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Enhancing our understanding of fish dispersal is central to the success of modern‐day conservation efforts in freshwater ecosystems. However, methods seeking to estimate dispersal are diverse; ranging from direct estimation of individual movements, computation of dispersal kernels, to indirect assessment using measures of gene flow across riverscapes. An important question is whether results from these different approaches provide a consistent picture of the spatial scales of dispersal. Here, we performed a review and meta‐analysis of the literature reporting both individual movements and genetic data to characterize patterns of dispersal for riverine fishes globally. Across all the studies considered (Ndᵢᵣₑcₜ = 206; Nᵢₙdᵢᵣₑcₜ = 205), our results suggest restricted magnitudes of dispersal for riverine fishes, but highlight a large heterogeneity among species, taxonomic orders and geographies. For instance, we found that the maximum parent–offspring dispersal distances varied from 69 m to 1,086 km (median = 12 km; Nₛₚₑcᵢₑₛ = 107), whereas the dispersal spread derived from isolation‐by‐distance slopes (σIBD) from genetic data ranged from 19 m to 250 km (median = 1 km; Nₛₚₑcᵢₑₛ = 56). Comparisons of species‐specific values also revealed significant and positive relationships between direct and indirect estimates of dispersal distances, indicating that organismal movement ability often translates into effective transmission of genes. Finally, this global overview pointed to important geographic and taxonomic disparities in the study of dispersal for riverine fishes. We thus encourage researchers to broaden the taxonomic and geographical scope of future investigations and identify emerging research frontiers where new scientific efforts are needed.

The smallmouth bass (Micropterus dolomieu) is a cool-water fish species native to central North America. Widespread introductions and secondary spread outside of its historical range have led to new recreational fisheries and associated economic benefits in western United States, but have also resulted in a number of ecological impacts to recipient ecosystems, including threats to Pacific salmon. Management of introduced smallmouth bass populations, now and into the future, relies on accurate detection and monitoring of this species. To address this need, we developed an environmental DNA assay that can detect smallmouth bass DNA extracted from filtered water samples in concentrations as low as 2 mtDNA copies per reaction. Field testing demonstrated that eDNA sampling produced results largely consistent with snorkel surveys, a traditional visual assessment, and gained a few additional positive detections. While this assay is robust against non-target detection, including the only other Micropterus in Pacific Northwest streams, largemouth bass (M. salmoides), the high genetic similarity within the sunfish family Centrarchidae made it unable to distinguish smallmouth bass from spotted bass (M. punctulatus) and some Guadalupe bass (M. treculii). The high sensitivity of this method and assay will be particularly useful for identifying the location of non-native smallmouth bass in the Pacific Northwest, quantifying its rate of spread, and aiding management actions.

Coal mining is a major cause of land-use change in the US, and according to the Energy Information Administration it is expected to remain a key part of the national electricity portfolio until at least 2040. It is therefore crucial to understand the environmental impact of coal mining. Although a scientific consensus has emerged that coal mining negatively affects water quality, a quantitative synthesis of biodiversity impacts is currently lacking. Here, we show that mining under current federal statutes—the 1972 Clean Water Act and the 1977 Surface Mining Control and Reclamation Act—has negative implications for freshwater biota. Streams affected by coal mining averaged one-third (32%) lower taxonomic richness and one-half (53%) lower total abundance than unmined streams, with these impacts occurring across all taxa investigated thus far (invertebrates, fish, and salamanders). Even after post-mining reclamation, biodiversity impacts persisted. Our investigation demonstrates that current US regulations are insufficient to fully protect stream biodiversity.

Reliable accounting of freshwater resources is key to managing hydrologic risk and balancing freshwater allocations for ecosystems and society. However, recent claims have argued that the global hydrometric network is not keeping pace with monitoring needs. Here we examine this question globally and reveal that over the past four decades the number of streamgaging stations reporting to global, open datasets has been declining. In the United States, a declining trend was reversed by the turn of the century, but high volatility at the river basin scale threatens continued monitoring in over a quarter of the river basins of the conterminous United States. We propose to prioritize streamgaging rescue by identifying watersheds that heavily rely on hydrologic data to support freshwater biodiversity conservation, and to manage flood or water scarcity risk to human populations. We argue that actions at different institutional levels are needed to secure the accumulation of long-term data needed for sustainable water management.

Non‐native species are now common in community assemblages, but the influence of multiple introductions on ecosystem functioning remains poorly understood. In highly invaded systems, one promising approach is to use functional traits to scale measured individuals’ effects on ecosystem function up to the community level. This approach assumes that functional traits provide a common currency among species to relate individuals to ecosystem functioning. The goals of this study were to (i) test whether the relationship between body size and ecosystem functioning (per capita nutrient recycling) was best described by general or species‐specific scaling models; (ii) relate community structure (total biomass, average body size, non‐native dominance) to aggregated, community‐level nutrient recycling rates and ratios; and (iii) determine whether conclusions regarding the relationships between community structure and aggregate ecosystem functioning differed between species‐specific and general scaling approaches. By combining experimental incubations and field surveys, we compare consumer‐mediated nutrient recycling of fish communities along a non‐native dominance gradient in the Verde River watershed of central Arizona, USA. Data from ˜340 field‐sampled freshwater fish demonstrated support for general allometric relationships predicted by the metabolic theory of ecology (NH₄‐N scaling coefficient = 0.72 [0.64–0.80]; PO₄‐P = 0.67 [0.47–0.86]). However, the best‐fit models for N and P included species‐specific random effects for both allometric slopes and intercepts. According to species‐specific models, stream fish communities recycled 1–12 mmol NH₄‐N/hr (median = 2.8 mmol/hr) and 0.02–0.74 mmol PO₄‐P/hr (median = 0.07 mmol/hr) at N:P ratios between 13.3 and 83.5 (median = 28.8). General models generated similar estimates for NH₄‐N recycling but less accurate estimates for PO₄‐P. Stochastic simulations that incorporated error around allometric parameter estimates led to qualitatively similar but larger differences between general and species‐specific results. Community structure influenced aggregate nutrient recycling, but specific conclusions depended on the scaling approach. Total biomass explained much of the among‐community variation in aggregate NH₄‐N and PO₄‐P for both model types, whereas non‐native dominance alone best predicted variation in aggregate N:P. Surprisingly, species‐specific and general models both reached significant yet quantitatively opposing conclusions regarding the relationship between N:P supply and non‐native dominance. Study results indicate that shifting fish community structure can substantially alter ecosystem functioning in this river system. However, some inferred relationships between community structure and aggregate nutrient recycling varied depending on whether general or species‐specific scaling approaches were taken. Although trait‐based approaches to link environmental change, community structure and ecosystem function hold much promise, it will be important to consider when species‐specific versus general models are necessary to scale from individuals to ecosystems.

