystem engineers, dam rivers and (re)-create a mosaic of flowing and standing water at the land-water interface. They directly influence the heterogeneity of local habitats, the diversity of aquatic and terrestrial organisms they harbour and the associated energy flows. By assessing the composition and abundances of different aquatic and terrestrial biotic communities, we can determine how beaver engineered habitat heterogeneity affects taxonomic and functional diversity, the strength and number of species interactions as well as the connectivity of the local ecological networks. By linking biodiversity changes, interactions and network structure to ecosystem processes we can, in addition, gain information on how and to what extent beaver-engineered ecosystems can mitigate anthropogenic impacts across land-water interfaces. Our project will provide fundamental and novel insights on species interactions and ecological networks that cross the terrestrial-aquatic boundary. By working with external partners from practice, our results will help to update and extend current beaver management practices and policies, locally, nationally and internationally.

The overarching goal of this project is to assess how habitat heterogeneity caused by beaver engineering influences the diversity, strength and nature (e.g., competitive, facilitative, trophic) of interactions within and between aquatic and terrestrial communities, and how changes in species assemblages relate to ecosystem processes (e.g., C cycle, nutrient uptake, bioremediation). We will do this i) by assessing abundance and traits of interacting terrestrial and aquatic organisms, ii) evaluating the richness and composition of their taxonomic and functional communities and iii) measuring ecosystem processes in streams and surrounding terrestrial areas with and without beaver activity along a gradient of human impact. We will assess if beaver engineered systems harbour ecological networks that are able to better mitigate these anthropogenic impacts. The main research questions are:

• Q1: Do the more complex and heterogeneous beaver-engineered habitats foster more diverse and tightly connected communities, within and between land and water ecosystems?

• Q2: What are the relationships between diversity, number and strength of interactions, and local terrestrial and aquatic ecosystem processes (e.g., C and nutrient cycling, water quality)?

• Q3: To what extent do beaver engineered habitats, and the ecological networks that they harbour, help mitigate human impact?

Together with the external collaborators, we have selected 16 beaver-engineered ecosystems that are distributed across Switzerland, and were chosen based on local environmental conditions that range from open land to forest, and natural to human-impacted. They can be sorted along a gradient of human-impact based on vegetation, stream eco-morphological parameters and beaver pond size. In each system we will collect data at the beaver dam (“pond”), below the beaver dam (“outflow”), at the “inflow of the pond and in the river located up-stream from the pond that has no beaver influence (“control”). In the surrounding terrestrial environment, each beaver-engineered system will be overlaid with a regular grid, to survey terrestrial plants and animals.

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