Alien Range Research Articles

Alien range size, habitat breadth, origin location, and domestication of alien species matter to their impact risks.

Invasive alien species are a major driver of biodiversity loss. Currently, the process of biological invasions is experiencing a constant acceleration, foreshadowing a future increase in the threat posed by invasive alien species to global biodiversity. Therefore, it is necessary to assess the impact risks of invasive alien species and related factors. Here, we constructed a dataset of negative environmental impact events to evaluate the impact risks of alien species. We collected information on 1071 established alien terrestrial vertebrates and then gathered negative environmental impacts for 108 of those species. Generalized linear mixed-effects model and phylogenetic generalized least-squares regression model were used to examine the characteristic (including life-history traits, characteristics related to distribution, and introduction event characteristics) correlates of species' impact risks at the global scale for 108 established alien terrestrial vertebrates (mammals, birds, reptiles and amphibians). Our results showed that a total of 3158 negative environmental impacts were reported for 108 harmful species across 71 countries worldwide. Factors associated with impact risks varied slightly among taxa, but alien range size, habitat breadth, origin location, and domestication were significantly correlated with impact risks. Our study aims to identify the characteristics of alien species with high-impact risks to facilitate urgent assessment of alien species and to protect the local ecological environment and biodiversity.

The cumulative niche approach: A framework to assess the performance of ecological niche model projections.

Ecological Niche Models (ENMs) are often used to project species distributions within alien ranges and in future climatic scenarios. However, ENMs depend on species-environment equilibrium, which may be absent for actively expanding species. We present a novel framework to estimate whether species have reached environmental equilibrium in their native and alien ranges. The method is based on the estimation of niche breadth with the accumulation of species occurrences. An asymptote will indicate exhaustive knowledge of the realised niches. We demonstrate the CNA framework for 26 species of mammals, amphibians, and birds. Possible outcomes of the framework include: (1) There is enough data to quantify the native and alien realised niches, allowing us to calculate niche expansion between the native and alien ranges, also indicating that ENMs can be reliably projected to new environmental conditions. (2) The data in the native range is not adequate but an asymptote is reached in the alien realised niche, indicating low confidence in our ability to evaluate niche expansion in the alien range but high confidence in model projections to new environmental conditions within the alien range. (3) There is enough data to quantify the native realised niche, but not enough knowledge about the alien realised niche, hindering the reliability of projections beyond sampled conditions. (4) Both the native and alien ranges do not reach an asymptote, and thus few robust conclusions about the species' niche or future projections can be made. Our framework can be used to detect species' environmental equilibrium in both the native and alien ranges, to quantify changes in the realised niche during the invasion processes, and to estimate the likely accuracy of model projections to new environmental conditions.

Patterns and drivers of climatic niche dynamics during biological invasions of island-endemic amphibians, reptiles, and birds.

Shifts between native and alien climatic niches pose a major challenge for predicting biological invasions. This is particularly true for insular species because geophysical barriers could constrain the realization of their fundamental niches, which may lead to underestimates of their invasion potential. To investigate this idea, we estimated the frequency of shifts between native and alien climatic niches and the magnitude of climatic mismatches using 80,148 alien occurrences of 46 endemic insular amphibian, reptile, and bird species. Then, we assessed the influence of nine potential predictors on climatic mismatches across taxa, based on species' characteristics, native range physical characteristics, and alien range properties. We found that climatic mismatch is common during invasions of endemic insular birds and reptiles: 78.3% and 55.1% of their respective alien records occurred outside of the environmental space of species' native climatic niche. In comparison, climatic mismatch was evident for only 16.2% of the amphibian invasions analyzed. Several predictors significantly explained climatic mismatch, and these varied among taxonomic groups. For amphibians, only native range size was associated with climatic mismatch. For reptiles, the magnitude of climatic mismatch was higher for species with narrow native altitudinal ranges, occurring in topographically complex or less remote islands, as well as for species with larger distances between their native and alien ranges. For birds, climatic mismatch was significantly larger for invasions on continents with higher phylogenetic diversity of the recipient community, and when the invader was more evolutionarily distinct. Our findings highlight that apparently common niche shifts of insular species may jeopardize our ability to forecast their potential invasions using correlative methods based on climatic variables. Also, we show which factors provide additional insights on the actual invasion potential of insular endemic amphibians, reptiles, and birds.

