Global distribution,entry routes,mechanisms and consequences of invasive freshwater fish

Biological invasion is now considered one of the three major environmental issues worldwide. Freshwater fish invasion becomes more serious with globalization of the world economy. We reviewed the current status of global freshwater fish invasions and discussed the definitions, distributions, introduction pathways, mechanisms, ecological and economic impacts, and risk assessments of freshwater fish invasions. Non-native fish are mainly introduced through food aquaculture (51%), as ornamental fish (21%), or for sport fishing (12%) and fisheries (7%). The number of introduced fish has reached 624 species, doubled the number found thirty years ago. Successful invasions may bring many negative ecological consequences, such as predation, hybridization, structure and function alteration of local freshwater ecosystems, as well as diseases transmission. However, it also brings positive biological and economic values. The number of fish invasion studies has increased eight times over the last 20 years, with studies mainly focusing on biology and the biological impact of invasive fish species. Risk assessments of freshwater fish invasions were studied over the last 10 years, and fish invasiveness screening models have been applied in countries of five continents. The number of non-native freshwater fish in China totaled 439. However, research papers on freshwater fish invasions in China was only 3.7% of the global total, and these researches were mainly on the distribution and biology of invasive fish species, and very few studies included risk assessments. Therefore, we suggest investigating the history, distribution, and mechanisms of invasive species at the national level, evaluating both the positive and negative effects of freshwater fish invasions, and also reinforcing studies of risk assessments in China.     

淡水鱼类入侵种的分布、入侵途径、机制与后果

生物入侵已经成为全球面临的三大环境问题之一。鱼类入侵现象也随全球经济一体化的进程日益严重。本文综述了全球淡水鱼类入侵的现状和研究进展, 包括鱼类入侵的定义及分布、入侵途径和机制、产生的生态和社会经济影响以及预防措施等。据统计, 目前全球外来鱼类达624种, 该数量超过30年前的两倍。外来鱼类主要通过水产养殖(51%)、观赏渔业(21%)、休闲垂钓(12%)、渔业捕捞运输(7%)等多种途径被引进。入侵鱼类对本地种产生了捕食、种内种间竞争、杂交和疾病传播等负面影响, 破坏本地生态系统, 但是其正面的生态及社会经济影响也不可忽略。近20年来全球鱼类入侵日益受到重视, 相关论文发表数量翻了8倍。值得提出的是, 近10年来全球鱼类入侵风险评价系统的研究显著增加, 一些鱼类入侵模型已应用于五大洲的多个国家。我国淡水外来鱼类共计439种。然而, 我国关于鱼类入侵的研究起步较晚, 发表文献数仅占全球的3.7%, 且主要研究方向仍集中在入侵物种的分布及生物学特性等基础研究上, 缺乏对于鱼类入侵机制及风险评价预测的研究。因此, 我们建议: (1)开展全国范围的本底调查并建立数据库, 实现数据共享, 明确鱼类入侵的历史与分布现状; (2)联合多个政府部门和机构, 对鱼类入侵进行长期观测, 从整个水生生态系统的角度出发, 深入了解其入侵机制及其产生的正面和负面生态和社会经济影响; (3)加强增殖放流的科学研究和管理; (4)构建区域性外来鱼类入侵风险评价系统, 有效预测鱼类入侵活动, 评价入侵种的危害, 并为相关政府部门的决策提供科学依据。     

