Freshwater conservation efforts require an understanding of how natural and anthropogenic factors shape the present-day biogeography of native and non-native species. This knowledge need is especially acute for imperiled native fishes in the highly modified Lower Colorado River Basin (LCRB), USA. In the present study we employed both a taxonomic and functional approach to explore how natural and human-related environmental drivers shape landscape-scale patterns of fish community composition in the LCRB. Our results showed that hydrologic alteration, watershed land use, and regional climate explained 30.3% and 44.7% of the total variation in fish community taxonomic and functional composition, respectively. Watersheds with greater dam densities and upstream storage capacity supported higher non-native functional diversity, suggesting that dams have provided additional ''niche opportunities'' for non-native equilibrium lifehistory strategists by introducing new reservoir habitat and modifying downstream flow and thermal regimes. By contrast, watersheds characterized by greater upstream land protection, lower dam densities, and higher variation in spring and summer precipitation supported fish communities with a strong complement of native species (opportunistic-periodic strategists). In conclusion, our study highlights the utility of a life-history approach to better understand the patterns and processes by which fish communities vary along environmental gradients.Résumé : Les efforts de conservation en eau douce nécessitent une compréhension de la manière dont les facteurs naturels et anthropiques affectent la biogéographie actuelle des espèces indigènes et non indigènes. Cette connaissance est particulièrement indispensable pour les poissons indigènes en péril dans le bassin versant inférieur fortement modifié du Colorado (LCRB). Nous utilisons dans notre étude à la fois des méthodologies taxonomiques et fonctionnelles pour explorer comment les facteurs environnementaux naturels et anthropiques transforment les patrons de la communauté de poissons à l'échelle du paysage dans le LCBR. Nos résultats montrent que les modifications hydrologiques, l'utilisation des terres du bassin versant et le climat régional expliquent respectivement 30,3 % et 44,7 % de la variation totale de la composition taxonomique et fonctionnelle de la communauté de poissons. Les bassins versants avec une densité plus élevée de barrages et une capacité plus importante de rétention en amont contiennent une diversité fonctionnelle non indigène plus élevée, ce qui laisse croire que les barrages fournissent des « possibilités de niches » pour des espèces non indigènes stratèges d'équilibre en créant de nouveaux habitats de réservoir et en modifiant les régimes de débit et de température en aval. En revanche, les bassins versants caractérisés par une plus grande protection des terres en amont, une densité plus faible de barrages et une variation plus importante des précipitations de printemps et d'été contiennent des communautés de poissons avec u...

Aim The highly endemic fishes of the arid Southwest USA have been heavily impacted by human activities resulting in one of the most threatened fish faunas in the world. The aim of this study was to examine the patterns and drivers of taxonomic and functional beta diversity of freshwater fish in the Lower Colorado River Basin across the 20th century.Location Lower Colorado River Basin (LCRB).Methods The taxonomic and functional similarities of watersheds were quantified to identify patterns of biotic homogenization or differentiation over the period 1900-1999. Path analysis was used to identify the relative influence of dam density, urban land use, precipitation regimes and non-native species richness on observed changes in fish faunal composition.Results The fish fauna of the LCRB has become increasingly homogenized, both taxonomically (1.1% based on b sim index) and functionally (6.2% based on Bray-Curtis index), over the 20th century. The rate of homogenization varied substantially; range declines of native species initially caused taxonomic differentiation ()7.9% in the 1960s), followed by marginal homogenization (observed in the 1990s) in response to an influx of non-native species introductions. By contrast, functional homogenization of the basin was evident considerably earlier (in the 1950s) because of the widespread introduction of non-native species sharing similar suites of biological traits. Path analysis revealed that both taxonomic and functional homogenization were positively related to the direct and indirect (facilitation by dams and urbanization) effects of non-native species richness.Main conclusions Our study simultaneously examines rates of change in multiple dimensions of the homogenization process. For the endemic fish fauna of the LCRB, we found that the processes of taxonomic and functional homogenization are highly dynamic over time, varying both in terms of the magnitude and rate of change over the 20th century.

