Local and regional drivers influence how aquatic community diversity, resistance and resilience vary in response to drying

Disturbance events govern how the biodiversity of ecological communities varies in both space and time. In freshwater ecosystems, there is evidence that local and regional‐scale drivers interact to influence ecological responses to drying disturbances. However, most research provides temporal snapshots at the local scale, whereas few studies encompass a gradient of drying severity spanning multiple years. Using a dataset of rare spatiotemporal extent and detail, we demonstrate how independent and interacting local and regional‐scale factors drive shifts in the α and β diversities of communities in dynamic river ecosystems. We examined aquatic invertebrate assemblage responses to hydrological variability (as characterized by monthly observations of instream conditions) at 30 sites over a 12‐year period encompassing typical years and two severe drought disturbances. Sites varied in their disturbance regimes and hydrological connectivity at both local (i.e. site‐specific) and regional (i.e. river catchment) scales. Whereas α diversity was mainly influenced by local factors including flow permanence and the temporal extent of ponded and dry conditions, both temporal and spatial β diversities also responded to regional‐scale metrics such as the spatial extent of flow and hydrological connectivity. We observed stronger local negative responses for taxa with lower capacities to tolerate drying (i.e. resistance) and/or to recover after flow resumes (i.e. resilience), whereas taxa with functional traits promoting resilience made an increasing contribution to spatial β diversity as hydrological connectivity declined. As droughts increase in extent and severity across global regions, our findings highlight the functional basis of taxonomic responses to disturbance and connectivity, and thus advance understanding of how drying disturbances shape biodiversity in river networks. Our identification of the role of regional hydrological factors could inform catchment‐scale management strategies that support ecosystem resilience in a context of global change

An invertebrate-based index to characterize ecological responses to flow intermittence in rivers

Intermittent streams occur across global regions, and are increasingly recognized to support high bio-diversity and perform important ecological roles within catchments. New tools are needed to better characterize biotic responses to the full spectrum of environmental conditions that occur in these dynamic systems, because the biological indices developed to assess ecological responses to flow in perennial rivers may be inaccurate in intermittent streams. We present the Monitoring Intermittent Streams index (MIS-index), a new biological index that can be used to assess invertebrate responses to environmental changes spanning flowing, ponded and drying states. As well as fully aquatic taxa, the index includes semi-aquatic and terrestrial invertebrates from marginal habitats, which are collected during the standard surveys used by regulatory agencies to assess ecological quality. We explore how including these taxa within an index informs our understanding of aquatic–terrestrial invertebrate community responses to changing habitat composition, as intermittent streams transition from lotic to lentic then drier conditions. We explain the development of the MIS-index and explore its performance compared with other indices. We suggest index combinations that can be used to detect different aspects of ecological responses to variation in instream conditions, and highlight the advantages of including semi-aquatic and terrestrial taxa. We call for researchers to test the performance of the MIS-index across a wide range of intermittent stream types, to enable its development into an internationally applicable tool for the holistic assessment of ecological responses to changing hydrological conditions including drying

Short-term streambed drying events alter amphipod population structure in a central European stream

Temporary streams are becoming increasingly common, but ecological responses to streambed drying are poorly characterized in the temperate continental region of central Europe. In addition, global research has focused on community responses to drying, whereas effects on individual populations remain unknown. We explored the population structure of Gammarus fossarum (Crustacea: Amphipoda) in a central European temporary stream. Benthic gammarids were sampled on five dates during a flow recession, one date between two drying events (of 10 and 20 days, respectively), and five dates after flow resumed. Additional benthic samples were taken from isolated pools and dry sediments during drying events, and freeze cores were collected to compare the vertical distribution of amphipods during wet and dry phases. Gammarids were measured, adults distinguished from juveniles, adults sexed, and female reproductive state determined. Densities increased during flow recession, potentially reflecting both a decline in submerged habitat availability and seasonal increases in juvenile abundance. Persistence within dry benthic sediments was minimal, whereas pools and saturated subsurface sediments supported high population densities. Juveniles comprised 80 % of the subsurface population, suggesting that their ability to inhabit small interstices promotes persistence within the dry reach. Juveniles also comprised 92 % of pool inhabitants, despite their potential exposure to predation. Adults dominated after flow resumed, and population structure was altered post-drying by the loss of spring-recruited juveniles and reproductive females. Our results suggest that streambed drying may have longer-term effects than typically characterized by community-level studies. We recommend management actions that support populations of ecologically important species as they adapt to changing flow regimes

Biological indices to characterize community responses to drying in streams with contrasting flow permanence regimes

