Upstream-downstream Gradient Research Articles

Response of Chironomidae (Diptera) to DDT, Mercury, and Arsenic Legacy Pollution in Sediments of the Toce River (Northern Italy).

The Toce River (Northern Italy) is characterized by legacy contamination of dichloro-diphenyl-trichloroethane (DDT), mercury, and arsenic deriving from an industrial plant active between ca. 1915 and 1996. Chironomidae taxa assemblages and sediments were collected in 2014 and 2019 upstream and downstream of the industrial area to analyze species responses to toxic substances in a river stretch with relatively uniform natural (i.e., hydro-morphological) characteristics. A total of 32 chironomid taxa were identified. Sediment concentrations reached levels potentially toxic for benthic invertebrates: 15.7 µg kg-1 1% organic carbon for DDT, 197 µg kg-1 dry weight (d.w.) for Hg, and 55.7 mg kg-1 d.w. for As. Canonical Correspondence Analysis (CCA) revealed a predominant seasonal gradient, followed by an upstream-downstream gradient. Partial CCA indicated that 5.2% of the total variation was associated with sediment contamination. Self-Organizing Maps (SOMs) were used to represent species responses to toxicants. Most species appeared to be tolerant, e.g., Chironomus riparius, Micropsectra atrofasciata, Conchapelopia pallidula, and Polypedilum spp. Sensitivity to contaminants was observed in only a few species: Diamesa spp., Sympotthastia spinifera, and Prodiamesa olivacea to DDT; Potthastia longimanus to Hg; Odontomesa fulva and Microtendipes pedellus to As. The chironomid community was characterized in presence of contamination levels commonly observed in freshwater ecosystems.

Spatial Patterns of Neutral and Functional Genetic Variations along Dendritic Networks of Riverscape in Brown Trout Populations

Understanding how environmental gradients shape the spatial patterns of intraspecific genetic diversity is a central issue in ecological and evolutionary sciences. In riverine ecosystems, there is generally an increase in neutral genetic diversity downstream, as well as an increase in genetic differentiation among upstream populations. However, selective pressures may vary markedly along the upstream–downstream gradient, which could modify these patterns, but this has rarely been tested empirically. Here, we investigated how environmental gradients in a river network could shape the spatial patterns of intraspecific genetic diversity and differentiation in both neutral SNP markers and functional genetic markers putatively under natural selection (candidate SNPs associated with physiological functions and immune Major Histocompatibility Complex (MHC) loci) in wild brown trout populations. First, we showed that both the distance from the confluence and the centrality on the river network could explain the variation in genetic diversity and differentiation. Second, we found that both neutral and functional markers followed a similar pattern, with a higher genetic diversity and a lower genetic differentiation among populations that were more central and/or near to the confluence. This study highlights the importance of considering both the spatial and hydrological factors of a river network to understand and predict the role of dendritic connectivity in the spatial patterns of genetic diversity and differentiation in wild fish populations.

Reproduction patterns of the bloody cockle Senilia senilis (Linnaeus 1758) in the Sine-Saloum inverse estuary

Understanding the reproductive biology of a species is an important means of determining the renewal capacity of natural stocks, especially in the case of heavily exploited species. It is a fundamental element in supporting the implementation of management measures. Here, we studied the bloody cockle (S. senilis) in the Sine-Saloum, with the aim of describing its seasonal and spatial reproductive cycle. S. senilis reproduction was studied over an annual cycle at two sites chosen for their contrasting situations along the upstream-downstream gradient. The reproductive cycle was studied by histological analysis of a pool of individuals maintained in-situ and sampled throughout the year. Our results showed that gamete maturation is asynchronous within and between individuals. Gametogenesis mostly occurred in October. The maturation stage showed a seasonal pattern with continuous reproduction throughout the year, with two preferred periods between May and July and December and February. The reproductive cycle is highly dependent on temperature and salinity variations, resulting in a seasonal cycle and spatial heterogeneity. The temperature induces gametogenesis and salinity synchronizes the spawning periods.