Dynamic flow regimes maintain critical connections between main channel and adjacent floodplain habitats that provide fish access to shelter, foraging, and spawning opportunities. Our study advances the understanding of these processes by exploring the importance of coupled longitudinal–lateral connectivity for determining species occurrence in headwater streams of the Amazon. Using a multispecies occupancy model, we revealed a clear pattern of species addition in the downstream direction in temporary floodplain ponds, associated with changes in the pool of potential colonists present in the channel and with increasing lateral hydrologic connectivity. Species that are more tolerant of stagnant waters and those able to disperse in shallow habitats (e.g., Anablepsoides micropus) occurred frequently in ponds along the entire longitudinal extent, whereas those species preferring lotic habitats were present only in the most downstream sites. We also observed increasing similarity of pond and channel communities with distance downstream. This study provides insights on the spatial structuring of tropical fish communities in response to flood-induced hydrologic connectivity and further highlights the vulnerability of floodplain fishes to modification in flooding regimes.

Large‐scale electricity policies that embrace renewable resources have led to continued investments in hydropower. Despite evolving viewpoints regarding the sustainability of large hydropower installations, there has been a major increase in support for the widespread development of small hydropower plants (SHPs). A global synthesis reveals that 82,891 SHPs are operating or are under construction (11 SHPs for every one large hydropower plant) and that this number is estimated to triple if all potential generation capacity were to be developed. Fueled by considerable political and economic incentives in recent decades, the growth of SHPs has greatly outpaced available ecological science. We provide evidence for not only the lack of scientifically informed oversight of SHP development but also the limitations of the capacity‐based regulations currently in use. The potential indiscriminate expansion of SHPs under the pretense of promoting sustainable energy is concerning, and we identify several important steps to help ensure new scientific advances, effective management, and policy reform in the future.

As the climate warms, we can’t restore waterways to pristine condition, but models can predict potential changes, argue Jonathan D. Tonkin, N. LeRoy Poff and colleagues. As the climate warms, we can’t restore waterways to pristine condition, but models can predict potential changes, argue Jonathan D. Tonkin, N. LeRoy Poff and colleagues.

Non-perennial streams are widespread, critical to ecosystems and society, and the subject of ongoing policy debate. Prior large-scale research on stream intermittency has been based on long-term averages, generally using annually aggregated data to characterize a highly variable process. As a result, it is not well understood if, how, or why the hydrology of non-perennial streams is changing. Here, we investigate trends and drivers of three intermittency signatures that describe the duration, timing, and dry-down period of stream intermittency across the continental United States (CONUS). Half of gages exhibited a significant trend through time in at least one of the three intermittency signatures, and changes in no-flow duration were most pervasive (41% of gages). Changes in intermittency were substantial for many streams, and 7% of gages exhibited changes in annual no-flow duration exceeding 100 days during the study period. Distinct regional patterns of change were evident, with widespread drying in southern CONUS and wetting in northern CONUS. These patterns are correlated with changes in aridity, though drivers of spatiotemporal variability were diverse across the three intermittency signatures. While the no-flow timing and duration were strongly related to climate, dry-down period was most strongly related to watershed land use and physiography. Our results indicate that non-perennial conditions are increasing in prevalence over much of CONUS and binary classifications of 'perennial' and 'non-perennial' are not an accurate reflection of this change. Water management and policy should reflect the changing nature and diverse drivers of changing intermittency both today and in the future. US National Science FoundationNational Science Foundation (NSF) [DEB-1754389] Published version This manuscript is a product of the Dry Rivers Research Coordination Network, which was supported by funding from the US National Science Foundation (DEB-1754389). Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the US Government. This manuscript was improved by constructive feedback from Kristin Jaeger and three anonymous reviews.

Riverine ecosystems are governed by patterns of temporal variation in river flows. This dynamism will change due to climate change and the near-ubiquitous human control of river flows globally, which may have severe effects on species distributions and interactions. We employed a combination of population modelling and network theory to explore the consequences of possible flow regime futures on riparian plant communities, including scenarios of increased drought, flooding and flow homogenization (removal of flow variability). We found that even slight modifications to the historic natural flow regime had significant consequences for the structure of riparian plant networks. Networks of emergent interactions between plant guilds were most connected at the natural flow regime and became simplified with increasing flow alteration. The most influential component of flow alteration was flood reduction, with drought and flow homogenization both having greater simplifying community-wide consequences than increased flooding. These findings suggest that maintaining floods under future climates will be needed to overcome the negative long-term consequences of flow modification on riverine ecosystems.

Calls for evaluating general principles in landscape genetics reflect a broader recognition that multispecies inference is a promising strategy for supporting conservation actions across wide-ranging taxonomies and geographies. Formal evaluation of frameworks for multispecies inference is critical to identify opportunities for generalization and to avoid misguided extrapolation that results in ineffective conservation and management efforts. Traits-based approaches are now widely recognized as useful in addressing knowledge gaps where species-specific data may not be available or feasible to obtain. Here we present a case for the application of traits-based approaches in landscape genetics to improve conservation application. We discuss the fundamental theoretical framework and growing empirical evidence supporting the utility of traits-based approaches in landscape genetics, and we highlight an example of the implementation of traits to predict landscape genetic relationships for a range of aquatic taxa native to the southwestern United States. Finally, we discuss opportunities, challenges, and future directions of using traits to characterize landscape genetic relationships. Ultimately, traits-based approaches can help address growing calls for the development and testing of general principles in landscape genetics in order to improve application to conservation challenges.

Environmental flow assessments are becoming increasingly central to ecologically-sustainable river management. Rigorous evaluations of flow–ecology relationships serve a vital role in guiding these assessments to meet targeted ecosystem objectives. However, limited resources and widespread environmental change are outpacing the ability to gain knowledge of species’ flow responses and assess environmental needs for rivers individually. Successfully transferring flow–ecology relationships across space and time would facilitate regional-scale environmental flow assessments, yet the necessary contexts for such success remains a knowledge gap. Here, we leverage long-term, multi-species datasets across multiple river basins in southwestern United States as a case study to explore whether relationships between species abundances and hydrological conditions are transferable across space and time. Additionally, we evaluate the potential for ecological guilds based on fluvial dependence and life-history strategies to facilitate the transfer of flow–ecology knowledge across taxonomic boundaries. Species varied in the spatial transferability of their flow–ecology relationships. Spatial transferability was similar when comparing a species’ flow–ecology relationships within a river basin versus across different river basins, although transferability was considerably greater across free-flowing rivers compared to regulated rivers. Species’ flow–ecology relationships transferred through time just as well as across space. Ecological guilds defined according to fluvial dependence and life-history strategies offered just as much potential for transferring flow–ecology knowledge among species as transferring within species across space or time. Our study provides insights into transferring flow–ecology knowledge to support effective, regional-scale environmental flows. Further research into developing transferable flow–ecology relationships for a wide range of environmental predictors and biological responses across different spatial scales and flow regimes will enable us to keep pace with the increasing demand for science to inform sustainable river management.

