A reassessment of historical records of avian introductions to Australia: no case for propagule pressure

Introduced species are widely believed to represent a significant threat to conservation of biological diversity. A better understanding of the ecological factors associated with successful species establishment should lead to improved management and mitigation of these introductions. The “propagule pressure hypothesis”, implying a greater chance of successful introduction with greater numbers introduced, has been widely accepted as a principal ecological factor in explaining establishment of exotic species. The historical record of bird introductions in a few locations, including the state of Victoria in Australia, has been advanced as the principal quantitative support for the hypothesis. We compiled lists of bird species introductions into Australia from several sources, and discovered inconsistencies in the records of introductions. In a series of comparisons, we found that the historical record of passerine introductions to Australia does not support the propagule pressure hypothesis unless superfluous introductions of already successful species are included. An additional problem with previous analyses is the inclusion of unsuccessful haphazard cage escapes.     

New parasites and predators follow the introduction of two fish species to a subarctic lake: implications for food-web structure and functioning

Introduced species can alter the topology of food webs. For instance, an introduction can aid the arrival of free-living consumers using the new species as a resource, while new parasites may also arrive with the introduced species. Food-web responses to species additions can thus be far more complex than anticipated. In a subarctic pelagic food web with free-living and parasitic species, two fish species (arctic charr Salvelinus alpinus and three-spined stickleback Gasterosteus aculeatus) have known histories as deliberate introductions. The effects of these introductions on the food web were explored by comparing the current pelagic web with a heuristic reconstruction of the pre-introduction web. Extinctions caused by these introductions could not be evaluated by this approach. The introduced fish species have become important hubs in the trophic network, interacting with numerous parasites, predators and prey. In particular, five parasite species and four predatory bird species depend on the two introduced species as obligate trophic resources in the pelagic web and could therefore not have been present in the pre-introduction network. The presence of the two introduced fish species and the arrival of their associated parasites and predators increased biodiversity, mean trophic level, linkage density, and nestedness; altering both the network structure and functioning of the pelagic web. Parasites, in particular trophically transmitted species, had a prominent role in the network alterations that followed the introductions.     

Life history responses to variations in temperature by the marine amphipod <Emphasis Type="Italic">Eogammarus possjeticus</Emphasis> (Gammaridae) and their implications for productivity in aquaculture

The invasion of tilapia can result in substantial impacts on native communities. Thus, understanding the spatial dynamics of invasions may help prevent future introductions and mitigate impacts. This study estimated the environmentally suitable areas for occurrence of eight tilapia species (genera Coptodon, Oreochromis, Pelmatolapia, and Sarotherodon) in the Americas and their invasive potential using Ecological Niche Models (ENMs). The United States is the most invaded country, receiving all tilapia species. In South America, the southeast and south regions of Brazil are highlighted as the areas where two species are concentrated. The ENMs predicted that all tilapia species have high invasive potential in the Americas, and despite having more tilapias in North America, South and Central Americas are more susceptible to tilapia invasion. All South American basins were predicted to harbor tilapia species that have not yet arrived on the subcontinent. Our study evidences the need to implement management measures and governmental policies in the Americas to deal with problems caused by tilapia introductions. In North America, the focus is on the control of tilapia populations and in Central and South America priority should be given to contention of introduction processes.     

153 Invasive Macroalgae on Tropical Reefs: Impacts, Interactions, Mechanisms and Management

Histories, patterns of introduction, management of impacts and predictable futures? Ecological impacts of weedy introduced and native marine algae have set Hawai'i apart from elsewhere in the tropics and offers a new show case for macroalgal blooms. Partly because of our isolation, impacts of non-indigenous species have been clearly identified, in some cases almost as quickly as introductions have occurred to Hawai'i. While hull fouling or intentional introductions may have been initial mechanisms for macroalgal introductions, spread among the Hawaiian Islands is not necessarily linked to the vector for arrival. Further, impacts of non-indigenous species are also not fully predictable, prior to introduction. This situation leads to challenging gaps in management strategies because few generalizations about the roles of nutrients or herbivory as drivers for macroalgal blooms can be supported at this time. Weedy native species represent a wide range of alternate impacts with other apparent combinations of forcing functions. Case histories for the most significant non-indigenous and weedy native algae will be presented with emphasis on potential new criteria to assess ecological impacts and provide resource biologists with critical new tools for the management of reef ecosystems.     