Diseases caused by parasites in the aquaculture of warm water fish

Parasitic infections of fish cultured in fresh and marine waters of subtropical and tropical geographic regions are reviewed. The following parasites are discussed: Ectoparasitic protozoa, Coccidia, Myxosporea, Monogenea, Metacercariae of trematodes, the Asian tapeworm, nematodes, ergasilids, lernaeids, and argulids. Criteria for selection were their impact on farmed fish and the availability of data beyond case reports and surveys. Epizootic ectoparasitic infections are usually the outcome of adverse growth conditions, either climatic or resulting from management practices. Epizootiology of infections by internal parasites, heteroxenous in particular, is more complex, particularly in man-made systems, as it is determined by a wider range of interacting ecological parameters. Exotic species, particularly cyprinids, comprise the bulk of freshwater fish farmed in warm water systems. Most important diseases affecting fishes in such systems are caused by introduced pathogens. Only a few of the autochthonous parasites become involved in epizootic infections, also where indigenous species are farmed. Marine farming is usually based on indigenous species. The relatively short history of piscine mariculture has already recorded epizootic infections and mortalities both by parasites contracted from the local environment and by specific parasites associated with the cultured species. As in freshwater systems, culture practices often create an environment favorable to epizootic infection.     

Effects of acidification on olfactory-mediated behaviour in freshwater and marine ecosystems: a synthesis

For many aquatic organisms, olfactory-mediated behaviour is essential to the maintenance of numerous fitness-enhancing activities, including foraging, reproduction and predator avoidance. Studies in both freshwater and marine ecosystems have demonstrated significant impacts of anthropogenic acidification on olfactory abilities of fish and macroinvertebrates, leading to impaired behavioural responses, with potentially far-reaching consequences to population dynamics and community structure. Whereas the ecological impacts of impaired olfactory-mediated behaviour may be similar between freshwater and marine ecosystems, the underlying mechanisms are quite distinct. In acidified freshwater, molecular change to chemical cues along with reduced olfaction sensitivity appear to be the primary causes of olfactory-mediated behavioural impairment. By contrast, experiments simulating future ocean acidification suggest that interference of high CO₂ with brain neurotransmitter function is the primary cause for olfactory-mediated behavioural impairment in fish. Different physico-chemical characteristics between marine and freshwater systems are probably responsible for these distinct mechanisms of impairment, which, under globally rising CO₂ levels, may lead to strikingly different consequences to olfaction. While fluctuations in pH may occur in both freshwater and marine ecosystems, marine habitat will remain alkaline despite future ocean acidification caused by globally rising CO₂ levels. In this synthesis, we argue that ecosystem-specific mechanisms affecting olfaction need to be considered for effective management and conservation practices.     

Parasites: Small Players with Crucial Roles in the Ecological Theater

Effective management of our natural resources requires an understanding of ecosystem structure and function; effectively, an ecosystem-based approach to management. Parasites occur, albeit cryptically, in almost all ecosystems, yet they are usually neglected in studies on populations and communties of organisms. Parasites can have pronounced or subtle effects on hosts affecting host behavior, growth, fecundity, and mortality. Furthermore, parasites may regulate host population dynamics and influence community structure. Many parasites have complex life cycles and depend for transmission on the presence of a variety of invertebrate and vertebrate intermediate hosts. Often transmission involves predator–prey interactions. Thus, parasites reflect the hosts position in the food web and are indicative of changes in ecosystem structure and function. Parasites can provide information on population structure, evolutionary hypotheses, environmental stressors, trophic interactions, biodiversity, and climatic conditions. I use examples from diverse freshwater and marine systems to demonstrate that parasites should be incorporated into research and monitoring programs to maximize information gathered in ecosystem-based studies and resource management.Supplementary Tables 3, 4, 5, 6 and additional references for this article are available for viewing by subscribers only at     

Climate effects on fish body size–trophic position relationship depend on ecosystem type

The energetic demand of consumers increases with body size and temperature. This implies that energetic constraints may limit the trophic position of larger consumers, which is expected to be lower in tropical than in temperate regions to compensate for energy limitation. Using a global dataset of 3635 marine and freshwater ray‐finned fish species, we addressed if and how climate affects the fish body size–trophic position relationship in both freshwater and marine ecosystems, while controlling for the effects of taxonomic affiliation. We observed significant fish body size–trophic position relationships for different ecosystems. However, only in freshwater systems larger tropical fish presented a significantly lower trophic position than their temperate counterparts. Climate did not affect the fish body size–trophic position relationship in marine systems. Our results suggest that larger tropical freshwater fish may compensate for higher energetic constraints feeding at lower trophic positions, compared to their temperate counterparts of similar body size. The lower latitudinal temperature range in marine ecosystems and/or their larger ecosystem size may attenuate and/or compensate for the energy limitation of larger marine fish. Based on our results, temperature may determine macroecological patterns of aquatic food webs, but its effect is contingent on ecosystem type. We suggest that freshwater ecosystems may be more sensitive to warming‐induced alterations in food web topology and food chain length than marine ecosystems.     

