The evolutionary consequences of biological invasions

A major challenge of invasion biology is the development of a predictive framework that prevents new invasions. This is inherently difficult because different biological characteristics are important at the different stages of invasion: opportunity/transport, establishment and spread. Here, we draw from recent research on a variety of taxa to examine the evolutionary causes and consequences of biological invasions. The process of introduction may favour species with characteristics that promote success in highly disturbed, human-dominated landscapes, thus exerting novel forms of selection on introduced populations. Moreover, evidence is accumulating that multiple introductions can often be critical to the successful establishment and spread of introduced species, as they may be important sources of genetic variation necessary for adaptation in new environments or may permit the introduction of novel traits. Thus, not only should the introduction of new species be prevented, but substantial effort should also be directed to preventing the secondary introduction of previously established species (and even movement of individuals among introduced populations). Modern molecular techniques can take advantage of genetic changes postintroduction to determine the source of introduced populations and their vectors of spread, and to elucidate the mechanisms of success of some invasive species. Moreover, the growing availability of genomic tools will permit the identification of underlying genetic causes of invasive success.     

网络理论在入侵生物学中的应用研究现状

生物入侵是一个动态有序的过程,其发生和危害存在异质性,通常由来源地、入侵地和它们之间的连接构成的系统中的自然、生物、社会等因素所决定。网络理论是研究复杂系统的一种新方法,本质是从复杂的信息中抽象出规律、揭示系统的结构特征共性。近20年,网络理论已被应用于生物入侵研究。本研究综述了网络理论在生物入侵研究中的应用进展,明确了主要的研究方向和前沿热点,认为:2000年以来国际上已开展的研究集中在评估外来物种入侵风险和入侵后对生态系统影响2个方面;外来物种随运输网络入侵的风险评估和景观连接性对入侵物种扩散的影响、外来物种入侵对本地物种间互作网络的影响及生态群落可入侵性是网络理论应用的热点;研究热点具有明显的时间发展特征,2013年以前多是对生态系统的影响,近10年来主要是风险评估。我国利用网络理论研究外来物种入侵较少且集中于对生态系统的危害,未来应加强对外来物种的时空定量传入和扩散风险评估,为我国制定和提升外来入侵物种早期监测预警、阻止新的入侵、抑制进一步扩散的管理措施提供依据。     

Assessing the risk of freshwater fish introductions into the Iberian Peninsula

1. Preventing the introduction of species likely to become invaders is the best management option to deal with biological invasions. A data set consisting of native, introduced and species not currently present in Iberian Peninsula (n = 167 species) was used to identify freshwater fish species that are likely to be introduced and become successful invaders in the near future. 2. Principal component analysis (PCA) of species traits was used to determine species likely to be introduced, assuming that the traits of species introduced in the future will resemble those of previously introduced species. The likelihood of introduction was calculated as the proportion of neighbour species (in the space defined by the PCA) that have been introduced to the Iberian Peninsula and, together with metrics related to different stages of invasion, was used to construct a region‐specific risk index (Iberian risk index). 3. Introduced species had higher index values compared with native species or species currently absent from the region. The Iberian risk index was positively related to the results of an independent risk analysis for freshwater fish as well as to the geographical spread of species previously introduced to the Iberian Peninsula. 4. Iberian risk index values were used to establish a cut‐off value for estimating the probability of a successful invasion. This threshold value was used to construct a list of 20 species to be included in a ‘watch list’ to prevent freshwater fish invasions in the Iberian Peninsula.     

