Janne Alahuhta

Geodiversity refers to the heterogeneity of abiotic characteristics in nature, and in freshwater ecosystems, it mostly mirrors the diversity of hydro‐geomorphological features in inland waters. Although several scholars have highlighted that geodiversity contributes to habitat formation and influences biodiversity and ecological processes, it remains largely overlooked in biological freshwater conservation research. The present study constitutes a systematic review of scientific publications examining geodiversity–biodiversity relationships in freshwaters using a bibliometric analysis. Database queries retrieved 178 publications, 111 of which were initially identified as relevant to the research objectives. The analysis revealed a noticeable increase in publications after 2016, with numerous articles focusing on large‐scale geographic units, such as geoparks, aiming to quantify geodiversity for geotourism promotion and geoconservation. However, only 24 ecological articles have explored geodiversity–biodiversity linkages, particularly for organisms like macrophytes and benthic macroinvertebrates. Most studies reported a positive relationship between geodiversity and biodiversity. Geodiversity was categorised into four abiotic dimensions (geology, paedology, geomorphology and hydrology), whereas biodiversity was quantified across diverse ecological levels and facets. We identified six key ecological mechanisms that drive the geodiversity–biodiversity relationships, including habitat heterogeneity, habitat creation, hydrochemical conditions, environmental filtering, connectivity/dispersal and ecosystem resilience, with anthropogenic influence acting as a modifying factor. Overall, our findings emphasise the importance of further research to incorporate geodiversity into aquatic biodiversity assessment and management, supporting a holistic strategy for the joint conservation of geological and biological entities of nature.

The leaf economics spectrum bridges plant demography with terrestrial biodiversity gradients, community ecology and ecosystem functions, providing a framework for the mechanisms underlying ecosystem change. However, our understanding of whether this framework applies to aquatic plant communities and how their biogeography is shaped by their unique adaptations to life in water is limited. Moreover, it remains unclear whether leaf trait expression of aquatic plants responds to changes in environmental conditions differently depending on their life form (i.e. emergent, submerged). Here, we compiled a dataset of community composition for 6953 lake and river plant communities across Europe. We appended leaf trait data and environmental data to each community. Then, we calculated the community mean traits for emergent and submerged plant communities to determine their position along the leaf economics spectrum and how they deviate from terrestrial expectations. We used Gaussian multivariate mixed linear regression models to investigate life form‐specific variation in trait‐environment relationships. We find that emergent communities exhibit trait–environment relationships comparable to terrestrial predictions, with high bicarbonate and phosphorus concentrations, and warm temperatures selecting for acquisitive leaf traits. In contrast, acquisitive submerged communities are selected for by high bicarbonate and low temperature, and not by phosphorus availability. We attribute these differences to freshwater‐specific adaptations which influence the leaf economics of submerged communities more profoundly than emergent communities, since submerged plants grow in particularly challenging conditions with respect to light and gas availability. These findings suggest that aquatic plants have adaptations to their unique environments that require trade‐offs between leaf form and function to facilitate underwater metabolism, which pushes the boundaries of the leaf economics spectrum. Synthesis . Our ability to apply existing knowledge of leaf economics based on terrestrial plants to the aquatic realm is limited, especially with respect to the influence of temperature on plant growth, which is key for predicting the impacts of climate change on vegetation globally. Our findings highlight the importance of a realm‐specific approach for linking functional traits to freshwater ecosystem functioning and biodiversity, as the distinct responses of freshwater plants to their environment are not captured by terrestrial‐derived frameworks.

