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Geo-politics and freshwater fish introductions: How the Cold War shaped Europe's fish allodiversity
Abstract
Activities that manipulate ecosystems to support economic activities provide major introduction pathways for non-native species. As such, substantial differences in the socioeconomic conditions between countries could influence how ecosystems are manipulated and thus impact the composition of their communities of non-native species. Here, we compared the influence of freshwater fish aquaculture production and macro-socioeconomic drivers on the freshwater fish allodiversity of Europe between 1970 and 2009. A divergence in the socio-economic conditions of Europe prevailed during much of the latter half of the 20th Century as a result of the Cold War. For example, GDP and GDP per capita were significantly higher in Western bloc countries compared to the Eastern bloc. In this 39 year period, aquaculture production in Eastern bloc countries was dominated by Asian cyprinid fish whereas in Western bloc countries it was dominated by the North American rainbow trout Oncorhynchus mykiss. Analysis of a European database on introduced fish into the wild from aquaculture revealed that in entirety, there were 279 separate freshwater fish introductions in Europe associated with aquaculture (Eastern bloc 118, Western bloc 161), involving 117 species from 32 families. There was relatively low homogeneity in these introduced fishes between the two blocs; only 28 species were introduced into both. Western bloc countries also had significantly more introduced fishes and more introduction events, and less similarity in the introduced fishes between their countries. Aquaculture production was a significant predictor of the number of non-native freshwater fish across all the countries, although additional factors, especially human population size and GDP per capita, were also significant predictors. Thus, aquaculture has been a strong introduction pressure in Europe and provides a reliable predictor of fish allodiversity.
... The Iranian population was particular, forming a distinct deme completely isolated from all European populations, consistent with observations of Hardouin et al. (2018), who revealed that Iran has a different mtDNA lineage. Differentiation between Eastern and Western Europe may be imputed to the former USSR era when on one side, the eastern introduction first opens and on the other commercial exchanges with Western Europe were limited (Britton and Gozlan 2013). The Danube river ensures structural connectivity which has favored colonization among a large central European region (Weiss et al. 2002), from Germany to Bulgaria through Austria and Hungary. ...
... 18 to 62 generations), and the time of Asian fish export increases. Likewise, development of aquaculture in this part of Europe may have subsequently facilitated the spread of P. parva in Turkey as early as 1982 (Ekmekçi and Kırankaya 2006;Britton and Gozlan 2013). ...
... The invasion time was approximately the same as for Eastern Europe, coincident with a trading cooperation period between countries of the Eastern Bloc and T. Brazier et al. China (Britton and Gozlan 2013). On average, genetic divergence amongst source demes was relatively high (mean F ST = 0.27; Fig. 3, Table S5), suggesting limited gene flow and a lower likelihood of native admixture, compared to that for Eastern Europe source demes (mean F ST = 0.13; Fig. 3, Table S5). ...
Insufficient data on the origins of the first introduced propagule and the initial stages of invasion complicate the reconstruction of a species’ invasion history. Phylogeography of the native area profoundly shapes the genomic patterns of the propagules on which subsequent demographic processes of the invasion are based. Thus, a better understanding of this aspect helps to disentangle native and invasive histories. Here, we used genomic data together with clustering methods, explicit admixture tests combined with ABC models and Machine Learning algorithms, to compare patterns of genetic structure and gene flow of native and introduced populations, and infer the most likely invasion pathways of the highly invasive freshwater fish Pseudorasbora parva. This species is the vector of a novel lethal fungal-like pathogen (Sphaerothecum destruens) that is responsible for the decline of several fish species in Europe. We found that the current genetic structuring in the native range of P. parva has been shaped by waves of gene flow from populations in southern and northern China. Furthermore, our results strongly suggest that the genetic diversity of invasive populations results from recurrent global invasion pathways of admixed native populations. Our study also illustrates how the combination of admixture tests, ABC and Machine Learning can be used to detect high-resolution demographic signatures and reconstruct an integrative biological invasion history.
... The Iranian population was particular, forming a consistent deme completely isolated from all European populations, consistent with observations of Hardouin et al. (2018), who revealed that Iran was a different mtDNA lineage. Differentiation between Eastern and Western Europe may be imputed to the former USSR era when on one side, the eastern introduction first opens and on the other commercial exchanges with western Europe were limited (see Britton & Gozlan, 2013). The Danube river ensures structural connectivity which has favoured colonization among a large central European region (Weiss et al., 2002), from Germany to Bulgaria through Austria and Hungary. ...
... 18 to 62 generations) and the time of Asian fish exports increase. Likewise, development of aquaculture in this part of Europe may have subsequently facilitated the spread of P. parva in Turkey as soon as 1982 (Ekmekçi & Kırankaya, 2006;Britton & Gozlan, 2013). ...
... Western Europe populations also include an admixed north Chinese origin to both the North East China and North China demes. The invasion time was approximately the same as for Eastern Europe, coincident with a trading cooperation period between countries of the Eastern Bloc and China (Britton & Gozlan, 2013). On average, genetic divergence amongst source demes was relatively high (mean F ST = 0.27; Table S5), suggesting limited gene flow and a lower likelihood of native admixture, compared to that for Eastern Europe source demes (mean F ST = 0.13; Table S5). ...
Invasive species are significant contributors to global changes and constitute a severe threat to biodiversity. Yet invasions offer an incredible framework to understand how small and low-diverse introduced populations adapt to novel environmental conditions and succeed in colonizing large areas. However, due to the insufficient data on the origin of the first introduced propagule and the first stage of invasion, reconstructing a species’ invasion history is challenging. Here, we applied genetic clustering methods and explicit admixture tests combined with ABC models and Machine Learning algorithms to describe the phylogeography of native and invasive populations and infer the most probable demographic invasion scenarios of Pseudorasbora parva, a highly invasive freshwater fish and the healthy carrier of a novel lethal fungi-like pathogen (Sphaerothecum destruens), which is responsible for the decline of several fish species in Europe. We found that the current genetic structuring of the native P. parva range has been shaped by waves of gene flow originating from southern and northern Chinese populations. Furthermore, our results strongly suggest that the invasive genetic diversity is the outcome of past recurrent global invasion pathways of admixed native populations. Our study also illustrates how the combination of admixture tests, ABC, Machine Learning can be used to detect high-resolution demographic signatures and reconstruct an integrative biological invasion history.
... We reviewed several lists of species that were introduced into Europe, which we obtained from scientific papers, books and technical reports (Vooren 1972;Welcomme 1988;Holčík 1991;Kottelat and Freyhof 2007;Savini et al. 2010;Tricarico 2012;Britton and Gozlan 2013;Nunes et al. 2015) or official databases, such as the Global Invasive Species Database (''GISD'' http://www.iucngisd.org/gisd/), Delivering Alien Invasive Species Inventories for Europe (''DAISIE'' http://www.europe-aliens.org/), ...
... Finally, countries with a higher GDP per capita, % of anglers and lower latitude were associated with an increase in the proportion of IANS relative to the total number of introduced species. Arlinghaus et al. (2015) or Britton and Gozlan (2013) found that GDP per capita was one of the most important predictors of recreational fishing rates. ...
In a context of the growing concern about the impact of biological invasions, our objective is to review the role of those non-native species that have primarily been introduced for angling purposes in at least one European country. We are particularly interested in: (1) the relative role of sport fish species in the context of non-native species introductions; (2) assessing the relative importance of different fish taxa; (3) identifying similarity patterns in the composition of the angling fish species introduced throughout the continent, and (4) assessing the underlying factors that drive their diversity in Europe. According to our results, 23.6% of the freshwater fish introduced into Europe during the last century were released primarily for angling purposes. The species composition differed among countries, with a higher diversity of introduced angling species in larger countries and in those with a greater GDP per capita, along with a lower latitude. This review stresses that angling was a significant pathway for the introduction of invasive fish species into Europe in the last century. Furthermore, some of the introduced angling species had severe environmental impacts on many European regions. However, introductions of non-native angling species are still occurring. Therefore, existing EU regulations need better enforcement as well as to increase public awareness regarding invasive fish. This will help to preserve biodiversity and improve the sustainability of current angling schemes in increasingly managed European freshwater ecosystems. However, non-native fish could make angling sustainable, although not for biodiversity generally
... Although a large propagule size facilitates establishment, it is not always necessary. For example, the life history traits of the topmouth gudgeon (Pseudorasbora parva) mean that its population can grow rapidly in uncompetitive environments (e.g., fishless environments), thus allowing the species to establish with only a few introduced individuals (Britton & Gozlan 2013). Indeed, the influence of propagule pressure on invasion success is highly dependent on the life cycle and life history traits of the introduced species, as well as on the suitability of the receiving habitat (Gertzen et al. 2008). ...
Freshwater fish have been widely introduced worldwide, and freshwater ecosystems are among those most affected by biological invasions. Consequently, freshwater fish invasions are one of the most documented invasions among animal taxa, with much information available about invasive species, their characteristics, invaded regions, invasion pathways, impacts, and management. While existing reviews address specific aspects of freshwater fish invasions, there is still a gaping lack of comprehensive assessments of freshwater fish invasions that simultaneously address pivotal and connected elements of the invasion process. Here, we provide a holistic review, together with quantitative assessments, divided into four major parts: ( a) introduction pathways, ( b) characteristics of nonnative species and invaded ecosystems that explain successful invasion processes, ( c) invasion impacts and their mechanisms, and ( d) management. We highlight data gaps and biases in the current databases and highlight a basic lack of understanding of several aspects of freshwater fish invasions. In addition, we provide recommendations for future studies.
Expected final online publication date for the Annual Review of Ecology, Evolution, and Systematics, Volume 53 is November 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
... The species has become the dominant benthic fish in many areas of the Great Lakes and is of great concern owing to intense predation of native fish species' eggs ( Jude 1997). Development of canals and waterways and the increase in commercial shipping and recreational boat traffic across both Europe and North America have provided new dispersal pathways and opportunities, greatly contributing to the species' rapid spread ( Britton and Gozlan 2013;Roche et al. 2013;Hirsch et al. 2016b). Previous research has demonstrated that Great Lakes populations of Round Goby are characterized by significant population structure ( Brown and Stepien 2009) and that this population structure has remained relatively consistent over time ( Snyder and Stepien 2017). ...