淡水鱼类入侵种的分布、入侵途径、机制与后果

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

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

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

The risk of invasion by angiosperms peaks at intermediate levels of human influence

Biological invasions are a growing threat to biodiversity. The control and eradication of exotic species established in earnest are of limited success despite high financial investments. Anticipating biological invasions based on species’ suitabilities is a cost-effective strategy given it helps identifying areas where exotic species can prosper, which can then translate in improving management and conservation efforts. Based on information from 191 invasive angiosperm species worldwide, we used ecological niche models to identify areas at high risk of invasion (cumulative predicted distribution of invasive species) in Mexico. Further, we explored the importance of bioclimatic and human influence variables as drivers of the distribution of invasive species and analyzed the status of the currently recognized priority conservation sites in Mexico. We found that areas with intermediate human activity scores had a high risk of invasion. Additionally, we found that many of the current priority conservation sites in Mexico had a high risk of invasion. Our findings contribute to disentangling the factors that drive environment susceptibility to invasions and urge management strategies to minimize the impacts of biological invasions in priority conservation sites.     

Human Agency in Biological Invasions: Secondary Releases Foster Naturalisation and Population Expansion of Alien Plant Species

The human mediation of biological invasions is still an underestimated phenomenon. This paper attempts to show that introductions on varying spatial scales may strongly foster invasions throughout the whole invasion process. As shown by data from central Europe, invasions frequently result from an interplay of biological and anthropogenic mechanisms. The latter, however, cannot be explained nor predicted by ecological rules. This may be an important reason for the limited predictability of invasions. Initial introductions from a donor to a new range are here distinguished from following secondary releases within the new range. The rate of naturalisation is higher in deliberately introduced plants as compared to accidental introductions. Due to higher numbers of accidental introductions, such species contribute significantly to the pool of naturalised species. Secondary releases of alien species are frequently made over long periods subsequent to the initial introduction. They may mimic demographic and dispersal processes that lead to population growth and range expansion. They also offer a pathway to overcome spatial isolation in species whose propagules are not naturally moved long distances. This even holds for most of Germany's noxious alien plant species. Secondary releases may thus promote invasions even beyond the threshold of naturalisation. In consequence, attempts at prevention should focus on secondary releases as well as on initial introductions. In the last section of the paper, the final invasion stage subsequent to naturalisation is shown as a multi-scale phenomenon. In consequence, the classification of a species as 'invasive' depends on the perspective chosen. Using different biologically or anthropocentrically based approaches leads to sub-sets of alien species that overlap only partially. In conclusion, the term `invasive' should preferably be used in a broader sense to describe the entire invasion process. This revised version was published online in July 2006 with corrections to the Cover Date.     

Niche conservatism among non‐native vertebrates in Europe and North America

Niche conservatism, the hypothesis that niches remain constant through time and space, is crucial for the study of biological invasions as it underlies native‐range based predictions of invasion risk. Niche changes between native and non‐native populations are increasingly reported. However, it has been argued that these changes arise mainly because in their novel range, species occupy only a subset of the environments they inhabit in their native range, and not because they expand into environments entirely novel to them. Here, using occurrences of 29 vertebrate species native to either Europe or North America and introduced into the other continent, we assess the prevalence of niche changes between native and non‐native populations and assess whether the changes detected are caused primarily by native niche unfilling in the non‐native range rather than by expansion into novel environments. We show that niche overlap between native and non‐native populations is generally low because of a large degree of niche unfilling in the non‐native range. This most probably reflects an ongoing colonization of the novel range, as niche changes were smaller for species that were introduced longer ago and into a larger number of locations. Niche expansion was rare, and for the few species exhibiting larger amounts of niche overlap, an unfilling of the niche in the native range (e.g. through competition or dispersal limitations) is the most probable explanation. The fact that for most species, the realized non‐native niche is a subset of the realized native niche allows native‐range based niche models to generate accurate predictions of invasion risk. These results suggest that niche changes arising during biological invasions are strongly influenced by propagule pressure and colonization processes, and we argue that introduction history should be taken into account when evaluating niche conservatism in the context of biological invasions.     