A primary ecological challenge is to disentangle how abiotic factors affect species richness using measured environmental variables in addition to broad proxies such as elevation. Considering direct ecogeographical gradients, such as climate harshness, it is therefore essential to understand whether these underlying abiotic factors might consistently drive the distribution of different groups of organisms along elevational gradients. To address how elevation shapes species richness patterns, we performed a systematic review and a subsequent meta‐analysis to answer the following questions: (i) Does elevation influence species richness in global freshwater zooplankton and macrophyte communities? (ii) Can climatic harshness, such as temperature and precipitation variability, geography and different freshwater ecosystem types explain relationships between elevation and species richness? (iii) Are these ecogeographical patterns consistent for both organismal groups? Our meta‐analysis included 84 effect sizes spanning 48 countries and both hemispheres from −54.9 S to 84.7 N, with an elevational range up to 4200 m above sea level within six distinct freshwater ecosystems. We found that the relationship between elevation and species richness in zooplankton and macrophyte communities is context‐dependent. These responses varied among different taxonomic groups and broad habitat categories (i.e., flowing vs. standing waters). We found a general negative relationship between zooplankton species richness and elevation. Zooplankton species richness decreased along the elevational gradient, but this pattern was primarily associated with a concomitant decrease in cladoceran species numbers. The negative correlation between elevation and species richness was observed solely in flowing waters for macrophytes. Additionally, we found that negative elevation–richness relationships were more pronounced at high latitudes in the global north for both zooplankton and macrophyte communities. This research challenges the prevailing assumption that elevational diversity gradients are universal, with species richness decreasing with increasing elevation in freshwater ecosystems. We also emphasize that the conventional ecogeographical measures employed in terrestrial studies, such as air temperature, may be insufficient on their own to explain richness patterns in freshwater organisms. These findings underscore the necessity for future freshwater assessments to build on well‐established biogeographical traditions rooted in terrestrial systems while recognizing the unique features of inland waters.

Aim: This study aims to evaluate whether the trait–environment relationships known for terrestrial plant height extend to freshwater macrophytes, and to identify the primary environmental factors influencing global height patterns in emergent and fully submerged aquatic plants. Location: Global. Time Period: Species occurrence records and height measurements compiled from 1931 to 2022. Major Taxa Studied: Freshwater plant species. Methods: We compiled a global dataset of maximum plant height records for 1735 aquatic plant species, categorised by life form (partially emergent vs. submerged). Using generalised additive models, we tested how plant height varied along latitudinal gradients and how it was related to environmental predictors including temperature, relative inorganic carbon supply, and water depth (indicated by habitat availability). We explicitly analysed whether these relationships differed between the two life forms and validated these patterns using site‐scale species and environmental data from northern temperate lakes and streams. Results: Species with emergent growth increase in height with warmer temperature. On the contrary, fully submerged species exhibit increased height with higher inorganic carbon availability and colder climates. At the local scale, submerged plant height is positively associated with relative inorganic carbon supply in lakes and streams of the northern temperate zone. Main Conclusions: The relationships between environmental variables and plant height differ between emergent to completely submerged life forms, consistent with realm‐specific patterns in trait‐environment correlations. These differing patterns highlight that trait‐environment coupling in freshwater systems may not parallel those in terrestrial ecosystems and suggest that life form mediates species' responses to environmental variation.

Freshwater macrophytes are fundamental to the health of inland waters, portraying unique eco‐physiological adaptive strategies that make them distinctive from terrestrial vascular plants. We integrated a novel, high‐resolution global distributional dataset of 3382 freshwater macrophyte species (representing 97% of all known freshwater macrophytes worldwide), encompassing 486,252 occurrence records across more than 12,700 1° grid cells to investigate species richness patterns and their underlying mechanisms across the world. Freshwater macrophyte richness shows a hump‐shaped pattern globally, peaking at approximately 40° N in temperate regions and at 20° S in tropical to subtropical latitudinal bands. Widespread species contributed the most to the northern peak while other species contributed to the southern peak. Coastlines and adjacent lowland regions are the macrophyte diversity hotspot globally. Contemporary temperature emerged as the dominant environmental gradient structuring global macrophyte richness across and within major continents, especially for widespread species, often displaying a quadratic relationship. However, our range‐size‐dependent analysis revealed a critical divergence: geometric constraints imposed by the mid‐domain effect are the pre‐eminent spatial drivers for intermediate and restricted‐range species. Model explanatory power varied significantly across continents and decreased sharply with species range size. The overall positive correlation between macrophyte richness and the Human Influence Index is driven entirely by widespread generalist species. This relationship vanishes for restricted and highly restricted species, demonstrating that macrophyte endemism centres are uniquely vulnerable. Synthesis . The high‐resolution, range‐size‐dependent analysis resolved critical ambiguities in macrophyte macroecology. We establish a robust framework for understanding that the drivers of freshwater plant diversity are strongly hierarchical and scale‐dependent, thereby laying the foundation for urgent spatially targeted conservation efforts focused on protecting vulnerable centres/regions of macrophyte endemism.