Towards clarifying the presence of alien algae in inland waters — can we predict places of their occurrence?

Small algae are the trophic basis in both marine and freshwater ecosystems. The identification of tiny microorganisms and place of their origin is laborious but necessary. This paper consists of a literature review of 17 species of planktonic algae, with a discussion of taxonomic problems. We also clarify whether these 17 species are non-native, invasive or cryptogenic species, with an indication whether they had been recognised as ‘alien’ in Europe. According to our observations, areas colonized by small and alien algal species, were anthropogenically altered. There were: systems with heated waters (‘heated islands’), which imitated tropical conditions; highly eutrophic to hypereutrophic water ecosystems, easily colonized by alien species, fishponds with intense fish cultivation, where alien species of fish are/had been introduced, which carried also other alien organisms; and inland water ecosystems with high salinity or high conductivity e.g. pits inundated by mine waters, imitating sea or brackish conditions acting as hubs of migration of alien species adapted to brackish or saline waters. We have prepared a map showing areas inhabited by alien species, both of documented places and hypothetical ones, where we would expect alien species to occur.     

The importance of ecological and behavioural data in studies of hybridisation among marine fishes

Natural hybridisation is a widespread phenomenon, particularly well documented in terrestrial and freshwater ecosystems, where it has been ascribed substantial evolutionary and adaptive relevance. Hybridisation has received comparatively less attention in marine systems, though there has been a recent surge of reported marine hybrids, particularly among corals and fishes. This review summarises the current knowledge of hybridisation in marine fishes, with a focus on ecological and behavioural factors that may play a role in hybridisation processes. Rarity of one or both parental species within the hybrid zone, overlap in habitat use, dietary overlap and the breakdown in assortative mating appear to have a role in facilitating hybridisation. Despite this, most of the recent literature on marine fish hybridisation has a strong genetic focus, with little or no quantitative information about the ecological and behavioural factors that initiate or facilitate hybridisation. Future studies should attempt to gather ecological and behavioural data from hybrid zones, thus teasing out which processes are most relevant to overcoming pre-zygotic barriers to reproductive isolation. Not only will this advance our understanding of the adaptive and evolutionary relevance of hybridisation in marine fishes, but it will also provide unique insights into the maintenance of reproductive isolation and the process of speciation in the marine environment.     

RAPID AND REPEATED INVASIONS OF FRESH WATER BY THE COPEPOD EURYTEMORA AFFINIS

Invasions of fresh water by marine organisms have been of great interest to evolutionary biologists and paleontologists because they typically constitute major evolutionary transitions. Recent (< 200 years) invasions of fresh water by brackish or marine species offer an opportunity to understand mechanisms underlying these events, but pathways of invasion from salt water have not been confirmed using genetic data. This study employed mitochondrial DNA sequences (652 base pairs from the cytochrome oxidase I (COI) gene) to reconstruct the geographic and evolutionary history of freshwater invasion by the common estuarine and saltmarsh crustacean Eurytemora affinis (Copepoda; Poppe 1880). Phylogenetic analysis of populations from North America, Europe, and Asia revealed at least eight independent invasions of fresh water from genetically distinct lineages. At least five of these freshwater invasions most likely arose independently in different river drainages, recently from saltwater sources within each river drainage. An analysis of molecular variance (AMOVA) was performed at three geographic scales (among continents, among drainages, and within drainages) to assess the hierarchical distribution of genetic variance. Results indicated that 52% of the genetic variance was explained by differences among drainages, 43% by differences among continents, but only 5% by differences within drainages, thus supporting geographic patterns of invasions inferred from the phylogeny. Physiological experiments were performed to determine whether adults and larvae from saltwater populations could tolerate freshwater conditions. Transfer to zero salinity resulted in high mortalities, but with some survival to the second generation in one population. This study provides genetic evidence and physiological support for rapid transitions from a saline life history into fresh water, with repeated invasions on a global scale.     