Numerous studies have shown how interactions between nonindigenous species (NIS) can accelerate the rate at which they establish and spread in invaded habitats, leading to an “invasional meltdown.” We investigated facilitation at an earlier stage in the invasion process: during entrainment of propagules in a transport pathway. The introduced bryozoan Watersipora subtorquata is tolerant of several antifouling biocides and a common component of hull‐fouling assemblages, a major transport pathway for aquatic NIS. We predicted that colonies of W. subtorquata act as nontoxic refugia for other, less tolerant species to settle on. We compared rates of recruitment of W. subtorquata and other fouling organisms to surfaces coated with three antifouling paints and a nontoxic primer in coastal marinas in Queensland, Australia. Diversity and abundance of fouling taxa were compared between bryozoan colonies and adjacent toxic or nontoxic paint surfaces. After 16 weeks immersion, W. subtorquata covered up to 64% of the tile surfaces coated in antifouling paint. Twenty‐two taxa occurred exclusively on W. subtorquata and were not found on toxic surfaces. Other fouling taxa present on toxic surfaces were up to 248 times more abundant on W. subtorquata. Because biocides leach from the paint surface, we expected a positive relationship between the size of W. subtorquata colonies and the abundance and diversity of epibionts. To test this, we compared recruitment of fouling organisms to mimic W. subtorquata colonies of three different sizes that had the same total surface area. Secondary recruitment to mimic colonies was greater when the surrounding paint surface contained biocides. Contrary to our predictions, epibionts were most abundant on small mimic colonies with a large total perimeter. This pattern was observed in encrusting and erect bryozoans, tubiculous amphipods, and serpulid and sabellid polychaetes, but only in the presence of toxic paint. Our results show that W. subtorquata acts as a foundation species for fouling assemblages on ship hulls and facilitates the transport of other species at greater abundance and frequency than would otherwise be possible. Invasion success may be increased by positive interactions between NIS that enhance the delivery of propagules by human transport vectors.

Gravel pit lakes are increasingly common, and there is an urgent need to better understand the functioning of these artificial and disconnected ecosystems. However, our knowledge of the environmental determinants of fish community structure within these types of lakes remains poor. In this study, we quantified the taxonomic diversity, fish species and life-stage composition in 17 gravel pit lakes sampled in 2012 and 2013 located in south-west France to determine the potential role of environmental variables (i.e. lake morphology, productivity, water quality and human-use intensity) as drivers of fish community structure and composition. Our results demonstrated that fish community structure significantly differed between gravel pit lakes, and we notably found that lakes managed for angling hosted higher levels of taxonomic diversity. We also found that young and large lakes supported higher native species biomass and were dominated by native European perch (Perca fluviatilis). Older, smaller and more productive lakes, located closer to the main urban area, supported a higher biomass of non-native species such as largemouth bass (Micropterus salmoides). Native and non-native sport fishing species such as northern pike (Esox lucius), pikeperch (Sander lucioperca), common carp (Cyprinus carpio) and cyprinid prey species were positively associated with fishery management effort, suggesting that management practices play also a critical role in shaping fish species composition. Overall, our study demonstrated that fish community composition followed a predictable shift along environmental gradients associated with the maturation of gravel pit lakes and the associated human practices.

We assessed the representation of freshwater fish diversity provided by the National Park Service (NPS) and the potential for parks to serve as freshwater protected areas (FPAs) in the United States. Although most parks were not designed with freshwater conservation in mind, nearly two-thirds (62%) of native U.S. fishes reside in national parks. However, only 18% of the nation's highly imperiled fish species are represented within the NPS. The ability for parks to serve as protected areas depends on activities upstream from their boundaries and we found that a substantial part of these watersheds has some form of conservation status. Using a conservation planning approach that integrates fish diversity representation provided by parks and their current and future ecological threats (i.e., climate change, dams, watershed impervious surface, invasive species) and management challenges (i.e., land stewardship beyond park boundaries), we identify 50 parks that could serve as core members of a nationally comprehensive FPA system. While the NPS has limitations as the potential basis for an FPA network, it provides considerable representation of freshwater fish diversity that should be taken into account during systematic conservation planning for freshwaters.

