Are beavers a solution to the freshwater biodiversity crisis?

Re-establishing historic ecosystem links through targeted species reintroduction: Beaver-mediated wetlands support increased bat activity

Despite the global significance of wetlands, conservation strategies often fall short in preserving these ecosystems due to failures in incorporating processes that sustain the ecosystem functioning, hydrological dynamics, ecological processes, and biodiversity of wetlands. Nature-based solutions, such as the reintroduction of beavers, have emerged as effective tools for promoting wetland restoration. Whilst the impact of beavers on wetland restoration is well known, their broader influence on ecosystem health, particularly in modifying habitats for other species, remains inadequately understood. Here we assess the impact that habitat modification through the reintroduction of beavers has on bat populations. There were significantly greater activity levels within beaver-modified wetland habitats for multiple bat species, including higher activity levels of 393 % for Barbastella barbastellus and 313 % for Plecotus spp.. Additionally, we observed positive effects on bat populations in the woodland habitat surrounding beaver-modified wetland for certain taxa. In the face of escalating challenges posed by climate change and habitat loss, addressing biodiversity loss necessitates a shift toward ecosystem-centric mitigation measures. Our study demonstrates that the reintroduction of keystone species like beavers can re-establish historical facilitative links between aquatic and terrestrial food webs, highlighting the importance of such interventions in fostering the resilience and sustainability of entire ecosystems.

Ecosystem engineers cause biodiversity spill-over: Beavers are associated with 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 adjacent aquatic and riparian 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 beaver's presence on the bird assemblage extended to adjacent terrestrial habitats located up to 100 m from the water's 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 adds 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 hotspots.

Water Colour Shapes Diving Beetle (Coleoptera: Dytiscidae) Assemblages in Urban Ponds

Dramatic land-use changes in urban landscapes can drive water colour darkening by washing compounds, such as organic matter and iron, from terrestrial ecosystems into urban blue space, consequentially affecting aquatic communities. Here, I studied how pond water colour changes along an urban gradient and how diving beetles (Dytiscidae) respond to the water colour gradient in 11 ponds with fish and 15 ponds without fish in the Helsinki Metropolitan Area, Finland. I found that the pond water colour exhibited a non-significant decreasing pattern along the urban gradient, indicating that urbanisation may not necessarily drive brownification in urban ponds. Dytiscid species richness and abundance exhibited significant positive correlations with increasing water colour in ponds with fish but no significant correlation in ponds without fish. Some species, such as Agabus spp. and Dytiscus spp., appeared tolerant to highly coloured water, whereas some species, such as Hyphydrus ovatus and Hygrotus spp., tended to occur in clear water, indicating that brown water may provide dytiscids with prey refuges, but some species are intolerant to brown water. The study highlights the importance of urban pondscape heterogeneity to meet the needs of aquatic invertebrates that prefer different water colours and for the multifunctioning of urban ponds.

Beaver Dams and Fallen Trees as Ecological Corridors Allowing Movements of Mammals across Water Barriers-A Case Study with the Application of Novel Substrate for Tracking Tunnels

Physical obstacles within animal habitats create barriers to individual movements. To cross those barriers, specific corridors are used, some of them created by keystone species such as Eurasian beavers (Castor fiber). Their dams on rivers may also increase habitat connectivity for terrestrial mammals, but the significance of that function has never been quantified. To investigate this, we placed tracking tunnels on beaver dams, fallen trees, and-as a control-on floating rafts. Additionally, we tested kinetic sand as a novel substrate for collecting tracks and found the paws of small mustelids precisely imprinted in that medium, allowing easy identification. However, we needed to lump all shrews and rodents smaller than water voles (Arvicola amphibius) into one category as they can only be detected but not identified. The highest mammalian activity was observed on dams, as they may provide shelter, offering protection from predators during a river crossing or permanent residence, and even the opportunity to hunt invertebrates. Slightly higher diversity was found on logs because of a higher proportion of mustelids, which select exposed locations for scent marking. Our results increase our body of knowledge about the beaver as an ecosystem engineer and provide a novel tool for the monitoring of mammal activity.

Threats, biodiversity drivers and restoration in temperate floodplain forests related to spatial scales

Floodplain forests offer a diversity of habitats and resources for a very wide range of plant and animal species. They also offer many benefits to humankind and are considered essential to the mitigation of the effects of climate change. Nevertheless, throughout the world they are suffering the most intense of anthropogenic pressures so are, of all ecosystems, among the most endangered. Here, we bring together and synthesise existing ecological understanding of the mechanisms underlying the high heterogeneity and diversity of temperate floodplain forests and of the pressures threatening their high biological value due to habitat homogenisation. Floodplain forests depend on the periodic disturbances under which they evolved, including fluvial dynamics, traditional management practices and the activities of herbivores. However, they have been heavily degraded by climate change, invasion of exotic species, river-flow regulation, landscape fragmentation, eutrophication and the cessation of traditional management. We can now observe two general trends in temperate floodplain forests: (1) Due to intensive landscape exploitation, they are now more open and thus prone to the spread of competitive species, including of invasive exotics and (2) Due to the cessation of traditional management, along with modified hydrological conditions, they are composed of species in the later successional stages (i.e., more shade-tolerant and mesic) while light-demanding species are quickly vanishing. Restoration practices have brought about contrasting results when restoration of floodplains to their natural states has been problematic. This is likely because of interplay between various natural and artificial processes not previously taken into proper consideration. We would like to draw attention to the fact that restoration projects or the preservation of existing floodplain forest ecosystems should combine the restoration of watercourses with the mitigation of other important threats acting at different scales of the landscape (spread of invasive species, eutrophication of watersheds and inappropriate forest management).