O efeito da deriva no aninhamento das ordens ephemeroptera, trichoptera e plecoptera no Rio Xingu

Abstract The drift movement consists of the displacement of the organisms inside the water column which allows its passive locomotion. This movement will result in a variation of the communities of organisms along the river, generating spatial patterns. Based on this, we tested the hypotheses a) the drift of individuals in an upstream-downstream direction creates a nestedness pattern, when the upstream is a subset of downstream communities of aquatic insects; b) there will be an increase in the number of individuals and genera as we approach the most downstream point. The present study was carried out in seven sampling points distributed along the Xingu River. The sampling occurred at night in the central area of the river. The number of genera along the river remained constant, and the nestedness distribution of the communities in the upstream-downstream gradient was not observed. Based on the results, it is possible to visualize a turnover of genera in the longitudinal gradient of the river, but with an accumulation of genera in the downstream region. Organisms that are transported by the flow of the water current respond to the characteristics of the body of water by adapting to the type of environment in which they are found.

DISTRIBUTION PATTERN OF THE AQUATIC ENTOMOFAUNA ABOUT ENVIRONMENTAL FACTORS IN THE HAUT-BANDAMA WILDLIFE RESERVE AREA OF THE BANDAMA RIVER (CENTRE-NORTH, COTE DIVOIRE)

The section of the Bandama River located in Haut-Bandama Wildlife Reserve was subject to several pressures induced by the anthropic activities that take place there. These activities could have impacts on the structure of biological communities such as aquatic insects which are indicators of the state of the ecological integrity of the environment. This study was conducted to evaluate the diversity and structure of the aquatic entomofauna of this part of Bandama River. Sampling was conducted from January 2018 to February 2019 at 06 sites defined according to the upstream-downstream gradient of the river. Insects were collected using a handled net and aVan Veen bucket. The inventory identified 127 species from 53 families and 10 orders. In this part of Bandama River, the order Hemiptera was the most prevalent with 30 species. The taxa Gerisella sp. (31% of individuals), Dineutus sp. (55%), and Laccophilus sp. (38%) wereabundant in the upstream, median and downstream sections of Bandama River respectively. Also, 33 species were common to all stations. Thraulus sp. AndLispe sp. wereonly found at station BYB, located downstream of this sectionof Bandama River. The distribution of entomofauna was influenced by pH, turbidity, dissolved oxygen, speed, depth and temperature. The entomological populations in this part of the Bandama River were well diversified and with awell balanced organisation.

Diversity and distribution of benthic invertebrates dwelling rivers of the Kruger National Park, South Africa

Meiobenthos (or meiofauna) are microscopic invertebrates that inhabit biofilms and interstitial spaces in rivers. They are diverse and extremely abundant, and they perform essential ecological functions by linking microbial production to higher trophic levels (e.g. macrobenthic invertebrates and fishes). However, meiobenthic communities remain poorly studied in Africa. Here, we sampled meio- and macrobenthic invertebrate communities associated with biofilms and sediments across an upstream–downstream gradient along the Olifants, Sabie and Crocodile rivers flowing through the Kruger National Park (KNP). We expected to link differences in community structure to environmental gradients as those rivers show different degrees of anthropogenic stress as they enter the park. Both meio- and macrobenthic communities differed across rivers and also structured along an upstream–downstream gradient. The upstream sites, which were the closest to the park borders, consistently showed a lower diversity in all three rivers. There, the invasive snail Tarebia granifera strongly dominated (making up 73% – 87% of the macrobenthos), crowding hard substrates, while concomitantly the abundances of biofilm-dwelling meiobenthos like nematodes and rotifers were substantially reduced. Nevertheless, the diversity and evenness of communities then tended to increase as water flowed downstream through the park, suggesting a beneficial effect of protected river reaches on benthic invertebrate diversity. However, for the Crocodile River, which makes up the southern border of the park, this trend was less conspicuous, suggesting that this river may experience the greatest threats. More generally, benthic invertebrate communities were driven by the concentrations of phosphates, sulphates, ammonium and organic matter and by substrate characteristics.Conservation implications: Meiobenthic organisms are very abundant in KNP rivers and react to environmental gradients; thus, they should be more considered for bio-monitoring or conservation of comprehensive assemblages of animals. Interestingly, protected reaches tended to show a reduced dominance of the invasive T. granifera and a higher diversity of benthic invertebrates.