Current and projected future risks of freshwater fish invasions in China

Biological invasions are a primary threat to global biodiversity, supporting mounting calls for the development of early‐warning systems to manage existing and emerging invaders. Here, we evaluated the geographical pattern of invasion risks of currently established and potentially emerging nonnative freshwater fishes in China by jointly considering the threats of introduction and establishment under climate change. Introduction threats were estimated according to proxies of human activities and propagule pressure for two primary pathways (aquaculture or ornamental). Establishment threats for 51 current and 64 potential invaders (based on whether having established or not self‐sustaining populations) were assessed using an ensemble of species distribution models under current (1960–1990) and future [2041–2060 (2050s) and 2061–2080 (2070s)] climate scenarios. Geographical patterns of invasion risk were then assessed by overlaying the threats of introduction and establishment for each species group both in present‐day and in the future. We found that eastern China displayed the highest threat of introduction. By contrast, southeastern and northwestern regions were identified as the most suitable for the establishment of both current and potential invaders. Under a changing climate, 83 out of 115 species displayed an increase in habitat suitability, resulting in an overall increase of 4.8% by 2050s and 7.1% by 2070s in the extent of suitable habitat for nonnative freshwater fishes. Taken together, invasion risk was found to be highest in southeastern China and lowest in the Tibet Plateau. Our research highlights the importance of assessing invasion risk by integrating the threats associated with the introduction and establishment stages. In particular, our findings revealed convergent patterns of invasion risk between current and potential nonnative freshwater fishes under climate change. Geographic patterns in hotspots of existing and emerging invasions provide critical insights to guide the allocation of resources to monitor and control existing and emerging invasions in China.     

The negative ecological impacts of a globally introduced species decrease with time since introduction

While there is a long‐history of biological invasions and their ecological impacts have been widely demonstrated across taxa and ecosystems, our knowledge on the temporal dynamic of these impacts remains extremely limited. Using a meta‐analytic approach, we investigated how the ecological impacts of non‐native brown trout (Salmo trutta), a model species with a 170‐year‐long and well‐documented history of intentional introductions across the globe, vary with time since introduction. We first observed significant negative ecological impacts immediately after the species introduction. Second, we found that the negative ecological impacts decrease with time since introduction and that the average ecological impacts become nonsignificant more than one century after introduction. This pattern was consistent across other ecological contexts (i.e., geographical location, levels of biological organization, and methodological approach). However, overall negative ecological impacts were more pronounced at the individual and population levels and in experimental studies. While the mechanisms leading to this decrease remain to be determined, our results indicate that rapid response of native organisms (e.g. adaptation, but also local extinction) may play an important role in this dynamic. Changes in native species traits and local extinction can have important conservation implications. Therefore, we argue that the decline of the negative ecological impacts over time should not be used as an argument to neglect the negative impacts of biological invasions.     

A review of global instruments to combat invasive alien species in forestry

Although impacts of biological invasions may be local, at least at first, the causes of introduction are mostly international. Through trade and transport pathways, countries both send and receive non-native species. There are numerous international and regional instruments, binding and nonbinding, which have been developed to deal with the problem of the movement of alien invasive species, however there are gaps in the current international framework. Global goals in the management of forestry-related threats from invasive alien species should include making best use of existing regulatory frameworks, investing more into global research initiatives, and targeting existing tools and resources more effectively. Given the lack of resources for many developing countries to undertake research, conduct risk assessments and implement quarantine measures, there is a need for regional and global support for countries that lack sufficient resources to implement effective phytosanitary systems.     

Historical introduction,geographical distribution,and biological characteristics of alien plants in China

Using the published literature and records, this study investigated the historical introduction, geographical distribution, and biological characteristics of 404 alien plants in 32 provinces (including municipalities) in China. The results showed that three fifths of the alien plants was introduced for intentional purposes, and the introduction of alien plants increased with time from 139 BC to the current time, especially during historical events that played an important part in the process of introduction. The geographical distribution of alien plant species tended to decrease from the south and the east to the north and the west. Annual average precipitation (Y = 7.51X + 7.05, R² = 0.67) and temperature (Y = 0.07X + 41.54, R² = 0.67) had a linear relationship with alien plant introduction throughout China. Furthermore, population density and economic conditions also affected and promoted plant invasions in China. The life forms were well adapted to regional precipitation and temperature, but different life forms of alien plants were not consistent with the distribution tendency based on the quantity of alien plants. There was a higher percentage of annual and biennial plants in the northern provinces (e.g. 66.7 and 15.7% in Inner Mongolia), whereas there were more perennial and woody plant species in the southern provinces (e.g. 37.0 and 21.2% in Hainan). Family characteristics could not accurately predict plant invasions; however, predictions based on genera were acceptable. In addition, the origin of alien plants can also predict the distribution and potential risk of invasions. Thus, our study investigated the factors affecting plant invasions in order to provide information on the prevention and control of alien plants.     

