Freshwater Realm Research Articles

Conservation for sustaining livelihoods: Adaptive co-management of fish no-take zones in the Mekong River

A major challenge in natural resource management in developing countries is to pursue conservation objectives while avoiding negative impacts on local livelihoods. Inland capture fisheries provide opportunities to demonstrate an integration of conservation and livelihood objectives when managed as a social-ecological system. While numerous marine no-take reserves have been found effective for the recovery of fisheries, few well-documented examples exist in the freshwater realm. Research gaps also remain in the role of co-management in balancing various management objectives and resolving conflicts. This paper offers critical reflection on adaptive co-management of fish conservation zones (FCZs) in the Mekong River in Cambodia and its social-ecological outcomes as perceived by local stakeholders. The management approach was found generally effective for the local stakeholders to negotiate between conservation and livelihood objectives at key stages of the implementation, and resolve conflicts; however, the lessons learned were not uniform across all sites. The degree of difficulty in conflict resolution was mainly a function of the fishing dependency of local communities on the protected site, the prevalence of severe poverty in adjacent villages, and the availability of livelihood options other than fishing. Growing stakeholder perception over time, of the FCZs as yielding positive outcomes—for both conservation and livelihood—motivated the local communities to create more FCZs. We argue clear recognition by local stakeholders of the achievements and the fairness in the FCZ management, facilitated through participatory approaches, can improve their acceptance of conservation rules and enhance their effectiveness. However, long-term mechanisms to support these community initiatives technically and financially are needed. Simple yet scientifically robust approaches for tropical freshwater fisheries monitoring, including periodical assessments of indicator species, are also needed to facilitate performance evaluation of specific management measures locally.

The scope and extent of literature that maps threats to species globally: a systematic map

BackgroundHuman activities are driving accelerating rates of species extinctions that continue to threaten nature’s contribution to people. Yet, the full scope of where and how human activities threaten wild species worldwide remains unclear. Furthermore, the large diversity of approaches and terminology surrounding threats and threat mapping presents a barrier to understanding the state of knowledge and uptake into decision-making. Here, we define ‘threats’ as human activities and direct human-initiated processes, specifically where they co-occur with, and impact the survival of, wild species. Our objectives were to systematically consolidate the threat mapping literature, describe the distribution of available evidence, and produce a publicly available and searchable database of articles for easy uptake of evidence into future decision-making.MethodsFour bibliographic databases, one web-based search engine, and thirteen organisational websites were searched for peer-reviewed and grey-literature published in English 2000–2020. A three-stage screening process (title, abstract, and full-text) and coding was undertaken by two reviewers, with consistency tested on 20% of articles at each stage. Articles were coded according to 22 attributes that captured dimensions of the population, threat, and geographic location studied in addition to methodological attributes. The threats studied were classified according to the IUCN Red List threat classification scheme. A range of graphical formats were used to visualise the distribution of evidence according to these attributes and complement the searchable database of articles.Review findingsA total of 1069 relevant threat mapping studies were found and included in the systematic map, most conducted at a sub-national or local scale. Evidence was distributed unevenly among taxonomic groups, ecological realms, and geographies. Although articles were found for the full scope of threat categories used, most articles mapped a single threat. The most heavily mapped threats were alien invasive species, aquatic or terrestrial animal exploitation, roads and railways, residential development, and non-timber crop and livestock agriculture. Limitations regarding the English-only search and imperfect ability of the search to identify grey literature could have influenced the findings.ConclusionsThis systematic map represents a catalogue of threat mapping evidence at any spatial scale available for immediate use in threat reduction activities and policy decisions. The distribution of evidence has implications for devising actions to combat the threats specifically targeted in the post-2020 UN Biodiversity Framework, and for identifying other threats that may benefit from representation in global policy. It also highlights key gaps for further research to aid national and local-scale threat reduction. More knowledge would be particularly beneficial in the areas of managing multiple threats, land-based threats to marine systems, and threats to plant species and threats within the freshwater realm.

Combined effects of heatwaves and micropollutants on freshwater ecosystems: Towards an integrated assessment of extreme events in multiple stressors research.