River networks are hierarchical dendritic habitats embedded within the terrestrial landscape, with varying connectivity between sites depending on their positions along the network. This physical organisation influences the dispersal of organisms, which ultimately affects metacommunity dynamics and biodiversity patterns. We provide a conceptual synthesis of the role of river networks in structuring metacommunities in relation to dispersal processes in riverine ecosystems. We explore where the river network best explains observed metacommunity structure compared to other measurements of physical connectivity. We mostly focus on invertebrates, but also consider other taxonomic groups, including microbes, fishes, plants, and amphibians. Synthesising studies that compared multiple spatial distance metrics, we found that the importance of the river network itself in explaining metacommunity patterns depended on a variety of factors, including dispersal mode (aquatic versus aerial versus terrestrial) and landscape type (arid versus mesic), as well as location-specific factors, such as network connectivity, land use, topographic heterogeneity, and biotic interactions. The river network appears to be less important for strong aerial dispersers and insects in arid systems than for other groups and biomes, but there is considerable variability. Borrowing from other literature, particularly landscape genetics, we developed a conceptual model that predicts that the explanatory power of the river network peaks in mesic systems for obligate aquatic dispersers. We propose directions of future avenues of research, including the use of manipulative field and laboratory experiments that test metacommunity theory in river networks. While field and laboratory experiments have their own benefits and drawbacks (e.g. reality, control, cost), both are powerful approaches for understanding the mechanisms structuring metacommunities, by teasing apart dispersal and niche-related factors. Finally, improving our knowledge of dispersal in river networks will benefit from expanding the breadth of cost-distance modelling to better infer dispersal from observational data; an improved understanding of life-history strategies rather than relying on independent traits; exploring individual-level variation in dispersal through detailed genetic studies; detailed studies on fine-scale environmental (e.g. daily hydrology) and organismal spatiotemporal variability; and synthesising comparative, experimental, and theoretical work. Expanding in these areas will help to push the current state of the science from a largely pattern-detection mode into a new phase of more mechanistically driven research.

To understand how species will cope with warming, knowledge of the thermal limits is needed. This study estimates 2,960 ray-fin fish species’ thermal sensitivity. Comparison with projected warming highlights vulnerable freshwater and marine regions. Climate change is a mounting threat to biological diversity1, compromising ecosystem structure and function, and undermining the delivery of essential services worldwide2. As the magnitude and speed of climate change accelerates3, greater understanding of the taxonomy and geography of climatic vulnerability is critical to guide effective conservation action. However, many uncertainties remain regarding the degree and variability of climatic risk within entire clades and across vast ecosystem boundaries4. Here we integrate physiological estimates of thermal sensitivity for 2,960 ray-finned fishes with future climatic exposure, and demonstrate that global patterns of vulnerability differ substantially between freshwater and marine realms. Our results suggest that climatic vulnerability for freshwater faunas will be predominantly determined by elevated levels of climatic exposure predicted for the Northern Hemisphere, whereas marine faunas in the tropics will be the most at risk, reflecting their higher intrinsic sensitivity. Spatial overlap between areas of high physiological risk and high human impacts, together with evidence of low past rates of evolution in upper thermal tolerance, highlights the urgency of global conservation actions and policy initiatives if harmful climate effects on the world’s fishes are to be mitigated in the future.

Studying the dynamics of species' borders can provide insight into the mechanisms limiting or promoting range expansion in response to environmental change. In the John Day River, Oregon (USA), rising stream temperatures are facilitating the upstream expansion of invasive smallmouth bass Micropterus dolomieu. Here, where smallmouth bass occupy the upstream limit of its thermal tolerance, we explore population structure and seasonal movement patterns to elucidate the environmental conditions and individual traits that define front edge (where individuals reside year-round) and leading edge (where individuals colonize, but may not establish) limits to its upstream distribution. Reporting on a multi-year, spatially extensive riverscape survey, our results show dramatic ebbs and flows of seasonal occupancies due to individual movement with an overall trend of upstream expansion. We revealed distinct front and leading edge invasion extents, each constrained by different ecological conditions. The front edge is largely constrained by the ability for juveniles to survive an overwinter starvation period, whereas the leading edge is associated with adult growth potential and seasonal hydrological conditions. We also found key morphological traits associated with more mobile individuals. By providing mechanistic insight into the factors that promote or limit range expansion of an invasive riverine species, our study enhances the ability to predict future range shifts and provides critical information to managers tasked with restricting further expansion.

Climate change is poised to alter the distributional limits, center, and size of many species. Traits may influence different aspects of range shifts, with trophic generality facilitating shifts at the leading edge, and greater thermal tolerance limiting contractions at the trailing edge. The generality of relationships between traits and range shifts remains ambiguous however, especially for imperiled fishes residing in xeric riverscapes. Our objectives were to quantify contemporary fish distributions in the Lower Colorado River Basin, forecast climate change by 2085 using two general circulation models, and quantify shifts in the limits, center, and size of fish elevational ranges according to fish traits. We examined relationships among traits and range shift metrics either singly using univariate linear modeling or combined with multivariate redundancy analysis. We found that trophic and dispersal traits were associated with shifts at the leading and trailing edges, respectively, although projected range shifts were largely unexplained by traits. As expected, piscivores and omnivores with broader diets shifted upslope most at the leading edge while more specialized invertivores exhibited minimal changes. Fishes that were more mobile shifted upslope most at the trailing edge, defying predictions. No traits explained changes in range center or size. Finally, current preference explained multivariate range shifts, as fishes with faster current preferences exhibited smaller multivariate changes. Although range shifts were largely unexplained by traits, more specialized invertivorous fishes with lower dispersal propensity or greater current preference may require the greatest conservation efforts because of their limited capacity to shift ranges under climate change.

Species can be rare or common in three different dimensions: geographic range size, habitat breadth, and local abundance. Understanding drivers of rarity are not only fundamentally interesting; it is also pertinent for their conservation. We addressed this challenge by analyzing the rarity of 292 native freshwater fishes occurring in ca. 3,500 independent stream reaches that span a broad environmental gradient across continental USA. Using phylogenetic regression and path analysis, we examined the concordance among the three rarity dimensions, and identified possible mechanisms by which species life-history, habitat affinities, and biogeography drive variation in rarity. Weak double extinction jeopardies were driven by weakly positive correlations between habitat breadth and local abundance, and between habitat breadth and geographic range size. However, a triple extinction jeopardy was averted as local abundance and range size were not positively linked in our study. This is because large-river and lacustrine habitat use mediated a trade-off between local abundance and range size. Large rivers and lacustrine habitats represent important dispersal pathways and refugia that enabled fishes to acquire wide ranges; however, species using these habitats are less abundant overall because they are less adapted to small lotic channels, which comprise the majority of stream habitats in the US. Life-history traits were key in governing the relationship between abundance and range size as large-river and lacustrine habitat use were driven by body size, egg size, and parental care. Our analysis contributes novel insights into mechanisms that underlie multiple dimensions of rarity in freshwater fish and informs the prioritization of multiply rare species for conservation. This article is protected by copyright. All rights reserved.

