Fish Invasions in the World's River Systems: When Natural Processes Are Blurred by Human Activities

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.     

Fish Invasions in the World's River Systems: When Natural Processes Are Blurred by Human Activities

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.     

Worldwide freshwater fish homogenization is driven by a few widespread non-native species

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.     

Landscape‐scale determinants of non‐native fish communities

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

Plant invasions on small Mediterranean islands: An overview

Biological invasions have become one of the main drivers of habitat degradation and a leading cause of biodiversity loss in island ecosystems worldwide. The spread of invasive species poses a particular environmental threat on the islands of the Mediterranean Basin, which are hot spots of biodiversity and contain rare habitats and endemic species, especially on small islands, which are highly vulnerable to biodiversity loss. Following a recent survey, in this paper we aim to provide an overview of the present-day non-native vascular flora of small Mediterranean islands based on a sample of 37 islands located in the middle of the Mediterranean Sea, off the coast of Italy. By comparing the current data with those gathered during a previous survey conducted in the same study area, we also aim to highlight the main changes that have occurred in non-native plant species diversity, establishment and distribution in recent years and to present a first general overview of the most prominent plant taxa in the island’s introduced flora, focusing on those most responsible for these changes and those that pose the greatest environmental threats. We recorded 203 non-native plant species, 147 of which have established on at least one of the islands investigated. Overall, we detected a sharp increase in the number of species, in their levels of establishment and in the extent of their distribution within the study area in recent years. This may be explained by the intensification of research on plant invasions, as well as to new introduction, escape, establishment and invasion events on the islands in recent decades. The most remarkable plants detected include acacias and succulents, two groups that appear to be emerging very rapidly and to be posing new threats to the conservation of the islands’ natural environment, especially the genus Carpobrotus, whose spread into natural habitats containing rare and endemic taxa is seriously threatening biodiversity on both a local and global scale. On the whole, our results show that the plant invasion phenomenon in the study area has in recent years intensified considerably. As this process seems likely to continue, we should expect more establishment events in the future and the further spread of species that are already present. This is of particular conservation concern on the islands investigated in this survey, which are rich in endemisms, but have been facing deep socio-economic and environmental transformations in these last decades as a consequence of the abandonment of traditional management practices and the development of tourism. Our study thus confirms that plant invasions on Mediterranean islands are a serious environmental problem that threatens biodiversity conservation not only in the Mediterranean biogeographic region, but also on the global scale, and highlights the need to further increase efforts aimed at preventing, controlling or mitigating the effects of plant invasions in island ecosystems.     

Abandoned Foreigners: is the stage set for exotic pet reptiles to invade Central Europe?

Considerable scientific, politic and economic attention has been directed to biological invasions. Multiple pathways serve to introduce species to new environments and the release or escape of pets are among the most important sources for species invasions. Risk assessments help to identify species that are likely to become invasive and to set up preventive measures. Weighing the relative importance of ecological and human factors driving the establishment success of abandoned pets, we here present a new methodological guideline to help prioritising management activities for frequently traded pet reptiles. Climate match scores between the different distribution ranges as well as traits and niche axes shared by native and non-native species were assessed. Moreover, we tested for discrepancies in niche breadth between native and non-native ranges and estimated the ability of species to coexist with humans. Potentially moderate to high establishment success in most species was linked to appropriate climate match scores, broader niches with restrained human impacts and high similarities in reproductive traits with the native herpetofauna. Providing baseline information on the invasion potential of pet reptiles, this assessment calls for trade regulations and, to an even greater degree, for large scale education campaigns to prevent the establishment of non-native populations.     

Invasibility of Mediterranean-Climate Rivers by Non-Native Fish: The Importance of Environmental Drivers and Human Pressures

