Freshwater Fish Assemblages Research Articles

Comparing diversity and structure of freshwater fish assemblages using environmental DNA and gillnetting methods: A case study of a large deep reservoir in East China

Environmental DNA (eDNA) technology, as an alternative to traditional gillnet surveys, has attracted widespread attention. However, comparisons between eDNA and traditional methods regarding biodiversity and community structure have not yet been fully elucidated. This study compared the ability of eDNA and gillnets for fish monitoring in a large deep reservoir (Qiandao Lake) in East China. The results showed that eDNA exhibited higher taxonomic resolution and detection rates, and significantly larger species diversity and richness indices compared with traditional gillnetting methods. Using abundance and biomass datasets from gillnets revealed significant differences in fish community composition between gillnetting and eDNA survey methods. Gillnet abundance was dominated by small-sized fish species, while gillnet biomass was dominated by larger-sized ones, and the prevailing species detected in eDNA reads included the dominant species from gillnet abundance and biomass, as well as a medium-sized invasive alien fish (Lepomis macrochirus). Non-metric multidimensional scaling (NMDS) showed that the spatial distribution in abundance of fish species sampled by gillnetting was more dispersed than that using eDNA. The explanatory power with the gillnet abundance and biomass together as predictor variables of the eDNA reads increased moderately compared with taking them separately, and the fitting degree of quadratic functions was also improved somewhat compared to linear equations when using biomass to predict eDNA reads. Furthermore, the key environmental factors affecting fish communities differed between the two methods. Current research indicates that eDNA has advantages over gillnets in detecting fish species diversity, and it is recommended to combine it with traditional sampling methods. Under natural aquatic ecosystem conditions, the eDNA reads may comprehensively reflect the biomass and abundance information obtained through gillnetting, but their relationship is complex and requires further research. This study will provide guidance for biodiversity monitoring.

Influence of hydrological variability and life history strategy on riverine fish assemblages in the Australian wet‐dry tropics

AbstractRiverine fish assemblages are strongly influenced by attributes of the flow regime. Tropical savannah river systems have distinct and predictable hydrologic seasonality, reflecting the wet‐dry climate, but can vary substantially in terms of dry season flow permanency and wet season flow‐pulse characteristics. Understanding how flow permanence and variability influence fish assemblages, and whether these factors can be used to predict responses to future hydrological change, are key knowledge gaps that impede effective management. We examined the influence of hydrological variability on the structure and diversity of freshwater fish assemblages across rivers of the wet‐dry tropics of northern Australia. We found distinct fish assemblages that varied predictably across three hydrological river types: Intermittent, Perennial Stable and Perennial Flashy flow regimes. This distinction emerged despite a common species pool across the region. Species richness was greatest in rivers with Perennial Stable flow regimes, whereas beta‐diversity was greatest in Intermittent rivers. However, life history strategies of constituent species were generally poor predictors of species abundances within each hydrological river type. The distinct fish assemblages evident among hydrological classes may provide some cautious ability to both predict potential fish assemblage changes with future hydrological changes (e.g. if perennial streams became more flashy or intermittent), and to predict fish assemblages expected in unsampled rivers with particular hydrological characteristics. Our findings provide further support for the importance of maintaining regional flow‐habitat heterogeneity and the connectivity between hydrological river types, and their essential role for conserving tropical fish species diversity into an uncertain hydrological future.