Bayesian Reconstruction of Disease Outbreaks by Combining Epidemiologic and Genomic Data

Recent years have seen progress in the development of statistically rigorous frameworks to infer outbreak transmission trees (“who infected whom”) from epidemiological and genetic data. Making use of pathogen genome sequences in such analyses remains a challenge, however, with a variety of heuristic approaches having been explored to date. We introduce a statistical method exploiting both pathogen sequences and collection dates to unravel the dynamics of densely sampled outbreaks. Our approach identifies likely transmission events and infers dates of infections, unobserved cases and separate introductions of the disease. It also proves useful for inferring numbers of secondary infections and identifying heterogeneous infectivity and super-spreaders. After testing our approach using simulations, we illustrate the method with the analysis of the beginning of the 2003 Singaporean outbreak of Severe Acute Respiratory Syndrome (SARS), providing new insights into the early stage of this epidemic. Our approach is the first tool for disease outbreak reconstruction from genetic data widely available as free software, the R package outbreaker. It is applicable to various densely sampled epidemics, and improves previous approaches by detecting unobserved and imported cases, as well as allowing multiple introductions of the pathogen. Because of its generality, we believe this method will become a tool of choice for the analysis of densely sampled disease outbreaks, and will form a rigorous framework for subsequent methodological developments.     

Evidence of a climatic niche shift following North American introductions of two crane flies (Diptera; genus Tipula)

Ecological niche models assume a species niche should be conserved over space and time. Increasingly, studies have determined that niche shifts may occur during biological invasion events. The aim of this study is to examine niche conservation for two invasive crane flies, Tipula oleracea Linnaeus and Tipula paludosa Meigen, after introductions into North America. These species have broadly sympatric invasive distributions but differ in time since introduction and dispersal abilities. As these factors may impact the area accessible to dispersal, I examined the impact of background area delineation on conclusions of niche conservation. Results indicated that alternative delineations of accessible area (i.e., background area) had no affect on measures of niche equivalence. Neither Tipula species was found to be occupying invasive niche space equivalent to that of their native ranges. Niche dissimilarity was found for both species, with results strongly impacted by the choice of background area. T. paludosa introductions displayed a niche shift across both invasive introductions when the model area drew climatic information from an area that buffered occurrences by 40 km. The eastern T. oleracea introduction displayed a niche shift when background information was drawn from within a 400 km buffered area. This study suggests that invasive populations may be displaying a niche shift when evaluated against one scale of background but conserved when evaluated against another scale. Dispersal limitations for T. oleracea in its eastern introduction and anthropogenic habitat associations for T. paludosa across both invasive introductions are indicated as causes for the observed niche shifts. The results of this study highlight the importance of carefully delineating the area accessible to invasive species in studies of niche conservation. Furthermore, it indicates that examining several spatial extents of background areas can be beneficial when examining niche conservation for species in non-equilibrium states.     