Many river networks include temporary reaches that stop flowing and may dry during unpredictable droughts (near-perennial) or more frequently (intermittent). A few biological indices have been developed to assess invertebrate community responses to hydrological variability, including the instream conditions associated with drought, but their performance in temporary streams remains poorly known. We evaluated the ability of two such indices, the Lotic-invertebrate Index for Flow Evaluation (LIFE) and the Drought Effect of Habitat Loss on Invertebrates (DEHLI), to predict responses to flow cessation and drying in temporary streams with contrasting flow permanence regimes. We used a 26-year dataset comprising spring-season invertebrate community samples and daily discharge measurements from 46 sites in a cool, wet temperate region, to examine relationships between hydrological variables and changes in index scores. We also identified taxon-specific thresholds at which occurrence changed with increasing drying and flowing durations. Both indices effectively characterized responses to increasing no-flow durations. DEHLI also reflected community changes following flow resumptions, identified differences in responses among flow permanence groups, and was particularly able to predict community responses at near-perennial sites. DEHLI scores at near-perennial sites took on average three years after a drying event to return to values typical of perennial sites, whereas responses to increasing flow duration were more erratic at intermittent sites. Lotic specialists declined whereas lentic and semi-aquatic taxa increased in occurrence with no-flow duration after summers with <50 days without flow, due to changes in the availability of preferred habitat types. Community responses to drying events were less predictable among intermittent than near-perennial sites, likely because differences in habitat conditions and connectivity may lead intermittent communities to harbour contrasting pools of species with strategies that promote persistence during and/or recolonization after drying. We identify DEHLI as an index that can characterize community responses to drying in temporary streams with contrasting flow permanence regimes. We also recommend the development of new indices that include lentic, semi-aquatic and terrestrial as well as lotic taxa, to more comprehensively describe and predict community responses to changing instream conditions

Community assembly mechanisms in river networks:exploring the effect of connectivity and disturbances on the assembly of stream communities

Abstract Community assembly results from a combination of deterministic and stochastic mechanisms, whose relative effects can vary in response to environmental heterogeneity, connectivity, disturbance regimes and anthropogenic stressors. Understanding how community assembly mechanisms vary in response to environmental changes and connectivity is crucial for the management and conservation of river ecosystems. In this thesis, I tested the effects of connectivity and natural flow disturbances on riverine invertebrate communities by assessing assembly mechanism changes in response to (I) habitat connectivity, (II) seasonal flow intermittency and (III) inter–annual hydrological variability. I also conducted a field experiment to test for (IV) the effects of human–induced nutrient enrichment on community assembly of microorganisms (diatoms and aquatic fungi) and stream ecosystem functioning under different environmental settings. Invertebrate community assembly changed gradually with habitat connectivity. While limited dispersal resulted in higher community variability in the most isolated streams, mass effects caused community homogenization in the most connected ones. Natural and human induced disturbances lead to changes in the relative importance of deterministic and stochastic factors but often through different, or even opposite, mechanisms depending on the natural background of the ecosystem and organism type considered. For instance, seasonal drying and high–flow periods in intermittent Mediterranean rivers promoted deterministic and stochastic assembly processes respectively, whereas environmental sorting and stochastic processes respectively dominated during high and low flow years in boreal streams. Diatom and fungal communities responded differently to nutrient enrichment, with detrital processes and fungal communities responding more in naturally acidic than in circumneutral streams. The results of this thesis highlight the complexity of community assembly mechanisms: they tend to be highly context dependent and temporally variable. Therefore, stream bioassessment and conservation will benefit from explicitly incorporating connectivity and natural disturbance regimes. Assessing the interactive effects of connectivity and disturbances at the river network scale would provide a greater understanding of community assembly mechanisms and river ecosystem functioning.Tiivistelmä Eliöyhteisöjen koostumus heijastelee determinististen ja stokastisten mekanismien vuorovaikutusta. Niiden suhteellinen merkitys vaihtelee suhteessa yhteisöjen kytkeytyneisyyteen sekä luontaisiin ja ihmisen aiheuttamiin häiriöihin. Yhteisöjen säätelymekanismit vaihtelevat jokiverkoston eri osissa ja tietoa tästä vaihtelusta tarvitaan jokiekosysteemien hoidon kehittämiseksi. Tässä tutkielmassa testasin elinympäristöjen kytkeytyneisyyden ja luontaisten häiriöiden (virtaamavaihtelut) vaikutuksia jokien selkärangatonyhteisöihin. Suoritin myös kenttäkokeen, jossa testattiin ihmisen aiheuttaman rehevöitymisen vaikutuksia mikro–organismeihin (piilevät, mikrobit) ja ekosysteemitoimintoihin erilaisissa ympäristöoloissa (luontaisesti happamat vs. neutraalit purot). Selkärangattomien yhteisökoostumus muuttui asteittain jokiverkostossa. Yhteisökoostumuksen vaihtelu oli suurinta eristäytyneimmissä latvapuroissa, kun taas isommissa, uomaston keskivaiheilla sijaitsevissa koskissa voimakas levittäytyminen eri suunnista (ns. massatekijät) aiheutti yhteisöjen rakenteen homogenisoitumista. Kuivuusjaksot ja niitä seuraavat korkean virtaaman jaksot edistivät determinististen prosessien merkitystä Välimeren alueen joissa, kun taas boreaalisissa puroissa Pohjois–Suomessa äärevät virtaamaolot, erityisesti poikkeuksellisen kuivat kesät, edistivät satunnaismekanismien vaikutusta. Perustuottajat (piilevät) ja hajottajat (akvaattiset sienet) vastasivat eri tavoin ravinnelisäykseen. Sienten hajotustoiminta nopeutui ravinnelisäyksen myötä, mutta vain luontaisesti happamissa puroissa. Tämän opinnäytetyön tulokset korostavat yhteisön kokoonpanomekanismien monimutkaisuutta: ne ovat usein erittäin tilanneriippuvaisia ja ajallisesti vaihtelevia. Siksi jokien ekologisen tilan arvioinnissa tulisi huomioida tutkimuspaikkojen kytkeytyneisyys jokimaisemassa