Monitoring tropical freshwater fish with underwater videography and deep learning

Context The application of deep learning to monitor tropical freshwater fish assemblages and detect potential anthropogenic impacts is poorly understood. Aims This study aimed to compare the results between trained human observers and deep learning, using the fish monitoring program for impact detection at Ranger Uranium Mine as a case study. Methods Fish abundance (MaxN) was measured by trained observers and deep learning. Microsoft’s Azure Custom Vision was used to annotate, label and train deep learning models with fish imagery. PERMANOVA was used to compare method, year and billabong. Key results Deep learning model training on 23 fish taxa resulted in mean average precision, precision and recall of 83.6, 81.3 and 89.1%, respectively. PERMANOVA revealed significant differences between the two methods, but no significant interaction was observed in method, billabong and year. Conclusions These results suggest that the distribution of fish taxa and their relative abundances determined by deep learning and trained observers reflect similar changes between control and exposed billabongs over a 3-year period. Implications The implications of these method-related differences should be carefully considered in the context of impact detection, and further research is required to more accurately characterise small-growing schooling fish species, which were found to contribute significantly to the observed differences.

European water frame directive ecoregions do not adequately represent freshwater fish biogeography

The quest to understand species' distribution patterns and delineate their limits has led to the establishment of the world's ecoregions, large units of land containing a distinct assemblage of species, both for terrestrial and marine ecosystems. However, freshwaters constitute their own special case within terrestrial ecosystems, and have only recently been divided into freshwater ecoregions, primarily based on watershed limits. Freshwater ecoregions used by the European Water Frame Directive (WFD), which guides freshwater management policies in the European Union, have been criticized for not adequately representing freshwater fish biogeography. This study compares the geographic agreement between WFD ecoregions and freshwater fish distribution at the European scale. Using IUCN Red List distribution maps, we determined the composition of freshwater fish communities in major European basins. Then, we calculated a similarity matrix in order to cluster freshwater basins with more related fish assemblages. We compare our findings with WFD ecoregions and global ecoregions from the Freshwater Ecoregions of the World (FEOW) database. Our results reveal that WFD ecoregions do not sufficiently capture freshwater fish assemblage differences across Europe. Mediterranean basins exhibit high freshwater fish endemism and greater species variation, whereas central European basins harbor more similar fauna. Overall, our results align more with those of FEOW. To enhance the relevance of freshwater ecoregions in Europe for management and conservation, we propose several measures to ensure a comprehensive study involving all stakeholders in the process of defining these ecoregions accurately.

A photographic atlas for European freshwater and migratory fish remains and key considerations for their analysis

AbstractIdentification of archeological fish remains requires the use of comparative reference materials, generally in the form of disarticulated fish skeletons. Photographic or illustrative atlases provide an additional resource for the analysis of fish remains. Photographic resources exist for many marine species and for specific geographic regions, whereas freshwater European species have not been covered in great detail. Here, we present a photographic atlas for the bones of freshwater and migratory fish commonly recovered from archeological sites in Central Europe, alongside a discussion of the difficulties and considerations for the analysis of freshwater fish remains. The atlas also highlights the morphological similarity of many species and the interpretive limits of freshwater fish assemblages. The atlas aims to act as an accessible and user‐friendly resource, which can be used for basic identification purposes when access to physical collections is not possible, to supplement pre‐existing collections, or for training purposes. This paper acts as a platform from which the full atlas can be downloaded.

Influence of invasive bigheaded carps on abundance of Gizzard Shad in the Tennessee River

AbstractObjectiveThe Tennessee River basin and its cascade of reservoirs are home to some of the most diverse freshwater fish assemblages in the world. This unique system is threatened by the ongoing invasion of Silver Carp Hypophthalmichthys molitrix and Bighead Carp H. nobilis, hereafter referred to together as “bigheaded carps.” Bigheaded carps may directly compete for food resources with native clupeid species such as Gizzard Shad Dorosoma cepedianum, and this potential interaction could have damaging ecological and economic consequences. High relative abundances of Gizzard Shad are crucial to the Tennessee River food web and associated fisheries because of their role as a forage base for piscivorous species.MethodsWe analyzed a collection of annual gillnetting and electrofishing data spanning from 1990 to 2017 to test whether Gizzard Shad relative abundances have changed in Tennessee River reservoirs since the arrival of bigheaded carps.ResultOur analyses indicated that Gizzard Shad abundances have been declining but were already declining prior to the arrival of bigheaded carps in the Tennessee River.ConclusionAt this stage in the invasion, we could not attribute a cause‐and‐effect relationship to the inverse correlation between Gizzard Shad and bigheaded carps, but we advise continued monitoring of indicators of harmful interactions.