A longitudinal snapshot of pioneer plant patterns along lowland temperate rivers

AbstractOverexploitation of water, loss of dynamism and current climate change cause river drought and baseflow events that are globally increasingly intense and prolonged. This strongly affects riverine plant communities, especially those of seasonally exposed sediments. However, few data are available concerning this key component of river biodiversity currently. Furthermore, the role of alien species is expected to be important in riverbeds since fluvial corridors have an extraordinary susceptibility to be invaded and act as primary routes for invader dispersal. This study provides a systematic investigation of the longitudinal patterns of pioneer plants—in terms of richness and cover—in three mid‐size rivers (Ticino, Adda and Oglio rivers) in northern Italy, from 15 different sampling sites. The alien plants dominated the pioneer richness (52 out of 91 species, 57% of the total richness found), whereas plant cover followed less‐defined patterns. Along the upstream–downstream gradient, native plants showed a steep decline (−69% in richness and −52% in cover rates on average), only partially offset by the local (extremely variable) changes in alien taxa (−41% on average, in the range of −2.7 to +4.1 species per plot and with cover rates varying form −10 to +1,018%). The magnitude and sign of the detected trends strongly reflected individual river identity. Further investigations are required to better assess the role of hydromorphology in driving the riverine pioneer plant assemblages.

Captive‐bred ancestry affects spatial patterns of genetic diversity and differentiation in brown trout (Salmo trutta) populations

AbstractIntraspecific genetic diversity is heterogeneously distributed in natural landscapes and often forms repeatable spatial patterns. For instance, in rivers, genetic diversity increases towards downstream areas, whereas genetic differentiation increases in isolated upstream areas. Nonetheless, these patterns can be modified by human‐induced perturbations, and documenting the extent to which human activities alter these natural patterns is important for conservation. Among the human pressures that affect freshwater biodiversity, stocking natural populations with captive‐bred strains is a common practice worldwide that can strongly alter the genetic integrity of wild populations.The main objectives of this study were to document the spatial distribution of captive‐bred ancestry in brown trout (Salmo trutta) populations from four French basins having been stocked according to different practices, and to quantify for each basin the effect of captive‐bred ancestry on the spatial distribution of genetic diversity and differentiation. The four basins were sampled along their upstream–downstream gradient, and a total of 1,686 individuals were genotyped at 192 single nucleotide polymorphism loci.For all basins, individuals with a strong assignment to the captive strain were mostly found in upper reaches, although the average proportion of captive‐bred ancestry varied strikingly among rivers (from 1.9 to 58.7%). Although spatial patterns of genetic differentiation were not affected by introgression and showed an expected increase with increasing distances from the river mouth in all basins, there was evidence that the classical pattern of downstream increase in genetic diversity was reversed when considering highly introgressed populations.These findings demonstrate that the stocking of captive‐bred strains can strongly modify natural spatial patterns of diversity, even when stocking occurred many generations ago and has now ended. The study illustrates the major impacts of humans on intraspecific biodiversity patterns, and emphasizes the importance of conservation plans that take into account this artificial distribution of genetic diversity.

Who will be where: Climate driven redistribution of fish habitat in southern Germany

To improve the robustness of projections of freshwater fish distributions under climate change, species distribution models (SDMs) were calculated for six fish species in southwestern Germany with different ecological requirements along an upstream-downstream gradient in a multi-general circulation model (GCM) approach. Using the maximum entropy (Maxent) algorithm and a high number of occurrence records (N = 4684), species distributions were projected to future climate conditions derived from 13 GCMs across the most likely representative carbon pathways (RCP4.5 and 8.5) and two time spans (near future 2050, and far future 2070), resulting in 104 distribution maps per species that were then used for the statistical analysis of future trends. Climate change is likely to affect the distribution of four of the six fish species. The potential ranges of salmonids are predicted to decline by up to 92% (brown trout) and 75% (grayling). In contrast, habitat suitability for perch and roach is predicted to increase by up to 108% and 53%, respectively. Even when accounting for broad variation in GCMs and realistic RCPs, these results suggest climate change will drive a significant redistribution of fish habitat. Salmonid-dominated communities in headwaters seem more sensitive to climate change than the fish communities of downstream sections. Because headwaters are a prevailing element of the hydrographic network in southwestern Germany, such changes may result in large-scale regressions of valuable fish communities that currently occupy broad geographic niches.