Aims: Human disturbances and environmental changes significantly influence riparian vegetation composition and dynamics by altering hydrological regimes. In high‐altitude river systems, snowmelt‐driven water‐level fluctuations add further complexity to these processes. However, little is known about how riparian plant functional strategies—competitor (C), stress‐tolerator (S), and ruderal (R)—respond to dam‐induced water‐level fluctuations. This study aimed to assess the effects of water‐level fluctuations and climatic factors on riparian vegetation functional strategies along the Nyang River, Qinghai–Tibet Plateau. Location: This study was conducted along the Nyang River, Qinghai–Tibet Plateau, China. A total of 33 sites were surveyed, spanning upstream, reservoir, and downstream zones, which were categorized based on water‐level fluctuation gradients. Methods: We classified riparian vegetation functional strategies using Grime's CSR framework based on species trait data. Hydrological and climatic variables, including water‐level fluctuations, temperature, precipitation, and snow cover, were derived from the Global Surface Water Mapping Layers and the FLDAS dataset. Soil properties were measured in the field. Redundancy analysis and partial least squares path modeling were applied to identify key drivers of CSR variation across different river zones. Results: Riparian vegetation exhibited significant differences in stress tolerance and ruderal strategies across the Nyang River. Plants in the reservoir and upstream zones had higher S‐strategy values, whereas downstream vegetation was predominantly characterized by high competitiveness. The primary drivers of CSR variation across the catchment were temperature, precipitation, and snow cover. In reservoir zones, water‐level fluctuations (e.g., retention time, river width) were the dominant influences, whereas downstream vegetation was mainly governed by climate variables. In upstream zones, precipitation, water‐level fluctuations, and snow cover jointly influenced CSR strategies. Water‐level fluctuations directly regulated functional strategies, whereas snow cover had both direct effects and indirect effects via soil moisture changes. Conclusions: This study highlights the interactive effects of climate change and flow regulation on riparian vegetation functional strategies in high‐altitude river systems. The findings provide critical insights into how water‐level fluctuations and climatic factors shape riparian plant strategies, offering valuable information for ecosystem‐based river management and conservation in alpine regions.

Content: A comprehensive understanding of how and to what extent beta diversity and community-environment relationships vary at various spatial scales is important to derive realistic forecasts of the future of freshwater communities. Objectives: We assessed how total beta diversity and its two components (species replacement and species richness differences) of river macrophytes change among and across Portugal, Poland, Germany, Denmark and Finland. We further addressed which and how environmental and spatial gradients explain compositional variation of macrophyte communities among European regions and differences in beta diversity across the continent. Methods: We employed generalized linear mixed models, permutational analysis of multivariate dispersions and generalized dissimilarity modelling to investigate beta diversity of river macrophytes among study regions, whereas generalized additive model for location, scale and shape was used to research patterns across regions. Results: Macrophytes beta diversity and its replacement component tended to increase or were not significantly related to latitude at regional scales, whereas total beta diversity showed a negative latitudinal effect across study regions in Europe. This finding suggests that patterns predicted at one spatial scale may not necessarily be predicted at other scales. Species replacements also dominated over species richness differences in explaining beta diversity patterns across all the study regions. However, different environmental variables contributed to beta diversity of river macrophytes among the study regions. Conclusion: Environmental heterogeneity manifested by altitude range and geodiversity was the major driver of total macrophyte beta diversity in Europe. These results highlight how spatial scale and context-dependency across different regions have a profound influence on how river macrophytes respond to their environment.

