Modelling of riverine ecosystems by integrating models: conceptual approach, a case study and research agenda

Aim Highly complex interactions between the hydrosphere and biosphere, as well as multifactorial relationships, characterize the interconnecting role of streams and rivers between different elements of a landscape. Applying species distribution models (SDMs) in these ecosystems requires special attention because rivers are linear systems and their abiotic and biotic conditions are structured in a linear fashion with significant influences from upstream/downstream or lateral influences from adjacent areas. Our aim was to develop a modelling framework for benthic invertebrates in riverine ecosystems and to test our approach in a data-rich study catchment. Location We present a case study of a 9-km section of the lowland Kielstau River located in northern Germany. Methods We linked hydrological, hydraulic and species distribution models to predict the habitat suitability for the bivalve Sphaerium corneum in a riverine system. The results generated by the hydrological model served as inputs into the hydraulic model, which was used to simulate the resulting water levels, velocities and sediment discharge within the stream channel. Results The ensemble model obtained good evaluation scores (area under the receiver operating characteristic curve 0.96; kappa 0.86; true skill statistic 0.95; sensitivity 86.14; specificity 85.75). Mean values for variables at the sampling sites were not significantly different from the values at the predicted distribution (MannWhitney U-test P > 0.05). High occurrence probabilities were predicted in the downstream half of the 9-km section of the Kielstau. The most important variable for the model was sediment discharge (contributing 40%), followed by water depth (30%), flow velocity (19%) and stream power (11%). Main conclusions The hydrological and hydraulic models are able to produce predictors, acting at different spatial scales, which are known to influence riverine organisms; which, in turn, are used by the SDMs as input. Our case study yielded good results, which corresponded well with ecological knowledge about our study organism. Although this method is feasible for making projections of habitat suitability on a local scale (here: a reach in a small catchment), we discuss remaining challenges for future modelling approaches and large-scale applications.Aim Highly complex interactions between the hydrosphere and biosphere, as well as multifactorial relationships, characterize the interconnecting role of streams and rivers between different elements of a landscape. Applying species distribution models (SDMs) in these ecosystems requires special attention because rivers are linear systems and their abiotic and biotic conditions are structured in a linear fashion with significant influences from upstream/downstream or lateral influences from adjacent areas. Our aim was to develop a modelling framework for benthic invertebrates in riverine ecosystems and to test our approach in a data-rich study catchment. Location We present a case study of a 9-km section of the lowland Kielstau River located in northern Germany. Methods We linked hydrological, hydraulic and species distribution models to predict the habitat suitability for the bivalve Sphaerium corneum in a riverine system. The results generated by the hydrological model served as inputs into the hydraulic model, which was used to simulate the resulting water levels, velocities and sediment discharge within the stream channel. Results The ensemble model obtained good evaluation scores (area under the receiver operating characteristic curve 0.96; kappa 0.86; true skill statistic 0.95; sensitivity 86.14; specificity 85.75). Mean values for variables at the sampling sites were not significantly different from the values at the predicted distribution (MannWhitney U-test P > 0.05). High occurrence probabilities were predicted in the downstream half of the 9-km section of the Kielstau. The most important variable for the model was sediment discharge (contributing 40%), followed by water depth (30%), flow velocity (19%) and stream power (11%). Main conclusions The hydrological and hydraulic models are able to produce predictors, acting at different spatial scales, which are known to influence riverine organisms; which, in turn, are used by the SDMs as input. Our case study yielded good results, which corresponded well with ecological knowledge about our study organism. Although this method is feasible for making projections of habitat suitability on a local scale (here: a reach in a small catchment), we discuss remaining challenges for future modelling approaches and large-scale applications

Revisiting global trends in freshwater insect biodiversity

A recent global meta-analysis reported a decrease in terrestrial but increase in freshwater insect abundance and biomass (van Klink et al., Science 368, p. 417). The authors suggested that water quality has been improving, thereby challenging recent reports documenting drastic global declines in freshwater biodiversity. We raise two major concerns with the meta-analysis and suggest that these account for the discrepancy with the declines reported elsewhere. First, total abundance and biomass alone are poor indicators of the status of freshwater insect assemblages, and the observed differences may well have been driven by the replacement of sensitive species with tolerant ones. Second, many of the datasets poorly represent global trends and reflect responses to local conditions or nonrandom site selection. We conclude that the results of the meta-analysis should not be considered indicative of an overall improvement in the condition of freshwater ecosystems.FH and GK are supported through the project“Species protection through environmental friendly lighting”funded bythe Federal Agency for Nature Conservation (BfN) within the framework of the Federal Programme for BiologicalDiversity with funds from the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU).AM acknowledges funding through US NSF Macrosystems Biology Program (grant no. 1442595), and SD by the LeibnizCompetition (J45/2018). The authors are grateful to the reviewers and the editor for their comments, which helpedimprove the text. Open access funding enabled and organized by Projekt DEA

Elevation, aspect, and local environment jointly determine diatom and macroinvertebrate diversity in the Cangshan Mountain, Southwest China