Freshwater ecosystems are strongly influenced by weather extremes such as heatwaves (HWs), which are predicted to increase in frequency and magnitude in the future. In addition to these climate extremes, the freshwater realm is impacted by the exposure to various classes of chemicals emitted by anthropogenic activities. Currently, there is limited knowledge on how the combined exposure to HWs and chemicals affects the structure and functioning of freshwater ecosystems. Here, we review the available literature describing the single and combined effects of HWs and chemicals on different levels of biological organization, to obtain a holistic view of their potential interactive effects. We only found a few studies (13 out of the 61 studies included in this review) that investigated the biological effects of HWs in combination with chemical pollution. The reported interactive effects of HWs and chemicals varied largely not only within the different trophic levels but also depending on the studied endpoints for populations or individuals. Hence, owing also to the little number of studies available, no consistent interactive effects could be highlighted at any level of biological organization. Moreover, we found an imbalance towards single species and population experiments, with only five studies using a multitrophic approach. This results in a knowledge gap for relevant community and ecosystem level endpoints, which prevents the exploration of important indirect effects that can compromise food web stability. Moreover, this knowledge gap impairs the validity of chemical risk assessments and our ability to protect ecosystems. Finally, we highlight the urgency of integrating extreme events into multiple stressors studies and provide specific recommendations to guide further experimental research in this regard.

InsectChange: a global database of temporal changes in insect and arachnid assemblages.

Insects are the most ubiquitous and diverse group of eukaryotic organisms on Earth, forming a crucial link in terrestrial and freshwater food webs. They have recently become the subject of headlines because of observations of dramatic declines in some places. Although there are hundreds of long-term insect monitoring programs, a global database for long-term data on insect assemblages has so far remained unavailable. In order to facilitate synthetic analyses of insect abundance changes, we compiled a database of long-term (≥10yr) studies of assemblages of insects (many also including arachnids) in the terrestrial and freshwater realms. We searched the scientific literature and public repositories for data on insect and arachnid monitoring using standardized protocols over a time span of 10yr or longer, with at least two sampling events. We focused on studies that presented or allowed calculation of total community abundance or biomass. We extracted data from tables, figures, and appendices, and, for data sets that provided raw data, we standardized trapping effort over space and time when necessary. For each site, we extracted provenance details (such as country, state, and continent) as well as information on protection status, land use, and climatic details from publicly available GIS sources. In all, the database contains 1,668 plot-level time series sourced from 165 studies with samples collected between 1925 and 2018. Sixteen data sets provided here were previously unpublished. Studies were separated into those collected in the terrestrial realm (103 studies with a total of 1,053 plots) and those collected in the freshwater realm (62 studies with 615 plots). Most studies were from Europe (48%) and North America (29%), with 34% of the plots located in protected areas. The median monitoring time span was 19yr, with 12 sampling years. The number of individuals was reported in 129 studies, the total biomass was reported in 13 studies, and both abundance and biomass were reported in 23 studies. This data set is published under a CC-BY license, requiring attribution of the data source. Please cite this paper if the data are used in publications, and respect the licenses of the original sources when using (part of) their data as detailed in Metadata S1: Table 1.

RivFishTIME: A global database of fish time‐series to study global change ecology in riverine systems

AbstractMotivationWe compiled a global database of long‐term riverine fish surveys from 46 regional and national monitoring programmes and from individual academic research efforts, with which numerous basic and applied questions in ecology and global change research can be explored. Such spatially and temporally extensive datasets have been lacking for freshwater systems in comparison to terrestrial ones.Main types of variables containedThe database includes 11,386 time‐series of riverine fish community catch data, including 646,270 species‐specific abundance records, together with metadata related to the geographical location and sampling methodology of each time‐series.Spatial location and grainThe database contains 11,072 unique sampling locations (stream reach), spanning 19 countries, five biogeographical realms and 402 hydrographical basins world‐wide.Time period and grainThe database encompasses the period 1951–2019. Each time‐series is composed of a minimum of two yearly surveys (mean = 8 years) and represents a minimum time span of 10 years (mean = 19 years).Major taxa and level of measurementThe database includes 944 species of ray‐finned fishes (Class Actinopterygii).Software formatcsv.Main conclusionOur collective effort provides the most comprehensive long‐term community database of riverine fishes to date. This unique database should interest ecologists who seek to understand the impacts of human activities on riverine fish biodiversity and to model and predict how fish communities will respond to future environmental change. Together, we hope it will promote advances in macroecological research in the freshwater realm.

