Daniel Hering

Fish migration through river networks is essential for completing life cycles and accessing critical habitats, but fragmentation increasingly disrupts spawning movements. In Europe, over one million barriers limit connectivity and create trade‐offs between ecological integrity and human uses, such as hydropower, flood control, fisheries and water storage. Furthermore, climate change can decrease habitat suitability, reinforcing migration needs to escape local extinctions. Limited knowledge of environmental triggers constrains species‐specific migration predictions. Here, we quantified the influence of seven environmental triggers—water temperature, flow, turbidity, cloud cover, rain, air pressure and radiation—on spawning migration of European freshwater fishes. A meta‐analysis of 112 studies (685,333 individuals, 953 effect sizes, 50 species) showed that water temperature was the dominant migration trigger. Radiation, turbidity and cloud cover showed weaker, context‐dependent effects, while effects of flow, rain and air pressure were non‐significant. Species‐specific average spawning migration temperatures correlated with upper limits of species‐specific thermal tolerances, indicating that migration timing reflects physiological constraints. Following this argument, we derive a new classification of thermal sensitivity for European freshwater fishes, distinguishing three thermal spawning guilds: cold (< 11°C), cool (11°C–15°C) and warm (> 15°C), with positive migration responses to temperature most frequently in warm‐water, less in cool‐water and rarely in cold‐water species. Our synthesis identifies gaps for species and triggers beyond temperature and flow, providing a quantitative basis for predicting spawning migration timing to guide conservation and connectivity restoration in European rivers.

Freshwater ecosystems, particularly rivers, are experiencing the most rapid biodiversity declines of any biome, driven by several interacting stressors operating across local to global scales. Despite growing research on these interactions, the lack of systematic quantification of individual stressor gradients limits our ability to disentangle their cumulative effects. Here we present a global synthesis of stressor–response relationships across five key riverine organism groups—prokaryotes, algae, macrophytes, invertebrates and fish. We screened 22,120 papers and extracted 276 studies with 1,332 stressor–response relationships. We used generalized linear mixed models and Bayesian meta-analyses to quantify the response to the seven most prevalent stressors. Consistently across taxa, biodiversity loss (taxon richness and evenness) reflected elevated salinity, oxygen depletion and fine sediment accumulation, while the association with nutrient enrichment and warming varied among groups. Predictive tools, including hypothetical outcome plots and partial dependence plots, revealed the interplay of stressors and predicted biodiversity response to stress increase. Our findings establish a quantitative baseline for a continuous global synthesis, refining predictions of anthropogenic stressor impacts, identifying key research gaps and informing conservation strategies for freshwater ecosystems.

Halting biodiversity loss, mitigating global warming and maintaining the long‐term viability of rural and urban areas requires urgent policy action. However, environmental policies often trigger resistance and highly polarised public debates, with some actors employing pseudo‐scientific claims. This raises concern about the increasing impact of misinformation on policymaking. Here, we analyse the role of science and scientists in the public debate around two pieces of legislation that were proposed in 2022 by the European Commission as part of the Green Deal, namely the Nature Restoration Regulation (NRR) and the Sustainable Use Regulation (SUR) of plant protection products. First, we examine key claims against these two legislative proposals and contrast them with scientific evidence. We show that these claims fail to consider ample scientific evidence that restoring nature and reducing the use of agrochemicals are essential for maintaining long‐term agricultural production and enhancing food security. Critics further failed to acknowledge that the NRR and SUR may generate new employment opportunities and stimulate innovation, with high return rates and multiple beneficiaries across society, fostering a transition to sustainable production and consumption models. Second, we examine how the publication of an open letter, signed by 6000 scientists, may have influenced the public debate. We contrast the role that scientific evidence played in the fate of the NRR, which was adopted, against the fate of the SUR, which was rejected by the European Parliament. We draw lessons from these two cases that illustrate the global tension between environmental protection and economic‐driven interests to spread misinformation. We argue that scientists should play an important role in making scientific evidence more accessible and available to the general public and policymakers for informed decision‐making. We recommend that scientists be proactive and unbiased in providing information and data and that policymakers use scientific evidence and engage scientists in developing much needed, well informed environmental policies. Read the free Plain Language Summary for this article on the Journal blog.

We investigated the role of woody riparian vegetation (WRV) in reducing the detrimental effects of extreme low-flow conditions on macroinvertebrate communities in Central European streams. We hypothesized that WRV decreases water temperature, thereby lessening the impacts of drought on streams. The study was conducted in the Lippe catchment in northwestern Germany at 26 study sections during the summer drought of 2022. Water temperature and macroinvertebrate communities were analyzed. WRV cover, groundwater influx, cross-section form and flow velocity were considered as predictors in structural equation models. We investigated how the immediate effects of extreme summer low-flow on water temperature and macroinvertebrates were mitigated by the four predictors. Shading by WRV and groundwater influx caused a significantly lower mean daily maximum water temperature of 6.6 °C and 4.8 °C, leading to a higher share of stream-type specific and temperature-sensitive macroinvertebrate taxa and feeding types typical for rhithral stream reaches. These results indicate that both WRV and groundwater influx play a crucial role in regulating stream temperature and maintaining stream-type specific macroinvertebrate communities under extreme low-flow conditions. The study highlights WRV management as a key tool for protecting stream ecosystems from the increasing frequency of droughts and related low-flow due to climate change.