The globally invasive Round Goby (Neogobius melanostomus) was introduced to the Great Lakes around 1990, spreading widely and becoming the dominant benthic fish in many areas. The speed and scope of this invasion is remarkable and calls into question conventional secondary spread models and scenarios. We utilized nine microsatellites to identify large-scale genetic structure in Round Goby populations in the eastern Great Lakes, and assessed the role of colonization vs. secondary transport and dispersal in developing this structure. We identified three clusters, corresponding with Lake Huron, eastern Lake Erie, and western Lake Erie plus eastern Lake Ontario, along with three highly divergent populations. Bottleneck analysis identified founder effects in two divergent populations. Regression analyses of isolation by distance and allelic richness vs. distance from the initial invasion site were consistent with limited migration. However, some populations in eastern Lake Erie and Lake Ontario showed anomalously low genetic distance from the original site of colonization, consistent with secondary transport of large numbers of individuals via ballast water. We conclude that genetic structure of Round Goby in the Great Lakes principally resulted from long-distance secondary transport via ballast water with additional movement of individual via bait buckets and natural dispersal. The success of Round Gobies represents an interesting model for colonization characterization; however, those same attributes present significant challenges for conservation and fisheries management. Current management likely prevents many new species from arriving in the Great Lakes, but fails to address the transport of species within the lakes after they arrive; this is an issue of clear and pressing importance.
... Indeed, this is typical of the non-native fish fauna of Neotropical reservoirs more generally (Ortega et al. 2015;Latini et al. 2016). However, non-native fishes were also present in the Paranapanema River from four other continents, revealing how globalization of activities such as the ornamental fish trade and aquaculture has resulted in some fishes, such as Cyprinus carpio Linnaeus, 1758 and O. niloticus, achieving a global distribution (Gozlan et al. 2010;Britton and Gozlan 2013). Moreover, given the propensity of fish farmers to diversify their cultured fishes using fish from different countries and continents (Gozlan 2008), it is probable that more non-South American fish will be introduced into the Paranapanema basin via this vector in future. ...
Understanding the pathways and impacts of non-native species is important for helping prevent new introductions and invasions. This is frequently challenging in regions where human activities continue to promote new introductions, such as in Brazil, where aquaculture and sport fishing are mainly dependent on non-native fishes. Here, the non-native fish diversity of the Paranapanema River basin of the Upper Paraná River ecoregion, Brazil, was quantified fully for the first time. This river has been subject to considerable alteration through hydroelectric dam construction and concomitant development of aquaculture and sport fishing. Through compilation of a non-native fish inventory by literature review, with complementary records from recent field studies, analyses were completed on the timings of introduction, and the taxonomy, origin and introduction vectors of the non-native fishes. A total of 47 non-native fishes are now present across the basin. Of these, 24 invaded from the Lower Paraná River following construction of Itaipu Dam that connected previously unconnected fish assemblages. Activities including fish stocking, aquaculture and sport angling continue to result in new introductions. Discounting Itaipu invasions, the introduction rate between 1950 and 2014 was approximately one new introduction every 3 years. Introduced fish were mainly of the Cichlidae and Characidae families; most species were from other South American ecoregions, but fishes of African, Asian, North American and Central American origin were also present. These introductions have substantially modified the river’s fish fauna; when coupled with altered lentic conditions caused by impoundment, this suggests that the river’s native fishes are increasingly threatened.
... The loss of biodiversity throughout freshwater ecosystems is linked to various factors including siltation, eutrophication, pollution, presence of hydroeletric plants and dams, flood control, over-exploitation of resources, and exotic species (Reis 2013, Britton and Gozlan 2013, Orsi and Britton 2014, Valiente-Banuet et al. 2015. Among these threats, the impacts of invasive species are particularly alarming, especially in degraded environments, such as near hydroelectric plants, that benefit the establishment of populations of invasive species , Pelicice et al. 2014, Kalous et al. 2015, Thomaz et al. 2015, Daga et al. 2015, Pagad et al. 2015. ...
Aquatic biodiversity loss can be attributed in part by the presence of invasive species that increase the risk of extinction of native species through competition, predation, transmission of parasites and disease, hybridization and introgression. This study reports the first record of Heterotilapia buttikoferi in the upper Paraná River basin, Brazil. Additionally, the effects of establishment of this invasive species and the lack of an effective political and environmental management in Brazil that hinder exotic species’ eradication are herein discussed
... In the past, most of the species were imported from North America, but there is a progressive increase of species from Eastern Europe and Asia. A similar pattern was already reported for Germany and Austria (Rabitsch et al. 2013), being probably common in Europe with Asian species often used in aquaculture and Eastern European species most introduced after the fall of the Berlin Wall (Britton & Gozlan 2013). The effect of this reshuffling is the loss of the typical Italian fish communities with their evolutionary and biogeographic uniqueness. ...
Inland waters are highly vulnerable to the introduction and spread of non-native species, due to heavy human use of aquatic ecosystems and the natural linkages among streams and lakes. This is particularly noticeable in freshwater fish communities. To better evaluate how these communities are affected by non-native species introductions, we conducted a fine scale analysis of the changes in Italian freshwater fish assemblages after species introduction. For this analysis, we collected information on fish species present in 44 basins. The present Italian freshwater fish fauna is composed of 48 native and 41 established introduced species, while a further 15 introduced species were reported but not yet considered naturalized. The changes of the fish assemblages mostly took place in the last two centuries and have increased recently, with nearly 60% of the species introduced in the last three decades. The number of species introduced per basin ranged from 0 to 35 (mean 10.85 ± 7.77 species/basin), and in ten basins the number of species introduced is now equal to the number of native species or even higher. In the past, introduced species mainly originated from America, but in last decades, an increase of introductions from other parts of Europe and Asia was recorded. Our results show that basins already rich in native species tend to get even richer as a consequence of the establishment of introduced species. This confirms the trend toward a biotic homogenization of ecosystems even at a local scale, due to an increase in the human-mediated spread of generalist species. This article is protected by copyright. All rights reserved.
... And a similar argument could be made for China, where C. carpio represents an important resource for local fisheries, even though in some areas of the species' native distribution interest has also been revolving around its conservation status ( Xu et al., 2012;Uchii et al., 2016). Finally, the relatively large number of studies from the Czech Republic (21 waterbodies) is a result of the rele- vance of this native and iconic species (now severely threatened or locally extinct in its wild form: Ko??o & Hol??k, 2008;Ko??o et al., 2010) for local fisheries and angling (Balon, 1995), especially as a traditional dish on Christmas Eve (Britton & Gozlan, 2013). ...
This review provides a meta-analytical assessment of the global patterns and clines in the growth of Cyprinus carpio as measured by length-at-age (Lt) or von Bertalanffy growth function (VBGF) parameters, mass-length relationship (W-Lt) and condition factor, based on literature data. In total, 284 studies were retrieved spanning 91years of research and carried out on 381 waterbodies-locations in 50 countries in all five continents. Although native C. carpio achieved larger (asymptotic) size relative to its non-native counterpart, the latter grew faster during the first 7years of life. Lentic populations (especially in natural lakes) also achieved larger sizes relative to lotic ones and the same was true for populations in cold and temperate v. arid climates. Unlike previous studies (on much more restricted datasets), only weak latitudinal clines in instantaneous growth rate, Lt at age 3 and mortality were observed globally and this was probably due to the presence of counter-gradient growth variation at all representative age classes (i.e. 1-10years). Slightly negative allometry was revealed by the W-Lt and the related form factor tended to distinguish the more elongated and torpedo-shaped body typical of the wild form from the deeper body of feral-domesticated C. carpio. Existing population dynamics models for C. carpio will benefit from the comprehensive range of waterbody type×climate class-specific VBGF parameters provided in the present study; whereas, more studies are needed on the species' growth in tropical regions and to unravel the possibility of confounding effects on age estimation due to both historical and methodological reasons.
... Intercontinental fish exchanges should decrease owing to the development of national and international laws regulating the transport and introduction of exotic species (Costello et al. 2005;Hulme et al. 2009). But under the current accelerated rates of nonnative species spread within realms (Britton and Gozlan 2013), exotic species are expected to establish over larger areas in the near future, and then turn their differentiation effect toward homogenization. Thus, this would favour a global homogenization, as forecasted by Villéger et al. (2015) using mathematical simulations. ...
Introduction of non-native species have changed the composition of freshwater fish assemblages throughout the world and hence the dissimilarity between them, either toward homogenization (i.e. decrease in dissimilarity) or differentiation (i.e. increase in dissimilarity). However, there is still no assessment of individual contributions of non-native species to this overall trend at the global scale. Here, we disentangle individual non-native species effect from the global effect of the whole introduced species pool at the biogeographic realm scale and test which determinant can explain the effect of non-native species on changes in assemblage dissimilarity. Our results show that the contribution of introduced species on changes in dissimilarity is highly variable and all directions of changes are observed through the introduction process, i.e. either toward homogenization, differentiation or no change. Overall, only a few widespread species contribute to the worldwide homogenization pattern, whereas most of introduced species slightly contribute to the global change in dissimilarity. The effect of species on change in dissimilarity was influenced by the introduction pressure but also by whether introduced species were translocated (i.e. introduced to other basins within their biogeographic realm) or exotic (i.e. introduced from other biogeographic realms). Homogenization is strongly determined by the species translocated within a realm and only by few widespread exotic species whereas the majority of exotics contribute to a differentiation effect. Nevertheless, under future intensified human pressure, the exotic species spread across realms is predicted to increase and their differentiation effect might turn towards homogenization, and might trigger the global homogenization trend.
... Since then, it has been spreading rapidly (Kornis et al. 2012). The building of waterways and the increased commercial and recreational shipping across Europe and North America is believed to have accelerated the spread of round goby by providing pathways and vectors for active and passive dispersal (Britton and Gozlan 2013;Roche et al. 2013). ...
Invasive species are one of the greatest threats to biodiversity worldwide, and to successfully manage their introductions is a major challenge for society. Knowledge on the impacts of an invasive species is essential for motivating decision makers and optimally allocating management resources. We use a prominent invasive fish species, the round goby (Neogobius melanostomus) to objectively quantify the state of scientific knowledge on its impacts. Focusing on how native fish species are affected by round goby invasions, we analyzed 113 peer-reviewed papers and found that impacts are highly ecosystem and time scale dependent. We discovered round goby impacts to be profound, but surprisingly complex. Even if identical native species were affected, the impacts remained less comparable across ecosystems than expected. Acknowledging the breadth but also limitations in scientific knowledge on round goby impacts would greatly improve scientists' ability to conduct further research and inform management measures.