Predicting introduction, establishment and potential impacts of smallmouth bass

Aim The introduction of non‐indigenous species has resulted in wide‐ranging ecological and economic impacts. Predictive modelling of the introduction and establishment of non‐indigenous species is imperative to identify areas at high risk of invasion to effectively manage non‐indigenous species and conserve native populations. Smallmouth bass (Micropterus dolomieu), a warm water fish species native to central North America has negatively impacted native fish communities, including cyprinids and salmonid populations, as a result of intentional introductions. We predicted the introduction risk; species establishment based on habitat suitability; identified lakes at high risk of invasion; and finally assessed the consequential impacts on native salmon, trout and cyprinid populations. Location Ontario and British Columbia, Canada. Methods Classification tree and logistic regression models were developed and validated to predict the introduction and establishment of smallmouth bass for thousands of lakes. Results Densely human populated areas and larger lake surface areas successfully identify lakes associated with the introduction of smallmouth bass (introduction model) in British Columbia. Climate, lake morphology and water chemistry variables were the driving environmental parameters to define suitable smallmouth bass habitat (establishment model). A combination of the introduction and establishment model identified 138 lakes that are currently at risk in British Columbia to the introduction and establishment of smallmouth bass. Of these 138 high‐risk lakes, 95% of them contain at least one species of salmon, trout or cyprinid, thereby increasing the potential impact of an invasion by smallmouth bass. Main conclusions Our framework can be applied to other terrestrial and aquatic species to obtain a better understanding of the potential risk posed by a non‐indigenous species to an ecosystem. Furthermore, our methodology can be used to focus management efforts on areas at higher risk (e.g. number of potential releases, more favourable habitats) to control future introductions of non‐indigenous species, thereby conserving native populations.     

Intentionally introduced terrestrial invertebrates: patterns,risks, and options for management

Our understanding and management of pathways of alien species introductions has improved significantly in the past few years. However, little attention has been paid in most parts of the world to the risks posed by the intentional introduction of alien terrestrial invertebrates which are not intended for use in biological control. We review the species and pathways involved in this intentional trade, and discuss key factors that mediate different aspects of risk. A total of 20 different intentions for the introduction of terrestrial invertebrates were identified. Uses and trade patterns have changed over time and further changes are likely in the future. In particular, invertebrates used in the pet trade, and as human food and animal feed are likely to increase in relevance. We assess priorities for future research and regulation based on the perceived “risk” of the uses including propagule pressure, security of captivity and ease of regulation. Regarding risk assessment, we examine three options: (a) using an existing generic protocol developed for a broad range of taxa; (b) developing a new protocol, possibly by adapting a protocol developed for other taxa; and (c) adopting the approach applied for biological control, i.e. structured experiments and observations. This review highlights the diversity of uses and associated threats of intentional terrestrial invertebrate introductions. It provides recommendations on how to tackle and prevent related issues and can therefore serve as a guideline for future work. We argue that the most suitable option for risk assessment might depend on the type or organism and the level of knowledge of the organism, as well as the intended use.     

The genetic structure of raccoon introduced in Central Europe reflects multiple invasion pathways

Invasions of non-native species are of great concern as they have a devastating impact on native biodiversity and can also affect the economy of a region. Multiple introductions in several locations of a new range greatly promote the success of non-native species. The raccoon (Procyon lotor) is an omnivore whose native distribution extends from southern Canada to Panama. It has been successfully introduced in many European countries. We examined the microsatellite and mitochondrial diversity of raccoon populations in Central Europe (Germany, Poland, and Czech Republic) in order to determine their introduction sources and pathways as well as the factors affecting genetic structure in this invasive species. We found low diversity of the mtDNA control region and moderate diversity of microsatellite markers. Raccoon showed three hierarchic levels of genetic structure which separate at different levels sampled from Czech Republic, Germany and raccoon inhabiting two different habitats in Poland. In Poland the raccoon population was established through migration from Germany to Czech Republic. Analysis of the intensity of migration between two different habitat types indicated source-sink dynamics in the Polish populations of raccoons. Our results confirm the high intensity of the raccoon invasion in Central Europe and point to specific measures needed as part of an effective management strategy.     