A review of the research on introduced freshwater fishes: new perspectives,the need for research,and management implications

Although freshwater fishes have a long history of human-induced introduction, recent globalization has accelerated worldwide introduction events even more, and those introduced fish species are now perceived to be a major threat to ecosystems. Over the last two decades, numerous studies have been published on introduced fish species; however, it has been challenging for researchers to understand the magnitude of the impact and the underlying mechanism of invasions. Recently, new perspectives in understanding invasive freshwater fish biology have been presented in a number of studies, which can be largely attributed to advances in analytical techniques and also to a growing need for proactive analysis in management strategies. The aim of this paper is to summarize new ecological perspectives, the need for research, and/or management implications with emphasis on technological advances in, for example, statistics, molecular analysis, modeling techniques, and landscape analysis addressed under the following five categories: introduction pathways, predicting spatial patterns, biotic homogenization, hybridization, and control and eradication. The conservation of native fish fauna and the management of introduced fish species will benefit from combining these new perspectives with fundamental studies such as those on life history and population biology.     

Introduction history of non-native freshwater fish in Okinawa-jima Island: ornamental aquarium fish pose the greatest risk for future invasions

We examined the introduction history of non-native freshwater fish in Okinawa-jima Island, Japan, to identify the pathway posing the greater risk for future invasions and to measure the strength of ornamental fish introductions as a vector of new invasions using all available records of freshwater fish introductions to date. At least 45 non-native freshwater fish have been introduced to Okinawa-jima Island. Of those, 22 species have successfully established in natural waters and, consequently, non-native fish species represent 76 % of the total freshwater fish fauna. The most important pathway was via the dumping of unwanted ornamental aquarium fish, which accounted for 71 % of the total introductions. The introduction of ornamental fish has occurred extensively in recent decades, and all fish introduced since the 1980s have been ornamental aquarium fish. The overall rate of establishment success was estimated at 51 %, although this is undoubtedly an overestimate because of unreported failed introductions. Establishment rates varied between stocked fish (100 %) and dumped ornamental fish (39 %), which may reflect the low propagule pressure of ornamental fish. From the observed trends in freshwater fish introductions, the dumping of ornamental fish into natural waters is expected to continue if no action is taken to reduce this most important pathway. We recommend regulations against the release of unwanted pet fish into natural waters, better programs for returning unwanted pet fish to stores or local zoos, educational programs for aquarists and retailers, and regulations against selling and trading ornamental fish that are judged to pose a high risk of causing economic or ecological harm.     

Do saline taxa evolve faster? Comparing relative rates of molecular evolution between freshwater and marine eukaryotes

The major branches of life diversified in the marine realm, and numerous taxa have since transitioned between marine and freshwaters. Previous studies have demonstrated higher rates of molecular evolution in crustaceans inhabiting continental saline habitats as compared with freshwaters, but it is unclear whether this trend is pervasive or whether it applies to the marine environment. We employ the phylogenetic comparative method to investigate relative molecular evolutionary rates between 148 pairs of marine or continental saline versus freshwater lineages representing disparate eukaryote groups, including bony fish, elasmobranchs, cetaceans, crustaceans, mollusks, annelids, algae, and other eukaryotes, using available protein‐coding and noncoding genes. Overall, we observed no consistent pattern in nucleotide substitution rates linked to habitat across all genes and taxa. However, we observed some trends of higher evolutionary rates within protein‐coding genes in freshwater taxa—the comparisons mainly involving bony fish—compared with their marine relatives. The results suggest no systematic differences in substitution rate between marine and freshwater organisms.     