Wind directionality and strength affects wetland invertebrate metacommunities in Patagonia

Wind has the potential to shape metacommunities by affecting organism dispersal strength and directionality. Here we evaluate the relative importance of wind in the assembly of wetland invertebrate metacommunitiesof active (i.e. flying adults) and passive (e.g. through birds) dispersers in Patagonia. This region experiences some of the strongest winds on Earth, with persistenceof westerly winds. The study included invertebrate samples collected from 82 pristine wetlands across the Argentinian Patagonia. For each wetland we measured water quality, morphology and plant cover. These variables were used to calculate an environmental distance between sites (i.e. how each pair of sites wasin terms of local habitat conditions). Then, we built two metric of landscape resistance to dispersal between sites: topographic (i.e. least cost path between sites taking into account topographic barriers) and wind (i.e. least cost path between sites taking into account wind speed). We built distance-decay relationships of macroinvertebrate community similarity for each distance. Wind had amuch stronger effect than environmental conditions and topography on the metacommunity organization of passive dispersers. On the contrary, wind had a weak effect on the organization of active dispersers? metacommunities when compared with topography and environmental conditions. Our results suggest that metacommunity studies should account for the effects on external dispersal agents, with e.g. wind being a major determinant of community organization.Fil: Cañedo Arguelles, M.. Universidad de Barcelona. Facultad de Biología. Departamento de Biología Animal; EspañaFil: Dos Santos, Daniel Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto de Biodiversidad Neotropical. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Instituto de Biodiversidad Neotropical. Instituto de Biodiversidad Neotropical; ArgentinaFil: Sarremejane, R.. University of California; Estados UnidosFil: Grech, Marta Gladys. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Centro de Investigación Esquel de Montaña y Estepa Patagónica. Universidad Nacional de la Patagonia "San Juan Bosco". Centro de Investigación Esquel de Montaña y Estepa Patagónica; ArgentinaFil: Macchi, Pablo Antonio. Universidad Nacional de Río Negro. Sede Alto Valle. Instituto de Investigaciones en Paleobiología y Geología; ArgentinaFil: Manzo, Luz Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Centro de Investigación Esquel de Montaña y Estepa Patagónica. Universidad Nacional de la Patagonia "San Juan Bosco". Centro de Investigación Esquel de Montaña y Estepa Patagónica; ArgentinaFil: Miserendino, Maria Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Centro de Investigación Esquel de Montaña y Estepa Patagónica. Universidad Nacional de la Patagonia "San Juan Bosco". Centro de Investigación Esquel de Montaña y Estepa Patagónica; ArgentinaFil: Bonada, Núria. Universidad de Barcelona. Facultad de Biología. Departamento de Biología Animal; EspañaFil: Epele, Luis Beltran. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Centro de Investigación Esquel de Montaña y Estepa Patagónica. Universidad Nacional de la Patagonia "San Juan Bosco". Centro de Investigación Esquel de Montaña y Estepa Patagónica; ArgentinaXX Congreso de la Asociación Ibérica de Limnología, III Congreso Iberoamericano de LimnologíaMurciaEspañaAsociación Ibérica de Limnologí