Increasing stability of a native freshwater fish assemblage following flow rehabilitation.

Stream restorations are increasingly critical for managing and recovering freshwater biodiversity in human-dominated landscapes. However, few studies have quantified how rehabilitative actions promulgate through aquatic communities over decades. Here, a long-term dataset is analyzed for fish assemblage change, incorporating data pre- and post-restoration periods, and testing the extent to which native assemblage stability has increased over time. In the late 1950s, a large capacity dam was installed on Putah Creek (Solano County, CA, USA), which altered the natural flow regime, channel structure, geomorphic processes, and overall ecological function. Notably, downstream flows were reduced (especially during summer months) resulting in an aquatic assemblage dominated by warm-water nonnative species, while endemic native species subsisted at low levels as subordinates. A court-mediated Accord was ratified in 2000, providing a more natural flow regime, specifically for native and anadromous fishes in the stream. The richness of nonnative species decreased at every site following the Accord, while the richness of native species increased or stayed constant. At the three most upstream sites, native species richness increased over time and ultimately exceeded nonnative richness. Native assemblage recovery was strongest upriver, closer to flow releases and habitat restoration activities, and decreased longitudinally downstream. Rank-abundance curves through time revealed that, while species evenness was low throughout the study, dominance shifted from nonnative to native species in the upstream sites coincident with rehabilitation efforts. Mean rank shifts decreased following flow rehabilitation; thus the assemblage became increasingly stable over time following flow rehabilitation. Putah Creek's rehabilitation may represent a model for others interested in improving endemic freshwater communities in degraded ecosystems.

Covariation of taxonomic and functional facets of β-diversity in Chilean freshwater fish assemblages: Implications for current and future processes of biotic homogenization.

The biodiversity of assemblages that experience the introduction and extinction of species may lead to responses in two important facets: The taxonomic and functional diversity. The way in which these facets are associated may reveal important implications and consequences for the conservation of those assemblages. Considering the critical situation of freshwater fishes in continental Chile (30° - 56° S), we analyzed how the taxonomic (TDβ) and functional (FDβ) facets of β-diversity, and their components of turnover and nestedness, are associated. We evaluated changes in β-diversity (ΔTDβ and ΔFDβ), turnover (ΔTDtur and ΔFDtur), and nestedness (ΔTDnes and ΔFDnes) in 20 fish assemblages from their historical (pre-European) to current composition. We also simulated future trends of these changes, assuming that native species with conservation issues would become extinct. Our results show that the fish assemblages studied are in a process of loss of β-diversity, both in taxonomic and functional facets (ΔTDβ = -3.9%; ΔFDβ = -30.4%); also, that these facets are positively correlated in the assemblages studied (r = 0.617; P < 0.05). Both components showed by loss in nestedness (ΔTDnes = -36.9%; ΔFDnes = -60.9%) but gain in turnover (ΔTDtur = 9.2%; ΔFDtur = 12.3%). The functional β-diversity decreased more than the taxonomic (ΔFDβ > ΔTDβ), which was caused chiefly by six exotic species of Salmonidae, whose geographical spread was wider and that at the same time shared several morpho-functional traits. Our forecasts, assuming an intensification in the extinction of Endangered and Vulnerable native species, indicate that the process of homogenization will continue, though at a lower rate. Our study shows that the freshwater ichthyofauna of continental Chile is undergoing biotic homogenization, and that this process involves the facets of taxonomic and functional β-diversity, which are show high correlation between historical and current compositions. Both facets show that process is influenced by nestedness, and while turnover contributes to differentiation (both taxonomic and functional), its importance is overshadowed by nestedness.