Macroecology of macrophytes in the freshwater realm: Patterns, mechanisms and implications

• Few broad-scale patterns are well-studied for aquatic macrophytes. • Local environmental predictors were important for freshwater plants at broad-scales. • Several knowledge gaps on macroecology of freshwater plants were identified. • Lack of lotic studies and databases of species traits and phylogeny were found. • Additional macroecological investigations on freshwater plants are clearly needed. Broad-scale studies of species distributions and diversity have contributed to the emergence of general macroecological rules. These rules are typically founded on research using well-known terrestrial taxa as models and it is thus uncertain whether aquatic macrophytes follow these macroecological rules. Our purpose is to draw together available information from broad-scale research on aquatic macrophytes growing in lakes, ponds, wetlands, rivers and streams. We summarize how different macroecological rules fit the patterns shown by freshwater plants at various spatial scales. Finally, we outline future actions which should be taken to advance macroecological research on freshwater plants. Our review suggested that some macroecological patterns are relatively well-evidenced for aquatic macrophytes, whereas little information exists for others. We found, for example, that the species richness-latitude relationship follows a unimodal pattern, and species turnover prevails over species nestedness, whereas higher nestedness-related richness differences are found in low beta diversity regions. Contrary to terrestrial plants, climate or history seem not to be dominant determinants explaining these broad-scale patterns; instead local explanatory variables (e.g., water quality, such as alkalinity and nutrients, and hydromorphology) are often important for freshwater plants. We identified several knowledge gaps related, for example, to a smaller number of studies in lotic habitats, compared with lentic habitats, lack of spatially-adequate aquatic plant studies, deficiency of comprehensive species traits databases for aquatic macrophytes, and absence of a true phylogeny comprising most freshwater plant lineages. We hope this review will encourage the undertaking of additional macroecological investigations on freshwater plants across broad spatial and temporal scales.

The seasonality of macroinvertebrate β diversity along the gradient of hydrological connectivity in a dynamic river-floodplain system

Anthropogenic disturbance to natural hydrological connectivity, both longitudinal, lateral, and vertical, is threatening the ecological integrity of the freshwater realm. River-floodplain system is particularly adversely affected by the reduction in lateral hydrological connectivity (LHC), representing one of major biodiversity hotspots under increasingly pressure. Many studies have demonstrated that LHC has great influence on the spatial variations of flora and fauna communities (i.e. spatial β diversity) through facilitating dispersal. However, to fully understand the impact of anthropogenic disturbances on biodiversity, we must also understand how ecological communities change over time (i.e. temporal β diversity, TBI) and the underlying processes. To evaluate the processes structuring ecological communities, we examined the macroinvertebrate TBI in habitats along the gradient of LHC for an entire hydrological cycle in West Dongting Lake, a Ramsar-listed floodplain wetland at the middle reach of Yangtze River. Our results showed that the total spatial β diversity fluctuated with water level and peaked at high-water phase, and LHC was the driving forcing affecting both species richness and abundance in all hydrological periods. In particular, species richness and abundance were highest in habitats with medium LHC levels for water-rising and high-water periods reflecting the intermediate disturbance hypothesis except for water-recessing, during which there was no clear pattern. While replacement determined β diversity in most sites at water-rising and high-water phases, the contribution of nestedness were high during water-withdrawing phase. From water-rising to high-water, macroinvertebrates from other habitats spread to the modified mudflats, which had the lowest LHC, along with the floods. During water-withdrawing period, β diversity and its turnover component of all habitats were low compared with other hydrological phases. Temporal β diversity analysis illustrated that the species dispersal was the main mechanism underlying the temporal and spatial variations in the observed community patterns. These findings demonstrated that hydrological connectivity was critical to maintaining the ecological integrity of river-floodplain ecosystems.