Invasive species are regarded as a biological pressure to natural aquatic communities. Understanding the factors promoting successful invasions is of great conceptual and practical importance. From a practical point of view, it should help to prevent future invasions and to mitigate the effects of recent invaders through early detection and prioritization of management measures. This study aims to identify the environmental determinants of fish invasions in Mediterranean-climate rivers and evaluate the relative importance of natural and human drivers. Fish communities were sampled in 182 undisturbed and 198 disturbed sites by human activities, belonging to 12 river types defined for continental Portugal within the implementation of the European Union''s Water Framework Directive. Pumpkinseed sunfish, Lepomis gibbosus (L.), and mosquitofish, Gambusia holbrooki (Girard), were the most abundant non-native species (NNS) in the southern river types whereas the Iberian gudgeon, Gobio lozanoi Doadrio and Madeira, was the dominant NNS in the north/centre. Small northern mountain streams showed null or low frequency of occurrence and abundance of NNS, while southern lowland river types with medium and large drainage areas presented the highest values. The occurrence of NNS was significantly lower in undisturbed sites and the highest density of NNS was associated with high human pressure. Results from variance partitioning showed that natural environmental factors determine the distribution of the most abundant NNS while the increase in their abundance and success is explained mainly by human-induced disturbance factors. This study stresses the high vulnerability of the warm water lowland river types to non-native fish invasions, which is amplified by human-induced degradation.     

Establishment patterns of non-native insects in New Zealand

Insects comprise the majority of non-native animal species established around the world. However, geographic biases in knowledge hamper an overall understanding of biological invasions globally. A dataset of accidentally introduced non-native insect species established in New Zealand was compiled from databases, entomological literature, and examination of specimens in the New Zealand Arthropod Collection. For each non-native species, the first recorded location and first recorded date of detection was obtained. Excluding intentionally introduced species, there are 1477 non-native insect species successfully established in New Zealand across 16 orders, 234 families and 1017 genera. Four orders (Coleoptera, Hemiptera, Hymenoptera and Diptera) contributed 77.5% of all established insect species. Herbivores represented the largest feeding guild (47.7%), comprised of polyphagous (48.3%) or oligophagous (39.7%) species. The majority of these species originated in the Australasian (36.7%) and Palearctic regions (24.8%). Regression trees, using a binary recursive partitioning approach, found the number of international tourist arrivals, exotic vegetation cover, and regional gross domestic product were the main factors explaining spatial patterns of recently established species. Gross domestic product best explained temporal patterns of establishment over the last century. Our findings demonstrate that broad-scale analyses of non-native species have important applications for border biosecurity by providing insight into the extent of invasions. In New Zealand, the current trajectory indicates fewer non-native species are establishing annually, suggesting biosecurity efforts are being effective at reducing rates of establishment.     

Fish assemblage changes over half a century in the Yellow River,China

Riverine environments have been threatened by anthropogenic perturbations worldwide, whereby their fish assemblages have been modified by habitat changes and nonendemic species invasions. We assessed changes in fish assemblages by comparing the species presence in historical and contemporary fish data in the Yellow River from 1965 to 2015. The temporal change in species assemblages was found with increased nonendemic species and fewer natives. Fish species richness of the river declined 35.4% over the past fifty years. Moreover, the decreased mean Bray–Curtis dissimilarity among reaches suggested that the fish assemblages of different reaches in the Yellow River were becoming more similar over time. However, temporal patterns of fish assemblages varied among reaches. In the upper Yellow River, higher species richness and more invasive species were found than those in the historical record, while the lower reaches experienced significant species loss. Dam constructions, exotic fish invasions, and flow reductions played the vital role in structuring the temporal fish assemblages in the Yellow River. It is suggested that river basins which experienced different types and levels of stressors by anthropogenic perturbations can produce varied effects on their temporal trends of species assemblages.     

Native vegetation structure,landscape features and climate shape non-native plant richness and cover in New Zealand native shrublands

Aim

Studies investigating the determinants of plant invasions rarely examine multiple factors and often only focus on the role played by native plant species richness. By contrast, we explored how vegetation structure, landscape features and climate shape non-native plant invasions across New Zealand in mānuka and kānuka shrublands.

Location

New Zealand.

Method

We based our analysis on 247 permanent 20 × 20-m plots distributed across New Zealand surveyed between 2009 and 2014. We calculated native plant species richness and cumulative cover at ground, understorey and canopy tiers. We examined non-native species richness and mean species ground cover in relation to vegetation structure (native richness and cumulative cover), landscape features (proportion of adjacent anthropogenic land cover, distance to nearest road or river) and climate. We used generalized additive models (GAM) to assess which variables had greatest importance in determining non-native richness and mean ground cover and whether these variables had a similar effect on native species in the ground tier.