Growth variation in the endangered fish Zingel asper: Contribution of substrate quality, hydraulics, prey abundance, and water temperature

Abstract Intraspecific variation in life histories and its environmental correlates can indicate the degree of vulnerability to extinction of endangered taxa and guide conservation actions. Zingel asper (Percidae) is an endangered fish endemic to the Rhône catchment (France and Switzerland), where five populations subsist in separate river systems (Loue, Beaume, Durance, Verdon, and Doubs). Two populations of Z. asper differ in growth and longevity, but the existence of broader intraspecific differentiation in life histories and the environmental origins of this variation (if any) remain unknown. The age structure and growth profile of four populations of Z. asper (Loue, Beaume, Durance, and Verdon) and nine additional sub‐populations within the Durance system were determined by scale‐reading analysis, before evaluating the contribution of measured variation in substrate quality, hydraulics, prey availability, and water temperature to growth differentiation among and within populations. A trade‐off between early growth and longevity largely differentiated the populations of Z. asper along a slow (i.e. slower growth, smaller adult size, longevity of >5 years) to fast (i.e. faster growth, larger adult size, longevity of <4 years) continuum of life histories. This continuum differentiated populations from different river catchments along a south (Durance, Verdon) to north (Beaume, Loue) latitudinal gradient, and mapped onto an upstream–downstream gradient of sub‐populations within the Durance system. Differences in prey availability, hydraulics, and water temperature explained most of the growth variation among populations from different catchments, whereas local variation in prey availability, substrate quality, and water temperature mostly contributed to within‐river growth differentiation. These results indicate that short life cycles strongly expose all populations of Z. asper to extirpation and should motivate additional conservation actions. This study illustrates how quantifying intraspecific variation in life histories and its sensitivity to ecological context can reliably assess extinction risk and guide conservation actions by identifying endangered populations requiring priority management.

Spatial and temporal variation of physico-chemical parameters of water and its impact on algal distribution in the Oualidia lagoon (Atlantic coast of Morocco)

The Oualidia lagoon is a restricted lagoon exposed to various sources of pollution, that have a negative impact on the quality of its water. Since 2015, a high increase of algal biomass was clearly observed. Therefore, this study was carried out in order to highlight the relationship between the trophic quality of the water and the appearance of algae. The study of spatiotemporal variation of physicochemical parameters (Temperature, pH, Salinity, Dissolved oxygen, Nitrate (NO3) and Orthophosphate (PO4)) and the spatial distribution of algae was conducted between March 2019 and February 2020. The results showed a significant spatial and seasonal variation (p<0.01) of the studied physicochemical parameters with the presence of upstream–downstream gradients for most of the parameters. 39 species of algae were identified in all the lagoon and during the whole study cycle. The distribution of algae was highly affected by the concentration of nutrients along the lagoon and also by the variation of physical factors such as stream, the downstream is rich in algal species, while the upstream has a limited biodiversity (around 6 species) with a high abundance of species.

Diversity, phenology and distribution of mayfly larvae (Ephemeroptera) along an altitudinal gradient in two permanent Wadis of Algeria

ABSTRACT The taxonomy of mayflies in Wadis of Seybouse and Kebir-Rhumel in Algeria is poorly studied since a long time. This research aimed at studying diversity and distribution of Ephemeroptera fauna at the Kebir-Rhumel and Seybouse Wadis. Using a hand net, mayfly larvae were collected from the running waters along an upstream–downstream gradient at seven sites in Kebir-Rhumel Wadi (altitude range = 677‒0.7 m) and 10 sites in Seybouse Wadi (altitude range = 622‒20.7 m). Samplings totalled 399 larvae classified into eight species belonging to eight genera and six families. Two species (Ecdyonurus rothschildi and Choroterpes (Choroterpes) atlas are endemic to the Maghreb). Caenis luctuosa, Baetis pavidus, Cloeon cf. dipterum and Ephemera glaucops occurred in both Wadis. Choroterpes atlas and Potamanthus luteus were exclusive to the watershed of Wadi Kebir-Rhumel and Ecdyonurus rothschildi and Labiobaetis neglectus were exclusive to Seybouse Wadi. In both Wadis, mayfly diversity increased in sites with dense vegetation and large bed width which offers a wide heterogeneity of habitats. Following regional IUCN Red Lists in Europe, E. glaucops has a critical conservation status, whereas Potamanthus luteus is near threatened. Our findings represent the first check-list of Ephemeroptera in northeastern Algeria Wadis, which are still not sufficiently charted.