One of the most influential environmental laws in the US – the 1972 Clean Water Act – included the visionary objective of maintaining and restoring aquatic ecological integrity. However, the efficacy of the Act depends on how integrity is assessed. Reviewing the assessment literature for fresh waters over the past 40 years, we found evidence of methodological trends toward increased repeatability, transferability, and robustness of assessments over time. However, implementation gaps were revealed, based on the relatively weak linkages to freshwater policies, stakeholder involvement, emerging threats, and conservation opportunities. A related survey of assessment practitioners underscored the disparity between need versus availability of assessments that guide management policies. Technological changes in data collection and synthesis have clearly influenced assessments, and appear to have led to a reduced reliance on ecological response indicators and corresponding increases in stressor-based metrics. We recommend designing assessments around specific freshwater policies and regulations to improve applicability of assessment products for management and conservation.

Many lotic ecosystems are spatially and temporally heterogeneous but none more so than dryland streams flowing through arid and semi-arid landscapes. Understanding seasonal variation in richness and trait composition is critical to our fundamental understanding of these dynamic stream networks. Here, we analyzed aquatic macroinvertebrate communities within perennial and intermittent reaches in replicate dryland watersheds in southwestern USA across 10 seasons and 4 years. We quantified how hydrology, season, and microhabitat type affected taxa richness and trait composition. Taxa richness was higher in perennial than intermittent reaches, in pools than riffles, and in fall and summer than in spring. The interaction between hydrology and season was important; the difference between fall high and spring low richness was greater in intermittent than perennial streams. Hydrology was the main predictor of trait composition; intermittent streams supported a larger fraction of small taxa, taxa with the ability to undergo diapause, and uni- or multivoltine taxa (i.e., taxa with shorter life cycles). Trait composition did not vary across seasons among perennial reaches whereas the fraction of aerial dispersers appeared to be greater in spring than other seasons among intermittent reaches. Our results were largely consistent with predictions of the habitat templet; r-selected traits were more frequently represented in intermittent communities. The temporal characterization of macroinvertebrate community structure in dryland streams provides a powerful glimpse of how stream communities may respond to a drying climate.

Aim Human-mediated species introductions and extirpations have resulted in the homogenization of biotas over time. However, there remains considerable uncertainty in our understanding of homogenization process for megadiverse regions of the world. Here, we investigate the consequences of widespread species invasions and extirpations for the biogeography of China's unique freshwater fish fauna. Location China. Methods By assembling a comprehensive dataset for distribution of Chinese freshwater fishes, we quantify how non-native fish species, from both overseas introductions and domestic translocations, has led to taxonomic homogenization of fish faunas at watershed, basin, ecoregion and country scales. We explore how the observed patterns in homogenization vary geographically, and identify those species most responsible for the faunal changes. Lastly, we simulate how China's fish fauna may continue to homogenize according to different scenarios of anticipated species introductions and extirpations. Results We demonstrate that species introductions and extirpations have homogenized freshwater fish faunas across China. Overall compositional similarity of watersheds increased by 7.0% (from a historical 14.9% to 21.9% in the present day; Sorensen index). Compositional similarity of 96 of 103 (93.2%) watersheds increased, with western basins exhibiting the highest magnitude. Translocated non-native species associated with aquaculture practices contributed the most to faunal homogenization when compared to alien species (7.3% and 0.4%, respectively). Furthermore, faunal homogenization is predicted to intensify an additional 0.5–4.2% with increasing numbers of new non-native species introductions and the extirpation of native species. Main conclusions Species introductions and extirpations have resulted in the significant impoverishment, and thus the loss of antiquity, of China's freshwater fish fauna over the past century. In the light of the growing realization that species composition (not richness) defines the role that biodiversity plays in maintaining ecosystem function, our study highlights the need for conservation strategies in China that consider changing patterns of β diversity.

Freshwater fishes have the distinction of being both a highly imperilled taxonomic group as well as one that has produced many invasive species with widespread ecological impacts. Faced with the difficult task of identifying those species with the greatest need for management action, ecologists have turned to using predictive suites of ecological and life-history traits to provide reasonable estimates of fish invasion and extinction risk. Whether traits associated with invasiveness are the inverse of those associated with imperillment, known as the ‘two-sides-of-the-same-coin’ hypothesis, remains unclear. A global trait analysis (including maximum total body size, longevity, size at maturation, age at maturation, fecundity and egg size) for 6293 freshwater fishes was conducted to examine the trait correlates of species proneness to invasion or extinction. A meta-analytical procedure was deployed using univariate and multivariate trait analyses that accounted for the effects of shared phylogeny. Mean trait differences (measured as Hedges' d effect size) were found between invasive and threatened species when compared with native species, thus supporting the two-sides-of-the-same-coin hypothesis for freshwater fish. Invasive species were characterized by larger body size, greater longevity, delayed maturation and higher fecundity than threatened species. Furthermore, invasive species were found to display greater trait variability compared with threatened species, suggesting that different traits may be selected at different stages of the invasion process (from pathway entrainment to establishment) whereas more specific trait combinations may predispose species to higher extinction risk. The present study demonstrated a strong trait basis to global-scale invasion risk and extinction vulnerability for freshwater fishes. Given that both time and resources are too limited for detailed species-by-species assessments, the results suggest that trait correlates provide a reasonable estimate of invasion and extinction risk that can inform more targeted and proactive conservation strategies.

Integrating knowledge of environmental degradation, biodiversity change, and ecosystem processes across large spatial scales remains a key challenge to illuminating the resilience of Earth's systems. There is now a growing realization that the manner in which communities will respond to anthropogenic impacts will ultimately control the ecosystem consequences. Here we examine the response of freshwater fishes and their nutrient excretion - a key ecosystem process that can control aquatic productivity - to human land development across the contiguous United States. By linking a continental-scale dataset of 533 fish species from 8,100 stream locations with species functional traits, nutrient excretion, and land remote sensing, we present four key findings. First, we provide the first geographic footprint of nutrient excretion by freshwater fishes across the United States and reveal distinct local- and continental-scale heterogeneity in community excretion rates. Second, fish species exhibited substantial response diversity in their sensitivity to land development; for native species, the more tolerant species were also the species contributing greater ecosystem function in terms of nutrient excretion. Third, by modeling increased land-use change and resultant shifts in fish community composition, land development is estimated to decrease fish nutrient excretion in the majority (63%) of ecoregions. Fourth, the loss of nutrient excretion would be 28% greater if biodiversity loss was random or 84% greater if there were no non-native species. Thus, ecosystem processes are sensitive to increased anthropogenic degradation but biotic communities provide multiple pathways for resistance and this resistance varies across space. This article is protected by copyright. All rights reserved.