Are species more harmful in their native, neonative or alien range? Insights from a global analysis of bark beetles

AbstractAimAnthropogenic environmental modifications such as climate or land‐use change are causing species to move on their own beyond their native ranges. As this phenomenon will increase in the near future, it is crucial to determine whether range‐expanding species, or neonatives, are more or less likely than native and alien species to impact their recipient ecosystems. Here, we compared impact magnitudes of bark beetle species from their native, neonative and alien ranges, simultaneously.LocationGlobal.MethodsWe formulated four general scenarios about the magnitude of environmental impacts in different ranges (native, neonative and alien) based on hypotheses commonly used in invasion biology. We tested these scenarios globally on Dendroctonus bark beetles, asking whether they have the most harmful impacts in their native, neonative or alien ranges. Impacts reported in the literature were assessed with the IUCN Environmental Impact Classification for Alien Taxa (EICAT).ResultsWe found that bark beetles cause the most harmful impacts in their native ranges, followed by the neonative ranges, while impacts in their alien ranges are the lowest. This indicates that the more dissimilar the environment is from that in the native range, the lower the probability of high‐impact magnitudes. Our results align with several non‐exclusive hypotheses, e.g. pre‐adaptation and habitat filtering, while they do not support others, e.g. enemy release or Darwin’s naturalization. The results are also in contrast with previous studies on vertebrates and plants, which found no or mixed differences in impact magnitudes with biogeographic origin.Main conclusionsOur analysis suggests that bark beetles, like other species that are keystone and abundant in their native ranges, have generally lower impacts when introduced to novel environments due to biotic resistance or lack of pre‐adaptation. Research and management implications regarding the impacts of neonative and alien populations are also discussed.

Invasive slipper limpets Crepidula fornicata are hosts for sterilizing digenean parasites.

Invasion and spread of alien species can drive ecosystem changes, such as, the dynamics of infectious diseases. The non-native, marine gastropod Crepidula fornicata has become established across European coastlines over the last century, but there remains little insight into its disease carrying capacity and potential role as a source/sink of parasites. To address this knowledge gap, we surveyed limpets from two sites in South Wales, UK for signatures of disease/pathology using polymerase chain reaction-based methods (haemolymph) and histology (solid tissue). We encountered trematode-like parasites in ~1% individuals (5 out of 462). Three limpets displayed gross damage in the gonad, i.e. castration, and encysted metacercariae were found in the muscle of two other individuals. On the basis of 28S rDNA and internal transcribed spacer 2 genomic targets, we identified the gonad-infecting trematodes as members of the family Microphallidae – putative novel species related to the genus Longiductotrema. Earlier reports suggest that C. fornicata is not a host for trematode parasites in either its native or alien range but may act as a sink due to its filter feeding lifestyle. We provide clear evidence that C. fornicata is parasitized by at least one trematode species at two sites in Wales, UK, and likely act as a spillback or accidental host among native littorinids.

DAMA: the global Distribution of Alien Mammals database.