Current climate overrides historical effects on species richness and range size of freshwater plants in Europe and North America

Abstract The latitudinal diversity gradient hypothesis suggests that species richness should be highest at low latitudes, whereas Rapoport's rule states that largest ranges ought to be found for species at high latitudes. However, there is no consensus over these patterns and their underlying drivers in the freshwater realm. We investigated species richness and mean range size of freshwater plants in 50 × 50 km grid cells across Europe (40°N–71°N) and North America (25°N–78°N), supplemented with data based on 1° latitudinal bands for mean range size. We were especially interested to find out whether there are similarities and differences in these ecogeographical patterns and their underlying drivers between the continents due to their contrasting historical characteristics, spatial extent and topography. First, we used partial regression to reveal whether species richness and mean range size of freshwater plants have a linear or quadratic relationship with latitude. Second, we employed variation partitioning based on partial regression to model relationships between plant species richness and mean range size and four explanatory variable groups (i.e. environmental features, current climate, historical climate and geographical location). Third, we utilized boosted regression tree analysis to further investigate species richness and mean range size of freshwater plants in relation to a set of explanatory variables. Our results revealed that species richness showed relatively similar patterns in relation to latitude between the continents. Similarly, mean range size trends were alike in North America whether we used 50 × 50 km grid cell data or 1° latitudinal bands. Instead, different patterns in mean range size emerged between the used datasets in Europe. For both species richness and mean range size, current climate (with different individual predictor variables) was the main driver in both the continents, but historical effects had a small influence on the response variables. Synthesis. Our findings indicated that major ecogeographical rules can strongly vary for the same taxonomic group across broad scales between continents. It is also premature to rely solely on well‐known terrestrial taxonomic groups when drawing generalizations about ecogeographical rules.

Same species, same habitat preferences? The distribution of aquatic plants is not explained by the same predictors in lakes and streams

Abstract Studying the geographical distribution of species can reveal conditions and processes that may drive species presence and abundance. Organism distribution has frequently been explained by climate, but the relative role of local environmental predictors is not fully understood. Moreover, in the freshwater realm, intrinsic differences existing between different categories of water bodies can lead to significant differences in species–environment relationships. Here, we tested the relative importance of broad‐scale climate and local environmental predictors in explaining plant species distributions in freshwater lakes and streams. We built species distribution models to investigate which predictors best explain aquatic plant distribution in two categories of water bodies. We used species inventories and records of three climate and eight local environmental predictors for 150 lakes and 150 streams in Finland. We found that sets of predictors that explain the distribution of macrophyte species are unique depending on if species are in a lake or a stream. Overall, air temperature and ecosystem size were essential to predict aquatic plant species presence in both water body categories. Broad‐scale climate predictors were always very important in explaining species distribution, while local environmental conditions such as water chemistry were of variable influence, depending on species and water body category. These results are probably due to high spatial and temporal variability and range of water physico‐chemical parameters, especially in streams. Nonetheless, despite a lower relative importance than climatic factors, local environmental predictors also strongly affected species distributions. Our findings highlight that incorporating local environmental conditions to species distribution models in addition to climate predictors is necessary to improve predictions, particularly for distribution of stream flora. Considering the species‐specific responses of aquatic plants to their environment, studying species individually with species distribution models represents a useful analysis.

Cross‐taxon congruence of multiple diversity facets of freshwater assemblages is determined by large‐scale processes across China

Abstract An intensively debated issue in ecology is whether variability in the patterns of diversity of different groups of organisms is congruent in space, a phenomenon referred to as cross‐taxon congruence. Whereas this has been previously mainly tested in terms of taxonomic dissimilarity, the role of ecological processes in determining the congruence of multiple diversity facets (i.e. α‐ and β‐diversity, taxonomic, and functional) remains poorly understood. We used a data set of observation records for 469 macrophyte and 543 fish taxa at the catchment‐scale from the existing literature and data bases to test the existence of multi‐faceted congruence patterns and investigate the variables driving them across 214 catchments covering the whole Chinese mainland. We found cross‐taxon congruence of multiple diversity aspects between fish and macrophyte communities. The energy (i.e. diversity is limited by energy availability), area/environmental heterogeneity (i.e. diversity is higher in larger and more heterogeneous areas), and dispersal (i.e. diversity is driven by dispersal) hypotheses were all significantly attributed to the cross‐taxon congruence, suggesting the existence of key repeated mechanisms underlying assemblage organisation. Our study provides new evidence that can further our understanding of the factors and underlying processes explaining cross‐taxon congruence patterns at broad spatial scales in the freshwater realm, the studies of which significantly lag those in the marine and terrestrial realms. The present findings also provide important baseline information for freshwater conservation initiatives.