... introductions of aquatic species in Europe (DAISIE 2009), these activities should be controlled in order to prevent further introductions (Britton and Gozlan 2013). Once established, the eradication of invasive species-and especially those in aquatic ecosystems-is strategically difficult, rarely feasible, expensive and ultimately unlikely to be of considerable ecological benefit (Britton et al. 2011;Mack and Lonsdale 2002). ...
Horizon scanning for high-risk invasive
non-native species (INNS) is crucial in preparing and
implementing measures to prevent introductions, as
well as to focus efforts in the control of species already
present. We initiated a trans-national horizon-scanning
exercise focused on four countries in western
Europe: Great Britain, France, Belgium and The
Netherlands, which share similar environmental and
socio-economic characteristics. We followed a structured
four-step approach combining existingknowledge about INNS, with a collaborative identifi-
cation of priorities for research and management: (1)
systematic review of potential INNS of concern, (2)
discrimination of INNS into an Alert and Black List
depending on their absence or presence in the study
area respectively, (3) risk analysis of the Alert List,
and (4) expert ranking of species in the Black List.
Amongst species not yet present in the four countries
(i.e. Alert List), assessors reliably pointed to the
Emerald ash-borer (Agrilus planipennis) and Sosnowski’s
hogweed (Heracleum sosnowskyi) as those
INNS with the highest risk of invasion and impact. The
Japanese knotweed (Fallopia japonica), Himalayan
balsam (Impatiens glandulifera), zebra mussel(Dreissena polymorpha) and killer shrimp
(Dikerogammarus villosus) were consistently highlighted
as some of the most problematic INNS already
present in the study area (i.e. Black List). The
advantages of our combined approach include that it
is inclusive of all-taxa, prioritizes both established and
emerging biological threats across trans-national
scales, and considers not only the ecological impact,
but also potential direct economic consequences as
well as the manageability of invasive species.
... As a result, the consequences of documented/potential carp impacts will become of relevance not only to the high-risk countries (for which additional scientific support was provided by the current findings) but also to a range of countries in which mounting concerns have been manifested about the risks associated with potential further carp spread. Clearly, the present evaluation will ultimately have to be gauged at the "higher decision-making echelons" so as to ensure proper balance between ecological requirements for habitat conservation and pressing economic demands (Copp et al., 2005;Gozlan, 2008;Britton and Gozlan, 2013). ...
As the most widely distributed freshwater fish worldwide, common carp Cyprinus carpio can be either invasive or ‘naturalised’ in most areas of introduction. This leads to different levels of perception regarding its role in freshwater ecosystems, with experimental research focusing either on its ‘middle-out’ impacts or overall function in limnological processes. At the same time, the large scales at which carp dynamics operate may severely limit the validity of laboratory and, oftentimes, field experiments in extrapolating results to real-world ecosystems. In this study, 129 laboratory, field and ‘natural’ experiments were systematically reviewed through causal criteria analysis, and within an historical/biogeographical and risk assessment context. Of the 19 countries where experiments were conducted, only four were considered as ‘low risk’ and one as ‘no risk’, the other being ‘medium’ to ‘high risk’. Experimental findings from 373 component-wise assessments supported the framework of effects on water quality, vegetation, invertebrates and vertebrates, with the latter including also amphibians and waterfowl, previously unreported. Stronger evidence was provided by natural and field relative to laboratory experiments, reflecting the reductionism of the latter. Critical biomass for an impact was highly dependent on experimental set-up, even though the overall threshold of ≈200 kg ha−1 under natural conditions supported recent findings. Management of carp should reflect the level of current and potential risk posed by the species in its different areas of distribution, thereby accounting for projections of further spread but also for unsuccessful colonisation. Future experimentation should favour a holistic→reductionist over a reductionist→holistic approach.
The genetic variability and population structure of introduced species in their native range are potentially important determinants of their invasion success, yet data on native populations are often poorly represented in relevant studies. Consequently, to determine the contribution of genetic structuring in the native range of topmouth gudgeon Pseudorasbora parva to their high invasion success in Europe, we used a dataset comprising of 19 native and 11 non-native populations. A total of 666 samples were analysed at 9 polymorphic microsatellite loci and sequenced for 597 bp of mitochondrial DNA. The analysis revealed three distinct lineages in the native range, of which two haplogroups were prevalent in China (100%), with a general split around the Qinling Mountains. Dating of both haplogroups closely matched past geological events. More recently, its distribution has been influenced by fish movements in aquaculture, resulting in gene flow between previously separated populations in Northern and Southern China. Their phylogeography in Europe indicate as few as two introductions events and two dispersal routes. Microsatellite data revealed native populations had higher genetic diversity than those in the invasive range, a contrast to previous studies on P. parva. This study confirms the importance of extensive sampling in both the native and non-native range of invasive species in evaluating the influence of genetic variability on invasion success.
Fisheries and aquaculture in developing countries are primarily a way of producing and providing daily food for millions of the world's poorest people and thus contribute significantly to the fabric of local economies. In other countries, fisheries are essentially used for sport fishing activities. However, these types of both food and sport activities rely heavily on the use and thus the introduction of non-native species. This is true for both marine and freshwater species but it is far more prevalent in the freshwater fish farming trade than across all other taxa. Asia has used the potential of available species cultured abroad more than any other region in the world, but as most of the cultured species are Asian, this still represents a small proportion of their fisheries and aquaculture economic activity. However, the proportion of species farmed that are non-native is the greatest in North/South America, Europe and Oceania (mean= 36, 35, 43, 34% respectively). In terms of production alone, Europe and the former USSR represent the largest production of non-native species (i.e. 62% of world non-native production, all taxa included). It is extremely difficult to objectively evaluate the cost of non-native species on ecosystem services and the cost of non-native fish species as part of the production of fish for food, which represents about 95.3 percent of the global non-native aquatic species production across the world (>81 M tonnes/year), barely reaches €0.04M/year. With a growing human population, new challenges are on the horizon, notably the increase and diversification of production using novel technologies (e.g. GMOs) whilst limiting negative side effects and additional costs.
Temporary streams naturally experience flow intermittence and hydrologic discontinuity that act to shape fish community structure. Yet, alteration of the flow regime of temporary rivers may lessen the resilience of fish communities to tolerate hydrologic change imposed by droughts. This long-term study (2001-2013) predicted spatial structuring (across catchments and amongst reaches) in fish community composition and abundance across a hydrologically-altered Mediterranean-type region dominated by temporary streams. Shifts from freshwater specialist and diadromous species to more generalist and tolerant species (i.e. freshwater generalist, aliens and estuarine species) were anticipated as the region experienced low flows (2001–2006) and critical water shortage (2007–2010) associated with a most severe drought. It was anticipated that the composition and abundance would be revealed during flood (2011) and post-flood (2012–2013) periods after the drought. Contrary to these predictions, fish community structure was broadly consistent across catchments, despite varying climatic and hydrologic (mainly, flow intermittence) regimes. As expected, significant spatial variability was revealed at the reach scale, with significant differences between upper reaches and terminal wetlands, and with a clear transition in fish community structure between these reach types. Significant temporal variability was also revealed with the reduced abundance of diadromous species (although congolli Pseudaphritis urvillii did increase) and increases in the abundance of aliens and surprisingly freshwater specialists over the period of critical water shortage relative to antecedent low flows. This was followed by mixed reach-dependent responses of fish during the flood and post-flood periods. The differential responses of fish communities across reaches and temporal periods must be considered as part of the management of threatened species in hydrologically-altered regions dominated by temporary streams.
Aquatic invasive species are a growing concern to environmental managers because of their diverse impacts on aquatic biodiversity and high eradication costs, necessitating effective management policies. In this study, we evaluate the ability of environmental and socio‐economic factors to predict the risk of invasion in Great Britain and Ireland of 12 potential aquatic invaders covering all major aquatic groups. Despite their potential to inform risk assessments, this is the first time socio‐economic factors related to propagule pressure have been specifically integrated in distribution modelling.Species distribution models (SDM, MaxEnt algorithm) were calibrated with a set of environmental factors (e.g. bioclimatic, geographical and geological) and integrated with socio‐economic (e.g. human influence index, population density, closeness to ports) predictors.The inclusion of socio‐economic factors in SDM did not affect accuracy scores (AUC already >0·90), but their effects were more pronounced in spatial predictions, resulting in up to a sixfold amplification of the area predicted suitable for each species. Despite the inclusion of potential surrogates of water chemistry (e.g. geology) and propagule pressure (e.g. population density), temperature‐related variables were most important predictors of aquatic species' distributions.According to SDM, the environmental suitability for a suite of invaders belonging to different taxonomic groups and regions of origin is greatest in east and south‐east England and decreases towards the north and west. Multiple invasions in this region are of special concern, as species are known to modify their habitat facilitating subsequent invasions, thereby potentially exacerbating their impacts.Major management regions to be prioritized in monitoring programmes include the Humber, Thames and Anglian River Basin Districts. Species of special concern include a mysid (Hemimysis anomala), a gammarid (Dikerogammarus villosus), a plant (Ludwigia grandiflora) and two crayfishes (Procambarus clarkii and P. fallax).Synthesis and Applications. The inclusion of socio‐economic factors in species distribution models has the potential to improve predictions of areas under a highest risk of multiple invasions and to help disentangle the complex interplay between biological invasions and global environmental and socio‐economic processes. Such understanding is pivotal to prioritize limited resources for the optimum prevention and control of biological invasions.
Biological invasions are a widespread and significant component of human-caused global environmental change. The extent of invasions of oceanic islands, and their consequences for native biological diversity, have long been recognized. However, invasions of continental regions also are substantial. For example, more than 2,000 species of alien plants are established in the continental United States. These invasions represent a human-caused breakdown of the regional distinctiveness of Earth's flora and fauna - a substantial global change in and of itself. Moreover, there are well-documented examples of invading species that degrade human health and wealth, alter the structure and functioning of otherwise undisturbed ecosystems, and/or threaten native biological diversity. Invasions also interact synergistically with other components of global change, notably land use change. People and institutions working to understand, prevent, and control invasions are carrying out some of the most important - and potentially most effective - work on global environmental change.