River flows connect people, places, and other forms of life, inspiring and sustaining diverse cultural beliefs, values, and ways of life. The concept of environmental flows provides a framework for improving understanding of relationships between river flows and people, and for supporting those that are mutually beneficial. Nevertheless, most approaches to determining environmental flows remain grounded in the biophysical sciences. The newly revised Brisbane Declaration and Global Action Agenda on Environmental Flows (2018) represents a new phase in environmental flow science and an opportunity to better consider the co-constitution of river flows, ecosystems, and society, and to more explicitly incorporate these relationships into river management. We synthesize understanding of relationships between people and rivers as conceived under the renewed definition of environmental flows. We present case studies from Honduras, India, Canada, New Zealand, and Australia that illustrate multidisciplinary, collaborative efforts where recognizing and meeting diverse flow needs of human populations was central to establishing environmental flow recommendations. We also review a small body of literature to highlight examples of the diversity and interdependencies of human-flow relationships-such as the linkages between river flow and human well-being, spiritual needs, cultural identity, and sense of place-that are typically overlooked when environmental flows are assessed and negotiated. Finally, we call for scientists and water managers to recognize the diversity of ways of knowing, relating to, and utilizing rivers, and to place this recognition at the center of future environmental flow assessments. This article is categorized under: Water and Life > Conservation, Management, and Awareness Human Water > Water Governance Human Water > Water as Imagined and Represented.

Free-flowing rivers (FFRs) support diverse, complex and dynamic ecosystems globally, providing important societal and economic services. Infrastructure development threatens the ecosystem processes, biodiversity and services that these rivers support. Here we assess the connectivity status of 12 million kilometres of rivers globally and identify those that remain free-flowing in their entire length. Only 37 per cent of rivers longer than 1,000 kilometres remain free-flowing over their entire length and 23 per cent flow uninterrupted to the ocean. Very long FFRs are largely restricted to remote regions of the Arctic and of the Amazon and Congo basins. In densely populated areas only few very long rivers remain free-flowing, such as the Irrawaddy and Salween. Dams and reservoirs and their up- and downstream propagation of fragmentation and flow regulation are the leading contributors to the loss of river connectivity. By applying a new method to quantify riverine connectivity and map FFRs, we provide a foundation for concerted global and national strategies to maintain or restore them. A comprehensive assessment of the world’s rivers and their connectivity shows that only 37 per cent of rivers longer than 1,000 kilometres remain free-flowing over their entire length.

The alteration of natural flow regimes by hydraulic infrastructure, exploitation for human uses, and changing climates has resulted in significant impacts on native species that inhabit freshwater ecosystems. Hydrologic alteration may promote new opportunities for nonnative species by creating novel habitats, modifying biotic interactions (including predation and competition), and promoting new dispersal pathways. Here, we review the relevant theory and current empirical evidence for additive, synergistic, and antagonistic interactions between hydrologic alteration and species invasions in flowing waters. Building on case studies of both animal and plant communities, we demonstrate the importance of the alteration-invasion nexus to mediate biotic interactions and alter food web structure via top-down and bottom-up effects. Finally, we describe how increasingly altered flow regimes and native-nonnative mixed communities pose a novel conservation challenge, and we explore emerging management strategies in highly-managed river basins.

The COVID-19 global pandemic and resulting effects on the economy and society (e.g., sheltering-in-place, alterations in transportation, changes in consumer behaviour, loss of employment) have yielded some benefits and risks to biodiversity. Here, we considered the ways the COVID-19 pandemic has influenced (or may influence) freshwater fish biodiversity (e.g., richness, abundance). In many cases, we could only consider potential impacts using documented examples (often from the media) of likely changes, because anecdotal observations are still emerging and data-driven studies are yet to be completed or even undertaken. We evaluated the potential for the pandemic to either mitigate or amplify widely acknowledged, pre-existing threats to freshwater fish biodiversity (i.e., invasive species, pollution, fragmentation, flow alteration, habitat loss and alteration, climate change, exploitation). Indeed, we identified examples spanning the extremes of positive and negative outcomes for almost all known threats. We also considered the pandemic's impact on freshwater fisheries demand, assessment, research, compliance monitoring, and management interventions (e.g., restoration), with disruptions being experienced in all domains. Importantly, we provide a forward-looking synthesis that considers the potential mechanisms and pathways by which the consequences of the pandemic may positively and negatively impact freshwater fishes over the longer term. We conclude with a candid assessment of the current management and policy responses and the extent to which they ensure freshwater fish populations and biodiversity are conserved for human and aquatic ecosystem benefits in perpetuity.

Water scarcity is a global threat to freshwater biodiversity, but connecting variation in streamflow to viability of imperiled faunas remains a challenge. Here we combined time-series modeling techniques on long-term ecohydrological data to quantify flow–ecology relationships on native and non-native riverine fish in the American Southwest, and simulate likely fish trajectories and “quasi-extinction” risks in the near future. Streamflow has been declining conspicuously over the past 30 years in the Colorado and Rio Grande river basins, and year-to-year variation in streamflow influences the covariation between native and non-native fish abundance. Risks of decline are high (>50%) for nearly three-quarters of the modeled native species, and current trends in streamflow increase quasi-extinction risk for natives (+8.5%) but reduce this risk for non-natives (–5.9%). Hydrological changes need to be mitigated if we are to slow down the rapid replacement of native biodiversity with non-native species in American Southwest rivers.

Summary Natural resource agencies are increasingly required to prioritise management of multiple non-native aquatic plants (macrophytes) in freshwater ecosystems. Characterising the consequences of invasions for ecological processes and corresponding ecosystem services is fundamental to this decision-making process, but requires an understanding of impacts across physical, chemical, and biological responses. Accordingly, we evaluated the multi-trophic impacts of the invasive macrophyte Myriophyllum aquaticum (Haloragaceae; parrotfeather) along the mainstem Chehalis River, Washington, U.S.A. We examined invertebrate, plant and fish community responses to varying degrees of parrotfeather abundance and simultaneously characterised variation in physical structure and dissolved oxygen (DO) across the dominant native and non-native plant species. DO concentrations were significantly reduced and approached hypoxic levels in areas dominated by parrotfeather compared with native vegetation. Increased structural complexity, volume and biomass of parrotfeather was associated with increased diversity of epiphytic invertebrates. However, these more diverse invertebrate assemblages were dominated by amphipods, whereas native macrophytes were characterised by cladocerans, chironomids and gastropods. Non-native fishes (primarily centrarchid species) were more strongly associated with sites where parrotfeather was present and diversity of non-native fishes was positively correlated along a gradient of parrotfeather abundance. Native fish associated with parrotfeather areas were those that tend to be tolerant of degraded or lower quality habitats. We saw little evidence of exclusion of other macrophytes; native and non-native plant diversity and abundance were positively correlated with the parrotfeather gradient. This may reflect that analysis was done at a site level, and competitive dominance might be apparent by changes in species richness at smaller (plot) scales or over longer periods. Alternatively, parrotfeather may demonstrate minimal effects on native plant composition. Given the effects observed across multiple habitat characteristics and biota, parrotfeather appears to be a highly impactful invader where it establishes. Many of the changes we observed appear to derive from the emergent leaves and dense mat formation of parrotfeather compared with a submersed structure more typical of the native community. Our results suggest that managers should specifically consider contrasting characteristics between non-native and native physical structure when assessing and prioritising threats of invasive macrophytes.

