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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.

Stream fishes are restricted to specific environments with appropriate habitats for feeding and reproduction. Interactions between streams and surrounding landscapes influence the availability and type of fish habitat, nutrient concentrations, suspended solids, and substrate composition. Valley width and gradient are geomorphological variables that influence the frequency and intensity that a stream interacts with the surrounding landscape. For example, in constrained valleys, canyon walls are steeply sloped and valleys are narrow, limiting the movement of water into riparian zones. Wide valleys have long, flat floodplains that are inundated with high discharge. We tested for differences in fish assemblages with geomorphology variation among stream sites. We selected rivers in similar forested and endorheic ecoregion types of the United States and Mongolia. Sites where we collected were defined as geomorphologically unique river segments (i.e., functional process zones; FPZs) using an automated ArcGIS‐based tool. This tool extracts geomorphic variables at the valley and catchment scales and uses them to cluster stream segments based on their similarity. We collected a representative fish sample from replicates of FPZs. Then, we used constrained ordinations to determine whether river geomorphology could predict fish assemblage variation. Our constrained ordination approach using geomorphology to predict fish assemblages resulted in significance using fish taxonomy and traits in several watersheds. The watersheds where constrained ordinations were not successful were next analyzed with unconstrained ordinations to examine patterns among fish taxonomy and traits with geomorphology variables. Common geomorphology variables as predictors for taxonomic fish assemblages were river gradient, valley width, and valley slope. Significant geomorphology predictors of functional traits were valley width‐to‐floor width ratio, elevation, gradient, and channel sinuosity. These results provide evidence that fish assemblages respond similarly and strongly to geomorphic variables on two continents., This study demonstrates the utility of spatial analysis in predicting functional process zones and fish assemblage variation in endorheic basins and forest steppe ecoregions of two continents.

Current understanding of how streamflow in terminal basins is driven by climatic and hydrogeomorphic characteristics is limited, despite the fact that these closed systems show an increased sensiti...

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.

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. ispartof: ECOLOGY LETTERS vol:25 issue:2 pages:255-263 ispartof: location:England status: published

Our project sought to determine ecological effects of adding low‐head dams and levees to large rivers by examining potential changes to aquatic food webs over a 70‐year period in the Lower Ohio River (LOR) and Upper Mississippi River (UMR). We employed museum collections of fish and compound specific stable isotope analysis of amino acids to evaluate long‐term changes in primary food sources for multiple species of fish in each river. Fishes in both rivers depended more on autochthonous than allochthonous carbon sources throughout the 70‐year period (based on measurements of isotopic signatures of algae, C₃ plants, C₄ plants, cyanobacteria, and fungi), but the relative use of different carbon sources differed between the UMR and LOR. Significant but opposite shifts in trophic positions (TP) between rivers over time (higher TP in the UMR; lower in the LOR) were correlated with major anthropogenic changes to habitat structure (e.g. slight decrease in abundance of side channels in the UMR; increase in pool water depth in the LOR) resulting from low‐head dam construction. They may also have been influenced by likely increased primary productivity in the UMR from agricultural nitrogen inputs and by possible shifts in the importance of phytoplankton versus benthic algae in the LOR from changes in water depth. Shifts in trophic position and reliance on various food sources were not correlated with variation in discharge, gage height, or temperature. Although these two rivers have contrasting hydrogeomorphic complexity (UMR is an anastomosing river, while the LOR is a constricted channel river) and different discharge patterns (seasonal versus yearly operation in some cases), both differ substantially from rivers having hydrogeomorphic changes resulting from construction of high dams (>15 m). It is not surprising, therefore, that factors controlling trophic position and reliance on different carbon sources vary among different types of dams and river structures.

The dissolved oxygen diel cycle is an inherent feature of stream ecosystems, and the amplitude in this diel fluctuation is thought to strongly influence the composition of stream communitie...