We developed the DAMA (Distribution of Alien Mammals) database, a comprehensive source reporting the global distribution of the 230 species of mammals that have established self-sustaining and free-ranging populations outside their native range due to direct or indirect human action. Every alien range is accompanied by information on its invasion stage, pathway, method of introduction, and date of introduction. We collected information from 827 different sources (scientific literature, books, risk assessments, reports, online biodiversity databases and websites), and used it to draw alien range maps for these species following the IUCN mapping framework. DAMA comprises 2,726 range polygons, covering 199 countries, 2,190 level 1 administrative areas, and 11 zoogeographic realms for the period 21500 BC-AD 2017. The most represented orders among introduced mammal species are Rodentia (n = 58, 25.22%), Cetartiodactyla (n = 49 species, 21.30%), Carnivora (n = 30 species, 13.04%), Diprotodontia (n = 28, 12.17%), and Primates (n = 26, 11.30%). Mammal species have been frequently introduced for hunting (n = 100), pet trade (n = 57), conservation (n = 51), and fauna improvement (n = 42). The majority of range polygons are placed on islands (n = 2,196, 80.56%), encompass populations that have moved beyond establishment and into the invasion stage (n = 1,655, 60.71%), and originated from 1500 AD to the present (n = 1,496, 54.88%). Despite inheriting literature biases towards more studied regions (e.g., developed countries), DAMA is the most up-to-date picture of alien mammal global distribution and can be used to investigate their invasion ecology across different biogeographical regions. There are no copyright or proprietary restrictions; IUCN range maps were modified into a derivative work according to the IUCN's terms of service.

Potential alien ranges of European plants will shrink in the future, but less so for already naturalized than for not yet naturalized species

AbstractAimsThe rapid increase in the number of species that have naturalized beyond their native range is among the most apparent features of the Anthropocene. How alien species will respond to other processes of future global changes is an emerging concern and remains poorly misunderstood. We therefore ask whether naturalized species will respond to climate and land use change differently than those species not yet naturalized anywhere in the world.LocationGlobal.MethodsWe investigated future changes in the potential alien range of vascular plant species endemic to Europe that are either naturalized (n = 272) or not yet naturalized (1,213) outside of Europe. Potential ranges were estimated based on projections of species distribution models using 20 future climate‐change scenarios. We mapped current and future global centres of naturalization risk. We also analysed expected changes in latitudinal, elevational and areal extent of species’ potential alien ranges.ResultsWe showed a large potential for more worldwide naturalizations of European plants currently and in the future. The centres of naturalization risk for naturalized and non‐naturalized plants largely overlapped, and their location did not change much under projected future climates. Nevertheless, naturalized plants had their potential range shifting poleward over larger distances, whereas the non‐naturalized ones had their potential elevational ranges shifting further upslope under the most severe climate change scenarios. As a result, climate and land use changes are predicted to shrink the potential alien range of European plants, but less so for already naturalized than for non‐naturalized species.Main conclusionsWhile currently non‐naturalized plants originate frequently from mountain ranges or boreal and Mediterranean biomes in Europe, the naturalized ones usually occur at low elevations, close to human centres of activities. As the latter are expected to increase worldwide, this could explain why the potential alien range of already naturalized plants will shrink less.

Around the world in 500 years: Inter‐regional spread of alien species over recent centuries

AbstractAimThe number of alien species has been increasing for centuries world‐wide, but temporal changes in the dynamics of their inter‐regional spread remain unclear. Here, we analyse changes in the rate and extent of inter‐regional spread of alien species over time and how these dynamics vary among major taxonomic groups.LocationGlobal.Time period1500–2010.Major taxa studiedVascular plants, mammals, birds, fishes, arthropods and other invertebrates.MethodsOur analysis is based on the Alien Species First Record Database, which comprises >60,000 entries describing the year when an alien species was first recorded in a region (mostly countries and large islands) where it later established as an alien species. Based on the number and distribution of first records, we calculated metrics of spread between regions, which we termed “inter‐regional spread”, and conducted statistical analyses to assess variations over time and across taxonomic groups.ResultsAlmost all (>90%) species introduced before 1700 are found in more than one region today. Inter‐regional spread often took centuries and is ongoing for many species. The intensity of inter‐regional spread increased over time, with particularly steep increases after 1800. Rates of spread peaked for plants in the late 19th century, for birds and invertebrates in the late 20th century, and remained largely constant for mammals and fishes. Inter‐regional spread for individual species showed hump‐shaped temporal patterns, with the highest rates of spread at intermediate alien range sizes. Approximately 50% of widespread species showed signs of declines in spread rates.Main conclusionsOur results show that, although rates of spread have declined for many widespread species, for entire taxonomic groups they have tended to increase continuously over time. The large numbers of alien species that are currently observed in only a single region are anticipated to be found in many other regions in the future.