Freshwater Mussel Assemblages in the Black River, Missouri and Arkansas

Freshwater mussel assemblages show predictable variation according to large-scale biogeographic factors and stream-size gradients, but smaller-scale assemblage patterns are less well known. The goal of this study was to classify and delineate mussel assemblages of the Black River, Missouri and Arkansas, USA, along an upstream–downstream gradient and with regard to physiography and biogeographical regions. We analyzed mussel assemblages using nonmetric multidimensional scaling and indicator-species analysis. Our results yielded three assemblage groupings distributed along the upstream–downstream gradient and thereby considered aquatic ecological systems (100–1,000 km2) in a hierarchical spatial classification scheme. These groupings also support previously proposed biogeographical differences for mussels and fishes between the Ozark Highlands and Mississippi Alluvial Plain physiographic regions. Each group was characterized by 2–13 indicator species. Our demonstration of small-scale patterns of mussel assemblage change will be useful for conservation planning and for a better understanding of mussel assemblage dynamics.

Using self–organizing maps and machine learning models to assess mollusc community structure in relation to physicochemical variables in a West Africa river–estuary system

The poor understanding of changes in mollusc ecology along rivers, especially in West Africa, hampers the implementation of management measures. We used a self–organizing map, indicator species analysis, linear discriminant analysis and a random forest model to distinguish mollusc assemblages, to determine the ecological preferences of individual mollusc species and to associate major physicochemical variables with mollusc assemblages and occurrences in the Sô River Basin, Benin. We identified four mollusc assemblages along an upstream–downstream gradient. Dissolved oxygen (DO), biochemical oxygen demand (BOD), salinity, calcium (Ca), total nitrogen (TN), copper (Cu), lead (Pb), nickel (Ni), cadmium (Cd) and mercury (Hg) were the major physicochemical variables responsible for structuring these mollusc assemblages. However, the physicochemical factors responsible for shaping the distribution of individual species varied per species. Upstream sites (assemblage I) showed high DO and low BOD and mineral compounds (i.e., TN, salinity, and Ca), which are primarily responsible for structuring the occurrences of bivalves (Afropisidium pirothi, Etheria elliptica, Sphaerium hartmanni) and the gastropod Lanistes varicus. Sites along the middle reach (assemblage II) were characterised by a high degree of organic pollution but low heavy metal pollution; we detected no specific mollusc indicator species. Downstream sites (assemblage III) displayed high mineral and heavy metal concentrations and a fauna without specific indicator species. Finally, downstream sites associated with brackish water (assemblage IV) displayed important levels of organic and heavy metal pollution. These sites are dominated by diverse gastropods (i.e., Bulinus spp., Gabbiella africana, Indoplanorbis exustus, Pachymelania fusca, Radix natalensis, Stenophysa marmorata and Tympanotonos fuscatus). Our results highlight that mollusc communities in the Sô River Basin are structured by key physicochemical variables related to the river–estuary continuum. Habitats that are progressively more downstream are confronted with increasing anthropogenic stress. Conservation and management plans should focus on downstream habitats.