Invasive species drive important ecological and economic losses across wide geographies, with some regions supporting especially large numbers of nonnative species and consequently suffering relatively high impacts. For this reason, integrated risk assessments able to screen a suite of multiple invaders over large geographic areas are needed for prioritizing the allocation of limited resources. A total of 16 Ponto-Caspian aquatic species (10 gammarids, one isopod, two mysids, and three fishes) have been short-listed as recent or potential future invaders of British waters, whose introduction and spread is of high concern. In this study, we use multiple modeling techniques to assess their risk of establishment and spread into Great Britain. Climate suitability maps for these 16 species differed depending on the eastern and western distribution of species in continental Europe, which was related to their respective migration corridor: southern (Danube-Rhine rivers), and northern (Don and Volga rivers and Baltic lakes). Species whose suitability was high across large parts of Great Britain included four gammarids (Cheliorophium robustum, Dikerogammarus bispinosus, D. villosus, and Echinogammarus trichiatus) and a mysid (Hemimysis anomala). A climatic "heat map" combining the results of all 16 species together pointed to the southeast of England as the area most vulnerable to multiple invasions, particularly the Thames, Anglian, Severn, and Humber river basin districts. Regression models further suggested that alkalinity concentration > 120 mg/L in southeast England may favor the establishment of Ponto-Caspian invaders. The production of integrated risk maps for future invaders provides a means for the scientifically informed prioritization of resources toward particular species and geographic regions. Such tools have great utility in helping environmental managers focus efforts on the most effective prevention, management, and monitoring programs.
The accelerating rates of international trade, travel, and transport in the latter half of the twentieth century have led
to the progressive mixing of biota from across the world and the number of species introduced to new regions continues to
increase. The importance of biogeographic, climatic, economic, and demographic factors as drivers of this trend is increasingly
being realized but as yet there is no consensus regarding their relative importance. Whereas little may be done to mitigate
the effects of geography and climate on invasions, a wider range of options may exist to moderate the impacts of economic
and demographic drivers. Here we use the most recent data available from Europe to partition between macroecological, economic,
and demographic variables the variation in alien species richness of bryophytes, fungi, vascular plants, terrestrial insects,
aquatic invertebrates, fish, amphibians, reptiles, birds, and mammals. Only national wealth and human population density were
statistically significant predictors in the majority of models when analyzed jointly with climate, geography, and land cover.
The economic and demographic variables reflect the intensity of human activities and integrate the effect of factors that
directly determine the outcome of invasion such as propagule pressure, pathways of introduction, eutrophication, and the intensity
of anthropogenic disturbance. The strong influence of economic and demographic variables on the levels of invasion by alien
species demonstrates that future solutions to the problem of biological invasions at a national scale lie in mitigating the
negative environmental consequences of human activities that generate wealth and by promoting more sustainable population
growth.
This study examines the invasion history of alien fish species based on exhaustive national data sets on fish invasions of two contiguous central European countries (Germany and Austria). Fifteen alien fish species are currently established in both countries, constituting 14 and 17% of the total freshwater fish fauna of Germany and Austria, respectively. In both countries, six alien species are present, but not established. The status of five alien species in Germany and three species in Austria remains unknown. Accumulation rates of alien fish species have increased in recent decades with >50% of them reported after 1971. North America and Asia were the primary sources of alien fish species in Germany and Austria up to the 1980s, whereas European species of Ponto-Caspian origin dominate now. Fisheries (including aquaculture) and the animal trade were responsible for most earlier introductions, whereas waterways were the main pathway for recent invaders. The extent of the spatial distribution of alien species was positively correlated with residence time, i.e. the time elapsed since the first national record. Different thermal preferences of early invaders (mostly coldwater species) and new invaders (typically warmwater adapted) may benefit the latter in the face of climate change. It is concluded that new challenges for alien fish management arise and that ecosystem-based approaches as endorsed by the E.U. Water Framework Directive (maintaining or restoring good ecological status of rivers and streams) should become the centrepiece of river management in Europe.
1. Biological invasion theory predicts that the introduction and establishment of non-native species is positively correlated with propagule pressure. Releases of pet and aquarium fishes to inland waters has a long history; however, few studies have examined the demographic basis of their importation and incidence in the wild. 2. For the 1500 grid squares (10 × 10 km) that make up England, data on human demographics (population density, numbers of pet shops, garden centres and fish farms), the numbers of non-native freshwater fishes (from consented licences) imported in those grid squares (i.e. propagule pressure), and the reported incidences (in a national database) of non-native fishes in the wild were used to examine spatial relationships between the occurrence of non-native fishes and the demographic factors associated with propagule pressure, as well as to test whether the demographic factors are statistically reliable predictors of the incidence of non-native fishes, and as such surrogate estimators of propagule pressure. 3. Principal coordinates of neighbour matrices analyses, used to generate spatially explicit models, and confirmatory factor analysis revealed that spatial distributions of non-native species in England were significantly related to human population density, garden centre density and fish farm density. Human population density and the number of fish imports were identified as the best predictors of propagule pressure. 4. Human population density is an effective surrogate estimator of non-native fish propagule pressure and can be used to predict likely areas of non-native fish introductions. In conjunction with fish movements, where available, human population densities can be used to support biological invasion monitoring programmes across Europe (and perhaps globally) and to inform management decisions as regards the prioritization of areas for the control of non-native fish introductions.
European countries in general, and England in particular, have a long history of introducing non-native fish species, but there exist no detailed studies of the introduction pathways and propagules pressure for any European country. Using the nine regions of England as a preliminary case study, the potential relationship between the occurrence in the wild of non-native freshwater fishes (from a recent audit of non-native species) and the intensity (i.e. propagule pressure) and diversity of fish imports was investigated. The main pathways of introduction were via imports of fishes for ornamental use (e.g. aquaria and garden ponds) and sport fishing, with no reported or suspected cases of ballast water or hull fouling introductions. The recorded occurrence of non-native fishes in the wild was found to be related to the time (number of years) since the decade of introduction. A shift in the establishment rate, however, was observed in the 1970s after which the ratio of established-to-introduced species declined. The number of established non-native fish species observed in the wild was found to increase significantly (P < 0·05) with increasing import intensity (log10x + 1 of the numbers of fish imported for the years 2000–2004) and with increasing consignment diversity (log10x + 1 of the numbers of consignment types imported for the years 2000–2004). The implications for policy and management are discussed.
Understanding the mechanisms by which nonnative species successfully in-vade new regions and the consequences for native fauna is a pressing ecological issue, and one for which niche theory can play an important role. In this paper, we quantify a com-prehensive suite of morphological, behavioral, physiological, trophic, and life-history traits for the entire fish species pool in the Colorado River Basin to explore a number of hypotheses regarding linkages between human-induced environmental change, the creation and mod-ification of ecological niche opportunities, and subsequent invasion and extirpation of species over the past 150 years. Specifically, we use the fish life-history model of K. O. Winemiller and K. A. Rose to quantitatively evaluate how the rates of nonnative species spread and native species range contraction reflect the interplay between overlapping life-history strategies and an anthropogenically altered adaptive landscape. Our results reveal a number of intriguing findings. First, nonnative species are located throughout the adaptive surface defined by the life-history attributes, and they surround the ecological niche volume represented by the native fish species pool. Second, native species that show the greatest distributional declines are separated into those exhibiting strong life-history overlap with nonnative species (evidence for biotic interactions) and those having a periodic strategy that is not well adapted to present-day modified environmental conditions. Third, rapidly spreading nonnative fishes generally occupy ''vacant'' niche positions in life-history space, which is associated either with ''niche opportunities'' provided by human-created envi-ronmental conditions (consistent with the environmental-resistance hypothesis of invasion) or with minimal overlap with native life-history strategies (consistent with the biotic-resistance hypothesis). This study is the first to identify specific life-history strategies that are associated with extensive range reduction of native species and expansion of nonnative species, and it highlights the utility of using niche and life-history perspectives to evaluate different mechanisms that contribute to the patterns of fish invasions and extirpations in the American Southwest.
The ecological and economic impact of non-native species introduction on local native biodiversity is often reported as undeniable scientific evidence on which to base management and sound policy. Here I used a combination of databases (Fishbase, FAO and IMPASSE) and an extensive review of existing literature to establish the proportion of non-native aquatic species introductions in Spain that are responsible for ecological and economic impacts. In Spain, aquaculture and angling are the two main ecosystem services responsible for introduction of non-native aquatic species. In total, forty two percent of all non-native aquatic introductions are intentional. Very little ecological impact resulting from these non-native species introductions has been demonstrated with some representing a benefit to Spanish ecosystem services. In 2007, the economic benefits to Spanish aquaculture arising from non-native aquatic species (n=9) was close to €46.73 million (about U.S. $69 million) annually for an estimated average ecological risk for all introductions of 16.5% (SD= 26.85). These results must be seen in the context of other environmental factors such as habitat destruction, water abstraction and pollution from agricultural farming which represent major environmental pressures on Spanish aquatic fauna.
Risk perceptions are important to the policy process, but there is often a well-established pattern of small risks being over assessed. This is also true with the issue of non-native freshwater fish introductions, where a great majority of research focuses on the few negative cases. The attitude towards ‘non-natives’ is a continually evolving process and varies according to current societal values. Here I show that on the global scale, the majority of freshwater fish introductions are not identified as having an ecological impact while having great societal benefits. Case studies from the African lakes are discussed in order to illustrate contrasting outcomes following fish introductions. Looking into the future, the environmental changes that freshwater ecosystems may encounter will have inevitable implications on the distribution of our native freshwater fish species and the need to rely on non-native introductions may become a growing reality. Aquaculture production is regularly increasing and our dependence on it is likely to become greater as it provides an important substitute for the declining production of capture fisheries. With it the number of freshwater fish introductions will increase and a more realistic attitude, albeit controversial, will need to be debated. This would mean protecting some introductions that present beneficial outcomes for biodiversity alongside a more systematic ban of species or families of fish presenting a higher historical ecological risk. The public perception of risk is something which cannot be ignored by any government or ruling body, but in order to gain public support in the fight for conservation of freshwater fish biodiversity, the message needs to be clear, detailed and educational.