A global assessment of human influence on niche shifts and risk predictions of bird invasions

AbstractAimEstimating the strength of niche conservatism is key for predictions of invasion risk. Most studies consider only the climatic niche, but other factors, such as human disturbance, also shape niches. Whether occupation of human habitats in the alien range depends on the native tolerances of species remains unexplored. We assessed niche conservatism in climatic and human spaces for bird species showing different responses to humans in native ranges and evaluated whether considering anthropogenic niche variables affects invasion predictions.LocationGlobal.Time periodFrom 500 CE to the present day.Major taxon studiedBirds.MethodsWe assessed niche conservatism by comparing the native and alien distributions of 150 bird species. We differentiated “niche expansions” into environments new to the species and “niche unfilling”, whereby a species fills its native niche only in part. Global predictions of alien bird distribution were generated using species distribution models (SDMs).ResultsClimatic niche similarity was higher than random expectation in 56% of species, and human disturbance niche similarity in 43%. Only 34 and 15% of species had >10% of their alien distribution in climates or human conditions, respectively, different from those of native ranges. Climatic niche expansions mostly involved colonization of colder and less seasonal climates. Human niche expansions involved colonization of more disturbed environments by species not responding positively to human influence in native ranges. Climatic and human niche unfilling was more common than expansions and was lower for species introduced earlier and those responding positively to human influence. Models including human variables do equally well for all species.Main conclusionsAlien birds tend to invade areas with similar climatic and human conditions to their native range, but niche unfilling and expansions occur and relate to species native tolerances to human‐modified habitats and first introduction year. Incorporation of human‐related variables in SDM results in more accurate predictions for all species.

Evidence for Rapoport’s rule and latitudinal patterns in the global distribution and diversity of alien bird species

AbstractAimTo quantify global latitudinal patterns in the distributions of alien bird species to assess whether these species conform to Rapoport's rule (i.e. show a positive latitudinal gradient in latitudinal range extent), and to test whether where species are introduced, and where species fail to establish, may help to drive observed patterns.LocationGlobal.TaxonBirds (group Aves).MethodsData on locations of introduction and establishment for 355 species with established alien populations were combined with data on native range extents (measured in 5° bands of latitude). Relationships between (a) latitude and introduced and established alien species richness, and (b) latitude and introduced and established alien range extent, were plotted. Linear regressions and paired t‐tests were used to compare latitudinal range extents, midpoints, and limits of each species in its introduced alien range, established alien range and native range.ResultsLatitudes that have more established alien bird species also have had more species introduced in total. The mean total latitudinal extents (i.e. geographic range size) of established alien bird species increase with latitude poleward of the tropics, consistent with Rapoport's rule, but are smaller in the tropics. This pattern is weaker in the range sizes of native bird species. Alien bird species are more likely to be introduced within the latitudinal confines of their native ranges, and are more likely to contract away from the more extreme latitudes to which they were introduced. Alien bird species are in general more likely to have established populations nearer the equator.Main conclusionsIncluding data on locations of introduction in addition to established distributions enables us to determine the extent to which large‐scale alien species distributions are determined by anthropogenic or natural processes. Latitudinal patterns in range extent (Rapoport's rule) and species richness in alien birds are largely a consequence of where species have been introduced, and hence are unlikely to be informative of equivalent patterns in native species.

Prunus serotina in Italy: a challenging candidate for the national list of priority invasive alien species

In accordance with the European regulation on Invasive Alien Species (IAS), the black cherry tree (Prunus serotina Ehrh.) has recently been indicated as one of the 96 species proposed for the development of the national list of priority invasive alien species in Italy. The species, native to North America, is recognised as one of the most harmful IAS in Europe, given its high spread potential and the associated ecological and economic impacts reported in its alien range. Although P. serotina is recognised as a pest within the EU, plants are still available on the market, confirming intentional introduction as a current potential pathway for this species arrival into new areas. Since a comprehensive overview of the main features characterizing the invasive potential of this species is still lacking, we aim to underpin the high priority status of P. serotina as a IAS of main concern in Italy by outlining the main biological features, pathways and impacts of the black cherry in its secondary range. Management measures to be potentially included in specific action plans are also summarised.