Effects of adoption of freshwater residency on life-history ecology of terapontid grunters

1. While fish reproduction has played a critical role in development of life-history theory, the collective effects of a marine-to-freshwater invasion on a clade's reproductive ecology have rarely been explored in a phylogenetic context. We analysed and compared a range of quantitative and qualitative components of reproductive ecology in the Australasian terapontid fishes, a family distributed widely across marine, estuarine and freshwater habitats in the Indo-Pacific region. We specifically tested hypotheses that life-history strategies such as larger egg sizes and reduced fecundities are a key characteristic of freshwater species in comparison with their close marine relatives, and also fit a range of currently available evolutionary models describing the processes of ecomorphological and macrohabitat-related diversification.
2. Using recently developed phylogenetic comparative methods, differences in several quantitative reproductive traits were evident between marine and freshwater species, with reductions in average fecundity and increases in average egg size specifically characterising freshwater species. Evolutionary modelling of major trait axes, as well as specific traits across the family, highlighted significant increases in rates of evolutionary diversification across both freshwater lineages and within freshwater subclades. Modelling also supported the evolution of distinctive morpho-ecotype optima between marine and freshwater species over simpler models of random-walk evolution or single morphological optima.
3. Review of life-history behaviour identified environmental stimuli related to photoperiod, temperature, and lunar-tidal cycles (and possibly combinations thereof) as playing an important role in stimulating spawning behaviour in most marine–euryhaline species. While some of these variables (temperature and photoperiod) continue to play an important role in some freshwater species, flow regime, particularly streamflow increases, appear more important in stimulating spawning responses, underlining the role of flow regime emerging as a master variable shaping evolutionary trajectories in freshwater clades.
4. In this review and meta-analysis, we document that adaptation to an entirely freshwater existence has catalysed significant, and in several cases, relatively rapid adaptive evolution to very different life-history strategies within freshwater species. The invasion of freshwaters has had profound impacts on the trajectory of terapontid life-history evolution, driving significant changes in a range of traits relating to fecundity, egg size, spawning stimuli, and spawning substratum. Collective results suggest a distinct adaptive landscape difference between marine and freshwaters. Terapontids can provide a useful model for assessing the consistency of these outcomes with other freshwater-invading groups.

     

Meta-analysis Shows a Consistent and Strong Latitudinal Pattern in Fish Omnivory Across Ecosystems

Several studies have demonstrated a latitudinal gradient in the proportion of omnivorous fish species (that is, consumers of both vegetal and animal material) in marine ecosystems. To establish if this global macroecological pattern also exists in fresh and brackish waters, we compared the relative richness of omnivorous fish in freshwater, estuarine, and marine ecosystems at contrasting latitudes. Furthermore, we sought to determine the main environmental correlates of change in fish omnivory. We conducted a meta-analysis of published data focusing on change in the relative richness of omnivorous fishes in native fish communities along a broad global latitudinal gradient, ranging from 41°S to 81.5 N° including all continents except for Antarctica. Data from streams, rivers, lakes, reservoirs, estuaries, and open marine waters (ca. 90 papers covering 269 systems) were analyzed. Additionally, the relationship between the observed richness in omnivory and key factors influencing trophic structure were explored. For all ecosystems, we found a consistent increasing trend in the relative richness of omnivores with decreasing latitude. Furthermore, omnivore richness was higher in freshwaters than in marine ecosystems. Our results suggest that the observed latitudinal gradient in fish omnivory is a global ecological pattern occurring in both freshwater and marine ecosystems. We hypothesize that this macroecological pattern in fish trophic structure is, in part, explained by the higher total fish diversity at lower latitudes and by the effect of temperature on individual food intake rates; both factors ultimately increasing animal food limitation as the systems get warmer.     

