Leonardo Capitani

Beavers have been promoted as a cost‐effective nature‐based solution to restore degraded stream ecosystems and enhance overall biodiversity. However, the extent to which beaver‐engineering boosts biodiversity in human‐impacted landscapes remains poorly understood. We assessed the responses of aquatic and terrestrial taxa (amphibians, damselflies and dragonflies, fish and crayfish, macrophytes, phytoplankton and zooplankton, terrestrial vascular plants, bats, aquatic invertebrates, flying and terrestrial invertebrates) to beaver‐engineering along a gradient of human land‐use intensity in Switzerland. In 16 streams, we measured species richness, abundance, unique species richness, evenness, beta diversity and gamma species richness in beaver‐engineered sites with beaver dams and corresponding control sites without beaver activity. Especially aquatic and semi‐aquatic taxa profited from beaver‐engineering. Amphibians, dragonflies, macrophytes and plankton had higher species richness, abundance and unique species richness with beaver‐engineering, while fishes and terrestrial plants only had higher species richness and unique species richness, but not abundance. Bats only increased in unique species richness, while for the other terrestrial taxa and aquatic invertebrates, we found no difference between beaver‐engineered and control sites. Community evenness remained largely unaffected across all taxa. Overall, beaver‐engineering with beaver dams increased biodiversity across a land‐use gradient. For macrophytes and amphibians (species richness, unique species richness, abundance) as well for dragonflies (species richness, unique species richness), increases were smaller under higher land‐use intensity. For the remaining taxa and metrics, we found no relationship between land‐use intensity and responses to beaver‐engineering. However, for beta diversity, we found that sites with a high land‐use intensity had a lower component of nestedness and stronger community turnover in comparison to more natural sites, with a significant effect for macrophytes. Gamma species richness was generally unaffected by land‐use intensity, except for amphibians, which disappeared from beaver‐engineered sites in high land‐use intensity landscapes despite being largely restricted to beaver‐engineered sites overall. Synthesis and applications . Our findings show that beaver‐engineering significantly enhances local biodiversity across aquatic and terrestrial ecosystems, even at sites with high land‐use intensity. Hence, beavers can effectively restore stream biodiversity across a range of urban to agricultural to natural ecosystems. Integrating beaver‐engineering into river restoration strategies could substantially contribute to biodiversity goals under frameworks such as the EU Water Framework Directive and national conservation policies.

As ecosystem engineers, Eurasian beavers ( Castor fiber ) modify aquatic and terrestrial ecosystems, which can benefit the biodiversity and community composition of plant and animal species. However, in contrast to aquatic taxa, beaver engineering impacts on terrestrial taxa, like bats, are so far largely overlooked. While it has been shown that bats prefer beaver‐engineered ecosystems, the reason for this choice is poorly understood. We hypothesized that this preference may be associated with beaver‐related changes in habitat characteristics and food availability. To address this knowledge gap, we recorded bat species richness, activity and feeding activity in eight beaver‐engineered ecosystems (pool) with paired control sites without beavers (control) along the same stream in Switzerland. In addition, we collected data on food availability (arthropods) with arthropod flight interception traps and characterized habitat suitability with deadwood volume and vegetation surveys, as well as assessing canopy heterogeneity based on different digital height models. The nighly bat species richness increased from four to five species between control and pool sites. Bat activity increased 1.6 times and bat feeding activity 2.3 times in beaver‐engineered systems compared to controls. These increases in richness and activity were explained by higher volumes of standing deadwood, higher canopy heterogeneity and higher arthropod abundance in beaver systems compared to controls. Overall, the volume of standing deadwood, a critical resource for bat roosting and foraging, had a stronger effect on bat species richness than canopy heterogeneity or arthropod availability. Bat feeding guilds (short‐, mid‐, long‐range echolocators) responded differently to beaver‐engineered habitat changes, with edge‐hunting mid‐range species benefiting the most. Our findings suggest that beaver engineering created structurally diverse habitats that supported a broader range of bat species. By modifying both habitat structure and prey abundance, beaver engineering affected bat activity, richness, and feeding activity directly and indirectly. These changes operated across aquatic–terrestrial boundaries, highlighting the cross‐ecosystem influence and ecological complexity of ecosystem engineering.