Aim We examined the current biogeographical patterns of native fish communities throughout France, using a multifaceted taxonomic, functional and phylogenetic diversity approach. We then identified the contribution of individual species to each facet of watershed's native fish diversity.Location Continental France.Methods The taxonomic, functional and phylogenetic diversity of the fish communities were quantified at the watershed-scale (i.e. alpha diversity approach), and congruencies between diversity facets were assessed. Variation between watersheds was then quantified (i.e. beta diversity approach) using Jaccard's dissimilarity index for all three facets of diversity, and congruencies were assessed. We subsequently determined the relationship between alpha and beta diversity for each diversity facet. Lastly, the mean relative contribution of each species to watershed's alpha taxonomic, functional and phylogenetic diversity was quantified. The conservation status of each species was considered to determine if threatened and endangered species contributed more significantly to watershed alpha diversity than common species.Results Across all watersheds, taxonomic, functional and phylogenetic diversity facets were found to be highly congruent using both the alpha and beta diversity approaches. In contrast, the relationship between the watersheds' alpha and beta diversity was primarily negative; watersheds with decreased beta diversity tended to have increased alpha diversity for all three facets. Individual species also rarely contributed prominently to more than one diversity facet, with conservation status insignificantly influencing species relative contributions.Main conclusions We found that native fish diversity 'hotspots' exist in France; exhibited in our results by areas of high, overlapping taxonomic, functional and phylogenetic diversity. Consequently, conservation planning approaches supported by species-based metrics may concurrently target areas of increased ecological and evolutionary importance at the watershed-scale. Interestingly, a diverse mosaic of species accounted for the different facets of diversity, suggesting that future reductions in species richness could have differential effects on each watershed's diversity facets.

Abstract. Species' responses to seasonal environmental variation can influence trophic interactions and food web structure within an ecosystem. However, our ability to predict how species' interactions will vary spatially and temporally in response to seasonal variation unfortunately remains inadequate within most ecosystems. Fish assemblages in the Tonle Sap Lake (TSL) of Cambodia-a dynamic flood-pulse ecosystem -were studied for five years (2010-2014) using stable isotope and Bayesian statistical approaches to explore both within-and among-species isotopic niche variation associated with seasonal flooding. Roughly 600 individual fish specimens were collected during 19 sampling events within the lake. We found that fishes within the same species tended to have a broader isotopic niche during the wet season, likely reflecting assimilation of resources from either a wider range of isotopically distinct prey items or a variety of habitats, or both. Furthermore, among-species isotopic niches tended to overlap and range more broadly during the wet season, suggesting that floodplain inundation promotes exploitation of more diverse and similar resources by different species in the fish community. Our study highlights that the flood-pulse dynamic that is typical of tropical aquatic ecosystems may be an essential element supporting freshwater fish community structure and the fish diversity that underpins the TSL food web. This flow regime is currently threatened by regional dam development, which may in turn impact the natural function and structure of the fishery food web.

The effects of environmental seasonality on food web structure have been notoriously understudied in empirical ecology. Here, we focus on seasonal changes in one key attribute of a food web, consumer trophic position. We ask whether fishes inhabiting tropical river–floodplain ecosystems behave as seasonal omnivores, by shifting their trophic positions in relation to the annual flood pulse, or whether they feed at the same trophic position all year, as much empirical work implicitly assumes. Using dietary data from the Tonle Sap Lake, Cambodia, and a literature review, we find evidence that some fishes, especially small piscivores, increased consumption of invertebrates and/or plant material during the wet season, as predicted. However, nitrogen stable isotope (δ15N) data for 26 Tonle Sap fishes, spanning a broader range of functional groups, uncovered high variation in seasonal trophic position responses among species (0 to ±0.52 trophic positions). Based on these findings, species respond to the flood pulse differently. Diverse behavioral responses to seasonality, underpinned by spatiotemporal variation at multiple scales, could be central for rerouting matter and energy flow in these dynamic ecosystems. Seasonally flexible foraging behaviors warrant further study given their potential influence on food web dynamics in a range of fluctuating environments.