Patterns of genetic diversity reveal multiple introductions and recurrent founder effects during range expansion in invasive populations of Geranium carolinianum (Geraniaceae)

Genetic diversity, and thus the adaptive potential of invasive populations, is largely based on three factors: patterns of genetic diversity in the species'' native range, the number and location of introductions and the number of founding individuals per introduction. Specifically, reductions in genetic diversity (‘founder effects'') should be stronger for species with low within-population diversity in their native range and few introductions of few individuals to the invasive range. We test these predictions with Geranium carolinianum, a winter annual herb native to North America and invasive in China. We measure the extent of founder effects using allozymes and microsatellites, and ask whether this is consistent with its colonization history and patterns of diversity in the native range. In the native range, genetic diversity is higher and structure is lower than expected based on life history traits. In China, our results provide evidence for multiple introductions near Nanjing, Jiangsu province, with subsequent range expansion to the west and south. Patterns of genetic diversity across China reveal weak founder effects that are driven largely by low-diversity populations at the expansion front, away from the introduction location. This suggests that reduced diversity in China has resulted from successive founder events during range expansion, and that the loss of genetic diversity in the Nanjing area was mitigated by multiple introductions from diverse source populations. This has implications for the future of G. carolinianum in China, as continued gene flow among populations should eventually increase genetic diversity within the more recently founded populations.     

Freshwater fish diversity in Algeria with emphasis on alien species

Little is known about freshwater fish diversity in Algeria, especially after the broad national program of introduction of exotic species applied for over 20 years. This paper is an attempt to describe the current situation emphasizing the characteristics of the various introductions of non-autochthonous species, their current status and their possible impacts. The freshwater fish fauna of Algeria is composed of 48 species belonging to 15 families. Twenty-one species are autochthonous, of which, three are endemic (Haplochromis desfontainii, Aphanius saourensis, Aphanius apodus), two are endangered (H. desfontainii, Aphanius iberus), and one is critically endangered (Anguilla anguilla). Twenty-seven species were introduced, of which, 18 never became established and 9 are established. Four species are reported for the first time: Abramis brama, Aspius aspius, Carassius carassius, Perca fluviatilis. Since 1860, 303 introduction events have been recorded at almost 107 different sites in Algeria. The number of introduction events per site was between 1 and 10. Most of the introduced fish are found in Oubéïra Lake (seven species). Aquaculture development was the main reason for fish introductions (37.0%). The five most often introduced species were Cyprinus carpio (86 records), Hypophthalmichthys molitrix (65 records), Aristichthys nobilis (51 records), Oreochromis niloticus niloticus (33 records), and Ctenopharyngodon idella (18 records). Since the adverse effects of introduced fish are risky and demonstrated in several countries, the adoption of the precautionary principle is recommended when new introductions are planned. It is important, therefore, to adopt regulations and procedures which will minimize the risks arising from introductions.     

Callosciurus squirrels: worldwide introductions,ecological impacts and recommendations to prevent the establishment of new invasive populations

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Species distribution models support the need of international cooperation towards successful management of plant invasions

To protect native biodiversity and habitats from the negative impacts of biological invasions, comprehensive studies and measures to anticipate invasions are required, especially across countries in a transfrontier context. Species distribution models (SDMs) can be particularly useful to integrate different types of data and predict the distribution of invasive species across borders, both for current conditions and under scenarios of future environmental changes. We used SDMs to test whether predicting invasions and potential spatial conflicts with protected areas in a transfrontier context, under current and future climatic conditions, would provide additional insights on the patterns and drivers of invasion when compared to models obtained from predictions for individual regions/countries (different modelling strategies). The framework was tested with the invasive alien plant Acacia dealbata in North of Portugal/NW Spain Euro-region, where the species is predicted to increase its distribution under future climatic conditions. While SDMs fitted in a transfrontier context and using “the national strategy (with Portugal calibration data) presented similar patterns, the distribution of the invasive species was higher in the former. The transfrontier strategy expectedly allowed to capture a more complete and accurate representation of the species’ niche. Predictions obtained in a transfrontier context are therefore more suitable to support resource prioritisation for anticipation and monitoring impacts of biological invasions, while also providing additional support for international cooperation when tackling issues of global change. Our proposed framework provided useful information on the potential patterns of invasion by A. dealbata in a transfrontier context, with an emphasis on protected areas. This information is crucial for decision-makers focusing on the prevention of invasions by alien species inside protected areas in a transfrontier context, opening a new way for collaborative management of invasions.     