Rivers are being increasingly analyzed from a holistic scale focus, imposing the challenge to establish a clear sampling framework that integrates complex valley-to-reach hydrogeomorphic features. Here, we address this challenge by examining macroinvertebrate communities of different hydrogeomorphic patches, or Functional Process Zones (FPZs), established by the GIS-based model RESonate. We delineated FPZs across three endorheic drainages in the Great Basin, USA, using a self-emerging clustering method that classifies segments of rivers with similar hydrogeomorphic characteristics. We sampled macroinvertebrate communities across different FPZs. We examined the taxonomic and functional organizations of these communities, and we assessed the relative contributions of in-stream and watershed-scale environmental filters in structuring these communities. We found discreet macroinvertebrate communities associated with FPZs across drainages, where elevation prevailed on valley confinement in structuring these communities. Communities of upland FPZs exhibited a higher heterogeneity suggested by higher β-diversity and nested structure of communities, while lowland FPZs showed a higher pairwise abundance agreement across communities. Eltonian trait composition, primarily describing bionomic traits, showed a higher degree of niche differentiation in upland FPZs, thereby increasing the overall ecosystem function. Differences in variance partitioning among environmental filters acting at different spatial scales show a strong spatial structure in the response of communities in different FPZs. Overall, environmental filters had a stronger control of the communities' functional organization than the taxonomic composition. Our results support the paradigm of different FPZs having distinct communities that express different ecosystem properties. Findings of this study constitute a fruitful avenue for expanding community-based research using the FPZ template as a tool for riverine ecology. However, the unique nature of rivers in endorheic basins needs to be considered when applying our conclusions to other systems, as some findings (e.g., the higher community homogenization in lowland FPZs) might be specific to this rarely examined type of river systems.

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., Valley‐scale hydrogeomorphology plays a fundamental role structuring river fish assemblages. These pictures show two distinct Functional Process Zones of the hydrogeomorphic gradient established in the Delgermörön river, a major tributary of the Selenge river network. Picture credit: Emily Arsenault, Mongolia, 2017.

Article, 1. Many freshwater systems receive substantial inputs of terrestrial organic matter. Terrestrially derived dissolved organic carbon (t-DOC) inputs can modify light availability, the spatial distribution of primary production, heat, and oxygen in aquatic systems, as well as inorganic nutrient bioavailability. It is also well-established that some terrestrial inputs (such as invertebrates and fruits) provide highquality food resources for consumers in some systems. 2. In small to moderate-sized streams, leaf litter inputs average approximately three times greater than the autochthonous production. Conversely, in oligo/mesotrophic lakes algal production is typically five times greater than the available flux of allochthonous basal resources. 3. Terrestrial particulate organic carbon (t-POC) inputs to lakes and rivers are comprised of 80%–90% biochemically recalcitrant lignocellulose, which is highly resistant to enzymatic breakdown by animal consumers. Further, t-POC and heterotrophic bacteria lack essential biochemical compounds that are critical for rapid growth and reproduction in aquatic invertebrates and fishes. Several studies have directly shown that these resources have very low food quality for herbivorous zooplankton and benthic invertebrates. 4. Much of the nitrogen assimilated by stream consumers is probably of algal origin, even in systems where there appears to be a significant terrestrial carbon contribution. Amino acid stable isotope analyses for large river food webs indicate that most upper trophic level essential amino acids are derived from algae. Similarly profiles of essential fatty acids in consumers show a strong dependence on the algal food resources. 5. Primary production to respiration ratios are not a meaningful index to assess consumer allochthony because respiration represents an oxidised carbon flux that cannot be utilised by animal consumers. Rather, the relative importance of allochthonous subsidies for upper trophic level production should be addressed by considering the rates at which terrestrial and autochthonous resources are consumed and the growth efficiency supported by this food. 6. Ultimately, the biochemical composition of a particular basal resource, and not just its quantity or origin, determines how readily this material is incorporated into upper trophic level consumers. Because of its highly favourable biochemical composition and greater availability, we conclude that microalgal production supports most animal production in freshwater ecosystems., final draft, http://purl.org/eprint/status/PeerReviewed

An updated taxonomic review of freshwater Hexapoda (insects and springtails) found in the Neotropical and Antarctic regions is presented in this chapter along with the introduction to the subphylum Crustacea. Dichotomous identification keys to classes of Crustacea and orders of Hexapoda are included, but readers are referred to “Vol. III: Keys to Neotropical Hexapoda” ( Hamada et al., 2018 ) in our book series for more detailed coverage of Neotropical Hexapoda. This chapter also provides information on material preparation methods, defines relevant morphological terms, and indicates current limitations in our knowledge of the group. Additional information on the “Ecology and General Biology” of hexapods and many other types of crustaceans can be found in Volume I of this book series (Thorp and Rogers, 2015, Elsevier).