Fossil‐based comparative analyses reveal ancient marine ancestry erased by extinction in ray‐finned fishes

The marine‐freshwater boundary is a major biodiversity gradient and few groups have colonised both systems successfully. Fishes have transitioned between habitats repeatedly, diversifying in rivers, lakes and oceans over evolutionary time. However, their history of habitat colonisation and diversification is unclear based on available fossil and phylogenetic data. We estimate ancestral habitats and diversification and transition rates using a large‐scale phylogeny of extant fish taxa and one containing a massive number of extinct species. Extant‐only phylogenetic analyses indicate freshwater ancestry, but inclusion of fossils reveal strong evidence of marine ancestry in lineages now restricted to freshwaters. Diversification and colonisation dynamics vary asymmetrically between habitats, as marine lineages colonise and flourish in rivers more frequently than the reverse. Our study highlights the importance of including fossils in comparative analyses, showing that freshwaters have played a role as refuges for ancient fish lineages, a signal erased by extinction in extant‐only phylogenies.     

Biotic resistance in marine environments

Biological invasions depend in part on the resistance of native communities. Meta‐analyses of terrestrial experiments demonstrate that native primary producers and herbivores generally resist invasions of primary producers, and that resistance through competition strengthens with native producer diversity. To test the generality of these findings, we conducted a meta‐analysis of marine experiments. We found that native marine producers generally failed to resist producer invasions through competition unless the native community was diverse, and this diversity effect was weaker in marine than in terrestrial systems. In contrast, native consumers equally resisted invasive producers in both ecosystems. Most marine experiments, however, tested invasive consumers and these invasions were resisted more strongly than were producer invasions. Given these differences between ecosystems and between marine trophic levels, we used a model‐selection approach to assess if factors other than the resistance mechanism (i.e. competition vs. consumption) are more important for predicting marine biotic resistance. These results suggest that understanding marine biotic resistance depends on latitude, habitat and invader taxon, in addition to distinguishing between competition with and consumption by native species. By examining biotic resistance within and across ecosystems, our work provides a more complete understanding of the factors that underlie biological invasions.     

Historical contingency and ecological determinism interact to prime speciation in sticklebacks, Gasterosteus

Historical contingency and determinism are often cast as opposing paradigms under which evolutionary diversification operates. It may be, however, that both factors act together to promote evolutionary divergence, although there are few examples of such interaction in nature. We tested phylogenetic predictions of an explicit historical model of divergence (double invasions of freshwater by marine ancestors) in sympatric species of three-spined sticklebacks (Gasterosteus aculeatus) where determinism has been implicated as an important factor driving evolutionary novelty. Microsatellite DNA variation at six loci revealed relatively low genetic variation in freshwater populations, supporting the hypothesis that they were derived by colonization of freshwater by more diverse marine ancestors. Phylogenetic and genetic distance analyses suggested that pairs of sympatric species have evolved multiple times, further implicating determinism as a factor in speciation. Our data also supported predictions based on the hypothesis that the evolution of sympatric species was contingent upon 'double invasions' of postglacial lakes by ancestral marine sticklebacks. Sympatric sticklebacks, therefore, provide an example of adaptive radiation by determinism contingent upon historical conditions promoting unique ecological interactions, and illustrate how contingency and determinism may interact to generate geographical variation in species diversity     