Variation in patterns of fish assemblage and their environmental correlates in a tropical river basin from the Gulf of Mexico slope

Abstract Understanding patterns of freshwater fish assemblage structure is key to protect them from ongoing human-induced threats to aquatic biodiversity. Yet, studies on associations between fish assemblages and habitat are lacking from many areas of high diversity in Middle America. We assessed fish assemblage structure and environmental associations from a portion of the Lacantún River sub-basin (Usumacinta River, Chiapas, Mexico). Based on environmental data and 17,462 individuals (56 species, 46 genera, and 22 families) captured from 13 sites sampled between 2017–2019, we found that stream order, distance to the Usumacinta, forest cover, temperature, and dissolved oxygen are key to explaining assemblage composition. Four clusters were found via multivariate regression tree analysis, with stream order and dissolved oxygen as defining variables. Our findings suggest that fish communities remain spatially structured even at small scales, in association to environmental gradients among habitats.

First insight into freshwater fish assemblages in the western part of the Endau-Rompin landscape, Malaysia

In Malaysia, our knowledge of freshwater ecosystem and its aquatic inhabitants, particularly freshwater fish, remains inadequate, even in protected regions. It is essential to understand the composition of freshwater fish, their distribution along river gradients, and their interactions between environmental variables to develop and strategize effective conservation and management plans. Consequently, an investigation into freshwater fish assemblages in three rivers draining off from the western part of Endau-Rompin Landscape was conducted in 12 established substations. Sampling sessions were conducted from September to December 2021 in the Labis district of Johor, using multiple sampling methods along 200 meters for each substation. The environmental variables were measured using water quality parameters. A total of 66 species were collected. The family Cyprinidae presented the highest species diversity (17 species), constituting 52% of total capture. Crossocheilus obscurus was the most dominant species, and the highest species richness was recorded in the Segamat River (45 species), followed by Juaseh (36 species) and Labis River (34 species). It was discerned that the composition of fish varied between the substations. The knowledge presented here is the first documentation on the freshwater fish from these rivers. It would serve as a baseline information for key authorities and stakeholders to conserve the biodiversity inhabiting freshwater ecosystems in Malaysia.

Environmental DNA reveals a mismatch between diversity facets of Amazonian fishes in response to contrasting geographical, environmental and anthropogenic effects.

Freshwater ecosystems are among the most endangered ecosystem in the world. Understanding how human activities affect these ecosystems requires disentangling and quantifying the contribution of the factors driving community assembly. While it has been largely studied in temperate freshwaters, tropical ecosystems remain challenging to study due to the high species richness and the lack of knowledge on species distribution. Here, the use of eDNA-based fish inventories combined to a community-level modelling approach allowed depicting of assembly rules and quantifying the relative contribution of geographic, environmental and anthropic factors to fish assembly. We then used the model predictions to map spatial biodiversity and assess the representativity of sites surveyed in French Guiana within the EU Water Framework Directive (WFD) and highlighted areas that should host unique freshwater fish assemblages. We demonstrated a mismatch between the taxonomic and functional diversity. Taxonomic assemblages between but also within basins were mainly the results of dispersal limitation resulting from basin isolation and natural river barriers. Contrastingly, functional assemblages were ruled by environmental and anthropic factors. The regional mapping of fish diversity indicated that the sites surveyed within the EU WFD had a better representativity of the regional functional diversity than taxonomic diversity. Importantly, we also showed that the assemblages expected to be the most altered by anthropic factors were the most poorly represented in terms of functional diversity in the surveyed sites. The predictions of unique functional and taxonomic assemblages could, therefore, guide the establishment of new survey sites to increase fish diversity representativity and improve this monitoring program.