Understanding environmental change through the lens of trait-based, functional, and phylogenetic biodiversity in freshwater ecosystems

In the era of the Anthropocene, environmental change is accelerating biodiversity loss across ecosystems on Earth, among which freshwaters are likely the most threatened. Different biodiversity facets in the freshwater realm suffer from various environmental changes that jeopardize the ecosystem functions and services important for humankind. In this work we examine how environmental changes (e.g., climate change, eutrophication, or invasive species) affect trait-based, functional, and phylogenetic diversity of biological communities. We first developed a simple conceptual model of the possible relationships between environmental change and these three diversity facets in freshwaters and, secondly, systematically reviewed articles where these relationships had been investigated in different freshwater ecosystems. Finally, we highlighted research gaps from the perspectives of organisms, ecosystems, stressors, and geographical locations. Our conceptual model suggested that both natural factors and global change operating at various spatial scales influence freshwater community structure and ecosystem functioning. The relationships between biodiversity and environmental change depend on geographical region, organism group, spatial scale, and environmental change gradient length. The systematic review revealed that environmental change impacts biodiversity patterns in freshwaters, but there is no single type of biodiversity response to the observed global changes. Natural stressors had different, even contradictory, effects (i.e., multiple, negative, and positive) on biodiversity compared with anthropogenic stressors. Anthropogenic stressors more often decreased biodiversity, although eutrophication and climate change affected freshwater ecosystems in a complex, more multi-dimensional way. The research gaps we identified were related, for example, to the low number of community-based biodiversity studies, the lack of information on true phylogenies for all freshwater organism groups, the missing evaluations whether species traits are phylogenetically conserved, and the geographical biases in research (i.e., absence of studies from Africa, Southern Asia, and Russia). We hope that our review will stimulate more research on the less well-known facets and topics of biodiversity loss in highly vulnerable freshwater ecosystems.

Different roles for geography, energy and environment in determining three facets of freshwater molluscan beta diversity at broad spatial scales

Current understanding of different facets of beta diversity and their underlying determinants remains limited at broad scales in the freshwater realm. We examined the geographical patterns and spatial congruence of three beta diversity facets of freshwater molluscs across all of China, and evaluated the relative importance of environmental and spatial factors underlying the observed patterns. Taxonomic (β-TD), functional (β-FD) and phylogenetic (β-PD) beta diversity were calculated for 212 drainage basins belonging to 10 hydrographic regions using compiled occurrence data of 313 molluscan species. Geographical patterns of the three diversity facets were visualized on maps and pairwise spatial congruence among them was evaluated using regression on distance matrices. Variation partitioning and multivariate regression trees were used to assess the relative importance of different factors underlying beta diversity patterns. Beta diversity maps revealed that geographical patterns of β-TD and β-PD showed strong spatial clustering and were well matched with hydrographic regions' boundaries, while β-FD showed only moderate spatial aggregation. The three facets were only moderately congruent, with over 60% of the variation in one facet remaining unexplained by any other facet. Remarkably, all diversity facets were best explained by the spatial factors with considerable unique effects. Environmental filtering associated with energy gradients also made a large contribution, while habitat availability only explained minor fractions of the variation in beta diversity. At the national scale, β-TD and β-PD were more strongly related to spatial processes, whereas β-FD was more strongly associated with energy gradients. Our results suggested that, for freshwater organisms with low dispersal capacity, dispersal processes may override environmental filtering in driving geographical diversity patterns. However, different ecological drivers were important for each diversity facet. Importantly, rather weak spatial congruence among the different diversity facets stresses the need to incorporate functional and phylogenetic facets into the development of conservation planning.