1 Beavers have been promoted as a cost-effective nature-based solution to restore degraded stream ecosystems and enhance overall biodiversity. However, the extent to which beaver-engineering boosts biodiversity in human-impacted landscapes remains poorly understood. 2 We assessed the responses of aquatic and terrestrial taxa (amphibians, dragonflies, fish, macrophytes, plankton, terrestrial vegetation, bats, aquatic, flying and terrestrial invertebrates) to beaver-engineering along a gradient of human land-use intensity in Switzerland. In 16 streams, we measured species richness, abundance, unique species richness, evenness, beta and gamma diversity in a beaver-engineered site with beaver dams and a control site without beaver activity. 3 Especially aquatic and semi-aquatic species profited from beaver-engineering. In response to beaver-engineering, amphibians, dragonflies, macrophytes, and plankton increased in species richness, abundance and unique species richness, while fish and terrestrial plants increased in species richness and unique species richness. Bats only increased in unique species richness, while for the other terrestrial taxa, we found no difference between beaver-engineered and control sites. Community evenness remained largely unaffected across all groups. 4 Overall, beaver-engineering increased biodiversity across a land-use gradient. For macrophytes and amphibians (species richness, unique species richness and abundance), as well for dragonflies (species richness and unique species richness), increases were smaller under higher land-use intensity. For the remaining taxa and metrics, we found no relationship between land-use intensity and responses to beaver engineering. 5 However, for beta-diversity, we found that sites with a high land-use intensity had a lower component of nestedness and stronger community turnover in comparison to more natural sites, with a significant effect for macrophytes. Gamma species richness was generally unaffected by land- use intensity, except for amphibians, which were often only found in beaver-engineered sites in high- land-use intensity areas. 6 Synthesis and applications . Our findings demonstrate that beaver-engineering significantly enhances local biodiversity across aquatic and terrestrial ecosystems, even at sites with high land-use intensity. Hence, beavers can effectively restore stream biodiversity from urban to agricultural to natural landscapes. Integrating beaver-engineering into river restoration strategies can substantially advance biodiversity goals under frameworks such as the EU Water Framework Directive and national conservation policies.

Marine heatwaves (MHWs) are episodes of anomalous warming in the ocean that can last from a few days to years. MHWs have different characteristics in terms of intensity, duration and frequency and generate thermal stress in marine ecosystems. In reef ecosystems, they are one of the main causes of the decreased presence and abundance of corals, invertebrates and fish. The deleterious capacity of thermal stress often depends on biotic factors, such as the trophic control of predators on prey. Despite the evidence of thermal stress and biotic factors affecting individual species, the combined effects of both stressors on entire reef ecosystems are much less studied. Here, using a food web modelling approach, we estimated the rate of change in species' biomass due to different MHW characteristics. Specifically, we modelled the mechanistic link between species' consumption rate and seawater temperature (thermal stressor), simulating species' biomass dynamics for different MHW characteristics under different trophic control assumptions (top‐down, mixed trophic control and bottom‐up). We find that total reef ecosystem biomass declined by 10% ± 5% under MHWs with severe intensity and a top‐down control assumption. The bottom‐up control assumption moderates the total ecosystem biomass reduction by 5% ± 5%. Irrespective of the MHW characteristics and the trophic control assumption, the most substantial biomass changes occur among top, mesopredators and corals (5% to 20% ± 10%). We show that reef ecosystems where predators exert top‐down control on prey are prone to suffer species abundance declines under strong MHW events. We identify food web trophic control as a crucial driver that modulates the impacts of MHWs. Overall, our results provide a unified understanding of the interplay between abiotic stressors and biotic factors in reef ecosystems under extreme thermal events, offering insights into present baselines and future ecological states for reef ecosystems.

In theoretical ecology, the quantity of resource consumed by a consumer per unit of time, defined as functional response, is of paramount importance. To better understand species interactions over time it is necessary to analyze whether consumer's functional response depends on resource density alone (which is the reference assumption) or on both resource and consumer densities. There are few field studies that, by varying the resource and consumer densities, provide solid empirical evidence to indicate the most suitable model of functional response in complex systems, such as coral reefs. We performed a field experiment with an herbivorous surgeonfish and their resource, a red seaweed, in a near‐pristine reef ecosystem. We measured algal consumption while varying densities of consumers and resources. We fit nine alternative functional response models, which either included or excluded consumer‐dependence. The model selection and the parameter estimation indicated that the functional response of the herbivorous surgeonfish depended on the ratio of seaweed to herbivorous fish densities. These results imply that, within a given density, surgeonfish can share resources but individual's consumption rate decrease with higher fish densities. These results also suggest that mutual intraspecific interference exists at herbivorous fish densities generally observed in the field and it should be considered in predicting consumption rates by herbivorous reef fishes. Finally, this study indicates that models incorporating consumer‐dependence must be considered for understanding herbivorous fish and algae population dynamics when placed in the context of the most biodiverse ecological communities, such as reef ecosystems.