Freshwater ecosystems in high-mountain regions are subject to emerging threats such as global warming and expanding human activities. Stream diatoms and macroinvertebrates form an essential component of freshwater ecosystems in high-mountain regions. Although these organisms are sensitive to environmental changes, knowledge regarding their elevational diversity patterns remains limited. Opposite aspects (e.g., north vs south; west vs east) usually receive different amounts of solar radiation and precipitation, leading to distinct in-stream characteristics such as discharge, flow regime, and water temperature. Despite the suggested strong influence of aspect on biodiversity patterns in mountains, its effect on stream diatoms and macroinvertebrates has been largely overlooked. The aims of our study were to 1) investigate whether macroinvertebrate and diatom taxon richness follows the same pattern along an elevational gradient; 2) test the effect of aspect on the elevational diversity (i.e., taxon richness and assemblage dissimilarity) patterns of macroinvertebrate and diatom assemblages; and 3) examine the relative importance of elevation, aspect, and the local environment (e.g., in-stream physicochemical variables) in shaping macroinvertebrate and diatom assemblages. We investigated macroinvertebrate and diatom assemblages in six nearly parallel streams (three streams on the east aspect and three on the west) in the Hengduan Mountains region. We found that the taxon richness of both macroinvertebrates and diatoms showed a monotonic increase with elevation (1623-2905 m a.s.l.) when aspect was not accounted for. When aspect was taken into consideration, macroinvertebrate taxon richness still showed a monotonically increasing elevational pattern on both the east and west aspects, but with significantly different model slopes, while a monotonical pattern for diatoms only remained on the west aspect. In addition, taxon richness of macroinvertebrates may also follow a potential unimodal pattern. The distance-decay relationships followed the same patterns as taxon richness, suggesting that the influence of aspect on diatom and macroinvertebrate assemblages was not negligible. Our results suggested that the diversity of both diatoms and macroinvertebrates was jointly determined by elevation, aspect and local environment. Compared to macroinvertebrates, the diatom assemblages were more strongly influenced by the local environment. To gain a better understanding of the underlying mechanisms driving elevational patterns of stream biodiversity in high-mountain regions, comparative studies that involve multiple organisms, streams, and mountains across a large elevational range are needed

Metacommunity Structures of Macroinvertebrates and Diatoms in High Mountain Streams, Yunnan, China

The metacommunity concept has received increasing interest in the past two decades. However, there has been limited research examining metacommunity structure of communities in high mountain streams. These ecosystems are often physically constrained and can display large environmental gradients within a relatively small spatial extent. Here, we examined metacommunity structures of stream organisms in a high mountain region, which is part of the Hengduan Mountains region in Southwest China. Macroinvertebrates and diatoms were collected from six streams in two opposite aspects of the same mountain with different connectivity between streams. On the west aspect, streams are tributaries of a river (i.e., river-connected) while streams flow into a lake (i.e., lake-connected) on the east aspect. We used Elements of Metacommunity Structure analysis to explore the metacommunity structuring of these two biological models. We also compared the contribution of dispersal and environmental filtering in structuring metacommunities by looking at Euclidean, network, topographic, and environmental distances. Communities of diatoms and macroinvertebrates were structured with clear turnover on both aspects. Further, diatom communities exhibited Clementsian structure on both aspects. Macroinvertebrates exhibited different metacommunity structures on the river-connected aspect (Quasi-Clementsian) and lake-connected aspect (Clementsian). Our results indicated that on the lake-connected aspect, environmental filtering had a stronger association with community dissimilarity than on the river-connected aspect for both macroinvertebrate and diatom communities. Diatom communities were more influenced by environmental filtering on the east aspect with weakened network connectivity compared with those on the west aspect. Our results also emphasized the potential effects of biotic interactions between macroinvertebrates and diatoms on shaping community structures of one other. Our study provides substantial elements to further understand metacommunity structure and highlights the necessity of future research to reveal the underlying mechanisms of community structuring in these remote ecosystems

Characterizing macroinvertebrate communities across China: Large-scale implementation of a self-organizing map