What remains today of pre‐industrial Alpine rivers? Census of historical and current channel patterns in the Alps

AbstractTo date, no survey on the diverse channel patterns existing prior to the major phase of river regulation in the mid‐19th–early 20th century has been elaborated at the scale of the whole European Alps. The present paper fills this knowledge gap. The historical channel forms of the 143 largest Alpine rivers with catchments larger than 500 km2 (total length 11,870 km) were reconstructed based on maps dating from the 1750s to 1900. In the early 19th century, one‐third of the large Alpine rivers were multi‐channel rivers. Single‐bed channels oscillating between close valley sides were also frequent in the Alps (28%). Sinuous and even more so meandering channels were much rarer. Historical river patterns generally followed an upstream–downstream gradient according to slope condition, floodplain width and distance from the sources. The local occurrence of certain channel patterns, however, primarily reflected the tectonic/orographic conditions. Multi‐channel reaches were widespread within the whole Alpine area, alternating with confined and oscillating reaches. This demonstrates that most areas were mainly transport‐limited rather than supply limited. Sinuous and meandering reaches were more frequent in the north‐eastern Alps and were characterized by lower denudation rates and less sediment delivery.Channel straightening caused the loss of about 510 km of river course length, equivalent to 4.3% of the historical extent. Multi‐channel stretches are currently a mere 15% of their historical length, and 45% of the larger Alpine rivers are intensively channelized or have been transformed into reservoirs. Channelization measures differed from one country to another. Human pressures directly affected both local channel geometry and the upstream controls (i.e., sediment supply). Accordingly, individual multi‐channel reaches also evolved into single‐thread channels without any local human interventions.

Taxonomic and functional diversity in a subtropical stream: A longitudinal pattern analysis

AbstractIdentifying the spatial patterns of fish diversity in streams is basic for the conservation and management of stream fishes. The “upstream–downstream” patterns in the taxonomic α‐diversity of stream fishes have been widely surveyed. However, the longitudinal patterns in the functional diversity and β‐diversity of stream fishes have been given less attention. In this study, we surveyed fishes along an upstream–downstream gradient in a headwater stream of the Qiantang River, China, and examined the longitudinal variations in fish diversity. Our aims were to assess whether the longitudinal patterns in fish diversity were consistent between the taxonomic and functional metrics and between the α‐ and β‐aspects of diversity. We found that both species richness and functional richness of fishes showed a hump‐shaped relationship with the distance from headwaters, while both taxonomic and functional β‐diversities presented the U‐shaped distributions along the river continuum. Functional diversity related more to the distance from headwaters than taxonomic diversity. Despite their similar relationship with the distance from headwaters, taxonomic and functional β‐diversities were dominated by species turnover and function nestedness components, respectively. Our results suggest that, along the river continuum in a subtropical stream, the α‐ and β‐aspects of fish diversity present different longitudinal variations. Although the taxonomic and functional diversity shows similar relationships with distance from headwaters, their spatial variations are driven by different ecological processes.

Linking intraspecific variability in trophic and functional niches along an environmental gradient

Abstract Intraspecific trophic variability has important ecological and evolutionary implications, and is driven by multiple interacting factors. Functional traits and environmental conditions are important in mediating the trophic niche of individuals because they determine their ability to consume certain prey, their energetic requirements, and resource availability. In this study, we aimed at investigating the interacting effects of functional traits and environmental conditions on several attributes of trophic niche in natural populations. Here, we quantified intraspecific variability in the trophic niche of 12 riverine populations of European minnow (Phoxinus phoxinus) using stable isotope analyses. Functional traits (i.e. morpho‐anatomical traits) and environmental conditions (i.e. upstream–downstream gradient, forest cover) were quantified to identify the determinants of (1) trophic position and resource origin, (2) trophic niche size, and (3) trophic differentiation (β‐diversity) among populations. We demonstrated that trophic position and resource origin covaried with functional traits related to body size and locomotion performance, and that the strength and shape of these relationships varied according to local environmental conditions. The trophic niche size also differed among populations, although no determinant was identified. Finally, trophic β‐diversity was correlated to environmental differentiation among sites. Overall, the determinants of intraspecific variability in trophic niche appeared highly context‐dependent, and related to the interactions between functional traits and environmental conditions. Because populations are currently facing important environmental changes, understanding this context‐dependency is important for predicting food web structure and ecosystem dynamics in a changing world.