Eurasian beaver - A semi-aquatic ecosystem engineer rearranges the assemblage of terrestrial mammals in winter

There is increasing awareness of the ecosystem engineering services provided by recovering populations of Eurasian beaver. By modifying aquatic environments, this species has a significant, positive influence on biodiversity. Beaver activity affects not only aquatic ecosystems but also terrestrial habitats and organisms. Our study compares and evaluates the species richness and activity of terrestrial mammals in winter at beaver ponds (N = 65) and randomly-selected reference sites along nearby watercourses unmodified by beavers (N = 65) in Poland (central Europe). Mammal assemblages were investigated near pond/watercourse edges, and also at some distance from them. The species richness of mammal and numbers of their tracks were respectively 25% and 33% greater on the beaver than on the reference sites. The higher species richness on beaver sites extended to areas 40-60 m distant from ponds, devoid any signs of beaver activity. Twenty-three mammal species were recorded on beaver sites (mean species richness 3.8 ± 1.6 SD), and 20 on reference ones (3.0 ± 1.5 SD). The numbers of tracks of grey wolf, least weasel and European polecat were higher on beaver than reference sites. Mammal species richness and activity were related to the existence of beaver ponds, but were also correlated with the numbers of snags and coverage of grass, bramble and coniferous saplings in neighbouring terrestrial habitats. Large and small carnivores occurred more frequently and were more active on beaver sites. The frequencies of occurrence of mesocarnivores, mesoherbivores and small herbivores were correlated with habitat characteristics, regardless of whether beavers were present or not. Our results highlight the fact that both pond creation and the habitat changes resulting from the presence of beavers rearrange the occurrence and activity of the terrestrial mammal assemblage.

How beavers affect riverine aquatic macroinvertebrates: a review

Background

As ecosystem engineers, the construction of dams by beavers alters stream habitat physically and biologically, making them a species of interest for habitat restoration. Beaver-created habitat changes affect a wide range of aquatic invertebrate species. However, despite numerous individual studies of how beavers affect aquatic macroinvertebrate assemblages, there has been no evaluation of the consensus of these effects across studies.

Methodology

We collated and examined studies comparing beaver-created ponds to nearby lotic reaches to determine general trends in aquatic macroinvertebrate richness, density, biomass, and functional composition between habitats. From this evidence, we highight knowledge gaps in how beaver activity affects aquatic macroinvertebrates.

Results

Overall, in the majority of studies, aquatic macroinvertebrate richness was higher in nearby lotic reaches compared to beaver-created ponds, but richness at coarser scales (gamma diversity) increased with the addition of beaver ponds due to increased habitat heterogeneity. Functional feeding group (FFG) patterns were highly context-dependent, though predator taxa were generally more abundant in beaver ponds than adjacent lotic reaches. Site-specific geomorphological changes, coupled with dam or riparian zone characteristics and resulting differences in basal food resources likely shape other FFG responses.

Conclusions

We identify a lack of long-term studies at single or multiple sites and conclude that fine-scale approaches may improve our understanding of the dynamics of macroinvertebrates within the freshwater realm and beyond. Due to the context-dependent nature of each study, further systematic studies of beaver engineering effects across a wider variety of environmental conditions and wetland types will also help inform land and species management decisions, such as where to prioritize protection of beaver habitats in the face of a global freshwater biodiversity crisis, or where to restore beaver populations to deliver maximum benefit.

Renewed coexistence: learning from steering group stakeholders on a beaver reintroduction project in England

Species reintroductions are growing in popularity, and example motivations include supporting species populations or the restoration of ecosystem function. Interactions between humans and the reintroduced species are likely to occur post-reintroduction. Coexistence between humans and wildlife is adaptive and dynamic, in part requiring management of conflicts between humans and wildlife, or of conflicts between humans over wildlife management. We seek to learn from the experiences of steering group members in a Eurasian beaver (Castor fiber) project in England and identify how governance of coexistence with reintroduced species may differ from the governance of coexistence with species that are already present in the landscape. Using a qualitative thematic analysis of an online survey, we identify a series of lessons in six key areas: (1) project governance, (2) stakeholder engagement, (3) research and monitoring programme, (4) strategy to manage arising conflicts, (5) public engagement, and (6) broad perspectives on reintroduction trials. We advocate for reflective evaluation as an essential component of reintroduction projects to enable knowledge-sharing from experiences, leading to improved practices in the future. Reflecting on our analysis, we identify and define ‘Renewed Coexistence’—a new term that draws on pre-existing coexistence knowledge but identifies the unique elements that relate to governing coexistence with reintroduced species.