Global introductions of salmon and trout in the genus <Emphasis Type="Italic">Oncorhynchus</Emphasis>: 1870–2007

The purpose of this review is to provide a global perspective on Oncorhynchus salmonine introductions and put-and-take fisheries based on modern stocking programs, with special emphasis on freshwater ecosystems. We survey the global introductions of nine selected salmonines of the genus Oncorhynchus: golden trout, cutthroat trout, pink salmon, chum salmon, coho salmon, masu/cherry salmon, rainbow trout/steelhead, sockeye salmon/kokanee, and chinook salmon. The information is organized on a geographical basis by continent, and then by species and chronology. Two different objectives and associated definitions of ‘success’ for introductions are distinguished: (a) seed introduction: release of individuals with the purpose of creating a wild-reproducing, self-sustaining population; and (b) put-and-take introduction: release of individuals with the purpose of maintaining some level of wild population abundance, regardless of wild reproduction. We identify four major phenomena regarding global salmonine introductions: (1) general inadequacy of documentation regarding introductions; (2) a fundamental disconnect between management actions and ecological consequences of introductions; (3) the importance of global climate change on success of previous and future introductions; and (4) the significance of aquaculture as a key uncertainty in accidental introductions. We conclude this review with a recognition of the need to terminate ongoing stocking programs for introduced salmonines worldwide.     

Using a unified invasion framework to characterize Africa’s first loricariid catfish invasion

This paper presents evidence of establishment of a loricariid population in the Nseleni River in South Africa and uses a unified framework to determine its invasion stage. Specimens were identified morphologically as Pterygioplichthys disjunctivus (Weber 1991), but genetic barcoding results indicated close association with specimens that may have a hybrid history. The species was introduced into South Africa via the pet trade and the first record of introduction into the wild was in 2004. Samples collected in 2011 and 2012 demonstrated that there were multiple length cohorts in the population including juveniles (12–130 mm total length TL) and large (>300 mm TL) adult fish. Gonadal assessment of adults demonstrated the presence of reproduction capable specimens. The concurrent occurrence of mature adults and juvenile fish demonstrated establishment. Locality records indicate that P. disjunctivus has already spread between two rivers through an inter basin water transfer. Using a unified framework for invasions this invasion was categorized as a self-sustaining population in the wild with individuals surviving and reproducing a significant distance from their original point of introduction. Containment is suggested as potential management strategy.     

A revised account of initial mute swan (<Emphasis Type="Italic">Cygnus olor</Emphasis>) introductions to the northeastern United States

The success or failure of species introductions is linked to their location, date, size, and frequency. However, reliance on synthetic works to identify and quantify these factors can lead to errors if original sources are misinterpreted or misquoted. Furthermore, information cannot be verified if authors fail to cite their sources and repetition may lead to compounded errors that have implications for studies of invasion patterns and processes. Naturalized populations of mute swans (Cygnus olor) in the Atlantic Flyway, for example, are repeatedly attributed to two large introductions in New York State. Tracing this belief back to original reports and using additional historical records, this inquiry investigates the first introductions of mute swans in New York State and presents evidence for three initial sites. Newspapers are also recommended as a newly searchable archive of species introduction records.     