Geographical gradients in the biodiversity of Chinese freshwater molluscs: Implications for conservation

AbstractAimLarge‐scale diversity patterns are generated by different but not mutually exclusive mechanisms. However, understanding of multiple facets of diversity and their determinants in the freshwater realm remains limited. Here, we characterized the geographical gradients, hotspots and spatial congruence of three facets of freshwater molluscan diversity and evaluated the relative importance of three different underlying mechanisms related to the energy, area/environmental heterogeneity and dispersal/historical hypotheses.LocationChina.MethodsSpecies richness (SR), functional richness (FR) and taxonomic distinctness (TD, a proxy of phylogenetic diversity) were calculated for 212 drainage basins with a total of 313 molluscan species. Spatial congruence between the diversity facets was evaluated with Pearson correlation coefficient and overlap among hotspots. Multiple linear regression models and variation partitioning were used to assess the relative importance of different mechanisms.ResultsHotspots of SR and FR were mainly concentrated in the Yangtze River and Huai River basins, while high TD values were patchily distributed across China. We found extremely low spatial congruence between TD and both SR and FR, while there was relatively high concordance between SR and FR. All diversity facets were best explained by the dispersal/historical hypothesis with strong unique effects, followed by the factors related to the energy hypothesis. The area/ environmental heterogeneity hypothesis was only weakly supported.Main conclusionsWe found a potentially strong influence of dispersal limitation and evolutionary history on the geographical diversity gradients of Chinese molluscs. This finding contrasts with the general finding that energy‐related factors are the strongest correlates of diversity patterns at large spatial scales. Moreover, our results do not support the idea that using any one diversity component as a surrogate of the others in developing conservation strategies. Instead, an integrative approach embracing multiple facets of diversity should be adopted in the conservation of freshwater biodiversity.

Integrating dispersal proxies in ecological and environmental research in the freshwater realm

Dispersal is one of the key mechanisms affecting the distribution of individuals, populations, and communities in nature. Despite advances in the study of single species, it has been notoriously difficult to account for dispersal in multispecies metacommunities, where it potentially has strong effects on community structure beyond those of local environmental conditions. Dispersal should thus be directly integrated in both basic and applied research by using proxies. Here, we review the use of proxies in the current metacommunity research, suggest new proxies, and discuss how proxies could be used in community modelling, particularly in freshwater systems. We suggest that while traditional proxies may still be useful, proxies formerly utilized in transport geography may provide useful novel insights into the structuring of biological communities in freshwater systems. We also suggest that understanding the utility of such proxies for dispersal in metacommunities is highly important for many applied fields such as freshwater bioassessment, conservation planning, and recolonization research in the context of restoration ecology. These research fields have often ignored spatial dynamics and focused mostly on local environmental conditions and changes therein. Yet, the conclusions of these applied studies may change considerably if dispersal is taken into account.

Untangling the assembly of littoral macroinvertebrate communities through measures of functional and phylogenetic alpha diversity

Abstract Recent studies have shown that species, functional and phylogenetic diversity are related to different environmental drivers, suggesting that different aspects of alpha diversity may be complementary and may provide different information about community assembly. Such multi‐facet community assembly studies are, however, rare in the freshwater realm. We examined the responses of species richness, functional alpha diversity and phylogenetic alpha diversity of littoral macroinvertebrates to environmental gradients in near‐pristine boreal lakes. We also examined community assembly mechanisms using null models of functional or phylogenetic clustering, overdispersion and randomness as indications of different assembly mechanisms. We found that the alpha diversity indices examined responded differently to the underlying environmental gradients. Also, phylogenetic and functional alpha diversity indices showed different levels of overdispersion, clustering and randomness, which also varied slightly between the analyses based on abundance and presence–absence data. These results suggested that different alpha diversity indices may provide different information about overdispersion (e.g. caused by biotic interactions) and clustering (e.g. caused by environmental filtering), and emphasised the fact that most individual lakes were inhabited by species that were merely random draws from the functional or phylogenetic species pools available in the study region. Our findings suggested that some individual lakes are assembled by deterministic mechanisms, including environmental filtering and biotic interactions, whereas most individual lake macroinvertebrate communities constitute random draws from the regional species pool or are affected by the antagonistic effects of different assembly processes. Our results may stem from site‐specific context dependency in the assembly mechanisms, which might also be a reason why statistical models in aquatic community studies typically explain only a small part of variation in community composition and local diversity.