Understanding the geographical patterns and divisions of communities is a fundamental step in achieving the sustainable management of ecosystems, especially in deteriorating global and local environments. The idea of geographical division has been applied on all continents but Antarctica, but it has never been rigorously tested for stream ecosystems in China, leaving a gap in knowledge for many basic and applied research questions regarding, for example, diversity patterns, conservation issues or climate change effects. To fill this gap, we aimed to (1) evaluate the geographical divisions of the macroinvertebrate communities in Chinese streams using the self-organizing map (SUM) method and (2) to characterize the distribution patterns in relation to different environmental variables. Macroinvertebrates were collected from 57 relatively clean stream sites covering a south-north gradient along the boundary of the geographic ladder (or altitudinal divide) in China. SUM was used to analyze large-scale biogeographical divisions of the macroinvertebrate communities. The sampling sites were divided into six clusters, distinguishing the samples from northern, central, and southern China. This pattern was also reflected by biotic metrics (abundance, biomass, taxa and sum of Ephemeroptera, Plecoptera, and Trichoptera richness, and diversity). The gradient of environmental variables, particularly water quality variables, was similar between the clusters, with the exceptions of two clusters from southwestern China when considering altitude and one cluster from northern China when considering conductivity and TN. The different clusters from the SUM were associated with indicator species, with clean-water adapted species dominating in southwestern China and pollution tolerant species in northern China. However, there were no significant correlations between environmental variables and biotic metrics. The overall combination of environmental variables and organism data suggests that spatial variation was the main predictor determining the composition of the macroinvertebrate communities on a large-scale, and the trained SUM appeared to be efficient at classifying streams on a broad geographic scale. (C) 2012 Elsevier Ltd. All rights reserved.Understanding the geographical patterns and divisions of communities is a fundamental step in achieving the sustainable management of ecosystems, especially in deteriorating global and local environments. The idea of geographical division has been applied on all continents but Antarctica, but it has never been rigorously tested for stream ecosystems in China, leaving a gap in knowledge for many basic and applied research questions regarding, for example, diversity patterns, conservation issues or climate change effects. To fill this gap, we aimed to (1) evaluate the geographical divisions of the macroinvertebrate communities in Chinese streams using the self-organizing map (SUM) method and (2) to characterize the distribution patterns in relation to different environmental variables. Macroinvertebrates were collected from 57 relatively clean stream sites covering a south-north gradient along the boundary of the geographic ladder (or altitudinal divide) in China. SUM was used to analyze large-scale biogeographical divisions of the macroinvertebrate communities. The sampling sites were divided into six clusters, distinguishing the samples from northern, central, and southern China. This pattern was also reflected by biotic metrics (abundance, biomass, taxa and sum of Ephemeroptera, Plecoptera, and Trichoptera richness, and diversity). The gradient of environmental variables, particularly water quality variables, was similar between the clusters, with the exceptions of two clusters from southwestern China when considering altitude and one cluster from northern China when considering conductivity and TN. The different clusters from the SUM were associated with indicator species, with clean-water adapted species dominating in southwestern China and pollution tolerant species in northern China. However, there were no significant correlations between environmental variables and biotic metrics. The overall combination of environmental variables and organism data suggests that spatial variation was the main predictor determining the composition of the macroinvertebrate communities on a large-scale, and the trained SUM appeared to be efficient at classifying streams on a broad geographic scale. (C) 2012 Elsevier Ltd. All rights reserved

Rethinking megafauna

Concern for megafauna is increasing among scientists and non-scientists. Many studies have emphasized that megafauna play prominent ecological roles and provide important ecosystem services to humanity. But, what precisely are ‘megafauna’? Here, we critically assess the concept of megafauna and propose a goal-oriented framework for megafaunal research. First, we review definitions of megafauna and analyse associated terminology in the scientific literature. Second, we conduct a survey among ecologists and palaeontologists to assess the species traits used to identify and define megafauna. Our reviewindicates that definitions are highly dependent on the study ecosystem and research question, and primarily rely on ad hoc size-related criteria. Our survey suggests that body size is crucial, but not necessarily sufficient, for addressing the different applications of the term megafauna. Thus, after discussing the pros and cons of existing definitions, we propose an additional approach by defining two function-oriented megafaunal concepts: ‘keystone megafauna’ and ‘functional megafauna’, with its variant ‘apex megafauna’. Assessing megafauna from a functional perspective could challenge the perception that theremay not be a unifying definition ofmegafauna that can be applied to all eco-evolutionary narratives. In addition, using functional definitions of megafauna could be especially conducive to cross-disciplinary understanding and cooperation, improvement of conservation policy and practice, and strengthening of public perception. As megafaunal research advances, we encourage scientists to unambiguously define how they use the term ‘megafauna’ and to present the logic underpinning their definition.http://royalsocietypublishing.org/journal/rspbam2021Centre for Wildlife Managemen

The recovery of European freshwater biodiversity has come to a halt

Owing to a long history of anthropogenic pressures, freshwater ecosystems are among the most vulnerable to biodiversity loss(1). Mitigation measures, including wastewater treatment and hydromorphological restoration, have aimed to improve environmental quality and foster the recovery of freshwater biodiversity(2). Here, using 1,816 time series of freshwater invertebrate communities collected across 22 European countries between 1968 and 2020, we quantified temporal trends in taxonomic and functional diversity and their responses to environmental pressures and gradients. We observed overall increases in taxon richness (0.73% per year), functional richness (2.4% per year) and abundance (1.17% per year). However, these increases primarily occurred before the 2010s, and have since plateaued. Freshwater communities downstream of dams, urban areas and cropland were less likely to experience recovery. Communities at sites with faster rates of warming had fewer gains in taxon richness, functional richness and abundance. Although biodiversity gains in the 1990s and 2000s probably reflect the effectiveness of water-quality improvements and restoration projects, the decelerating trajectory in the 2010s suggests that the current measures offer diminishing returns. Given new and persistent pressures on freshwater ecosystems, including emerging pollutants, climate change and the spread of invasive species, we call for additional mitigation to revive the recovery of freshwater biodiversity