Ajouter pagination et wos; International audience; The introduction of organisms within the native range of wild conspecifics is a widespread phenomenon and locally modifies patterns in intraspecific diversity. However, our knowledge of the resulting ecological effects, as opposed to those caused by invasion-induced changes in interspecific diversity, is still limited. Here, we investigated the ecological effects of native and non-native invaders across levels of biological organisations and recipient organisms using the global and long history introductions of salmonids. Our meta-analysis demonstrated that the global effects of native species introductions exceeded those induced by non-native invaders. The impacts of native invaders were primarily manifested at the individual level on wild conspecifics, but remained largely unexplored on other native organisms and at the community and ecosystem levels. Overlooked and poorly appreciated, quantifying the impacts of native invaders has important implications because human-assisted introductions of domesticated organisms are ubiquitous and likely to proliferate in the future.

Impacts of invasive species may manifest most strongly if these organisms are highly distinct functionally from the native species they often replace. Yet, should we expect functional differences between native and invasive species of generalist organisms like freshwater crayfish? Some existing evidence has pointed to native and invasive crayfish species as ecologically equivalent. We contribute to this literature by comparing the trophic niches of the globally invasive crayfishes Pacifastacus leniusculus and Procambarus clarkii, by applying carbon and nitrogen stable isotope analyses to replicated allopatric (alone) and sympatric (together) lake populations in western Washington State, USA, where P. clarkii has been recently introduced and P. leniusculus is presumed native. Our study corrected for potential inherent differences in lake food webs as a consequence of lake abiotic or biotic characteristics using random effects in linear mixed effects models. We found that although overall trophic niche size or area of these species was not significantly different, P. leniusculus was significantly higher in trophic position than P. clarkii when also accounting for the effects of body size, sex, and lakes as random effects. This pattern of increased trophic position of P. leniusculus over P. clarkii was conserved over time in one sympatric lake for which we had data over multiple years. Cumulatively, our findings point to trophic differences between the globally cosmopolitan crayfishes P. leniusculus and P. clarkii, particularly when accounting for the ways that ecosystem context can affect food web structure of communities and the trophic resources available to these consumers.

Successful invasion by nonindigenous species is often attributed to high propagule pressure, yet some foreign species become widespread despite showing reduced genetic variation due to founder effects. The signal crayfish (Pacifastacus leniusculus) is one such example, where rapid spread across Japan in recent decades is believed to be the result of only three founding populations. To infer the history and explore the success of this remarkable crayfish invasion, we combined detailed phylogeographical and morphological analyses conducted in both the introduced and native ranges. We sequenced 16S mitochondrial DNA of signal crayfish from across the introduced range in Japan (537 samples, 20 sites) and the native range in western North America (700 samples, 50 sites). Because chela size is often related to aggressive behavior in crayfish, and hence, their invasion success, we also measured chela size of a subset of specimens in both introduced and native ranges. Genetic diversity of introduced signal crayfish populations was as high as that of the dominant phylogeographic group in the native range, suggesting high propagule pressure during invasion. More recently established crayfish populations in Japan that originated through secondary spread from one of the founding populations exhibit reduced genetic diversity relative to older populations, probably as a result of founder effects. However, these newer populations also show larger chela size, consistent with expectations of rapid adaptations or phenotypic responses during the invasion process. Introduced signal crayfish populations in Japan originate from multiple source populations from a wide geographic range in the native range of western North America. A combination of high genetic diversity, especially for older populations in the invasive range, and rapid adaptation to colonization, manifested as larger chela in recent invasions, likely contribute to invasion success of signal crayfish in Japan. © 2016 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.

Aim The elucidation of patterns and drivers of community assembly remains a fundamental issue in ecology. Past studies have focused on a limited number of communities at local or regional scales, thus precluding a comprehensive examination of assembly rules. We addressed this challenge by examining stream fish community assembly within numerous independent watersheds spanning a broad environmental gradient. We aimed to answer the following questions: (1) are fish communities structured non-randomly, and (2) what is the relative importance of environmental filtering, predator–prey interactions and interspecific competition in driving species associations? Location The conterminous USA. Methods We used null models to analyse species associations in streams. Non-random communities were defined as those where the summed number of segregated and aggregated species pairs exceeded the number expected by chance. We used species traits to characterize species dissimilarity in environmental requirements (ENV), identify potential predator–prey interactions (PRED) and estimate likely degree of competition based on species similarity in body size, feeding strategies and phylogeny (COMP). To evaluate the effect of environmental filtering, predation and competition on species associations, we related ENV, PRED and COMP to the degree of species segregation. Results The majority (75–85%) of watersheds had non-random fish communities. Species segregation increased with species dissimilarity in environmental requirements (ENV). An increase in competition strength (COMP) did not appear to increase segregation. Species pairs engaging in predator–prey interactions (PRED) were more segregated than non-predator–prey pairs. ENV was more predictive of the degree of species segregation than PRED. Main conclusions We provide compelling evidence for widespread non-random structure in US stream fish communities. Community assembly is governed largely by environmental filtering, followed by predator–prey interactions, whereas the influence of interspecific competition appears minimal. Applying a traits-based approach to continent-wide datasets provides a powerful approach for examining the existence of assembly rules in nature.

Attempts to mitigate greenhouse gas emissions or manage the effects of climate change traditionally focus on management or policy options that promote single outcomes (e.g., either benefiting ecosystems or human health and well-being). In contrast, co-benefits approaches to climate change mitigation and adaptation address climate change impacts on human and ecological health in tandem and on a variety of spatial and temporal scales. The article engages the concept of co-benefits through four case studies. The case studies emphasize co-benefits approaches that are accessible and tractable in countries with human populations that are particularly vulnerable to climate change impacts. They illustrate the potential of co-benefits approaches and provide a platform for further discussion of several interdependent principles relevant to the implementation of co-benefits strategies. These principles include providing incentives across multiple scales and time frames, promoting long-term integrated impact assessme...

Climate change and land-use practices are causing widespread warming of streams, forcing resident species to adapt or migrate. For instance, in the John Day River, Oregon (Columbia River basin), rising temperatures are facilitating the range expansion of Smallmouth Bass Micropterus dolomieu into critical salmon rearing habitat. Understanding Smallmouth Bass reproductive ecology at its range boundaries is integral to understanding and ultimately predicting its upstream range expansion. We addressed this knowledge gap by exploring potential temperature-mediated effects on Smallmouth Bass reproduction at the leading edge of its nonnative riverine distribution in the Pacific Northwest. We used continuous snorkel surveys to characterize its upstream extent in the North Fork John Day River, where we observed spawning patterns and measured adult nest-guarding male size, fecundity, brood development, habitat attributes, and nest success over 2 years (2014, 2015). We found a pattern of asynchronous and pro...