Aim Biotic homogenization describes the process by which species invasions and extinctions increase the genetic, taxonomic or functional similarity of two or more biotas over a specified time interval. The study of biotic homogenization is a young and rapidly emerging research area in the budding field of conservation biogeography, and this paper aims to synthesize our current knowledge of this process and advocate a more systematic approach to its investigation.
Methods Based on a comprehensive examination of the primary literature this paper reviews the process of biotic homogenization, including its definition, quantification, underlying ecological mechanisms, environmental drivers, the empirical evidence for different taxonomic groups, and the potential ecological and evolutionary implications. Important gaps in our knowledge are then identified, and areas of new research that show the greatest promise for advancing our current thinking on biotic homogenization are highlighted.
Results Current knowledge of the patterns, mechanisms and implications of biotic homogenization is highly variable across taxonomic groups, but in general is incomplete. Quantitative estimates are almost exclusively limited to freshwater fishes and plants in the United States, and the principal mechanisms and drivers of homogenization remain elusive. To date research has focused on taxonomic homogenization, and genetic and functional homogenization has received inadequate attention. Trends over the past decade, however, suggest that biotic homogenization is emerging as a topic of greater research interest.
Main conclusions My investigation revealed a number of important knowledge gaps and priority research needs in the science of biotic homogenization. Future studies should examine the homogenization process for different community properties (species occurrence and abundance) at multiple spatial and temporal scales, with careful attention paid to the various biological mechanisms (invasions vs. extinctions) and environmental drivers (environmental alteration vs. biotic interactions) involved. Perhaps most importantly, this research should recognize that there are multiple possible outcomes resulting from the accumulation of species invasions and extinctions, including biotic differentiation whereby genetic, taxonomic or functional similarity of biotas decreases over time.
It seems axiomatic that rivers, lakes, freshwater marshes, and other inland wetlands have an infinite value to humankind. They contribute for 20% (about US$6.6 trillion) to the estimated annual global value of the entire biosphere (Costanza et al. 1997). High-quality water has also become a strategic factor that allows for the viability and development of an increasing number of countries affected by both climate change and rising water-demand. All this justifies the current concern about the degradation of freshwater systems leading to rapid extinctions of organisms — in some cases even matching the declines recorded in tropical forests (Ricciardi and Rasmussen 1999).
There is general consensus today that some alien species will continue to be major drivers of degradation and loss of aquatic systems (Sala et al. 2000; Millennium Ecosystem Assessment 2005). The vulnerability of inland waters to bioinvasions is due to several factors (Gherardi 2007a), including the higher intrinsic dispersal ability of freshwater species compared with terrestrial organisms (Beisel 2001) and the strong impact of both human disturbance (Ross et al. 2001) and altered seasonal temperature regimes (Eaton and Scheller 1996). Species introduction into inland waters is associated with the intensity with which humans utilise these systems for recreation, food sources, and commerce (Rahel 2000), being a direct consequence of economic activity and trade globalisation that benefit millions worldwide (Lodge and Shrader-Frechette 2003). This situation has generated a conflict between two often competing goals — increasing economic activity and protecting the environment, which makes it difficult to decision-makers to develop policies aimed at containing the spread of aliens and mitigating the ecological risks they pose (Gherardi 2007a).
The eastern mosquitofish (Gambusia holbrooki) is among the most invasive fish worldwide and yet, while very abundant in most Mediterranean countries, it is unable to tolerate the colder winters of northern and central Europe. Understanding the effects of latitude on its life history traits is essential to predict the potential for its invasion of central Europe in current scenarios of climate change. We studied the variation of life-history traits and parasite load in the eastern mosquitofish along a latitudinal gradient from southern France to southern Spain, sampling mosquitofish populations in eight Mediterranean river mouths ranging 5° in latitude. Southern mosquitofish populations displayed higher catch rates, allocated more energy to reproduction (gonadosomatic index and gonadal weight after accounting for fish size) and had a lower condition (total weight and eviscerated weight after accounting for fish size) than in northern populations. Despite variability among populations, size-at-maturity (L50) significantly varied with latitude and northern individuals matured at smaller size (lower L50). Parasite prevalence ranged from 0.0 to 26.7% but parasite richness was very low; all the parasites identified were larvae of pleurocercoid cestodes belonging to the order Pseudophyllidea. The abundance of mosquitofish parasites decreased with latitude and the presence and number of parasites infecting the mosquitofish had a significant negative effect on fish condition. The significant effects of latitude on the catch rates, life history and parasites of mosquitofish highlight the importance of latitudinal studies of invasive species to understand the interactive mechanisms of climate change and biological invasions.
Non-native fishes are frequently used to enhance aquaculture and fisheries; if introduced into the wider environment, then the majority will have negligible effects on native biodiversity. However, a minority will become invasive, causing adverse ecological effects, and so management actions may be needed to minimize their dispersal and impacts. These actions include eradication attempts from specific waters or well-defined spatial areas, population control by suppression (e.g. through removal programmes) and containment of existing populations to prevent their further spread. These remedial actions have generally only been undertaken across large spatial areas in developed countries; experience suggests a fundamental constraint is a lack of selective removal methods that target the non-native fish species only. For example, eradication methods tend to be limited to low technology, 'scorched-earth' techniques (e.g. biocide chemicals) whose use is generally constrained to relatively small and enclosed water bodies. Risk management of non-native fishes should ensure that actions taken are commensurate with the level of risk posed by that species in the environment; although pre-introduction risk assessment schemes have been developed, there remains a lack of decision support tools for post-introduction situations. Although this inhibits the management of non-native fishes in the environment, control programmes such as those against common carp Cyprinus carpio in Australia and topmouth gudgeon Pseudorasbora parva in England and Wales suggest there is potential for invasions to be managed and controlled within large spatial areas, even if their eradication may not be feasible.
The aim of this paper is to detail a control programme of the invasive Asian cyprinid fish Pseudorasbora parva in the UK that was initiated in March 2005. Described as Europe's most invasive fish, P. parva presents a risk to native fishes through the transmission of a novel pathogen and undesirable impacts arising from processes including increased inter-specific competition. Populations have been recorded in 32 UK waters since their first recording outside of aquaculture in 1996; the majority are lakes < 5 ha used for recreational angling in England. The aims of the control programme were to develop a basic evaluation framework that assesses populations by risk (high, medium and low), determine commensurate management actions according to that risk and then execute those actions. For populations assessed as 'high-risk', for example those that could result in P. parva dispersal into a river catchment, eradication was determined as the commensurate management action and six operations have since been completed, principally using rotenone, and all have been successful to date. For P. parva populations in sites evaluated as lower risk, techniques such as biomanipulation were determined as more appropriate actions and have been used to successfully reduce their abundance by > 99%. To date, the total direct cost of this programme of sustained and on-going P. parva control is approximately A 190,000 pound.
This review provides a contemporary account of knowledge on aspects of introductions of non-native fish species and includes issues associated with introduction pathways, ecological and economic impacts, risk assessments, management options and impact of climate change. It offers guidance to reconcile the increasing demands of certain stakeholders to diversify their activities using non-native fishes with the long-term sustainability of native aquatic biodiversity. The rate at which non-native freshwater fishes have been introduced worldwide has doubled in the space of 30 years, with the principal motives being aquaculture (39%) and improvement of wild stocks (17%). Economic activity is the principal driver of human-mediated non-native fish introductions, including the globalization of fish culture, whereby the production of the African cichlid tilapia is seven times higher in Asia than in most areas of Africa, and Chile is responsible for c. 30% of the world's farmed salmon, all based on introduced species. Consequently, these economic benefits need balancing against the detrimental environmental, social and economic effects of introduced non-native fishes. There are several major ecological effects associated with non-native fish introductions, including predation, habitat degradation, increased competition for resources, hybridization and disease transmission. Consideration of these aspects in isolation, however, is rarely sufficient to adequately characterize the overall ecological effect of an introduced species. Regarding the management of introduced non-native fish, pre-introduction screening tools, such as the fish invasiveness scoring kit (FISK), can be used to ensure that species are not introduced, which may develop invasive populations. Following the introduction of non-native fish that do develop invasive populations, management responses are typified by either a remediation or a mitigation response, although these are often difficult and expensive to implement, and may have limited effectiveness.
Human activities are not random in their negative and positive impacts on biotas. Emerging evidence shows that most species are declining as a result of human activities (‘losers’) and are being replaced by a much smaller number of expanding species that thrive in human-altered environments (‘winners’). The result will be a more homogenized biosphere with lower diversity at regional and global scales. Recent data also indicate that the many losers and few winners tend to be non-randomly distributed among higher taxa and ecological groups, enhancing homogenization.
Human population and urbanization is unprecedented in its rate of growth and geographic scope. With the help of humans, exotic species have piggybacked their way to distant lands, which in combination with the loss of endemic native species, has led to the convergence of biological communities toward common and ubiquitous forms. However, the extent to which this “biotic homogenization” varies along gradients of human population size and urbanization remains mostly unexplored, especially at broad spatial scales. The present paper combines a recent conceptual model of homogenization with estimates of species invasions and extinctions to provide the first estimates of homogenization for five major taxonomic groups – land birds, freshwater fish, terrestrial mammals, plants, and freshwater reptiles and amphibians – at the continental-scale of North America (exclusive of Mexico). On average, the greatest levels of biotic homogenization were predicted for plants (22%) and fishes (14%), followed by reptiles/amphibians (12%), mammals (9%) and birds (8%). Substantial spatial variation in predictions of community similarity exists and emphasize that the outcome of species invasions and extinctions may not only increase community similarity, but may also decrease it (i.e., differentiation). Homogenization is predicted to be greatest for fish in southwestern and northeastern US, highest in eastern North America for plants, greatest for birds and mammals along the west coast of North America, and peak in southern US for reptiles and amphibians. We show that predicted change in community similarity for all taxonomic groups is positively related to human population size and urbanization, thus providing the first quantitative linkage between human population geography and homogenization for a number of major taxonomic groups at the continental-scale of North America. Our study helps identify regional hotspots of biotic homogenization across North America, thus setting the stage for future studies where more directed investigations of biotic homogenization along urban gradients can be conducted.
