1. Determined by landscape structure as well as dispersal-related traits of species, connectivity influences various key aspects of population biology, ranging from population persistence to genetic structure and diversity. Here, we investigated differences in small-scale connectivity in terms of gene flow between populations of two ecologically important invertebrates with contrasting dispersal-related traits: an amphipod (Gammarus fossarum) with a purely aquatic life cycle and a mayfly (Baetis rhodani) with a terrestrial adult stage. 2. We used highly polymorphic markers to estimate genetic differentiation between populations of both species within a Swiss pre-alpine catchment and compared these results to the broader-scale genetic structure within the Rhine drainage. Landscape genetic approaches were used to test for correlations of genetic and geographical structures and in-stream barrier effects. 3. We found overall very weak genetic structure in populations of B. rhodani. In contrast, G. fossarum showed strong genetic differentiation, even at spatial scales of a few kilometres, and a clear pattern of isolation by distance. Genetic diversity decreased from downstream towards upstream populations of G. fossarum, suggesting asymmetric gene flow. Correlation of genetic structure with landscape topography was more pronounced in the amphipod. Our study also indicates that G. fossarum might be capable of dispersing overland in headwater regions and of crossing small in-stream barriers. 4. We speculate that differences in dispersal capacity but also habitat specialisation and potentially the extent of local adaptation could be responsible for the differences in genetic differentiation found between the two species. These results highlight the importance of taking into account dispersal-related traits when planning management and conservation strategies.

We present a new hydro-morphological index of diversity (HMID), a tool aimed for use in river engineering projects and firstly developed at gravel-bed streams in Switzerland, but intended for a broader use. We carried out field work with extensive hydraulic and geomorphic data collection, conducted correlation analysis with hydro-morphological variables, formulated the HMID, and analyzed the correlation between HMID and a visual habitat assessment method. The HMID is calculated by means of the coefficient of variation of the hydraulic variables flow velocity and water depth, which have been demonstrated to sufficiently represent the hydro-morphological heterogeneity of alpine gravel-bed stream reaches.Based on numerical modeling, the HMID can be calculated easily for a comparison of different alternatives in river engineering projects and thus achieves predictive power for design decisions. HMID can be applied at a reach-related scale in engineering programs involving geomorphic measures that aim at the enhancement of habitat heterogeneity of a stream. However, the application of HMID has to be integrated with evaluations of the long-term streambed evolvements that are considered at a catchment scale and strongly related to the sediment regime of the stream under study.

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Dispersal is an essential process in population and community dynamics, but is difficult to measure in the field. In freshwater ecosystems, information on biological traits related to organisms’ morphology, life history and behaviour provides useful dispersal proxies, but information remains scattered or unpublished for many taxa. We compiled information on multiple dispersal-related biological traits of European aquatic macroinvertebrates in a unique resource, the DISPERSE database. DISPERSE includes nine dispersal-related traits subdivided into 39 trait categories for 480 taxa, including Annelida, Mollusca, Platyhelminthes, and Arthropoda such as Crustacea and Insecta, generally at the genus level. Information within DISPERSE can be used to address fundamental research questions in metapopulation ecology, metacommunity ecology, macroecology and evolutionary ecology. Information on dispersal proxies can be applied to improve predictions of ecological responses to global change, and to inform improvements to biomonitoring, conservation and management strategies. The diverse sources used in DISPERSE complement existing trait databases by providing new information on dispersal traits, most of which would not otherwise be accessible to the scientific community.

Although climate warming has been widely demonstrated to induce shifts in the timing of many biological events, the phenological consequences of other prominent global change drivers remain largely unknown. Here, we investigated the effects of biological invasions on the seasonality of leaf litter decomposition, a crucial freshwater ecosystem function. Decomposition rates were quantified in 18 temperate shallow lakes distributed along a gradient of crayfish invasion and a temperature-based model was constructed to predict yearly patterns of decomposition. We found that, through direct detritus consumption, omnivorous invasive crayfish accelerated decomposition rates up to fivefold in spring, enhancing temperature dependence of the process and shortening the period of major detritus availability in the ecosystem by up to 39 days (95% CI: 15-61). The fact that our estimates are an order of magnitude higher than any previously reported climate-driven phenological shifts indicates that some powerful drivers of phenological change have been largely overlooked.