A nearly 40-year debate on the origins of carbon supporting animal production in lotic systems has spawned numerous conceptual theories emphasizing the importance of autochthonous carbon, terrestrial carbon, or both (depending on river stage height). Testing theories has been hampered by lack of adequate analytical methods to distinguish in consumer tissue between ultimate autochthonous and allochthonous carbon. Investigators initially relied on assimilation efficiencies of gut contents and later on bulk tissue stable isotope analysis or fatty acid methods. The newest technique in amino acid, compound specific, stable isotope analysis (AA-CSIA), however, enables investigators to link consumers to food sources by tracing essential amino acids from producers to consumers. We used AA-CSIA to evaluate nutrient sources for 5 invertivorous and 6 piscivorous species in 2 hydrogeomorphically contrasting large rivers: the anastomosing Upper Mississippi River (UMR) and the mostly constricted lower Ohio River (LOR). Museum specimens we analyzed isotopically had been collected by other investigators over many decades (UMR: 1900–1969; LOR: 1931–1970). Our results demonstrate that on average algae contributed 58.5% (LOR) to 75.6% (UMR) of fish diets. The next highest estimated contributions of food sources were from C3 terrestrial plants (21.1 and 11.5% for the LOR and UMR, respectively). Moreover, results from 11 individually examined species consistently demonstrated the importance of algae for most fish species in these trophic guilds. Differences among rivers in relative food source availability resulting from contrasting hydrogeomorphic complexity may account for relative proportions of amino acids derived from algae.

Trophic dynamics and the relative importance of allochthonous versus autochthonous production in supporting invertebrate consumers have been studied from headwaters to large rivers but rarely in springs. Our goals were to examine spatial and temporal invertebrate feeding pathways in three U.S. karst springs differing in canopy coverage and type (coniferous, open, or deciduous). Based on current food web models for headwaters, we initially hypothesized that: (a) overall biomass production would primarily depend on allochthonous carbon; (b) terrestrial carbon would be most important following leaf litter input; and (c) autochthonous carbon would be responsible for most of the biomass production in open canopy areas. To test these predictions, we analyzed trophic pathways using carbon and nitrogen stable isotopes, biomass measurements, and stoichiometric analyses. Contrary to our initial hypotheses, the proportional contribution of autochthonous carbon to consumer biomass exceeded that of allochthonous in each spring along temporal and spatial scales. Autochthony increased spatially along the gradient between spring sources and lower springbrook reaches and was highest in the open canopy spring. Allochthony increased slightly during the winter following litter fall. Despite the reported importance of periphyton to zoobenthic consumers, macroinvertebrate biomass was primarily supported by moss and water cress in these springs.

Ephemeral wetlands commonly experience events that would be drastic disturbances in permanent aquatic ecosystems, such as the elimination of all water. It is well known that survival in these harsh habitats requires flexibility in response to natural perturbations, but scientists have rarely investigated if this flexibility translates to anthropogenic stresses. Therefore, we evaluated aquatic crustacean communities in ephemeral wetlands in response to environmental and anthropogenic constraints. We sampled crustacean communities from 73 ephemeral wetlands across 5 states of the North American high plains. Neither habitat size, habitat depth, nor whether a wetland was natural or artificially created had any recognizable effect on the crustacean community. Moreover, natural communities have great flexibility, which seems to impart resilience under some anthropogenic forces. Communities of artificial waterbodies (roadside ditches and stock ponds) were indistinguishable from those in naturally formed wetlands. Cattle grazing, which in some ways resembles effects of native vertebrate grazers, was generally associated with increased invertebrate densities and richness. In contrast, tilling for row-crop agriculture decreased invertebrate density and richness. Overall, current conservation strategies in ephemeral wetlands may need to be revised to include artificial habitats as viable, important habitats, and cattle grazing as an essential ecosystem component in areas now lacking large native grazers, such as bison.