The world is currently undergoing an unprecedented decline in biodiversity, which is mainly attributable to human activities. For instance, nonnative species introduction, combined with the extirpation of native species, affects biodiversity patterns, notably by increasing the similarity among species assemblages. This biodiversity change, called taxonomic homogenization, has rarely been assessed at the world scale. Here, we fill this gap by assessing the current homogenization status of one of the most diverse vertebrate groups (i.e., freshwater fishes) at global and regional scales. We demonstrate that current homogenization of the freshwater fish faunas is still low at the world scale (0.5%) but reaches substantial levels (up to 10%) in some highly invaded river basins from the Nearctic and Palearctic realms. In these realms experiencing high changes, nonnative species introductions rather than native species extirpations drive taxonomic homogenization. Our results suggest that the "Homogocene era" is not yet the case for freshwater fish fauna at the worldwide scale. However, the distressingly high level of homogenization noted for some biogeographical realms stresses the need for further understanding of the ecological consequences of homogenization processes.
During the Late Devonian Biodiversity Crisis, the primary driver of biodiversity decline was the dramatic reduction in speciation rates, not elevated extinction rates; however, the causes of speciation decline have been previously unstudied. Speciation, the formation of new species from ancestral populations, occurs by two primary allopatric mechanisms: vicariance, where the ancestral population is passively divided into two large subpopulations that later diverge and form two daughter species, and dispersal, in which a small subset of the ancestral population actively migrates then diverges to form a new species. Studies of modern and fossil clades typically document speciation by vicariance in much higher frequencies than speciation by dispersal. To assess the mechanism behind Late Devonian speciation reduction, speciation rates were calculated within stratigraphically constrained species-level phylogenetic hypotheses for three representative clades and mode of speciation at cladogenetic events was assessed across four clades in three phyla: Arthropoda, Brachiopoda, and Mollusca. In all cases, Devonian taxa exhibited a congruent reduction in speciation rate between the Middle Devonian pre-crisis interval and the Late Devonian crisis interval. Furthermore, speciation via vicariance is almost entirely absent during the crisis interval; most episodes of speciation during this time were due to dispersal. The shutdown of speciation by vicariance during this interval was related to widespread interbasinal species invasions. The lack of Late Devonian vicariance is diametrically opposed to the pattern observed in other geologic intervals, which suggests the loss of vicariant speciation attributable to species invasions during the Late Devonian was a causal factor in the biodiversity crisis. Similarly, modern ecosystems, in which invasive species are rampant, may be expected to exhibit similar shutdown of speciation by vicariance as an outcome of the modern biodiversity crisis.
Adapted from the weed risk assessment (WRA) of Pheloung, Williams, and Halloy, the fish invasiveness scoring kit (FISK) was proposed as a screening tool for freshwater fishes. This article describes improvements to FISK, in particular the incorporation of confidence (certainty/uncertainty) ranking of the assessors' responses, and reports on the calibration of the score system, specifically: determination of most appropriate score thresholds for classifying nonnative species into low-, medium-, and high-risk categories, assessment of the patterns of assessors' confidences in their responses in the FISK assessments. Using receiver operating characteristic (ROC) curves, FISK was demonstrated to distinguish accurately (and with statistical confidence) between potentially invasive and noninvasive species of nonnative fishes, with the statistically appropriate threshold score for high-risk species scores being >/=19. Within the group of species classed as high risk using this new threshold, a "higher risk" category could be visually identified, at present consisting of two species (topmouth gudgeon Pseudorasbora parva and gibel carp Carassius gibelio). FISK represents a useful and viable tool to aid decision- and policymakers in assessing and classifying freshwater fishes according to their potential invasiveness.
Both human-related and natural factors can affect the establishment and distribution of exotic species. Understanding the relative role of the different factors has important scientific and applied implications. Here, we examined the relative effect of human-related and natural factors in determining the richness of exotic bird species established across Europe. Using hierarchical partitioning, which controls for covariation among factors, we show that the most important factor is the human-related community-level propagule pressure (the number of exotic species introduced), which is often not included in invasion studies due to the lack of information for this early stage in the invasion process. Another, though less important, factor was the human footprint (an index that includes human population size, land use and infrastructure). Biotic and abiotic factors of the environment were of minor importance in shaping the number of established birds when tested at a European extent using 50 x 50 km2 grid squares. We provide, to our knowledge, the first map of the distribution of exotic bird richness in Europe. The richest hotspot of established exotic birds is located in southeastern England, followed by areas in Belgium and The Netherlands. Community-level propagule pressure remains the major factor shaping the distribution of exotic birds also when tested for the UK separately. Thus, studies examining the patterns of establishment should aim at collecting the crucial and hard-to-find information on community-level propagule pressure or develop reliable surrogates for estimating this factor. Allowing future introductions of exotic birds into Europe should be reconsidered carefully, as the number of introduced species is basically the main factor that determines the number established.
Biologists have identified 25 areas, called biodiversity hotspots, that are especially rich in endemic species and particularly threatened by human activities. The human population dynamics of these areas, however, are not well quantified. Here we report estimates of key demographic variables for each hotspot, and for three extensive tropical forest areas that are less immediately threatened. We estimate that in 1995 more than 1.1 billion people, nearly 20% of world population, were living within the hotspots, an area covering about 12% of Earth's terrestrial surface. We estimate that the population growth rate in the hotspots (1995-2000) is 1.8% yr(-1), substantially higher than the population growth rate of the world as a whole (1.3% yr(-1)) and above that of the developing countries (1.6% yr(-1)). These results suggest that substantial human-induced environmental changes are likely to continue in the hotspots and that demographic change remains an important factor in global biodiversity conservation. The results also underline the potential conservation significance of the continuing worldwide declines in human fertility and of policies and programs that influence human migration.
Aquaculture is a fast-growing segment of the world food economy and a leading vector of aquatic invasive species in the United States and abroad. Surprisingly, little national or international oversight exists even for deliberate introductions of exotic species in aquaculture. The authors of this [Policy Forum][1] propose a policy agenda on exotic introductions as aquaculture expands that includes scientific risk assessment for all nonnative introductions and single-agency oversight for the prevention, containment, and monitoring of ecologically harmful species.
[1]: http://www.sciencemag.org/cgi/content/full/294/5547/1655
Because species invasions are a principal driver of the human-induced biodiversity crisis, the identification of the major determinants of global invasions is a prerequisite for adopting sound conservation policies. Three major hypotheses, which are not necessarily mutually exclusive, have been proposed to explain the establishment of non-native species: the "human activity" hypothesis, which argues that human activities facilitate the establishment of non-native species by disturbing natural landscapes and by increasing propagule pressure; the "biotic resistance" hypothesis, predicting that species-rich communities will readily impede the establishment of non-native species; and the "biotic acceptance" hypothesis, predicting that environmentally suitable habitats for native species are also suitable for non-native species. We tested these hypotheses and report here a global map of fish invasions (i.e., the number of non-native fish species established per river basin) using an original worldwide dataset of freshwater fish occurrences, environmental variables, and human activity indicators for 1,055 river basins covering more than 80% of Earth's surface. First, we identified six major invasion hotspots where non-native species represent more than a quarter of the total number of species. According to the World Conservation Union, these areas are also characterised by the highest proportion of threatened fish species. Second, we show that the human activity indicators account for most of the global variation in non-native species richness, which is highly consistent with the "human activity" hypothesis. In contrast, our results do not provide support for either the "biotic acceptance" or the "biotic resistance" hypothesis. We show that the biogeography of fish invasions matches the geography of human impact at the global scale, which means that natural processes are blurred by human activities in driving fish invasions in the world's river systems. In view of our findings, we fear massive invasions in developing countries with a growing economy as already experienced in developed countries. Anticipating such potential biodiversity threats should therefore be a priority.
World trade has become the primary driver of one of the most dangerous and least visible forms of environmental decline: Thousands of species are hitchhiking to new homes aboard ships, planes, and trains and in the process are degrading ecosystems, threatening public health, and costing billions of dollars annually.
Aim We quantify biotic homogenization of fish fauna caused by the elimination of a natural barrier between two freshwater ecoregions. We also evaluated fish introductions by different mechanisms such as aquaculture, angling and the aquarium trade in the homogenization of fish assemblages. The relative importance of native extinctions in the homogenization process was assessed by simulating the exclusion of threatened species in the data set.
Location Paraná River, south-eastern South America.
Methods A fish species list of the Parana River Basin was organized in a subset of species distributions, according to pre- and post-introductions caused by the elimination of the natural barrier and by other mechanisms. Biotic homogenization was verified by the use of Jaccard’s and Bray–Curtis’s coefficients, Whittaker’s beta diversity index, non-metric multidimensional scaling analysis (NMDS) and nonparametric tests.
Results For all subsets of species distributions, we observed an increase in the number of non-native species in common related to the introductions. Between 40 and 52% of the species currently present in the Upper Paraná Basin dispersed upstream from the Lower Paraná after the construction of Itaipu Dam, including at least 1 class, 2 orders, 4 families and 16 genera of fish. Jaccard’s coefficient between the Upper and Lower Parana River increased by 6–7.5% only considering the Itaipu Dam influence and 10.5% considering all mechanisms of fish introductions. More than 50% of the increase in similarity was caused by the elimination of the barrier. Our results indicated functional homogenization related to large-bodied Siluriformes (catfish).
Main conclusions Itaipu Lake flooded a natural barrier and allowed hydrologic connectivity between the Upper and Lower Paraná River, and many fishes of the lower part of the river were able to colonize the upper stretches. The homogenization of the two assemblages between these adjacent aquatic regions was an unpredicted result of hydropower implementation. Introductions by dam can also shift longitudinal and latitudinal body size patterns (i.e. Bergmann's rule).
Introduced species represent an accelerated global change, and current efforts to manage them, though effective in particular situations, are not controlling the general problem. In the US, this failure is the result of insufficient policy, inadequate research and management funding, and gaps in scientific knowledge. Comparative policy analysis is urgently needed; the main US shortcoming is the absence of a coherent set of policies to address the entire issue, rather than individual invaders. Deliberate introductions should be more stringently regulated and risk assessments must become more predictive. Monitoring and attempts to identify new invasions (both deliberate and inadvertent) are technically feasible but not sufficiently funded and coordinated. Techniques to manage established invaders have often succeeded, but have been hamstrung by inconsistent funding. All of these problems could be improved by more fundamental research, ranging from basic natural history and simple advances in control technologies to more sophisticated ecological modeling and remote sensing techniques.