Diet partitioning and trophic guild structure of fish assemblages in Chishui River, the last undammed tributary of the upper Yangtze River, China

AbstractKnowledge of trophic ecology of fish species is fundamental to understand the organization mechanism of fish assemblages and crucial for developing effective management and conservation strategies. This study examined the diet partitioning and trophic guild structure of fish assemblages in Chishui River, the last undammed tributary of the upper Yangtze River, China. Specimens were collected in three sections along the upstream–downstream gradient in 2012. Digestive tract contents of 54 fish species, represented by 692 individuals, were analysed and quantified. Analysis showed that fish assemblages in the Chishui River utilized aquatic insects, algae, detritus, molluscs, and fishes as the main food resources, whereas terrestrial insects were consumed only occasionally. The trophic guild structure of fish assemblages changed gradually with the longitudinal gradient. Specially, the number of trophic guilds increased with downstream distance. In addition, the relative number of omnivorous species increased longitudinally, whereas the relative number of insectivorous species declined downstream. This study demonstrated how fish assemblages utilize the food resources under near‐natural conditions. These results provide valuable information for fish conservation and ecological restoration.

Environmental filtering governs the spatial distribution of alien fishes in a large, human‐impacted Mediterranean river

AbstractAimTo analyse the occurrence and abundance of native versus alien fish species in relation to climate, land use, hydrologic alteration and habitat fragmentation in a heavily invaded and human‐impacted riverine ecosystem. To test whether co‐occurrence patterns of native versus alien species are structured by environmental filtering or biotic associations.LocationMediterranean, Iberian Peninsula, Ebro River catchment.MethodsWe modelled freshwater fish distributions and their association with environmental conditions using a hurdle model‐like approach involving boosted regression trees. Additionally, we applied a joint species distribution model to quantify the co‐occurrence of native versus alien fish species that can be attributed to shared environmental responses or potentially to biotic interactions.ResultsOur results point to environmental factors, rather than biotic associations, as major correlates of the increase of alien and the decline of native fishes in the Ebro River. We observed contrasting patterns of native versus alien species along the upstream‐downstream gradient. Alien species dominated in the lower reaches associated with warmer temperatures, higher shares of intensive land use and appeared facilitated by dams and river regulation. Native species richness was highest in the larger tributaries followed by a strong decline in the main stem which was related to the river network position and land use type. Fragmentation played a subordinate role in explaining fish richness and abundance patterns.Main conclusionsGiven the strong association with temperature, a further range expansion of alien fishes in the Ebro with future climate change may be expected. More local‐scale factors related to habitat degradation and hydrologic alteration will further exacerbate the invasion success of many alien fishes. Further multiple, independent species introductions might mask isolation and fragmentation effects of dams on the future spread and distribution of alien fish.

Distribution strategy of Nimbapanchax petersi (Sauvage, 1882) and Epiplatys chaperi sheljuzhkoi (Poll, 1953) fish, in Banco National Park (Côte d’Ivoire, West Africa)

Objective: This study highlights the distribution strategy of two fish species of Nothobranchiidae ( Nimbapanchax petersi and Epiplatys chaperi sheljuzhkoi ) according to environmental variables of Banco River in the National Park of Banco in order to characterize their preferential habitat. Methodology and results: Sampling was conducted from December 2015 to January 2017 using dip nets. Four defined stations (B1 to B4) along the Banco River were visited. A total of 397 samples of Nimbapanchax petersi were collected. This species is more abundant upstream with 82.87% of the sampling. However, the 186 individuals of Epiplatys chaperi sheljuzhkoi captured were distributed homogeneously over the entire river along an upstream-downstream gradient. Canonical Correlation Analysis (CCA) has shown that the nature of the substrate (clay-mud mixture, rocks and deadwood-foliage mixture) and dissolved oxygen levels are critical factors in the distribution pattern of these species in the Banco River. Epiplatys chaperi sheljuzhkoi select habitats with mud, clay and deadwood-foliage mixture while Nimbapanchax petersi target rocky and more oxygenated environments. Conclusion and application of results: These results, which are essential data on the ecology of aquatic species in the wild, could contribute to ensure better conservation of small freshwater fish. These baseline data for future studies will enable a sustainable stock conservation policy for these species to be put in place. In addition, faced with the anthropogenic pressures of the surrounding communities on this environment, park managers should pay more attention to the preservation of biodiversity in general and to the two species of Nothobranchiidae in particular. Keywords: Distribution, Nothobranchiidae, aquarists, environmental factors, Banco River