Summary Scientists know relatively little about the ecology of ephemeral aquatic habitats beyond the importance of hydroperiod and vertebrate predators, especially regarding trophic structure. We used playa wetlands, ephemeral habitats common in arid to semi-arid regions, as our study ecosystem. We predicted that larger, more species-rich playas would have food webs with larger dimensions (longer food chains and more energy sources used), more variation (more niches filled) and more redundancy (niche overlap). We used geometric properties of stable C and N isotope biplots to explore: (i) what regulates trophic structure in ephemeral wetlands, (ii) the role of anthropogenic forces in altering factors controlling trophic structure and (iii) how trophic structure in ephemeral systems differs from that typical of permanent systems. We sampled aquatic animal food webs of 21 playa wetlands located mostly in the short-grass prairies of the Pawnee National Grassland in Colorado, U.S.A. Playas with higher insect diversity had more complex trophic structures than those dominated by large branchiopods (tadpole, clam and fairy shrimps). Insect diversity seemed dependent on length of the hydroperiod and time since filling, both of which are determined by playa depth. The key to understanding trophic structure in playas is an interaction between hydroperiod and the traits, lifespans and trophic niches of the species present. The trophic structure of naturally created playas was marginally more complex than artificial playas, and playas buffered by native vegetation were more likely to have food webs that included unique trophic strategies. Food webs of playas influenced by row crop agriculture had a broader selection of food sources. Playas grazed by cattle had food-web structures comparable to those in ungrazed playas, suggesting that playa biota may be adapted to large mammal disturbances. The trophic structure of ephemeral aquatic habitats may not respond to disturbance in the same way as permanent systems. Indeed, food chain length in a playa can actually increase as the ephemeral ecosystem approaches the end of its hydroperiod. Measures of ecosystem size need to include more than the two dimensions of surface area when being applied to general ecological theory. Food webs increase in complexity with time, and many of the same factors that control trophic structure in ephemeral habitats could be important at least at some time in the life of a relatively permanent ecosystem.

Riverine macrosystems are described here as watershed-scale networks of connected and interacting riverine and upland habitat patches. Such systems are driven by variable responses of nutrients and organisms to a suite of global and regional factors (eg climate, human social systems) interacting with finer-scale variations in geology, topography, and human modifications. We hypothesize that spatial heterogeneity, connectivity, and asynchrony among these patches regulate ecological dynamics of whole networks, altering system sensitivity, resistance, and resilience. Long-distance connections between patches may be particularly important in riverine macrosystems, shaping fundamental system properties. Furthermore, the type, extent, intensity, and spatial configuration of human activities (eg land-use change, dam construction) influence watershed-wide ecological properties through effects on habitat heterogeneity and connectivity at multiple scales. Thus, riverine macrosystems are coupled social–ecological sy...

Summary A metamorphic shift in the focus of aquatic ecological research is needed to (i) better understand the functioning of river ecosystems at large spatiotemporal scales; (ii) respond to threats from climate change, species invasions and increased pressure for more river dams and interbasin water transfer; and (iii) meet critical needs for catchment-level management. Implementing changes in research and management necessitate new spatiotemporal and research domains and a partial shift from reach-level studies to macrosystem ecology. Macroecology, as defined here, and associated processes usually cannot be understood simply by scaling up information from smaller extent and finer grain samples because of problems of connectivity and spatial heterogeneity of crucial system components and entanglements from cross-scale interactions producing threshold responses and other nonlinear dynamics. An important driver of macrosystem research in terrestrial and aquatic ecosystems is the immediate and long-term danger from global climate change, which will alter flow regimes, water temperatures and dissolved oxygen in riverine landscapes. An initial step in implementing metamorphic change in river science is to integrate the newest macroecological perspectives with current large-scale riverine concepts, especially ones emphasising the importance of tributary patterns and junctions (Network Dynamics Hypothesis) or the hydrogeomorphic patch nature of rivers at multiple scales (Riverine Ecosystem synthesis). The hierarchical nature, system boundaries and research domains of riverine macrosystem ecology are examined, and twelve sample research questions are provided to help direct future research. Current research impediments to riverine macroecology are discussed, and a partial solution based on the need for Long-Term Ecological Research-like sites (each with a central organisational hub and a diffuse, multi-institutional network of data collection stations at strategic catchment points) is proposed.