Within conservation biology human factors are treated as driving forces of biodiversity loss, yet there are few empirical studies on how human actions affect biodiversity. We developed and tested an interdisciplinary model of biodiversity loss using socioeconomic and ecological data from 107 countries and structural equation modeling techniques. Some portions of the model fit the data well, other parts were less predictive. Counterintuitive results may be a result of the quality and availability of cross-national data and statistical limitations in testing a model of such complex processes. This model test provides insight into future research needs for examining human impacts on biodiversity. Issues including data quality, temporal and spatial scale, and model refinement are outlined. The results highlight the importance of relations between human social systems and biodiversity and the potential of interdisciplinary research.Dentro de la biología de la conservación, los factores humanos son tratados como fuerzas que conducen a la pérdida de biodiversidad, pero existen pocos estudios empíricos sobre como las acciones humanas afectan la biodiversidad. Desarrollamos y probamos un modelo interdisciplinario de pérdida de la biodiversidad usando datos socioeconómicos y ecológicos de 107 paises asi como técnicas de modelado con ecuaciones estructurales. Resultados contraintuitivos pueden ser el resultado de la calidad y la viabilidad de datos entre naciones y las limitaciones estadísticas al evaluar un modelo de tan complejo proceso. Esta evaluación de modelo provee elementos para investigación necesaria para examinar el impacto humano en la biodiversidad. Se señalan aspectos que incluyen la calidad de los datos, escalas espaciales y temporales y el refinamiento del modelo. Los resultados resaltan la importancia de las relaciones entre sistemas sociales y la biodiversidad y el potencial de la investigación interdisciplinaria.
In this paper, we respond to Gozlan’s views of the introduction of freshwater fish, as we strongly disagree with his view and approach. We demonstrate that many real-world examples of freshwater fish introductions have catastrophic ecological consequences. We detail a few noteworthy examples, such as those of the Nile perch, carp, tilapias, catfishes, and the zebra mussel. We discuss within-nation introductions, and we explore several related problems, such as hybridization and spread of pathogens and parasites. We propose that Gozlan’s analysis is biased, as more reliable data on impacts that are already widespread are urgently needed, mainly in the biologically richest areas of the world. Thus, we continue to advocate the precautionary principle, because species introductions, once established, are largely irreversible.
I examined a data set of 77 protected areas in the USA (including national and state parks) to determine which of the following variables most strongly influence alien plant species richness: park area, climate (temperature and precipitation), native species richness, visitation rate, local human population size, total road length, park shape and duration of European settlement. Many of these predictor variables are intercorrelated, so I used multiple regression to help separate their effects. In support of previous studies, native species richness was the best single predictor of alien species richness, probably because it was a good estimator of both park area and habitat diversity available for establishment of alien species. Other significant predictors of alien species richness were years of occupation of the area by European settlers and the human population size of adjacent counties. Climate, visitation rate, road length and park shape did not influence alien species richness. The proportion of alien species (alien richness/native richness) is inversely related to park area, in agreement with a previous study. By identifying which variables are most important in determining alien species richness, such findings suggest ways to reduce alien species establishment.
Summary • Humans have traded and transported alien species for millennia with two notable step-changes: the end of the Middle Ages and beginning of the Industrial Revolution. However, in recent decades the world has entered a new phase in the magnitude and diversity of biological invasions: the Era of Globalization. This Special Profile reviews the links between the main drivers of globalization and biological invasions and examines state-of-the-art approaches to pathway risk assessment to illustrate new opportunities for managing invasive species. • Income growth is a primary driver of globalization and a clear association exists between Gross Domestic Product and the richness of alien floras and faunas for many regions of the world. In many cases, the exposure of these economies to trade is highlighted by the significant role of merchandise imports in biological invasions, especially for island ecosystems. • Post-1950, technical and logistic improvements have accelerated the ease with which commodities are transported across the globe and hindered the traceability of goods and the ease of intercepting pests. New sea, land and air links in international trade and human transport have established novel pathways for the spread of alien species. Increasingly, the science advances underpinning invasive species management must move at the speed of commerce. • Increasing transport networks and demand for commodities have led to pathway risk assessments becoming the frontline in the prevention of biological invasions. The diverse routes of introduction arising from contaminant, stowaway, corridor and unaided pathways, in both aquatic and terrestrial biomes are complex. Nevertheless, common features enable comparable approaches to risk assessment. By bringing together spatial data on climate suitability, habitat availability and points of entry, as well a demographic models that include species dispersal (both natural and human-mediated) and measures of propagule pressure, it is possible to generate risk maps highlighting potential invasion hotspots that can inform prevention strategies. • Synthesis and applications. To date, most attempts to model pathways have focused on describing the likelihood of invader establishment. Few have modelled explicit management strategies such as optimal detection and inspection strategies and assessments of the effectiveness of different management measures. A future focus in these areas will ensure research informs response.
Distribution patterns of non-native fishes in Germany have been analysed starting from their first introductions reported, with the objectives to determine indicators of their invasiveness, to identify the most important distribution pathways, and to predict their further development. In Germany, 14 out of 93 non-native freshwater and migratory fish species ever registered are established today, a further six are possibly established, eight have failed to establish, and the rest were single records. Five of the established and three potentially established species were restricted to single locations. Of the remaining species, only the gobiid species are actually spreading throughout the waterway network, whereas other stocks rather tend to decline or did not change. The most wide-spread species is rainbow trout Oncorhynchus mykiss, with 5,872 records in open waters being the most important fish for German’s commercial inland fisheries with an annual yield of > 21 000 tons. But rainbow trout is widely stocked and its establishment status is a subject of debate. Inland fisheries management has contributed most to the recent distribution of non-native fishes, but it became also the best regulated pathway. Therefore, it is expected that ornamental fish trade and aquaculture will become most important for introducing new non-native fishes in the near future, even if unintentionally. Every single fish escaping from a garden pond or holding facility is a potential founder of an invasive species stock and in particular raising water temperatures in winter might promote the establishment of ornamental fish. Once established, there are nearly no legal means to remove a non-native species successfully from a water body.
We used historical data to parameterize species-accumulation models relating international trade to the establishment rates of nonindigenous species in the United States over the past century. We then coupled these relationships with published trade forecasts to predict future invasion rates for insects, plant pathogens, and mollusks. Relationships between the accumulation of non-native species and merchandise imports were reasonably described by log-log and log-linear species-area models and Michaelis-Menten accumulation functions. However, the latter two models produced markedly better fits. When coupled with projected trade forecasts, the log-linear species-area model predicted 16–24% taxon-specific increases in the number of nonindigenous species established in the United States from 2000 to 2020. The Michaelis-Menten model predicted much lower 3–6% increases, but even this meant 115 new insect species and 5 new plant pathogens. These results suggest that the ecological and economic costs associated with human-caused biological invasions may continue to rise substantially over the coming decades.
The Laurentian Great Lakes basin has been invaded by at least 182 non-indigenous species. A new invader is discovered every 28 weeks, which is the highest rate recorded for a freshwater ecosystem. Over the past century, invasions have occurred in phases linked to changes in the dominant vectors. The number of ship-vectored invaders recorded per decade is correlated with the intensity of vessel traffic within the basin. Ballast water release from ocean vessels is the putative vector for 65% of all invasions recorded since the opening of the St. Lawrence Seaway in 1959. As a preventive measure, ocean vessels have been required since 1993 to exchange their freshwater or estuarine ballast with highly saline ocean water prior to entering the Great Lakes. However, this procedure has not prevented ship-vectored species introductions. Most ships visiting the Great Lakes declare ‘no ballast on board’ (NOBOB) and are exempt from the regulation, even though they carry residual water that is discharged into the Great Lakes during their activities of off-loading inbound cargo and loading outbound cargo. Recently introduced species consist predominantly of benthic invertebrates with broad salinity tolerance. Such species are most likely to survive in a ballast tank following ballast water exchange, as well as transport in the residual water and tank sediments of NOBOB ships. Thus, the Great Lakes remain at risk of being invaded by dozens of euryhaline invertebrates that have spread into Eurasian ports from whence originates the bulk of foreign ships visiting the basin.
The information extracted from IMPASSE, DAISIE, FishBase, and FAO-DIAS inventories of alien species were used to draw a list of the 27 most utilized animal alien species for aquaculture and related activities (e.g. stocking, sport fishing, ornamental purposes) in Europe. Three variables have been considered to assess their negative ecological impacts when these species escape from aquaculture facilities: (i) their distribution across Europe (including non-EU Member States); (ii) evidence of their environmental impact in the wild; and (iii) evidence of their being vectors of non-target alien species and other hitchhikers (e.g. pathogens). Drivers of use and mechanisms of dispersal in the wild have been also considered and reviewed. Twenty of the species are freshwater fishes: alien cyprinids and salmonids have been introduced into Europe mainly for food production, sport fishing and ornamental purposes. The most widespread species are the goldfish Carassius auratus and the rainbow trout Oncorhynchus mykiss, established in 29 and 28 European countries, respectively. Notwithstanding their successful distribution in Europe, only the Gibel carp Carassius gibelio and the peneid shrimp Marsupenaeus japonicus were found to have environmental impact in all the countries of establishment. Crayfish and predatory fishes (e.g. catfishes and salmonids) cause major environmental impacts in Europe by outcompeting native species and altering habitat structure. Alien crayfish, Procambarus clarkii and Pacifastacus leniusculus, are responsible for the largest range of impacts (i.e. crayfish plague dissemination, bioaccumulation of pollutants, community dominance, competition and predation on native species, habitat modifications, food web impairment, herbivory and macrophytes removal). Cyprinids (e.g. herbivorous carps) are vectors of diseases and parasites, while salmonids (e.g. Salvelinus fontinalis) often cause genetic impairment of native stocks by hybridization. The importation of alien farmed (target) species frequently leads to the introduction of associated non-target species. The cultures of the Pacific cupped oyster Crassostrea gigas and Manila clam Ruditapes philippinarum were responsible for the introduction of the largest number (60) of non-native invertebrates and algae, often attached to packaging material, fouling the shell or parasitizing bivalve tissues.
