1. Community assembly in aquatic habitats is heavily influenced by hydrology, but understanding the influence of other habitat conditions is also critical. Most studies focus on comparisons of geographically close communities that exist under diverse hydrological regimes, but this framework limits our ability to understand how conditions other than hydrology shape ephemeral wetland communities. Here, we investigated how macroinvertebrate communities vary with local, landscape, and climate variables in ephemeral wetlands across a large geographic range with few geographic barriers. 2. We sampled ephemeral wetlands in North Dakota, New Mexico, and Texas (USA) in 2021 and in North Dakota and New Mexico in 2022. We used an array of hydrographic, climate, landscape, and spatial variables to relate taxonomic and functional macroinvertebrate community composition and diversity to habitat conditions. 3. Taxonomic composition was overwhelmingly different among states and between years: landscape-scale refuge availability explained variation in taxonomic composition, but local and climate-scale variables only explained variation within the context of other variables. Trait composition was similar between most sampling groups, but distinct trait assemblages occurred in the North Dakota 2021 communities. No predictor variable matrix explained trait composition alone, but local, climate, landscape, and spatial arrangement predicted composition when considering the overlapping influence of other variables. Taxa and trait diversity indices were associated with increased refuge habitat at landscape scale. 4. Our results show consistent trait structure across a large geographical scale in hydrologically similar wetlands, despite almost complete taxonomic turnover between regions. Patterns in taxonomic and functional composition imply that incorporating predictor variables at multiple scales is critical in understanding ephemeral wetland community composition. 5. Despite similar hydrological regimes and potential for connectivity via dispersal, taxa replacement is high in ephemeral wetlands across regions within a single grassland macrosystem. Taxonomic composition and overall diversity change with the context provided by a diverse suite of structuring variables. Further, we show that in most cases, ephemeral hydrology elicits a similar trait response across climate regions.

Large branchiopods are a group of aquatic crustaceans known for possessing hardy resting eggs capable of dispersal between temporary wetland habitats by wind and animal vectors. In this study, we rehydrated dry sediments from bison wallows to assess large branchiopod use of these habitats and potentially the capacity of bison to act as dispersal vectors of cysts. We observed one clam shrimp genus and one tadpole shrimp species in our rehydrated samples, providing strong evidence of large branchiopod establishment in bison-created habitats. We failed to see a relationship between spatial arrangement, bison utilization, and large branchiopod abundance, so future studies are encouraged to assess dispersal capability by bison.

Fish assemblages, defined by taxonomy or functional traits, -respond to regional and local habitat variation. Our hypothesis was that fish assemblages could be best predicted using reach-scale (RS) hydrology variables over valley-scale (VS) hydrogeomorphology variables for US and Mongolian rivers. We further predicted that fish traits were predicted better by RS than VS variables. We evaluated the FS and VS hydrogeomorphologies of rivers in the United States and Mongolia in each of three ecoregions: grassland, forest and endorheic. Fishes were collected using a backpack electrofisher, following standard protocols. Constrained ordination analyses were conducted at three scales: among continents, by continents and by individual ecoregions within continents. We found no significant difference in mean variation explained by VS versus RS or by taxonomy versus traits. Ecoregions differed in factors contributing to fish assemblage patterns, likely a result of differences in hydrogeomorphology, hydrological connectivity and historical influences. We found that fish assemblages were structured by hydrogeomorphic processes occurring at VS and RS, and that variables predicting fish assemblages varied with scale and whether fishes were classified by taxonomy or traits. Although anthropogenic impacts were substantially higher for western US rivers than for Mongolian rivers, we were unable to detect strong differences in our ability to predict fish assemblage variation from RS and VS habitat variables.

Societal perceptions of river floods are typically negative because of the death and destruction they may cause, although scientists and natural resource managers have long recognized the critical ecological role of floods. Like fire and some other ecological disturbances, river flooding intersects many aspects of ecology and society. But unlike fire, flooding receives relatively little attention in the disturbance ecology literature. We call for more focused recognition of flood ecology as a discipline to help river science better inform societal perceptions through developing a better understanding of the ecological roles of flooding. We contend that the absence of a discipline of flood ecology has constrained progress in our understanding of how rivers function and that a formal conceptualization could help reveal the positive aspects of flooding. Finally, we propose a series of questions that we believe a discipline of flood ecology should address.