Global trade will accelerate plant invasions in emerging economies under climate change

Trade plays a key role in the spread of alien species and has arguably contributed to the recent enormous acceleration of biological invasions, thus homogenizing biotas worldwide. Combining data on 60‐year trends of bilateral trade, as well as on biodiversity and climate, we modeled the global spread of plant species among 147 countries. The model results were compared with a recently compiled unique global data set on numbers of naturalized alien vascular plant species representing the most comprehensive collection of naturalized plant distributions currently available. The model identifies major source regions, introduction routes, and hot spots of plant invasions that agree well with observed naturalized plant numbers. In contrast to common knowledge, we show that the ‘imperialist dogma,’ stating that Europe has been a net exporter of naturalized plants since colonial times, does not hold for the past 60 years, when more naturalized plants were being imported to than exported from Europe. Our results highlight that the current distribution of naturalized plants is best predicted by socioeconomic activities 20 years ago. We took advantage of the observed time lag and used trade developments until recent times to predict naturalized plant trajectories for the next two decades. This shows that particularly strong increases in naturalized plant numbers are expected in the next 20 years for emerging economies in megadiverse regions. The interaction with predicted future climate change will increase invasions in northern temperate countries and reduce them in tropical and (sub)tropical regions, yet not by enough to cancel out the trade‐related increase.     

Invasive species in Southeast Asia: the knowledge so far

This review deals with alien species invasion in Southeast Asia, an important conservation and management concern in the region. I report on the current and potential future impacts of biological invasions on biodiversity in Southeast Asia. Current knowledge of the invasive species in Southeast Asia is mostly based on anecdotal observations. Nevertheless, I attempt to compile existing empirical evidence on the negative effects of the biological invaders found in the region. These impacts include displacement of native biota, modification of ecosystems, hybridization, environmental disturbance, and economic loss. Any effective counter-measure will need to involve a multi-national strategy, yet such measure is challenging due to a broad spectrum of political and economic development models among the Southeast Asian countries. An overview of the taxonomic structure of the invasive species in Southeast Asia shows that the invasive plant and fish are the most represented taxonomic groups in all countries. The current research effort in invasion ecology from Southeast Asia is not being up to international standard in comparison to other regions, and the absence of recent international journal articles on invasive plant species reveals the biases in biological invasion-related research. The lack of research capacity and financial support from governments, and the inability to disseminate scholarly data in international journals are the possible reasons for the dearth of research literature on biological invasions from the region. Finally, a forward-looking agenda for the region should include improving the quality and quantity of biological invasion research; adopting a tough approach to the illegal release of wildlife; and applying multi-national strategies that integrate data sharing, prioritization, public awareness, policy work, capacity building, conservation actions and surveillance.     

城市绿地外来物种风险分析体系构建及其在上海世博会管理中的应用

外来物种风险分析是防止生物入侵的有效手段之一。本文按照风险识别、风险评估和风险管理3个阶段,构建了城市绿地外来物种风险分析体系。文中提出了4个层次、26个指标构成风险评估指标体系,此体系囊括了城市绿地外来物种的传入、定殖、扩散、危害等入侵风险形成的基本要素,并规范了风险指数的计算方法。以2010年上海世博会引进日本景观苗木可能携带的外来物种为对象,对该体系在生产实践中进行了应用。结果表明:高风险物种共7种,涉及害虫4种、植物病原微生物2种、植物线虫1种;中风险物种共10种,涉及害虫3种、植物病原微生物4种、植物线虫3种;低、极低风险物种各1种。根据风险分析结果,对以上物种提出了有针对性的风险管理措施。实践表明,该风险分析体系实用性强,在上海世博会植物引种过程中为防止外来物种入侵起到了较好的预警效果,为管理者提供了有价值的决策参考,有力保障了上海世博会期间的生态安全。     

