Biology subjects

Sarremejane, R.

Publications and source records attributed to Sarremejane, R..

4 recordsLinked to original sources

bioRxiv2025

Drying halves decomposition rates in river networks by disrupting structure-function linkages

River drying is intensifying worldwide due to climate change and water abstraction, with major consequences for biodiversity and ecosystem functioning. In river networks, drying not only alters local environmental conditions but also disrupts hydrological connectivity, reshaping the movement of organisms and resources at the network scale. Leaf litter decomposition--a key ecosystem function in freshwater systems--is particularly sensitive to changes in the structure of decomposer communities. We hypothesized that spatiotemporal patterns of drying regulate decomposition by altering the diversity and composition of detritivore macroinvertebrates, bacteria and fungi. We combined data from six European drying river networks (DRNs) spanning a wide latitudinal gradient to assess how local drying intensity and regional hydrological connectivity affect decomposition through changes in these decomposer groups. We found that short drying events ([≤] six dry days) reduced decomposition rates by up to 50% by shifting the control of decomposition from a balanced contribution of fungi, bacteria, and detritivores to one dominated by dry-tolerant but less efficient bacteria. These community shifts persisted after flow resumption, leading to sustained reductions in decomposition even under flowing conditions. Regional connectivity alleviated these negative effects of local drying by facilitating the recovery of more efficient aquatic decomposers through dispersal. However, this effect depended on DRN context. In particular, in southern, more arid DRNs, stronger fragmentation hindered the recovery of decomposer communities after flow resumption. Overall, our results provide mechanistic evidence that spatiotemporal patterns of drying can regulate the linkages between community structure and ecosystem functioning in river networks. As drying events become more frequent and prolonged, increasing disruption of these linkages will impact carbon cycling and energy fluxes in freshwater ecosystems under global change.

ecology↗

bioRxiv2025

Community resilience in a river network: the roles of connectivity and drying regime

The cross-scale resilience model suggests that resilience, the amount of disturbance an ecosystem can absorb before collapsing and reorganizing, can be measured by evaluating the diversity and redundancy of functions performed by species at different spatiotemporal scales. Yet, little is known about the effects of flow intermittence and associated hydrological connectivity on the resilience capacity of instream communities, and the ecosystem functions they perform. We expected lower resilience capacity in non-perennial and isolated reaches. Here, we used fish and invertebrate community data and litter decomposition rates across 20 sites in a river network naturally fragmented by drying to characterize the drivers of resilience at the river-network scale. Using discontinuity analysis, a set of resilience indicators were calculated from body size distribution and species traits, and related to flow intermittence, network fragmentation and position in the stream network. We found that non-perennial reaches were characterized by lower resilience with fewer species, lower levels of functional redundancy of five out of eight functional feeding groups. Functional redundancy and response diversity in shredders were decoupled, translating into low litter decomposition rates in non-perennial reaches. Upstream reaches were characterized by low community resilience, likely reflecting their isolated position in the river network, but flow intermittence affected more strongly the resilience of downstream than upstream reaches. Cross-scale functional redundancy and grazer response diversity were driven by network fragmentation, meaning that the functions these groups perform might be at risk when facing other anthropogenic pressures. Finally our study suggests that reliable resilience assessments need to be based on several standardized indicators and call for more studies comparing these indicators in diverse ecosystems.

ecology↗

bioRxiv2024

Natural disturbances and connectivity shape the seasonal variability of aquatic macroinvertebrate communities across Europe

Understanding the joint influence of natural disturbance, spatial connectivity and biogeography on biodiversity is essential to forecast its responses to climate change. Macroinvertebrate communities in drying river networks constitute an ideal study system to understand the interplay of these ecological processes. We analyze the taxonomic and functional structure of macroinvertebrate communities sampled across 126 reaches with perennial and intermittent streamflow, surveyed in six drying river networks (DRN) across Europe, six times over one year. Drying frequency decreased community richness and functional diversity of communities, whereas spatio-temporal connectivity increased community richness in intermittent reaches. Communities experiencing a high drying frequency increased the proportion of taxa with K-strategies and drying resistance traits. Communities experiencing a long drying duration compensated by high spatio-temporal connectivity had more taxa with a r-strategy and high dispersal ability. Perennial communities varied from taxa-poor communities of r-strategists in spring and autumn and taxa-rich communities of K-strategists in summer and had a constant functional diversity throughout the year. When drying frequency increased, communities showed a similar pattern except in autumn when they shifted towards species-poor communities of K-strategists. Functional diversity then peaked in summer. Community trait structure and in particular optimal drying resistance traits changed across biogeographical scales. It opposed communities from mountainous DRN (with more r-strategies and high dispersal ability) to non-mountainous DRN (with more K-strategies). Drying frequency, drying duration, and spatio-temporal connectivity drive divergent community structures, suggesting the presence of an ecological threshold that explains the variability of disturbed ecosystems across broad spatial scales. These factors also shaped seasonal community variations, particularly after summer, with intermittent communities influenced by stochastic recolonization events in spring and autumn. Spatial-temporal connectivity proved crucial for maintaining diversity in communities subjected to intense drying. Lastly, the effectiveness of drying resistance traits was dependent on the biogeographical and environmental conditions of drying river networks.

ecology↗

bioRxiv2020

DISPERSE: A trait database to assess the dispersal potential of aquatic macroinvertebrates

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 39 trait categories grouped into nine dispersal-related traits 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 questions in metapopulation ecology, metacommunity ecology, macroecology and evolutionary ecology research. Information on dispersal proxies can be applied to improve predictions of ecological responses to global change, and to inform improvements to biomonitoring and conservation 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.

ecology↗