Effects of non‐native species on phylogenetic dispersion of freshwater fish communities in North America

AbstractAimMost studies focusing on terrestrial ecosystems have shown that non‐native species are more likely to invade phylogenetically clustered communities, that the introduction of non‐native species increases phylogenetic clustering in the recipient communities, and that the latter is more conspicuous for recipient communities at a larger spatial scale. However, whether these patterns hold for aquatic ecosystems is rarely tested. Here, we investigate the phylogenetic structure of native and non‐native freshwater fish assemblages at a continental spatial extent.LocationThe continental United States and Canada.Time periodCurrent.MethodsWe collated native and naturalized non‐native species lists of freshwater fishes for each watershed at local and regional spatial scales. Two phylogenetic metrics (MPDses and MNNDses) representing different evolutionary depths were used to quantify the phylogenetic dispersion of each watershed fish assemblage and were related to temperature and precipitation using correlation and regression analyses. Values of the metrics were compared between the two spatial scales.ResultsOur study found that (1) phylogenetically more diverse fish communities tended to be invaded by fewer non‐native fish species, and that non‐native species more frequently invaded communities with lower phylogenetic dispersion (i.e. higher phylogenetic clustering), (2) introduction of non‐native fishes reduced phylogenetic clustering in some watershed but increased clustering in others, (3) introduction of non‐native species caused phylogenetic dispersion to increase in watersheds with low phylogenetic diversity and to decrease in watersheds with high phylogenetic diversity and (4) phylogenetic clustering for fish assemblages at the larger spatial scale was smaller than that at the smaller spatial scale.Main conclusionsSupport for Darwin's naturalization and preadaptation hypotheses in freshwater fish assemblages depends on the phylogenetic diversity of assemblages within the invaded watersheds. Our results are contrary to previous studies that found that the introduction of non‐native species increases phylogenetic clustering in the recipient communities more strongly at a larger spatial scale.

Increasing stability of a native freshwater fish assemblage following flow rehabilitation

Increasing stability of a native freshwater fish assemblage following flow rehabilitation

A desktop study on fish assemblages in Malaysian lotic habitats

A desktop study on freshwater fish in Malaysian lotic habitats was conducted to provide an overview of the freshwater fish assemblages in Malaysia. Secondary data was extracted from literature that retrieved from major scientific databases including Google Scholar, ScienceDirect, and SpringerLink. A total of 385 fish species from 49 families were documented in Malaysian lotic habitats based on secondary data analysis. The Cyprinidae family is the most abundant fish family in Malaysia with 88 species recorded, followed by Danionidae (44), Bagridae (27), and Osphronemidae (21). The Cyprinidae family has the top five fish species recorded most frequently in Malaysian lotic habitats, which are present in the majority of Malaysia’s states. Approximately 47% of fish species are restricted to just one state of Malaysia, demonstrating endemism of freshwater fish is high in Malaysian lotic habitats. Fish assemblages were found to be similar in Kedah, Kelantan, Pahang, Perak, Terengganu, and Johor, but very different in Sabah, Sarawak, Penang, Negeri Sembilan, and Selangor. Connectivity between lotic habitats in each state, land use, endemism, and invasive species may all influence the fish assemblages in each Malaysian state. This study revealed that ichthyofaunal research is lacking in several Malaysian states. More research should be done in those states to fill in the research gaps and present the most up-to-date information on Malaysia’s ichthyofaunal study.

Stage-structured feeding by freshwater fish assemblages in eastern South Dakota, USA

Stage-structured feeding by freshwater fish assemblages in eastern South Dakota, USA

How does a reservoir affect the fish assemblage structure in a Mediterranean River (Turkey)?