Most introduced species apparently have little impact on native biodiversity, but the proliferation of human vectors that transport species worldwide increases the probability of a region being affected by high-impact invaders – i.e. those that cause severe declines in native species populations. Our study determined whether the number of high-impact invaders can be predicted from the total number of invaders in an area, after controlling for species–area effects. These two variables are positively correlated in a set of 16 invaded freshwater and marine systems from around the world. The relationship is a simple linear function; there is no evidence of synergistic or antagonistic effects of invaders across systems. A similar relationship is found for introduced freshwater fishes across 149 regions. In both data sets, high-impact invaders comprise approximately 10% of the total number of invaders. Although the mechanism driving this correlation is likely a sampling effect, it is not simply the proportional sampling of a constant number of repeat-offenders; in most cases, an invader is not reported to have strong impacts on native species in the majority of regions it invades. These findings link vector activity and the negative impacts of introduced species on biodiversity, and thus justify management efforts to reduce invasion rates even where numerous invasions have already occurred.
A modular assessment scheme for assisting the risk management of introduced fishes is described, with its recent application
to England and Wales demonstrated. The initial module prioritises the introduced fishes in the risk assessment area according
to their potential invasiveness and current distribution. The second module then assesses populations of the prioritised species
in relation to the character of their receiving waters and the potential risks posed by their population in that circumstance;
the output is a suggested management action for each population. The third module evaluates the suggested management action
in relation to its potential impacts in the environment and how these impacts may be mitigated. The final module assesses
the estimated cumulative cost of the selected management action relative to an alternative action. To demonstrate its potential
value for managing extant populations of introduced fish, three eradication case-studies from England were assessed retrospectively
using the scheme. This revealed eradication of two topmouth gudgeon Pseudorasbora parva populations was commensurate with their levels of ecological risk in the environment. By contrast, initial assessment of
the eradication of a feral population of fathead minnow Pimephales promelas suggested control and containment was the commensurate management action due to a relatively low risk of natural dispersal.
Application of the scheme elsewhere in the world and to other faunal groups should enable more objective decision-making in
management programmes and enhance conservation outcomes.
KeywordsDecision support–Alien–Introductions–Invasive–Risk management
The finfish and crustacean aquaculture sector is still highly dependent upon marine capture fisheries for sourcing key dietary nutrient inputs, including fish meal and fish oil. This dependency is particularly strong within compound aquafeeds for farmed carnivorous finfish species and marine shrimp.Results are presented concerning the responses received from a global survey conducted between December 2006 and October 2007 concerning the use of fish meal and fish oil within compound aquafeeds using a questionnaire sent to over 800 feed manufacturers, farmers, researchers, fishery specialists, and other stakeholders in over 50 countries. On the basis of the responses received, it is estimated that in 2006 the aquaculture sector consumed 3724 thousand tonnes of fish meal (68.2% total global fish meal production in 2006) and 835 thousand tonnes of fish oil (88.5% total reported fish oil production in 2006), or the equivalent of 16.6 million tonnes of small pelagic forage fish (using a wet fish to fish meal processing yield of 22.5% and wet fish to fish oil processing yield of 5%) with an overall fish-in fish-out ratio of 0.70. At a species-group level, calculation of small pelagic forage fish input per unit of farmed fish or crustacean output showed steadily decreasing fish-in fish-out ratios for all cultivated species from 1995 to 2006, with decreases being most dramatic for carnivorous fish species such as salmon (decreasing from 7.5 to 4.9 from 1995 to 2006), trout (decreasing from 6.0 to 3.4), eel (decreasing from 5.2 to 3.5), marine fish (decreasing from 3.0 to 2.2) and to a lesser extent shrimp (decreasing by 1.9 to 1.4 from 1995 to 2006. Net fish producing species in 2006 (with fish-in fish-out ratios below 1), included herbivorous and omnivorous finfish and crustacean species, including non-filter feeding Chinese carp (0.2), milkfish (0.2), tilapia (0.4), catfish (0.5), and freshwater crustaceans (0.6).On the basis of increasing global fish meal and fish oil costs, it is predicted that dietary fish meal and fish oil inclusion levels within compound aquafeeds will decrease in the long term, with fish meal and fish oil usage increasingly being targeted for use as a high value specialty feed ingredient for use within higher value starter, finisher and broodstock feeds, and by so doing extending supply of these much sought after and limited feed ingredient commodities.
Little is known about how socio-economic factors quantitatively contribute to shaping introductions of exotic species in space and time. Here, we discover that socio-economic, historical and political factors are largely responsible for shaping exotic bird introductions into Europe. We find that the Cold War and its resulting commercial alliances in Eastern vs. Western Europe led to contrasting patterns in the numbers, composition and origin of birds introduced into each of the two European blocs. The isolation of the Eastern European bloc from the west during the Cold War led to a decline in the number of birds introduced, the number of introduction events and the number of bird species established. Birds introduced during the Cold War originated largely from economically allied countries of each of the two blocs. The Cold War provided a hitherto unexpected benefit to the Eastern European bloc by limiting exotic species introductions, and subsequent population establishment, due to its restrictions on international trade. We suggest that work on the factors shaping invasive species establishment, spread and impacts should incorporate a socio-economic context. Given the ongoing increase in human movement and trade in Europe and the integration of most former Eastern European countries to the European Union, clear policies should be urgently established to prevent inflow of exotic species into formerly more isolated regions and reduce the risk of future biotic invasions.
The extent of plant invasions was studied in 302 nature reserves located in the Czech Republic, central Europe. Lists of vascular plant species were obtained for each reserve, alien species were divided into archaeophytes and neophytes (introduced before and after 1500, respectively). The statistical analysis using general linear models made it possible to identify the effects of particular variables. Flora representation by neophytes decreased with altitude (explained 23.8% of variance) while, with archaeophytes, the effect of altitude depended on their interaction with native species in particular vegetation types. The proportion of neophytes increased with increasing density of human population. Both the number and proportion of aliens plants significantly increased with increasing number of native species in a reserve. This relationship was affected by altitude, and after filtering out this variable, the effect remained positive for neophytes but became negative for archaeophytes in humid grasslands. The positive relationship between neophytes and native species is not a mere side effect of species–area relationship of native flora, but indicates that the two groups do not directly compete. Vegetation type alone explained 14.2 and 55.5% of variation in proportion of aliens in regions of mesophilous and mountain flora, respectively. Humid grasslands were the least invaded vegetation type. Positioning the reserve within large protected sections of landscape significantly decreases probability of it being invaded by potentially invasive alien species. Within the context of SLOSS debate, a new model — several small inside single large (SSISL) — is suggested as an appropriate solution from the viewpoint of plant invasions to nature reserves.
1. Even though intensive aquaculture production of salmonids in lakes occurs in many locations around the world published studies on the survival and reproductive success of escaped cultured salmonids in freshwater ecosystems are not common. A recent expansion of aquaculture in Chile has led it to become the world's second largest producer of cultured salmonids. 2. We document the recent history of escaped and self-sustaining salmonid populations over a wide spatial scale and a long temporal scale in Chilean Patagonian lakes. Our hypotheses are that salmonid density in lakes will be higher where there is intensive aquaculture, due to greater numbers of potential escapees. Secondly, if non-native salmonids have adverse impacts on native fishes, increases in the abundance of non-native species should be associated with decreases in relative abundance of native species. Finally, if the first two hypotheses are correct we anticipate that diets of salmonids may show evidence of predation on native fishes, diet overlap with native species, and evidence of the influence of feed from aquaculture operations in the diets of salmonids and native fishes. 3. We sampled six lakes with gill nets from 1992 to 2001. Our results show that the relative abundance of free-living salmonids is closely related to the level of fish farming production. Salmonids are the top predators and in lakes with fish farming the main prey item is native fishes. The relative abundance of native fishes has decreased, most likely due to predation by salmonids. 4. Our study contributes to the understanding of the effects of non-native salmonids in oligotrophic lakes, and it provides a starting point to judge the establishment of new fish farming sites in lakes around the world.
Aim To identify key research questions and challenges that will, if addressed in a timely manner, significantly advance the field of freshwater fish biogeography and conservation. Location Globe. Methods By drawing on expertise from different regions of the world, we integrate an illustrative conspectus of recent scientific advancements in fish biogeography with a prospectus of needed areas of scientific inquiry to identify information gaps and priority research needs to advance the science. Results We identified the following core challenges: (1) Testing current and forging new theories in biogeography; (2) Advancing a trait-based biogeography of freshwater fishes; (3) Quantifying extinction risk and loss of fish species in a changing environment; (4) Evaluating the magnitude and geography of extinction debt for freshwater fishes; (5) Elucidating the patterns and drivers of freshwater fish invasions; (6) Forecasting the future geography of freshwater fishes; (7) Understanding the interactive effects of multiple stressors in freshwater ecosystems; (8) Quantifying new features of the biodiversity crisis: fish faunal homogenization and the emergence of novel assemblages; (9) Promoting scientific rigour in emerging freshwater fish conservation strategies and (10) Improving conservation planning strategies for freshwater fish species. Main conclusions By reflecting on recent scientific progress in fish conservation biogeography, we have identified a set of core challenges and priorities requiring future research investment. Yes Yes
Biological invasions are gaining attention as a major threat to biodiversity and an important element of global change. Recent research indicates that other components of global change, such as increases in nitrogen deposition and atmospheric CO2 concentration, favor groups of species that share certain physiological or life history traits. New evidence suggests that many invasive species share traits that will allow them to capitalize on the various elements of global change. Increases in the prevalence of some of these biological invaders would alter basic ecosystem properties in ways that feed back to affect many components of global change.
Fish faunas across the continental United States have become more similar through time because of widespread introductions
of a group of cosmopolitan species intended to enhance food and sport fisheries. On average, pairs of states have 15.4 more
species in common now than before European settlement of North America. The 89 pairs of states that formerly had no species
in common now share an average of 25.2 species. Introductions have played a larger role than extirpations in homogenizing
fish faunas. Western and New England states have received the most introductions, which is a reflection of the small number
of native fishes in these areas considered desirable gamefish by settlers.
Human-mediated species invasions are a significant component of current global environmental change. There is every indication that the rate at which locations are accumulating non-native species is accelerating as free trade and globalization advance. Thus, the need to incorporate predictive models in the assessment of invasion risk has become acute. However, finding elements of the invasion process that provide consistent explanatory power has proved elusive. Here, we propose propagule pressure as a key element to understanding why some introduced populations fail to establish whereas others succeed. In the process, we illustrate how the study of propagule pressure can provide an opportunity to tie together disparate research agendas within invasion ecology.