Results

A positive relationship between native and non-native plant species richness was not due to their similar responses to the variables examined in this study. Higher native canopy richness resulted in lower non-native richness and mean ground cover, whereas higher native ground richness was associated with higher native canopy richness. Non-native richness and mean ground cover increased with the proportion of adjacent anthropogenic land cover, whereas for native richness and mean ground cover, this relationship was negative. Non-native richness increased in drier areas, while native richness was more influenced by temperature.

Main Conclusions

Adjacent anthropogenic land cover seems to not only facilitate non-native species arrival by being a source of propagules but also aids their establishment as a result of fragmentation. Our results highlight the importance of examining both cover and richness in different vegetation tiers to better understand non-native plant invasions.     

Patterns of fish species richness in China's lakes

Aim To document the patterns of fish species richness and their possible causes in China's lakes at regional and national scales. Location Lakes across China. Methods We compiled data of fish species richness, limnological characteristics and climatic variables for 109 lakes across five regions of China: East region, Northeast region, Southwest region, North‐Northwest region, and the Tibetan Plateau. Correlation analyses, regression models and a general linear model were used to explore the patterns of fish species richness. Results At the national scale, lake altitude, energy availability (potential evapotranspiration, PET) and lake area explained 79.6% of the total variation of the lake fish species richness. The determinants of the fish richness pattern varied among physiographic regions. Lake area was the strongest predictor of fish species richness in the East and Southwest lakes, accounting for 22.2% and 82.9% of the variation, respectively. Annual PET explained 68.7% of the variation of fish richness in the Northeast lakes. Maximum depth, mineralization degree, and lake area explained 45.5% of the fish variation in the lakes of the North‐Northwest region. On the Tibetan Plateau, lake altitude was the first predictor variable, interpreting 32.2% of the variation. Main conclusions Lake altitude was the most important factor explaining the variation of fish species richness across China's lakes, and accounted for 74.5% of the variation. This may stem in part from the fact that the lakes investigated in our study span the largest altitudinal range anywhere in the world. The effects of the lake altitude on fish species richness can be separated into direct and indirect aspects due to its collinearity with PET. We also found that the fish diversity and its determinants were scale‐dependent. Fish species richness was probably energy‐determined in the cold region, while it was best predicted by the lake area in the relatively geologically old region. The independent variables we used only explained a small fraction of the variations in the lake fish species richness in East China and the Tibetan Plateau, which may be due to the effects of human activity and historical events, respectively.     

基因组学: 理解植物入侵性的重要工具

入侵植物基因组学是一个新兴的研究领域, 它利用基因组学方法研究与植物入侵性相关的分子基础和表达调控机制, 甄别入侵性基因型, 进而在基因组水平上揭示外来种入侵性产生和进化的分子机制。本文扼要综述了可用于植物入侵生物学研究的主要基因组学方法, 包括比较基因组学、群体基因组学和表观基因组学等方法; 运用基因组学技术研究入侵植物除草剂抗性和根状茎发育的分子基础已取得了重要进展。然而, 入侵植物基因组学仍处于发展初期, 选择理想的入侵植物模式种, 建立入侵性研究的模式系统, 是当前亟待解决的问题。本文还提出了入侵植物基因组学研究值得关注的几个发展方向, 包括基因组信息的完善、不同环境条件下入侵植物的分子响应机制以及入侵性的系统生物学研究等。     

Diversity–invasibility relationships across multiple scales in disturbed forest understoreys

Non-native plant species richness may be either negatively or positively correlated with native species due to differences in resource availability, propagule pressure or the scale of vegetation sampling. We investigated the relationships between these factors and both native and non-native plant species at 12 mainland and island forested sites in southeastern Ontario, Canada. In general, the presence of non-native species was limited: <20% of all species at a site were non-native and non-native species cover was <4% m⁻² at 11 of the 12 sites. Non-native species were always positively correlated with native species, regardless of spatial scale and whether islands were sampled. Additionally, islands had a greater abundance of non-native species. Non-native species richness across mainland sites was significantly negatively correlated with mean shape index, a measure of the ratio of forest edge to area, and positively correlated with the mean distance to the nearest forest patch. Other factors associated with disturbance and propagule pressure in northeastern North America forests, including human land use, white-tailed deer populations, understorey light, and soil nitrogen, did not explain non-native richness nor cover better than the null models. Our results suggest that management strategies for controlling non-native plant invasions should aim to reduce the propagule pressure associated with human activities, and maximize the connectivity of forest habitats to benefit more poorly dispersed native species.     