Opportunities to understand and protect natural aquatic diversity in both relatively pristine and managed rivers can be enhanced with a comprehensive, system-wide understanding of a river’s hydrogeomorpholgy and its effects on ecological structure and functioning from the river’s headwaters to its terminus in an ocean, lake, or natural endorheic basin. While a moderate number of macrosystem ecology studies have been undertaken recently in headwaters, comparable ecological approaches to studying whole rivers or at least their larger components from upstream to downstream are relatively rare. This is partially correlated with the paucity of applicable river ecosystem models developed over the last half century which could otherwise provide diverse, testable tenets (hypotheses). This manuscript focuses on a 15+ year updated, system-wide analysis of the applicability of the 17 tenets included in our previously published, lotic model - the Riverine Ecosystem Synthesis, or RES. We also propose here four new tenets and analyze the system-wide applicability of the revised RES. Those new tenets hypothesize that: (H-18) “The range and degree of impacts of a Functional Process Zone on biodiversity and ecological processes differ among several factors, including types of FPZs, total river area covered, and dependent variables examined, even in the same river network position”; (H-19) “The degree of ecological differences among types of FPZs vary seasonally with the process being examined while also differing among types of life history characteristics - especially when contrasting responses among seasonal periods of either maximum or minimum growth and reproduction”; (H-20) “The relative importance of in-stream versus watershed drivers of ecological processes in streams can vary within macrosystems and among ecoregions and partially depends on elevation, terrestrial characteristics (natural or human modified), and FPZ type and extent”; and (H-21) “The provision of ecosystem services varies significantly with FPZ type, river size, and location vis-à-vis human populations”. Where appropriate, we also evaluate aspects of several other models published by colleagues that pertain to river ecology.

Macrosystem ecology is a fundamental and applied discipline focused on spatial scales spanning ecoregional to continental scales. Studies generally occur at or above the level of metacommunity ecology, whereas the related discipline of macroecology concentrates at the lower level of populations through communities. Lotic ecologists are primarily interested in how spatial patterns of basin characteristics—elevation, stream size, hydrogeomorphology, substrates, riparian features, land use, and human alterations—influence ecological properties. Lentic researchers often focus on lakes or wetlands in ecoregions through continents varying in spatial patterns of basin characteristics, such as lake morphometry, connections with other waters, thermal properties, and human impacts.

Quantifying the trophic basis of production for freshwater metazoa at broad spatial scales is key to understanding ecosystem function and has been a research priority for decades. However, previous lotic food web studies have been limited by geographic coverage or methodological constraints. We used compound-specific stable carbon isotope analysis of amino acids (AAs) to estimate basal resource contributions to fish consumers in streams spanning grassland, montane and semi-arid ecoregions of the temperate steppe biome on two continents. Across a range of stream sizes and light regimes, we found consistent trophic importance of aquatic resources. Essential AAs of heterotrophic microbial origin generally provided secondary support for fishes, while terrestrial carbon did not seem to provide significant, direct support. These findings provide strong evidence for the dominant contribution of carbon to higher-order consumers by aquatic autochthonous resources (primarily) and heterotrophic microbial communities (secondarily) in temperate steppe streams.

Energetics, food webs, and species diversity in large rivers reflect river depth and hydrogeomorphic complexity. Rivers with extensive lateral slackwater channels feature high fish, zoobenthic, and zooplanktonic diversities, with side channel fauna more closely resembling those in mid-order rivers than adjacent main channels. Communities are energetically supported primarily by autochthonous carbon (algae and some vascular macrophytes) from main channel, lateral slackwaters, or periodically connected lentic habitats and secondarily by allochthonous carbon from floodscape plants. System metabolism is sustained principally by bacteria-viral loop processing of allochthonous carbon from local and upstream riparia. Contributions of floodscape carbon to riverine food webs varies with the length and predictability of major floods and temporal links with periods of maximum animal production and reproduction.

Theoretical models have spurred empirical testing to understand how anthropogenic disturbances cause sudden shifts between alternative functional states. Most studies are done over short periods of time, making it difficult to determine the occurrence of ecological thresholds or regime shifts. This study used carbon stable isotope ratios (δ 13 C) from museum specimens of fish, mussels, and snails over a timeline of 75+ years to ascertain if trophic structure of two hydrologically modified rivers changed between premodification and postmodification periods. An alternative state model following Scheffer's shallow lake model was developed. As long‐lived species, mussels and snails are time integrators with long tissue turnover time and serve as a surrogate for the balance of benthic and pelagic basal food resource contributions to fish biomass. Hydrological datasets over the period of record for the Upper Mississippi (UMR) and lower Ohio (LOR) rivers were placed in 5‐year intervals, as were δ 13 C data for invertivorous and piscivorous fish. The model indicated changes in δ 13 C of fish relative to changes in mean stage height (UMR) and mean minimum stage height (LOR) over time. Evidence based on the model and empirical data of δ 13 C‐stage height relationship suggests a regime shift occurred during the postdam period in the LOR. Postdam, fish from the UMR revealed little change in δ 13 C of invertivores, whereas postdam decreases in variability of δ 13 C for piscivores shifted from a threshold to an unstable equilibrium. Decreases in hydrological variability led to a loss of resilience, with both rivers becoming metastable due to hydrological modification.