Climate change is poised to have fundamental impacts on the freshwater environments of the Amazon River Basin, and protected areas are routinely proposed as a possible management strategy to conserve freshwater fishes. However, there remains a paucity of information regarding the sensitivity of threatened fish species to climate‐induced changes in water quantity and quality. An expert‐based survey was used to address the following questions: (1) Are currently threatened fish species in Brazil also sensitive to projected effects of climate change? (2) Does the current conservation status of fish species also reflect their degree of sensitivity to climate change? and (3) What are the specific aspects of climate change that are likely to contribute the most to species sensitivity? Survey respondents evaluated 35 species (11 families) representing 50% of the threatened species in the Brazilian Amazon. The results suggest that the majority of threatened Brazilian fish species are considered highly sensitive to climate change impacts. Climate‐induced changes in water quality were, on average, considered a greater threat to species persistence than potential changes in water quantity. Survey results also suggest that fishes exhibit high sensitivity to changes in temperature and dissolved oxygen, and moderate to high sensitivity to changes in high‐flow (i.e. flood) and low‐flow (i.e. drought) regimes. A considerable mismatch was found between species conservation status and sensitivity to climate change, suggesting that perceptions of present‐day extinction risk do not necessarily provide insight into future risks associated with climate change. Species sensitivity to climate change showed no relationship to dispersal ability, indicating that protected areas may serve as important refugia for those species unable to keep pace with climate change. Despite this, the number and size of protected areas in Brazil have decreased over the past decade, largely to support the exploitation of hydropower and mining. Strategic conservation planning that involves existing and new protected areas for those species most at risk to climate change is warranted. Copyright © 2016 John Wiley & Sons, Ltd.

Despite growing evidence that biotic interactions limit the distribution of species and their potential redistribution under climate change, the recent surge of interest in niche conservatism has predominantly focused on the Grinellian (abiotic) niche, whereas few studies have attempted to quantify potential lability in the Eltonian (biotic or trophic) niche. Here, we test for conservatism in the Eltonian niche of 32 freshwater fish species between their introduced and native ranges from 435 populations across the globe. We used stable isotope data to quantify niche shifts along the horizontal (δ13C: indicating the origin of the resources consumed) and vertical (δ15N: describing the trophic position) dimensions of the isotopic niche, as well as shifts in overall isotopic niche breadth. Using an assemblage centroid standardized isotope vector analysis and controlling for phylogenetic relatedness among species, we demonstrated that introduced freshwater fishes exhibited flexibility in both resource use and trophic position that was beyond levels of natural variability observed in their native ranges. By contrast, niche breadth showed variability only within the limits recorded in native populations and varied independently from shifts in mean isotopic niche positions. Across all species and introduction histories, we found a consistent shift towards more balanced acquisition of resources with mixed origins and at intermediate trophic positions, suggesting a general mechanism by which fish species successfully establish into recipient communities. The mechanisms that promote or inhibit species from shifting their Eltonian niche remains unknown, but trophic flexibility is likely to contribute to both the success and the ecological impacts of invasive species and range shifts of native species under future global change.

Residential shoreline and watershed development by humans are leading agents of environmental change in lake ecosystems that reduce abundances and diversity of littoral invertebrates. Invertebrate functional and life history traits are robust indicators of environmental quality and ecosystem functioning, yet surprisingly few studies have utilized trait-based approaches to assess impacts of human development to lake littoral communities. We assessed environmental characteristics of human development that impact functional diversity and structure the trait composition of invertebrate communities in lakes of northwestern United States. Multiple linear regressions revealed that functional diversity declined with increasing watershed development, lake total phosphorus, and littoral macrophyte cover. Results from multivariate constrained ordination and fourth corner analysis indicated that high phosphorus concentrations and abundant macrophyte cover removed taxa with semivoltine life histories and filter feeders from lake communities, and that both regional ecosystem and local habitat characteristics of human development were important determinants of invertebrate community structure. Human development had particularly pronounced effects on invertebrate communities in the sublittoral zone, for which overall community abundances declined. Our study indicates that human development favors lake communities dominated by multivoltine taxa and herbivores, which may have important implications for energy flow among terrestrial, littoral, and pelagic food webs.

The Olympic Mudminnow Novumbra hubbsi is a highly endemic freshwater fish found only in Washington State, where their distribution is limited to low-elevation wetland habitats. The distributional extent of the Olympic Mudminnow is well established, but local and watershed environmental features associated with their presence or absence within the range are poorly understood, making it difficult to determine habitat needs versus availability. We surveyed 22 sites in 2 years along the Chehalis River with the objective of modeling environmental characteristics associated with occupancy by Olympic Mudminnows, while also accounting for incomplete detection. Occupancy and detection probabilities were highly similar between years, and occupancy that incorporated detection probabilities was 47% higher than naive estimates in a given year. Modeling with environmental covariates supported the importance of low temperatures for predicting the occurrence of Olympic Mudminnows at sites, and detection within sites was associated most strongly with shallow depths and low dissolved oxygen. These results are consistent with prior research indicating the preferential use of groundwater springs by Olympic Mudminnows, particularly in warmer summer months. Our research expands the existing knowledge of Olympic Mudminnow distributions by documenting main-stem-oriented populations at varying levels of abundance and suggesting habitat features that may increase occupancy and detection probabilities. The sampling and modeling approach we describe also informs development of standardized survey protocols for Olympic Mudminnows, helping to optimize resources for monitoring occupancy and abundance across their limited range.

Body size is a fundamental functional trait that can be used to forecast individuals' responses to environmental change and their contribution to ecosystem functioning. However, information on the mean and variation of size distributions often confound one another when relating body size to aggregate functioning. Given that size‐based metrics are used as indicators of ecosystem status, it is important to identify the specific aspects of size distributions that mediate ecosystem functioning. Our goal was to simultaneously account for the mean, variance, and shape of size distributions when relating body size to aggregate ecosystem functioning. We take advantage of habitat‐specific differences in size distributions to estimate nutrient recycling by a non‐native crayfish using mean‐field and variance‐incorporating approaches. Crayfishes often substantially influence ecosystem functioning through their omnivorous role in aquatic food webs. As predicted from Jensen's inequality, considering only the mean body size of crayfish overestimated aggregate effects on ecosystem functioning. This bias declined with mean body size such that mean‐field and variance‐incorporating estimates of ecosystem functioning were similar for samples at mean body sizes >7.5 g. At low mean body size, mean‐field bias in ecosystem functioning mismatch predictions from Jensen's inequality, likely because of the increasing skewness of the size distribution. Our findings support the prediction that variance around the mean can alter the relationship between body size and ecosystem functioning, especially at low mean body size. However, methods to account for mean‐field bias performed poorly in samples with highly skewed distributions, indicating that changes in the shape of the distribution, in addition to the variance, may confound mean‐based estimates of ecosystem functioning. Given that many biological functions scale allometrically, explicitly defining and experimentally or statistically isolating the effects of the mean, variance, and shape of size distributions is necessary to begin generalizing relationships between animal body size and ecosystem functioning.