The abiotic and biotic factors limiting establishment of predatory fishes at their expanding northern range boundaries in Ontario,Canada

There is a poor understanding of the importance of biotic interactions in determining species distributions with climate change. Theory from invasion biology suggests that the success of species introductions outside of their historical ranges may be either positively (biotic acceptance) or negatively (biotic resistance) related to native biodiversity. Using data on fish community composition from two survey periods separated by approximately 28 years during which climate was warming, we examined the factors influencing the establishment of three predatory centrarchids: Smallmouth Bass (Micropterus dolomieu), Largemouth Bass (M. salmoides), and Rock Bass (Ambloplites rupestris) in lakes at their expanding northern range boundaries in Ontario. Variance partitioning demonstrated that, at a regional scale, abiotic factors play a stronger role in determining the establishment of these species than biotic factors. Pairing lakes within watersheds where each species had established with lakes sharing similar abiotic conditions where the species had not established revealed both positive and negative relationships between the establishment of centrarchids and the historical presence of other predatory species. The establishment of these species near their northern range boundaries is primarily determined by abiotic factors at a regional scale; however, biotic factors become important at the lake‐to‐lake scale. Studies of exotic species invasions have previously highlighted how spatial scale mediates the importance of abiotic vs. biotic factors on species establishment. Our study demonstrates how concepts from invasion biology can inform our understanding of the factors controlling species distributions with changing climate.     

Investigating Support for Management of the Pet Trade Invasion Risk

The non-native pet trade contributes directly to species invasions, thereby threatening wildlife. Biological invasions influence environmental change, resulting in species extinctions and biodiversity loss. To mitigate the pet trade invasion risk, interventions are required to prevent trade in non-native animals with high invasion potential, impulse or ill-informed purchases of non-native pets by individuals who may release these animals, and the deliberate release of non-native animals by pet owners. Interventions are also required to prevent the establishment of non-native animals that have been released by pet owners (e.g., euthanasia). The successful implementation of these interventions depends on the support of pet owners and the public in the form of political support for, and compliance with, interventions. In 2017–2018, using both mail and online surveys, we measured the support of 1,171 members of the public and 550 owners of non-native pets in Florida, USA, for 7 different interventions to mitigate the pet trade invasion risk, and we investigated determinants of this support. We found that individuals' support for interventions depended on their concern related to the invasion risks associated with the pet trade, trust in government to manage the pet trade, perceptions of how effective interventions would be in mitigating the pet trade invasion risk, and demographic characteristics. Support for interventions differed across pet owners and the public. Educating pet owners about the traits and cost of care for non-native animals and providing them with options to relinquish unwanted pets may reduce the pet trade invasion risk. Engaging the pet trade in the design of interventions to mitigate invasion risks is likely important to attain voluntary compliance with these interventions. The effectiveness of interventions also depends on enforcement by agencies. Implementing interventions that effectively reduce the pet trade invasion risk is important to protect native and endangered wildlife. © 2020 The Wildlife Society.     

Life-history traits of non-native fishes in Iberian watersheds across several invasion stages: a first approach

Freshwater ecosystems are seriously imperiled by the spread of non-native fishes thus establishing profiles of their life-history characteristics is an emerging tool for developing conservation and management strategies. We did a first approach to determine characteristics of successful and failed non-native fishes in a Mediterranean-climate area, the Iberian Peninsula, for three stages of the invasion process: establishment, spread and integration. Using general linear models, we established which characteristics are most important for success at each invasion stage. Prior invasion success was a good predictor for all the stages of the invasion process. Biological variables relevant for more than one invasion stage were maximum adult size and size of native range. Despite these common variables, all models produced a different set of variables important for a successful invasion, demonstrating that successful invaders have a combination of biological traits that may favor success at all invasion stages. However, some differences were found in relation to published studies on fish invasions in other Mediterranean-climate areas, suggesting that characteristics of the recipient ecosystem are as relevant as the characteristics of the invading species.     