Most rivers around the Mediterranean region, regardless of size, are interrupted by human induced barriers. Although various studies have been conducted to investigate the impacts of reservoirs on undisrupted freshwater biota, what kind of effects they exert on the distribution of freshwater fish assemblages with respect to the presence of invasive species remains to be answered. To attend to this research need, the Karamenderes River, which is disrupted by the Bayramiç Reservoir, was selected as the research site. Relying on the river continuum concept (RCC), we hypothesized that fish assemblages in a given river would demonstrate a gradual downstream change unless the river is interrupted by any reservoir. The ad hoc unweighted pair group method with arithmetic means (UPGMA) agglomerative hierarchical cluster analyses revealed 11 fish assemblages 100 km down the studied river, which is characterized by four environmental gradients. Besides, co-occurrence network analyses were performed to gain a better understanding of the constructs of the observed fish assemblages. The analyses yielded two distinct clusters along the river and showed that the Bayramiç Reservoir had no decisive part in the spatial clustering of these fish assemblages. The migratory species Anguilla anguilla was found only in and around the river mouth area. The co-occurrence network analyses indicated that the freshwater, estuarine and introduced species were observable in distinct groups. It is notable that the non-native Cyprinus carpio and invasive Carassius gibelio were determined in the native freshwater fish species module. The research evidenced that the reservoir had a triple effect, that is, a migration barrier to migratory fish species, a donor facilitating invasion, and a cause of homogenization of river fish assemblages along the river. The results suggest that the impact of the reservoir should be assessed in view of multiple nested model and fish passageways and controlling invasive species are two contradictory problems as far as the impacts of reservoirs are concerned. Therefore, river management should be performed in a way to allow the native migratory species to migrate freely while preventing the introduced species from moving upstream or downstream to preserve and promote rivers' heterogeneity.

Change in beta diversity of riverine fish during and after supra-seasonal drought

ContextA core theme in ecohydrology is understanding how hydrology affects spatial variation in the composition of species assemblages (i.e., beta diversity). However, most empirical evidence is from research in upland rivers spanning small spatial extents. Relatively little is known of the consequences of hydrological variation for beta diversity across multiple spatial scales in lowland rivers.ObjectivesWe sought to examine how spatial variation in hydrology and fish beta diversity within and among rivers changed over time in response to intensification and cessation of hydrological drought.MethodsWe used monitoring data of fish assemblages, coupled with hydrological and biophysical data, to test how spatial variation in hydrology and multiple components of fish beta diversity in lowland rivers of the Murray—Darling Basin (Australia) varied across spatial scales during contrasting hydrological phases.ResultsSpatial variation in hydrology among rivers declined with increasing duration of drought before increasing during a return to above-average flows. Spatial variation in hydrology within rivers did not show consistent changes between hydrological phases. Beta diversity among and within rivers showed variable, river-specific changes among hydrological phases for both incidence- and abundance-based components of assemblage composition.ConclusionsInconsistent hydrology—beta diversity patterns found here suggest that mechanisms and outcomes of drought and flooding impacts to beta diversity are context-dependent and not broadly generalisable. Our findings indicate that hydrological fluctuations occurring in the Murray—Darling Basin in the period analysed here did not cause significant or consistent homogenisation or differentiation of freshwater fish assemblages.

Historical connectivity and environmental filtering jointly determine the freshwater fish assemblages on Taiwan and Hainan Islands of China.

The biotas of Taiwan and Hainan Islands are of continental origin, but the manner with which historical and ecological factors shaped these insular species is still unclear. Here, we used freshwater fish as a model to fill this gap by quantifying the phylogenetic structure of the insular faunas and disentangling the relative contribution of potential drivers. Firstly, we used clustering and ordination analyses to identify regional species pools. To test whether the insular freshwater fish faunas were phylogenetically clustered or overdispersed, we calculated the net relatedness index (NRI) and the nearest taxon index (NTI). Finally, we implemented logistic regressions to disentangle the relative importance of species attributes (i.e., maximum body length, climatic niche dissimilarity [ND], and diversification) and historical connectivity (HC) in explaining the insular faunas. Our results showed that the most possible species pools of Taiwan are Zhejiang and Fujian provinces, and those of Hainan are Guangdong and Guangxi provinces. These insular faunas showed random phylogenetic structures in terms of NRI values. According to the NTI values, however, the Taiwanese fauna displayed more phylogenetic clustering, while the Hainanese one was more overdispersed. Both the standard and phylogenetic logistic regressions identified HC and climatic ND as the 2 top explanatory variables for species assemblages on these islands. Our reconstruction of the paleo-connected drainage basins provides insight into how historical processes and ecological factors interact to shape the freshwater fish fauna of the East Asian islands.