SUMMARY1. Molecular genetic techniques have been used in freshwater biology for more than 30 years. Early work focussed on studies of population structure, systematics and taxonomy. More recently, the range of studies has broadened to include ecology and adaptation. Advances in analytical methods and in technology (e.g. next-generation sequencing) and decreasing costs of data production ensure that the field will continue to develop and broaden in scope. 2. At least three factors make the application of molecular techniques to freshwater biology exciting. First, the highly variable nature of many aquatic habitats makes them excellent models for the study of environmental change on ecological and evolutionary time scales. Second, the mature state of the field of freshwater biology provides an extensive foundation of ecological knowledge of freshwater organisms and their distinct adaptations. Third, the methodological advances allow researchers to focus more on merging molecular and ecological research and less on designing studies around technical limitations. 3. We identified eight research areas in freshwater biology in which the integration of molecular and ecological approaches provides exceptional opportunities. The list is not exhaustive, but considers a broad range of topics and spans the continuum from basic to applied research. The areas identified use a combination of natural, experimental and in silico approaches. 4. With advancing molecular techniques, freshwater biology is in an unusually strong position to link the genetic basis and ecological importance of adaptations across a wide range of taxa, ecosystems and spatiotemporal scales. Our aim was to identify opportunities for the integration of molecular and ecological approaches, to motivate greater collaboration and crossover, and to promote exploitation of the synergies of bridging ecological and evolutionary freshwater research.

BIOSKETCH 39 Many of the authors are members of the European Cooperation in Science and Technology 40 (COST) Action CA15113 Science and Management of Intermittent Rivers and Ephemeral 41 Streams (SMIRES, www.smires.eu), which aims to improve our understanding of intermittent 42 rivers and ephemeral streams (IRES) and translate this into science-based, sustainable 43 management of river networks. One of the main goals of SMIRES is to facilitate sharing of 44 data and experience, bringing together researchers from many disciplines and stakeholders 45 and creating synergies through networking. The dataset provided and analyzed herein reflects 46 3 networking and collaboration within the SMIRES working group dedicated to Community 47 Ecology and Biomonitoring. 48 49 Abstract 50 Motivation: Dispersal is an essential process in population and community dynamics but is 51 difficult to measure in the field. In freshwater systems, relevant information on the dispersal 52 of many taxa remains scattered or unpublished, and biological traits related to organisms' 53 morphology, life history and behaviour offer useful dispersal proxies. We compiled 54 information on selected dispersal-related biological traits of European aquatic 55 macroinvertebrates in a unique source: the DISPERSE database. Information within 56 DISPERSE can be used to address fundamental questions in metapopulation ecology, 57 metacommunity ecology, macroecology, and eco-evolutionary research. From an applied 58 perspective, the consideration of dispersal proxies can also improve predictions of ecological 59 responses to global change, and contribute to more effective biomonitoring and conservation 60 management strategies. 61 Main types of variable contained: Selected macroinvertebrate dispersal-related biological 62 traits: maximum body size, adult female wing length, adult wing pair type, adult life span, 63 number of reproductive cycles per year, lifelong fecundity, dispersal mode (i.e. active, 64 passive, aquatic, aerial), and propensity to drift. 65 Spatial location: Europe.66 Time period: Taxa considered are extant with recent records. Most data were collected in the 67 20th century and in the period 2000-2019.68 4 Major taxa and level of measurement: Aquatic macroinvertebrates from riverine and 69 lacustrine ecosystems, including Mollusca, Annelida, Platyhelminthes, and Arthropoda such 70 as Crustacea and Insecta. For Insecta, aquatic stages and the aerial (i.e. flying) phases of 71 adults were considered separately. Genus-level taxonomic resolution used, except for some 72 Annelida and Diptera, which are coded at the sub-class, family or sub-family level. In total, 73 the database includes 39 trait categories grouped into nine dispersal-related traits for 480 taxa.74 Software format: The data file is in Excel workbook.75

Stable isotopes (13 C and 15 N) are widely applied in studies of trophic links. We used this method to investigate the contribution of aquatic and terrestrial prey to the diet of riparian predatory arthropods in two mountain headwater streams in Colorado, USA. Aquatic and terrestrial prey and riparian predators were collected during summer 2009. To evaluate the reliability of conclusions based on stable isotope ratios, we compared the isotopic signatures of aquatic larval and terrestrial adult stages of three abundant stream insect species and assessed variation in mixing model estimates for spider diet composition under varying assumptions for trophic fractionation. Adult isotopic signatures of some aquatic prey species were indistinguishable from those of prey species with exclusively terrestrial life histories (stoneflies: 13 C and 15 N, chironomids: 13 C). Other prey had distinctly aquatic isotopic signatures as both larvae and adults (a mayfly and a caddisfly). There was no evidence that prey with aquatic isotopic signatures contributed to the diet of the spiders near one stream. For the other stream, mixing model analysis suggested that chironomids were included in the diets of lycosid, linyphiid and liocranid spiders. Reliable estimates of the contributions of prey sources were compromised by the sensitivity of mixing models to assumptions on trophic fractionation and the presence of ''isotopically cryptic'' prey. This study emphasizes the importance of supporting isotope-based studies on crossboundary trophic links with data on isotopic shifts in prey with complex life cycles and assessment of fractionation rates specific to the study system.