Exploiting Allee effects for managing biological invasions

Biological invasions are a global and increasing threat to the function and diversity of ecosystems. Allee effects (positive density dependence) have been shown to play an important role in the establishment and spread of non-native species. Although Allee effects can be considered a bane in conservation efforts, they can be a benefit in attempts to manage non-native species. Many biological invaders are subject to some form of an Allee effect, whether due to a need to locate mates, cooperatively feed or reproduce or avoid becoming a meal, yet attempts to highlight the specific exploitation of Allee effects in biological invasions are surprisingly unprecedented. In this review, we highlight current strategies that effectively exploit an Allee effect, and propose novel means by which Allee effects can be manipulated to the detriment of biological invaders. We also illustrate how the concept of Allee effects can be integral in risk assessments and in the prioritization of resources allocated to manage non-native species, as some species beset by strong Allee effects could be less successful as invaders. We describe how tactics that strengthen an existing Allee effect or create new ones could be used to manage biological invasions more effectively.     

生物入侵的危害与防治对策

生物入侵是一个世界范围的生态学现象。入侵种通过竞争、捕食、改变生境和传播疾病等方式对本地种及其系统产生影响。生物入侵的危害表现为：造成巨大的经济损失,仅美国每年因外来种入侵造成的经济损失近1370亿美元;威胁到人类的健康和生存。成千上万的人被外来种传染疾病以致死亡;引起严重的社会恐慌和动荡,人们寝食不安;改变了生态系统的结构和功能,全球自然灾害频频爆发;导致生物多样性的急剧下降,威胁到子孙后代的生存和发展。防治生物入侵有3条途径：实行全面检疫,阻止外来种的偶然入侵;采取全面的生态评估和监测,防范引进品种的入侵灾难;对已入侵的外来种采用机械法、化学法和生物防治法进行根除和控制,应用生物防治法、筛选天敌和对其进行危害评估时要特别慎重。     

Parasites as Drivers and Passengers of Human-Mediated Biological Invasions

We provide an overview of the current state of knowledge of parasites in biological invasions by alien species. Parasites have frequently been invoked as drivers of invasions, but have received less attention as invasion passengers. The evidence to date that parasites drive invasions by hosts is weak: while there is abundant evidence that parasites have effects in the context of alien invasions, there is little evidence to suggest that parasites have differential effects on alien species that succeed versus fail in the invasion process. Particular case studies are suggestive but not yet informative about general effects. What evidence there is for parasites as aliens suggests that the same kind of factors determine their success as for non-parasites. Thus, availability is likely to be an important determinant of the probability of translocation. Establishment and spread are likely to depend on propagule pressure and on the environment being suitable (all necessary hosts and vectors are present); the likelihood of both of these dependencies being favourable will be affected by traits relating to parasite life history and demography. The added complication for the success of parasites as aliens is that often this will depend on the success of their hosts. We discuss how these conclusions help us to understand the likely effects of parasites on the success of establishing host populations (alien or native).

     

Addressing the threat to biodiversity from botanic gardens

Increasing evidence highlights the role that botanic gardens might have in plant invasions across the globe. Botanic gardens, often in global biodiversity hotspots, have been implicated in the early cultivation and/or introduction of most environmental weeds listed by IUCN as among the worst invasive species worldwide. Furthermore, most of the popular ornamental species in living collections around the globe have records as alien weeds. Voluntary codes of conduct to prevent the dissemination of invasive plants from botanic gardens have had limited uptake, with few risk assessments undertaken of individual living collections. A stronger global networking of botanic gardens to tackle biological invasions involving public outreach, information sharing and capacity building is a priority to prevent the problems of the past occurring in the future.