We examined changes in density, distribution, and size of migratory sculpins (Coastrange Sculpin [Cottus aleuticus] and Prickly Sculpin [C. asper]) in 4 small lowland urban tributaries following the removal of instream barriers. In 3 of the streams, a complete or partial barrier to upstream movements of migratory sculpins was removed. In the 4th stream where sculpin were not known to be present, the lower reach was daylighted (stream channel was reconfigured from an underground culvert to a more natural stream channel at the surface). In Lyon Creek, where a partial barrier was removed, sculpin densities upstream of the barrier site increased only slightly. Poor habitat conditions in this stream section may have limited recovery. In Taylor and Zackuse Creeks, where barriers were also removed, Coastrange Sculpin quickly colonized the stream section upstream of the barrier site and densities became similar to or higher than downstream study sections. In the daylighted Mapes Creek, both sculpin species were common throughout the new channel shortly after the project was completed. In both Lyon and Taylor creeks, body size of migratory sculpin in the upstream section decreased dramatically following barrier improvement. Prior to barrier removal, only a few large sculpin migrated upstream; whereas, after barrier removal sculpin of all sizes were able to move upstream except young-of-the-year. Our results indicate that migratory sculpin have the ability to recolonize new habitats shortly after connectivity is restored, but habitat quality may limit sculpin use of newly accessible areas.

To better understand how ecosystems are changing, a multifaceted approach to measuring biodiversity that considers species richness (SR) and evolutionary history across spatial scales is needed. Here, we compiled 162 datasets for fish, bird and plant assemblages across the globe and measured how taxonomic and phylogenetic diversity changed at different spatial scales (within site α diversity and between sites spatial β diversity). Biodiversity change is measured from these datasets in three ways: across land use gradients, from species lists, and through sampling of the same locations across two time periods. We found that local SR and phylogenetic α diversity (Faith's PD (phylogenetic diversity)) increased for all taxonomic groups. However, when measured with a metric that is independent of SR (phylogenetic species variation, PSV), phylogenetic α diversity declined for all taxonomic groups. Land use datasets showed declines in SR, Faith's PD and PSV. For all taxonomic groups and data types, spatial taxonomic and phylogenetic β diversity decreased when measured with Sorensen dissimilarity and phylogenetic Sorensen dissimilarity, respectively, providing strong evidence of global biotic homogenization. The decoupling of α and β diversity, as well as taxonomic and phylogenetic diversity, highlights the need for a broader perspective on contemporary biodiversity changes. Conservation and environmental policy decisions thus need to consider biodiversity beyond local SR to protect biodiversity and ecosystem services.

Animal species often show substantial intraspecific trait variability (ITV), yet evidence for its flexibility across multiple ecological scales remains poorly explored. Gaining this knowledge is essential to better understand the different processes maintaining ITV in nature. Due to their broad geographic ranges, widespread invasive species are expected to display strong phenotypic variations across their distribution. Here, we quantified the scale-dependent patterns of morphological variability among invasive populations of two global freshwater invaders—red swamp crayfish Procambarus clarkii and pumpkinseed sunfish Lepomis gibbosus—both established in American and European lakes. We quantified patterns in body morphology across different ecological (Individual and Population) and spatial scales (Region). We then analyzed the scale-dependency of morphological variations among lake populations that span a diversity of abiotic and biotic conditions. Next, we used stable isotope analyses to test the existence of ecomorphological patterns linking morphology and trophic niche of individuals. We found that trait variations mainly accounted for at the regional and individual levels. We showed that populations of both species strongly differed between United States and Europe whereas habitat characteristics had a relatively minor influence on morphological variations. Stable isotope analyses also revealed that ecomorphological pattern for the trophic position of L. gibbosus was region-dependent, whereas no ecomorphological patterns were observed for P. clarkii. Overall, our study strongly supports the notion that the patterns of phenotypic variability among invasive populations are likely to modulate the ecological impacts of invasive species on recipient ecosystems.

Mounting evidence supports health and well-being benefits associated with nature experiences, while also highlighting race- and class-based inequalities in access and exposure. We synthesized the literature on nature contact by Latinos in the United States to assess the state of knowledge and strategically identify research needs to improve outcomes and reduce health disparities for this rapidly growing ethnic group. Our systematic review revealed 108 articles with a notable increase in number of papers over the past 3 decades. We noted that the body of research is focused on certain demographic targets (adults in urban areas) with a relative dearth of knowledge for others (children, seniors, and rural areas). Our analysis also revealed strong compartmentalizing of studies into research “clusters” based on nonoverlapping topics and types of outcomes that are measured. Although one-third of studies explored health outcomes, these studies rarely examined other outcomes or research topics. Moreover, less than 7% of studies reported on interventions. Given the potential for nature contact to enhance health and well-being, there is substantial need for multidisciplinary research that explores interactions between social, cultural, and economic factors, and how those ultimately relate to nature contact and outcomes for Latinos in the United States.

Human influence on the climate system, through greenhouse gas emissions, is clear and climate warming unequivocal. Recent climate change has had widespread impacts on natural systems including shifts in the ranges (distributions) of land, freshwater, and marine organisms. Effects of these biogeographical shifts transcend single-species to impact on ecosystem goods and services resulting in significant social and economic costs to human communities. In this article we provide a general overview of these factors by reviewing current evidence from terrestrial, freshwater, and marine ecosystems.

Through their dam-building activities and subsequent water storage, beaver have the potential to restore riparian ecosystems and offset some of the predicted effects of climate change by modulating streamflow. Thus, it is not surprising that reintroducing beaver to watersheds from which they have been extirpated is an often-used restoration and climate-adaptation strategy. Identifying sites for reintroduction, however, requires detailed information about habitat factors—information that is not often available at broad spatial scales. Here we explore the potential for beaver relocation throughout the Snohomish River Basin in Washington, USA with a model that identifies some of the basic building blocks of beaver habitat suitability and does so by relying solely on remotely sensed data. More specifically, we developed a generalized intrinsic potential model that draws on remotely sensed measures of stream gradient, stream width, and valley width to identify where beaver could become established if suitable vegetation were to be present. Thus, the model serves as a preliminary screening tool that can be applied over relatively large extents. We applied the model to 5,019 stream km and assessed the ability of the model to correctly predict beaver habitat by surveying for beavers in 352 stream reaches. To further assess the potential for relocation, we assessed land ownership, use, and land cover in the landscape surrounding stream reaches with varying levels of intrinsic potential. Model results showed that 33% of streams had moderate or high intrinsic potential for beaver habitat. We found that no site that was classified as having low intrinsic potential had any sign of beavers and that beaver were absent from nearly three quarters of potentially suitable sites, indicating that there are factors preventing the local population from occupying these areas. Of the riparian areas around streams with high intrinsic potential for beaver, 38% are on public lands and 17% are on large tracts of privately-owned timber land. Thus, although there are a large number of areas that could be suitable for relocation and restoration using beavers, current land use patterns may substantially limit feasibility in these areas.

Water, food, and energy security are cornerstones of a sustainable and prosperous future. Rivers play a key role in delivering critical ecosystem services that contribute to this security on a global scale. But decisions concerning how rivers are harnessed or otherwise used for the benefit of human societies inevitably create environmental and social conflicts, particularly when new dams threaten valued ecosystem services. Given the proposed proliferation of thousands of new dams in many developing countries ( 1 ), can policy-makers and managers be smarter in dam design and operation to reduce these inherent conflicts to generate valuable co-benefits? On page 1270 of this issue, Sabo et al. ( 2 ) propose a novel approach to designing flow releases from existing and proposed dams in the Mekong River Basin in order to sustain a highly valued and threatened natural fishery.