A Time-Calibrated Mitogenome Phylogeny of Catfish (Teleostei: Siluriformes)

A very significant part of the world’s freshwater ichthyofauna is represented by ancient, exceptionally diverse and cosmopolitan ray-finned teleosts of the order Siluriformes. Over the years, catfish have been established as an exemplary model for probing historical biogeography at various scales. Yet, several tantalizing gaps still exist in their phylogenetic history, timeline and mode of diversification. Here, we re-examine the phylogeny of catfish by assembling and analyzing almost all publicly available mitogenome data. We constructed an ingroup matrix of 62 full-length mitogenome sequences from 20 catfish families together with four cypriniform outgroups, spanning 15,557 positions in total. Partitioned maximum likelihood analyses and Bayesian relaxed clock dating using fossil age constraints provide some useful and novel insights into the evolutionary history of this group. Loricarioidei are recovered as the first siluriform group to diversify, rendering Neotropics the cradle of the order. The next deepest clade is the South American Diplomystoidei placed as a sister group to all the remaining Siluroidei. The two multifamilial clades of “Big Asia” and “Big Africa” are also recovered, albeit nodal support for the latter is poor. Within “Big Asia”, Bagridae are clearly polyphyletic. Other interfamilial relationships, including Clariidae + Heteropneustidae, Doradidae + Auchenipteridae and Ictaluridae + Cranoglanididae are robustly resolved. Our chronogram shows that siluriforms have a Pangaean origin, at least as far back as the Early Cretaceous. The inferred timeline of the basal splits corroborates the “Out-of-South America” hypothesis and accords well with the fossil record. The divergence of Siluroidei most likely postdated the final separation of Africa and South America. An appealing case of phylogenetic affinity elaborated by biogeographic dispersal is exemplified by the Early Paleogene split between the Southeast Asian Cranoglanididae and Ictaluridae, with the latter radiating into North America’s freshwater realm by Eocene. The end of Cretaceous probably concludes the major bout of diversification at the family level while with the dawn of the Cenozoic a prolific radiation is evident at the generic level.

Structural and physiological characteristics of Limnodrilus sulphurensis (Oligochaeta, Annelida) thriving in high sulphide conditions

Populations of Limnodrilus sulphurensis Fend, Liu & Erseus, 2016 (Naididae, Oligochaeta) were found on sulphur bacterial mats in a stream with sulphidic and hypoxic water in Sulphur Cave, Colorado (USA). In order to reveal adaptations to the hostile conditions, we assessed physical and chemical factors in reference to anatomical and physiological details of L. sulphurensis and compared with the common L. hoffmeisteri from non-sulphidic waters. Sections and 3D reconstructions of the posterior body of L. sulphurensis showed an extensively ramified integumental blood system and an extraordinarily rich circumintestinal chloragogue tissue. This contained accumulations of sulphide and iron. These features coincided with an unusual blood physiology of these haemoglobin-containing annelids living under permanent sulphide exposure. The blood of L. sulphurensis has a high oxygen binding capacity and the binding sites seem unaffected by sulphide (sulphhaemoglobin is not formed). Exposure experiments indicated oxidation of sulphide to thiosulphate, which can be easily released. Hplc analysis of the chloragosomes showed the presence of haemin (presumably haematin), a known catalyst of sulphide oxidation. L. sulphurensis shares these features with many marine “sulfide-annelids”. For the freshwater realm these data are novel. The proposed “sulfur-haeme scenario” would explain the unrivalled existence of L. sulphurensis under sulphidic conditions.

Drying as a primary hydrological determinant of biodiversity in river systems: a broad‐scale analysis