Ecological forecasts reveal limitations of common model selection methods: predicting changes in beaver colony densities

Over the past two decades, there have been numerous calls to make ecology a more predictive science through direct empirical assessments of ecological models and predictions. While the widespread use of model selection using information criteria has pushed ecology toward placing a higher emphasis on prediction, few attempts have been made to validate the ability of information criteria to correctly identify the most parsimonious model with the greatest predictive accuracy. Here, we used an ecological forecasting framework to test the ability of information criteria to accurately predict the relative contribution of density dependence and density-independent factors (forage availability, harvest, weather, wolf [Canis lupus] density) on inter-annual fluctuations in beaver (Castor canadensis) colony densities. We modeled changes in colony densities using a discrete-time Gompertz model, and assessed the performance of four models using information criteria values: density-independent models with (1) and without (2) environmental covariates; and density-dependent models with (3) and without (4) environmental covariates. We then evaluated the forecasting accuracy of each model by withholding the final one-third of observations from each population and compared observed vs. predicted densities. Information criteria and our forecasting accuracy metrics both provided strong evidence of compensatory density dependence in the annual dynamics of beaver colony densities. However, despite strong within-sample performance by the most complex model (density-dependent with covariates) as determined using information criteria, hindcasts of colony densities revealed that the much simpler density-dependent model without covariates performed nearly as well predicting out-of-sample colony densities. The hindcast results indicated that the complex model over-fit our data, suggesting that parameters identified by information criteria as important predictor variables are only marginally valuable for predicting landscape-scale beaver colony dynamics. Our study demonstrates the importance of evaluating ecological models and predictions with long-term data and revealed how a known limitation of information criteria (over-fitting of complex models) can affect our interpretation of ecological dynamics. While incorporating knowledge of the factors that influence animal population dynamics can improve population forecasts, we suggest that comparing forecast performance metrics can likewise improve our knowledge of the factors driving population dynamics.

Beaver: Nature's ecosystem engineers

Beavers have the ability to modify ecosystems profoundly to meet their ecological needs, with significant associated hydrological, geomorphological, ecological, and societal impacts. To bring together understanding of the role that beavers may play in the management of water resources, freshwater, and terrestrial ecosystems, this article reviews the state-of-the-art scientific understanding of the beaver as the quintessential ecosystem engineer. This review has a European focus but examines key research considering both Castor fiber-the Eurasian beaver and Castor canadensis-its North American counterpart. In recent decades species reintroductions across Europe, concurrent with natural expansion of refugia populations has led to the return of C. fiber to much of its European range with recent reviews estimating that the C. fiber population in Europe numbers over 1.5 million individuals. As such, there is an increasing need for understanding of the impacts of beaver in intensively populated and managed, contemporary European landscapes. This review summarizes how beaver impact: (a) ecosystem structure and geomorphology, (b) hydrology and water resources, (c) water quality, (d) freshwater ecology, and (e) humans and society. It concludes by examining future considerations that may need to be resolved as beavers further expand in the northern hemisphere with an emphasis upon the ecosystem services that they can provide and the associated management that will be necessary to maximize the benefits and minimize conflicts. This article is categorized under:Water and Life > Nature of Freshwater Ecosystems.

Beaver dam influences on streamflow hydraulic properties and thermal regimes

Beaver dams alter channel hydraulics which in turn change the geomorphic templates of streams. Variability in geomorphic units, the building blocks of stream systems, and water temperature, critical to stream ecological function, define habitat heterogeneity and availability. While prior research has shown the impact of beaver dams on stream hydraulics, geomorphic template, or temperature, the connections or feedbacks between these habitat measures are not well understood. This has left questions regarding relationships between temperature variability at different spatial scales to hydraulic properties such as flow depth and velocity that are dependent on the geomorphology. We combine detailed predicted hydraulic properties, field-based maps with an additional classification scheme of geomorphic units, and detailed water temperature observations throughout a study reach to demonstrate the relationship between these factors at different spatial scales (reach, beaver dam complexes, and geomorphic units). Over a three-week, low flow period we found temperature to vary 2 °C between the upstream and downstream extents of the reach with a net warming of 1 °C during the day and a net cooling of 0.5 °C at night. At the beaver dam complex scale, net warming of 1.15 °C occurred during the day with variable cooling at night. Regardless of limited temperature changes at these larger scales, the temperature variability within a beaver dam complex reached up to 10.5 °C due to the diversity of geomorphic units. At the geomorphic unit scale, the highly altered flow velocity and depth distributions within primary geomorphic units provide an explanation of the temperature variability within the dam complex and insight regarding increases in habitat heterogeneity.