There is a lack of empirical evidence on how biotic and abiotic mechanisms interact to structure freshwater metacommunities. We explored using Hierarchical Modelling of Species Communities whether consistent species-to-species associations remain after accounting for species’ different responses to environmental and spatial variation in lake macrophyte communities across seven regions. We found that environmental filtering, a concept suggesting that the abiotic environment selects species with similar trait values within communities, was the primary mechanism structuring these metacommunities. Variance explained by environmental features varied from one region to another, showing context dependency. Species functional traits explained a relatively modest proportion of the total variation in species occurrences and species niches; however, environmental features had a statistically significant contribution to individual species traits. Phylogenetic signals were generally weak, and species-to-species associations showed context dependency across study regions. Alien-invasive species showed mostly negative associations with native species, whereas positive relationships between alien-invasive species were also evidenced. Moreover, we did not find any relationship between certain known alien-invasive and native species. Overall, metacommunity research in freshwater ecosystems should more resolutely integrate potential biotic interactions to future investigations to comprehensively understand the interplay between environmental factors, dispersal and biotic interactions in shaping freshwater community dynamics.

Motivation: Freshwater ecosystems have been heavily impacted by land‐use changes, but data syntheses on these impacts are still limited. Here, we compiled a global database encompassing 241 studies with species abundance data (from multiple biological groups and geographic locations) across sites with different land‐use categories. This compilation will be useful for addressing questions regarding land‐use change and its impact on freshwater biodiversity.Main Types of Variables Contained: The database includes metadata of each study, sites location, sample methods, sample time, land‐use category and abundance of each taxon.Spatial Location and Grain: The database contains data from across the globe, with 85% of the sites having well‐defined geographical coordinates.Major Taxa and Level of Measurement: The database covers all major freshwater biological groups including algae, macrophytes, zooplankton, macroinvertebrates, fish and amphibians.

Understanding spatial variation of species composition at different scales is essential for efficient conservation planning. Here, we investigate ecological uniqueness patterns of freshwater macrophyte assemblages at continental extents. We explored the similarities and differences in the patterns of ecological uniqueness between Europe and North America in relation to species richness and environmental variables using macrophyte presence–absence data in 50 × 50 km grid cells. To describe the ecological uniqueness of macrophyte assemblages, we used an index called ‘local contribution to beta diversity’ (LCBD). First, we used linear regression to evaluate the relationship between ecological uniqueness and species richness. Second, the variation of ecological uniqueness was modelled using environmental variables in generalized additive modelling (GAM). Third, boosted regression tree (BRT) analysis was performed with the same environmental variables to compare BRT results with the results from GAM. The results revealed relatively similar patterns of ecological uniqueness in both continents. The relationship between species richness and ecological uniqueness was overall negative but showed differences in the form and degree of the relationship between Europe and North America. The main driver of ecological uniqueness in both continents was mean annual temperature, with further effects associated with annual precipitation, elevation range, alkalinity and the proportion of freshwaters in a grid cell. Synthesis. Our results showed that species richness and ecological uniqueness may be negatively correlated at large spatial extents, and that the form of the relationship is likely to depend on the species richness profile of the area. The significant influence of climate on the ecological uniqueness of macrophyte assemblages suggests that changes in climate and land use may shape unique macrophyte assemblages. Thus, conservation strategies should consider protection measures, especially in the northern areas with unique macrophyte species assemblages, as they are expected to face many changes in the future. Identifying areas with high ecological uniqueness at different scales is important for efficient implementation of biodiversity conservation practices.