Island properties dominate species traits in determining plant colonizations in an archipelago system

The extrinsic determinants hypothesis emphasizes the essential role of environmental heterogeneity in species’ colonization. Consequently, high resident species diversity can increase community susceptibility to colonizations because good habitats may support more species that are functionally similar to colonizers. On the other hand, colonization success is also likely to depend on species traits. We tested the relative importance of environmental characteristics and species traits in determining colonization success using census data of 587 vascular plant species collected about 70 yr apart from 471 islands in the archipelago of SW Finland. More specifically, we explored potential new colonization as a function of island properties (e.g. location, area, habitat diversity, number of resident species per unit area), species traits (e.g. plant height, life-form, dispersal vector, Ellenberg indicator values, association with human impact), and species’ historical distributions (number of inhabited islands, nearest occurrence). Island properties and species’ historical distributions were more effective than plant traits in explaining colonization outcomes. Contrary to the extrinsic determinants hypothesis, colonization success was neither associated with resident species diversity nor habitat diversity per se, although colonization was lowest on sparsely vegetated islands. Our findings lead us to propose that while plant traits related to dispersal and establishment may enhance colonization, predictions of plant colonizations primarily require understanding of habitat properties and species’ historical distributions.     

Fish species introductions provide novel insights into the patterns and drivers of phylogenetic structure in freshwaters

Despite long-standing interest of terrestrial ecologists, freshwater ecosystems are a fertile, yet unappreciated, testing ground for applying community phylogenetics to uncover mechanisms of species assembly. We quantify phylogenetic clustering and overdispersion of native and non-native fishes of a large river basin in the American Southwest to test for the mechanisms (environmental filtering versus competitive exclusion) and spatial scales influencing community structure. Contrary to expectations, non-native species were phylogenetically clustered and related to natural environmental conditions, whereas native species were not phylogenetically structured, likely reflecting human-related changes to the basin. The species that are most invasive (in terms of ecological impacts) tended to be the most phylogenetically divergent from natives across watersheds, but not within watersheds, supporting the hypothesis that Darwin''s naturalization conundrum is driven by the spatial scale. Phylogenetic distinctiveness may facilitate non-native establishment at regional scales, but environmental filtering restricts local membership to closely related species with physiological tolerances for current environments. By contrast, native species may have been phylogenetically clustered in historical times, but species loss from contemporary populations by anthropogenic activities has likely shaped the phylogenetic signal. Our study implies that fundamental mechanisms of community assembly have changed, with fundamental consequences for the biogeography of both native and non-native species.     

Global tests of regional effect on species richness of vascular plants and terrestrial vertebrates

Determining the effects of regional and contemporary factors on large-scale patterns in species richness has been a fundamental question in modern ecology and biogeography. However, few studies have examined effects of historical and regional factors on species richness at the global scale, and conclusions are often inconsistent or controversial. Here, I use a comprehensive dataset to examine regional effects on species richness of vascular plants and four taxa of terrestrial vertebrates (mammals, birds, reptiles, and amphibians) in the same set of sample units (ecoregions) in seven biogeographic realms across the globe. The same spatial scale and the same set of environmental variables, which are thought to influence large-scale patterns in species richness of vascular plants and terrestrial vertebrates, are used for all the five taxa. Species richness of each taxon is compared across biogeographic realms. Regional effect on species richness has been found for all the five taxa. Of the 90 realm-pair comparisons for the five taxa between observed richness of a region and the richness of the region predicted by the richness–environment relationship derived from the data of another region, 74 (82.2%) showed significant differences between observed and predicted species richness, indicating that a species richness–environment relationship developed for one region cannot accurately predict species richness in other regions of similar environments.     

Understanding the establishment success of non-indigenous fishes: lessons from population genetics

During the last 10 years, an increasing number of studies have explored evolutionary aspects of biological invasions. It is becoming increasingly clear that evolutionary processes play an important role during the establishment of non-native species. Genetic drift during the colonization process followed by strong selection imposed through a change in biotic conditions and co-evolutionary disequilibrium set the conditions for rapid evolutionary change in introduced populations. Different hypotheses, which have been proposed to explain how evolutionary and genetic processes, can facilitate invasiveness are explored and their relevance for fish invasions is discussed. Empirical evidence increasingly suggests that admixture after multiple introductions, hybridization between native and non-native species and enemy release can all catalyse the evolution of invasiveness. A number of studies also suggest that genetic bottlenecks might represent less of genetic paradox than previously thought. Much of the theoretical developments and empirical evidence concerning the importance of evolution during biological invasions has been provided from studies on invasive plants. Despite their prominence, fish invasions have received little attention from evolutionary biologists. Recent advances in population genetic analysis such as non-equilibrium methods and genomic techniques such as microarray technology provide suitable tools to address such issues.