Comparison of two introduction methods for African elephants (Loxodonta africana)

Managers must consider an animal's potential for aggression when they decide to change or form a captive social group formation. In this study we compared two introduction methods (termed “sequential” and “nonsequential” introductions) in African elephants to assess their effectiveness in managing aggression and minimizing stress. Both introduction methods included four phases: baseline, visual contact, limited tactile contact, and physical introduction. In the sequential introduction, these steps were followed sequentially, and empirical data were considered during decision‐making. In the nonsequential introduction, these steps were not followed sequentially, and decision‐making was based primarily on intuitive assessments by animal managers. Behavioral data and fecal corticoid concentrations were measured throughout both types of introduction. The behavior categories measured included active aggression, passive aggression, submissive behavior, undesirable/stress‐related behavior, and affiliative behavior. While the role of affiliative behavior was surprising, general behavior patterns were characterized by increases in behavior as animals progressed to the next phase of introduction regardless of introduction type. These increases then attenuated over time during each phase. Overall, less behavior was observed during the sequential introduction, as predicted. The data suggest that the sequential introduction managed aggression more effectively. Similar patterns were predicted for undesirable/stress‐related behavior and fecal corticoid concentration. Undesirable/stress‐related behavior was a poor predictor of observed behavior patterns. Although the patterns differed from those predicted, higher concentrations of fecal corticoids were measured during the nonsequential introduction and correlated significantly only with submissive behavior. While more investigation is warranted, the data indicate that the nonsequential introduction brought about an increased physiological response. Overall, the sequential introduction method appeared to manage aggression and stress better than the nonsequential technique. Every introduction is subject to factors that can influence success, such as staff experience, the design of the facility, and the animals' social histories. It is hoped that the rigorous sequential protocol will be a useful tool in the animal manager's “toolbox” for planning and implementing introductions. Applications of this introduction method are also discussed. Zoo Biol 23:109–126, 2004. © 2004 Wiley‐Liss, Inc.     

Propagule size and the relative success of exotic ungulate and bird introductions to New Zealand

We investigated factors affecting the success of 14 species of ungulates introduced to New Zealand around 1851-1926. The 11 successful species had a shorter maximum life span and were introduced in greater numbers than the three unsuccessful species. Because introduction effort was confounded with other life-history traits, we examined whether independent introductions of the same species were more likely to succeed when a greater number of individuals were introduced. For the six species with introductions that both succeeded and failed, successful introductions always involved an equal or greater number of individuals than unsuccessful introductions of the same species. For all independent introductions, there was a highly significant relationship between the number of individuals introduced and introduction success. When data for ungulate and bird introductions to New Zealand were combined, a variable categorizing species as ungulate or bird was a highly significant predictor of introduction success, after variation in introduction effort was controlled. For a given number of individuals introduced, ungulates were much more likely to succeed than birds.     

Conservation genomics in the fight to help the recovery of the critically endangered Siamese crocodile Crocodylus siamensis

Endangered species are often characterized by low genetic diversity and it is imperative for conservation efforts to incorporate the knowledge obtained from genetic studies for effective management. However, despite the promise of technological advances in sequencing, application of genome‐wide data to endangered populations remains uncommon. In the present study we pursued a holistic conservation‐genomic approach to inform a field‐based management programme of a Critically Endangered species, the Siamese crocodile Crocodylus siamensis. Using thousands of single nucleotide polymorphisms from throughout the genome, we revealed signals of introgression from two other crocodile species within our sample of both wild and captive‐bred Siamese crocodiles from Cambodia. Our genetic screening of the Siamese crocodiles resulted in the subsequent re‐introduction of 12 individuals into the wild as well as the selection of four individuals for captive breeding programmes. Comparison of intraspecific genetic diversity revealed an alarmingly low contemporary effective population size in the wild (<50) with evidence of a recent bottleneck around Tonle Sap Lake. We also projected a probable future extinction in the wild (within fewer than five generations) in this population in the absence of re‐introduction efforts. However, an increase in the number of potential breeders through re‐introductions, including the one resulting from this project, could counter this trend. Our results have been implemented in ongoing re‐introduction and captive breeding programmes, with major implications for the conservation management of Siamese crocodiles, and provide a blueprint for the rescue effort of other “terminally ill” populations of critically endangered species.     

Current knowledge on non‐native freshwater fish introductions

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.