In an era of unprecedented human impacts on the planet, macrosystems biology (MSB) was developed to understand ecological patterns and processes within and across spatial and temporal scales. We used machine‐learning and qualitative literature review approaches to evaluate the thematic composition of MSB from articles published since the 2010 creation of the US National Science Foundation’s MSB Program. The machine‐learning analyses revealed that MSB articles studied scale and human components similarly to six ecology subdisciplines, indicating that MSB has deep ecological roots. A comparison with 84,841 ecological studies demonstrated that MSB has extended the knowledge space of ecology by examining large‐scale patterns and processes alongside anthropogenic factors, which was also confirmed by the qualitative literature review approach. Our analyses indicated that MSB emphasizes large scales, has deep roots in ecological disciplines, and may emerge as a new research frontier, but this last point has yet to be proven.

Macrosystems are integrated human–natural systems, in recognition of the fact that virtually every natural system on Earth influences and is influenced by human activities, even over long distances. It is therefore crucial to incorporate inherent properties of broad‐scale systems, such as human–nature connectivity and feedbacks at multi‐scales, into macrosystems biology studies. Here, we propose the “metacoupling” framework as a macrosystems biology approach. This framework incorporates the study of ecological and socioeconomic dimensions and their interactions within, between, and among adjacent and distant locations. We present examples highlighting that (1) human activities are increasing multi‐scale interactions; (2) the increase in frequency and intensity of distant interactions reduces the importance of proximity as a dominant factor connecting systems; and (3) metacoupling generates both ecological and socioeconomic feedbacks, with profound impacts. The metacoupling framework discussed here can advance macrosystems biology, create opportunities for innovative scientific discoveries, and address global challenges.

Global freshwater biodiversity is declining dramatically, and meeting the challenges of this crisis requires bold goals and the mobilisation of substantial resources. While the reasons are varied, investments in both research and conservation of freshwater biodiversity lag far behind those in the terrestrial and marine realms. Inspired by a global consultation, we identify 15 pressing priority needs, grouped into five research areas, in an effort to support informed stewardship of freshwater biodiversity. The proposed agenda aims to advance freshwater biodiversity research globally as a critical step in improving coordinated actions towards its sustainable management and conservation.

We examined how communities of macroinvertebrates occurring in functional process zones (FPZs) are affected by the location of FPZs in the river continuum. We delineated FPZs for three rivers displaying significant disparities in elevation, annual precipitation, valley shape, and other valley‐scale hydrogeomorphic variables. We extracted corresponding macroinvertebrate community data from the US National Water Quality Monitoring Council database and matched it to the stream order (SO) and FPZ delineations. We examined community structure in the three rivers by partitioning the variances associated with the FPZ and SO delineations. Then, we examined community variation as patterns of beta‐diversity for communities of FPZs in different SOs. In total, 23 FPZ‐SO configurations were examined. SO and FPZ delineations contributed similarly to the variance in the structure of macroinvertebrate communities. Taxa turnover accounted for the majority of the compositional change in communities of FPZs along the river continuum, while the functional composition showed primarily a nested structure. Pairwise comparison of communities for each FPZ along the river continuum showed that significant differences in community composition occurred at high SO in the three examined rivers. In this manuscript, we show that communities of FPZs are only partially comparable along the river continuum as significant compositional changes occur when comparing communities of FPZs in distant SOs. We bring, therefore, new elements to improve the interpretation of the River Ecosystem Synthesis concept that can have wider implications for understanding the biocomplexity of hydrogeomorphic patchiness in river networks.

Abstract River hydrogeomorphology is a major driver shaping biodiversity and community composition. Here, we examine how hydrogeomorphic heterogeneity expressed by Functional Process Zones (FPZs) in river networks is associated with fish assemblage variation. We examined this association in two distinct ecoregions in Mongolia expected to display different gradients of river network hydrogeomorphic heterogeneity. We delineated FPZs by extracting valley‐scale hydrogeomorphic variables at 10 km sample intervals in forest steppe (FS) and in grassland (G) river networks. We sampled fish assemblages and examined variation associated with changes in gradients of hydrogeomorphology as expressed by the FPZs. Thus, we examined assemblage variation as patterns of occurrence‐ and abundance‐based beta diversities for the taxonomic composition of assemblages and as functional beta diversity. Overall, we delineated 5 and 6 FPZs in river networks of the FS and G, respectively. Eight fish species were found in the FS river network and seventeen in the G, four of them common to both ecoregions. Functional richness was correspondingly higher in the G river network. Variation in the taxonomic composition of assemblages was driven by species turnover and was only significant in the G river network. Abundance‐based taxonomic variation was significant in river networks of both ecoregions, while the functional beta diversity results were inconclusive. We show that valley‐scale hydrogeomorphology is a significant driver of variation in fish assemblages at a macrosystem scale. Both changes in the composition of fish assemblages and the carrying capacity of the river network were driven by valley‐scale hydrogeomorphic variables. River network hydrogeomorphology as accounted for in the study has, therefore, the potential to inform macrosystem scale community ecology research and conservation efforts.