Determining and understanding relationships between biodiversity and hydrology is a critical goal in ecology, particularly given biodiversity in the freshwater realm is in crisis. Despite the prevalence of rivers experiencing natural drying disturbances (which we collectively refer to as intermittent rivers), and projections of increased frequency and duration of drying events, the importance of drying relative to other flow‐related determinants of river biodiversity remains understudied. We assessed the influence of drying on alpha‐ and beta‐diversity using discharge and macroinvertebrate data collated from Australia and southwest Europe over broad spatial and temporal scales, providing information on current and past drying events, and combining a wide variety of flow metrics. We found clear evidence that drying acts as a strong environmental filter and is a primary hydrological determinant of alpha‐diversity; even when considering both intermittent and perennial rivers, drying‐event conditions were its most important predictors. Macroinvertebrate richness declined with increasing durations of drying over the long‐term (Australia) and recent (Australia and southwest Europe) history of river discharge, and with decreasing predictability of event timing (Australia). Our analysis also revealed that: responses can be taxon specific due to variation in traits of resistance and resilience to drying; some taxa may respond just as or more strongly to variation in other discharge components (e.g. high‐ or low‐flow events) than to drying; and together these phenomena may result in differing community‐level responses within and across regions. Patterns of beta‐diversity across the wide biogeographical range of our study suggested that convergent and divergent niche‐selection processes may act in combination on aquatic communities of rivers experiencing drying disturbances. However, strong ability to disperse by flight (not by water) weakened beta‐diversity patterning among rivers. Our findings can be used to improve understanding of biodiversity organisation in disturbed systems, notably in those with dendritic features, including intermittent rivers.

Model‐based integration of observed and expert‐based information for assessing the geographic and environmental distribution of freshwater species

Freshwater ecosystems harbor specialized and vulnerable biodiversity, and the prediction of potential impacts of freshwater biodiversity to environmental change requires knowledge of the geographic and environmental distribution of taxa. To date, however, such quantitative information about freshwater species distributions remains limited. Major impediments include heterogeneity in available species occurrence data, varying detectability of species in their aquatic environment, scarcity of contiguous freshwater‐specific predictors, and methods that support addressing these issues in a single framework. Here we demonstrate the use of a hierarchical Bayesian modeling (HBM) framework that combines disparate species occurrence information with newly‐developed 1 km freshwater‐specific predictors, to account for imperfect species detection and make fine‐grain (1 km) estimates of distributions in freshwater organisms. The approach integrates a Bernoulli suitability and a Binomial observability process into a hierarchical zero‐inflated Binomial model. The suitability process includes point presence observations, records of site visits, 1 km environmental predictors and expert‐derived species range maps integrated with a distance‐decay function along the within‐stream distance as covariates. The observability process uses repeated observations to estimate a probability of observation given that the species was present. The HBM accounts for the spatial autocorrelation in species habitat suitability projections using an intrinsic Gaussian conditional autoregressive model. We used this framework for three fish species native to different regions and habitats in North America. Model comparison shows that HBMs significantly outperformed non‐spatial GLMs in terms of AUC and TSS scores, and that expert information when appropriately included in the model can provide an important refinement. Such ancillary species information and an integrative, hierarchical Bayesian modeling framework can therefore be used to advance fine‐grain habitat suitability predictions and range size estimates in the freshwater realm. Our approach is extendable in terms of data availability and generality and can be used on other freshwater organisms and regions.

Contrasting “Fish” Diversity Dynamics between Marine and Freshwater Environments

Two theoretical models have been proposed to describe long-term dynamics of diversification: the equilibrium model considers the Earth as a closed system with a fixed maximum biological carrying capacity, whereas the expansion model hypothesizes a continuously increasing diversification of life. Based on the analysis of the fossil record of all organisms, Benton suggested contrasting models of diversity dynamics between marine and continental realms. Diversity in marine environments is characterized by phases of rapid diversification followed by plateaux, i.e., an equilibrium model directly derived from insular biogeography theories, whereas diversity in continental environments is characterized by exponential growth. Previous studies that aimed at testing these models with empirical data were based on datasets extracted directly from the reading of the vagaries of the raw fossil record, without correcting for common fossil record biases (preservation and sampling). Although correction of datasets for the incompleteness of the fossil record is now commonly performed for addressing long-term biodiversity variations, only a few attempts have been made to produce diversity curves corrected by phylogenetic data from extant and extinct taxa. Here we show that phylogenetically corrected diversity curves for "fish" (actinopterygians and elasmobranchs) during the last 200 million years fit an equilibrium model in the marine realm and an expansion model in the freshwater realm. These findings demonstrate that the rate of diversification has decreased for marine fish over the Cenozoic but is in sharp expansion for freshwater fish.