Beaver activities modify floodplains of small streams fundamentally. Prevailing lotic sections are supplemented with several additional habitats (e.g., ponds, dams and side channels). While there are several investigations into the invertebrate fauna of single beaver‐induced habitats, the ways beavers modify aquatic invertebrate assemblages of entire floodplain sections have not been explored. We investigated three beaver territories and three upstream floodplain sections (“non‐beaver territories”). We quantified the areas covered by different aquatic habitat types and collected 188 habitat‐specific invertebrate samples that yielded more than 82,000 individuals. We used GLMMs with logit links and PCoA to quantify the differences between territory types in terms of aquatic habitat area, abundance, species richness, general community composition, and flow preferences. The area of aquatic habitats increased six‐fold in beaver territories. The abundance of benthic invertebrates increased by a factor of 4.5. From species extrapolation analysis, we inferred that species richness in beaver territories increased by factor of 2.7, compared to non‐beaver territories. Of the 254 taxa recorded, 141 occurred exclusively in beaver territories and only four taxa occurred exclusively in non‐beaver territories. The most taxa‐rich habitat type was side channels in beaver territories. Community composition was most similar between habitat types with comparable flow patterns (e.g., beaver ponds and pools in non‐beaver territories). In both territory types, rheophile taxa accounted for the largest percentage, with a median of 57% in beaver territories and 61 % in non‐beaver territories. The number of rheobiont taxa (21 in total) was higher in beaver territories (20 taxa) than non‐beaver territories (16 taxa), while the overall proportion of rheobiont taxa was higher in non‐beaver territories. Beaver activities greatly enhanced species richness and abundance of aquatic invertebrates. While a predominantly lotic community shifts to an assemblage with more heterogeneous flow preferences, almost no taxa (not even those dependent on high currents) were eliminated from beaver territories. Beavers thus enhance aquatic invertebrate biodiversity while maintaining the original community. Beaver activities are cost‐effective means by which the biodiversity of small floodplains can be enhanced and should be an integral part of restoration plans in regions where beavers were formerly present.

Cemeteries are biodiversity hotspots in urban areas, while the drivers of their floristic diversity are poorly understood. We investigated 153 cemeteries in the western Ruhr Metropolitan Region and generated comprehensive species lists of wild plants. Altogether, we found 964 species, equivalent to 53.6% of the flora known from the region. Cluster analysis revealed five distinct cemetery types based on their species composition and prevalence. Subsequently, we used ANOVAs to relate the most effective environmental descriptors identified with a CCA to the five clusters, thus revealing the drivers of species composition. Two of the main clusters had clear regional foci, which could be explained by soil types, while the third main cluster included most of the large cemeteries with many different habitat types, and encompassed sites from the entire study region. Here, the number of species is highest. Two smaller clusters included old historic and Jewish cemeteries, respectively, which were characterized by a smaller number of neophytes and heat indicators. Through the various functional types, the cemeteries contribute to the biodiversity of urban areas like the Ruhr Metropolitan Region and thus counteract the floristic homogenization of cities.

Background and Objective: Extensively managed grasslands play a crucial role in sustaining biodiversity by providing habitats for a wide range of plant and animal species. The most common management is either grazing or mowing, or grasslands are abandoned. The differential effects of these management or abandoning schemes on biodiversity patterns of extensively managed grasslands have not yet been systematically evaluated with a large number of available case studies. We aimed to identify by a meta‐analysis the best option for biodiversity in extensively managed grassland in Europe.Materials and Methods: Scopus and Web of Science were systematically searched for publications that appeared before 31 January 2024 and that reported the effects of management schemes on biodiversity patterns of extensively managed grassland. Out of 971 original records, 54 full‐text articles were included in the final analysis. We extracted values for mean, SD and sample size of species numbers and calculated Hedge's g to rate treatment effects.Results: Extensive management (grazing, mowing) increased species number compared to abandonment (effect size: Hedge's g = 1.30). For plant diversity, extensive management had a strong positive effect (g = 1.78), while the effect of grazing and mowing was minor for animal biodiversity (g = 0.03). The results were recognizably influenced by the investigated plot sizes. Small plots (2) showed a much stronger effect (g = 2.19) than larger plots (g = 0.56). The type of extensive management, grazing or mowing, had no influence on the results.Conclusion: In line with results on grasslands in general, our results underline that biodiversity of extensively managed grasslands benefits from extensive grazing or mowing. Although abandonment had a negligible effect on animal species richness, the effect on vegetation was strong. The low effect of abandonment on the fauna can be explained by the relatively short duration of the studies. The characteristics of grassland were still present, and it had not turned into forest. Extensive grazing or mowing are therefore the best options for grassland managed for conservation purposes.

Rivers globally are impacted by numerous anthropogenic stressors, including water pollution, habitat degradation, and climate change, which collectively stress biodiversity and ecosystem functioning. This study systematically reviews and analyses published and unpublished data to understand how five aquatic organism groups (bacteria, algae, macrophytes, invertebrates, fish) respond to seven common stressors (salinization, oxygen depletion, fine sediment enrichment, temperature increase, flow modifications and nitrogen or phosphorus enrichment). Using an analytical framework that includes Generalized Linear Models (GLMs) and Robust Bayesian Meta Analysis (RoBMA), we extracted data from 143 relevant datasets out of 29,749 screened articles. Our results reveal a negative relationship between invertebrates and salinity, fine sediment enrichment, and temperature increase, while fish respond positively to increased oxygen levels and temperature. Bacteria and algae show variable responses, with algae positively associated with nitrogen. The findings highlight strong variability in stressor-response relations across organism groups and stressor types, and emphasize the need for more targeted studies on underrepresented groups like macrophytes and microorganisms. This analysis enhances the predictive understanding of stressor impacts on riverine biodiversity, informing future river ecosystem management and restoration efforts.