Ramesh Gulati: a personal approach,based on his retirement lecture

Historical and modern migrations and dispersal of most marine organisms (intertidal, benthic, meiofaunal, planktonic, nektonic, or neustonic) are classically interpreted in terms of their natural dispersal potential. Exceptions are introduced species, largely recognized since the 19th century, known to have been transported by human activities. However, humans were transporting species along coastlines and across oceans for millennia and centuries prior to the advent of the first biological surveys. Thus, the presumptive natural distributions of many species may be questioned. Reviewed here are some basic concepts about invasions of non-native species. Human activities move species isolated in time and space from other oceans or continents, and thus human-mediated transport does not simply speed up natural dispersal processes. Both past and modern-day invasions are often overlooked, leading to an underestimation of the scale of invasion diversity and impact. Because vectors, donor regions, and recipient regions change over time, invasions will continue along long-standing but un-managed corridors. The impact of most invasions has never been studied and, therefore, it is not possible to conclude that most invasions have no impact, nor is it generally possible to say that invasions have become `integrated' into a community or ecosystem in ecological time. Finally, invasions in the ocean are not limited to harbours and ports, but are found in a wide variety of marine habitats, ranging from the open ocean continental shelf to exposed rocky shores. The existence of human-mediated vectors has created extraordinary challenges to our understanding and interpretation of the ecology, biogeography, evolutionary biology, and conservation biology of marine communities.     

Relative Invasion Risk for Plankton across Marine and Freshwater Systems: Examining Efficacy of Proposed International Ballast Water Discharge Standards

Understanding the implications of different management strategies is necessary to identify best conservation trajectories for ecosystems exposed to anthropogenic stressors. For example, science-based risk assessments at large scales are needed to understand efficacy of different vector management approaches aimed at preventing biological invasions associated with commercial shipping. We conducted a landscape-scale analysis to examine the relative invasion risk of ballast water discharges among different shipping pathways (e.g., Transoceanic, Coastal or Domestic), ecosystems (e.g., freshwater, brackish and marine), and timescales (annual and per discharge event) under current and future management regimes. The arrival and survival potential of nonindigenous species (NIS) was estimated based on directional shipping networks and their associated propagule pressure, environmental similarity between donor-recipient ecosystems (based on salinity and temperature), and effects of current and future management strategies (i.e., ballast water exchange and treatment to meet proposed international biological discharge standards). Our findings show that current requirements for ballast water exchange effectively reduce invasion risk to freshwater ecosystems but are less protective of marine ecosystems because of greater environmental mismatch between source (oceanic) and recipient (freshwater) ecoregions. Future requirements for ballast water treatment are expected to reduce risk of zooplankton NIS introductions across ecosystem types but are expected to be less effective in reducing risk of phytoplankton NIS. This large-scale risk assessment across heterogeneous ecosystems represents a major step towards understanding the likelihood of invasion in relation to shipping networks, the relative efficacy of different invasion management regimes and seizing opportunities to reduce the ecological and economic implications of biological invasions.     

Landscape‐scale determinants of non‐native fish communities

Aim Predicting and preventing invasions depends on knowledge of the factors that make ecosystems susceptible to invasion. Current studies generally rely on non‐native species richness (NNSR) as the sole measure of ecosystem invasibility; however, species identity is a critical consideration, given that different ecosystems may have environmental characteristics suitable to different species. Our aim was to examine whether non‐native freshwater fish community composition was related to ecosystem characteristics at the landscape scale. Location United States. Methods We described spatial patterns in non‐native freshwater fish communities among watersheds in the Mid‐Atlantic region of the United States based on records of establishment in the U.S. Geological Survey’s Nonindigenous Aquatic Species Database. We described general relationships between non‐native species and ecosystem characteristics using canonical correspondence analysis. We clustered watersheds by non‐native fish community and described differences among clusters using indicator species analysis. We then assessed whether non‐native communities could be predicted from ecosystem characteristics using random forest analysis and predicted non‐native communities for uninvaded watersheds. We estimated which ecosystem characteristics were most important for predicting non‐native communities using conditional inference trees. Results We identified four non‐native fish communities, each with distinct indicator species. Non‐native communities were predicted based on ecosystem characteristics with an accuracy of 80.6%, with temperature as the most important variable. Relatively uninvaded watersheds were predicted to be invasible by the most diverse non‐native community. Main conclusions Non‐native species identity is an important consideration when assessing ecosystem invasibility. NNSR alone is an insufficient measure of invasibility because ecosystems with equal NNSR may not be equally invasible by the same species. Our findings can help improve predictions of future invasions and focus management and policy decisions on particular species in highly invasible ecosystems.