Drivers of phylogenetic structure in Amazon freshwater fish assemblages

AbstractAimPhylogenetic relatedness among species can provide useful information on the diversification history and past dispersal events that may have shaped contemporary assemblages. Here, using of the most comprehensive fish occurrence database currently available and a global molecular phylogeny of ray‐finned fishes, we evaluate the respective roles of historical and contemporary processes in generating and maintaining fish assemblage phylodiversity patterns among 97 sub‐drainages covering the Amazon River basin.LocationAmazon River basin.TaxonFreshwater fishes.MethodsUsing a large comprehensive database of freshwater fish species distributions, and a global molecular phylogeny of ray‐finned (actinopterygian) fishes, we estimated historical and contemporary environmental effects on sub‐drainage fish phylodiversity patterns using three phylogenetic metrics standardized for richness effect: Phylogenetic Diversity (ses.PD), Mean pairwise Phylogenetic Distance between species capturing patterns at older evolutionary timescales (ses.MPD), and Mean Nearest Taxon Distance capturing patterns at younger evolutionary timescales (ses.MNTD).ResultsWe found significant effects of elevation gradients, contemporary climate, and water types on assemblage phylodiversity patterns. Furthermore, we found significant relationships among the three phylogenetic metrics used, and between these metrics and the distance of sub‐drainages to the Amazon River mouth, representing the Amazon basin West‐East longitudinal gradient.Main conclusionsPhylogenetic diversity showed a highly non‐random spatial distribution across the Amazon basin. Beyond significant regional effects of several contemporary and historical drivers, there was a significant West‐East decline in sub‐drainage assemblages phylogenetic clustering, along with an increase in phylogenetic diversity. These latter patterns suggest deeper evolutionary divergences among taxa located to the East, and more recent radiations in the Western sub‐drainages. Based on these findings and given that assemblages are, on average more species‐rich in sub‐basins of the Western part of the basin than in their Eastern relatives, we conclude that Western Amazon can be seen as an evolutionary “cradle” of biodiversity for freshwater fishes.

Exotic species elicit decoupled responses in functional diversity components of freshwater fish assemblages in Chile

In the freshwater basins of central Chile, 28 exotic species have been introduced, which have contributed to increase taxonomic diversity. Nevertheless, how these species have modified the components of functional diversity in these assemblages, a key aspect in learning about their present and future stability within an ecosystem, is unknown. In this study, we analyzed how the introduction of exotic species affects the functional diversity components of richness (FRic), divergence (FDiv), specialization (FSpe), and functional originality (FOri). Additionally, we simulated the effect of the loss (extinction/extirpation) of threatened native species. To do so, we gathered information on the distribution and functional characters of native and exotic species. Through Principal Coordinates Analysis (PCo), we obtained three independent axes (PCoA1, PCoA2, and PCoA3), which allowed us to define a multidimensional space and then to calculate FRic, FDiv, FSpe, and FOri. Our results indicate that richness and functional originality have increased significantly with the introduction of exotic species (263% and 32%, respectively). In contrast, functional divergence and specialization have remained the same. The possible extinction of threatened native species may promote increases in functional originality, decreases in functional richness and divergence, and unchanged functional specialization. On the other hand, a subset of exotic species presents novel features, while another shows redundant features with native ichthyofauna. We emphasize that the possible extinction of native species currently classified as threatened may lead to the disappearance of unique functional groups, which puts at risk the persistence and stability of these assemblages.