Characteristics of the soil seed bank of invasive and non-invasive plants in their native and alien distribution range

The ability to form persistent seed banks might contribute substantially to determine the invasion potential of alien plants in their new distribution ranges, given the role of seed banks as sources of propagules, genetic diversity, and in spreading the risk of germination failure over time. Using the largest seed bank dataset collated to date, comprising 14,293 records for 2566 species, we examined whether the type (transient vs persistent) and density of the seed banks of invasive species differ in their native (home) and alien (abroad) range, and whether these attributes differ among invasive and non-invasive congeners, at home and abroad. A lower probability of forming a persistent seed bank in the alien range was identified when analyzing data for 140 invasive species, although phylogenetic analyses run for 104 of those species did not confirm such differences. However, invasive woody species formed denser seed banks in the alien range, suggesting greater seed production and/or lower seed predation or mortality in the alien than native range. Interestingly, invasive species consistently showed a higher probability of forming persistent seed banks as well as denser seed banks than their non-invasive congeners in their native range, but not in their alien range. These findings provide the first quantitative evidence, based on a large number of species globally, of preadaptation with respect to species life-history traits resulting in the formation of a persistent seed bank in invasive species compared to their non-invasive congeners. The fact that both invasive and non-invasive congeners have similar probabilities of forming persistent seed banks abroad suggests that this might be an important attribute for the establishment of alien species in new ranges (naturalization phase), but not for their spread (invasion phase). Our findings also indicate that the characteristics of native seed banks should be an important component of risk assessments aimed at identifying species that are more likely to become invasive if introduced in new ranges.

Species invasions and the phylogenetic signal in geographical range size

AbstractAimAccelerating rates of anthropogenic introductions are leading to a dramatic restructuring of species distributions globally. However, the extent to which invasions alter the imprint of evolutionary history in species geographical ranges remains unclear. Here, we provide a global assessment of how the introduction, establishment and spread of alien species alters the phylogenetic signal in geographical range size using birds as a model system.LocationGlobal.Time periodContemporaneous.TaxaBirds.MethodsWe compare the phylogenetic signal in alien range size with that of native distributions of species globally (n = 9,993) and across different stages in the invasion pathway, from introduced (n = 965) to established species (n = 359). Using stochastic simulations, we test whether differences in phylogenetic signal arise from nonrandom patterns of species introduction, establishment or spread.ResultsGeographical range size in birds exhibits an intermediate phylogenetic signal, driven by the spatial clustering of closely related species. Nonrandom introductions, biased towards wide‐ranging species from particular clades and regions, produce an anomalously strong phylogenetic signal in the native range size of introduced species. In contrast, the phylogenetic signal in alien range size is substantially weaker than for native distributions. This weak phylogenetic signal cannot be explained by a lack of time for dispersal but is instead regulated by phylogenetic correlations across species in the location and number of introduction events.Main conclusionsWe demonstrate that the effects of anthropogenic introductions on the phylogenetic signal in range size vary across different stages in the invasion pathway. The process of transport and introduction amplifies the phylogenetic signal in the pool of potential invaders, whereas the subsequent pattern of spread decouples variation in alien range size from phylogenetic ancestry. Together, our findings suggest that evolutionary relatedness is likely to be a relatively weak predictor of the spread of invasive species.

"Liaisons dangereuses": The invasive red-vented bulbul (Pycnonotus cafer), a disperser of exotic plant species in New Caledonia.

The biodiversity hotspot of New Caledonia hosts high levels of endemism (74% of flora) that is threatened increasingly by climate change, habitat reduction, and invasive species. The fruit‐eating red‐vented bulbul (Pycnonotus cafer) is currently invading the main island of the archipelago, and its recent dispersal out of urbanized habitats raises questions about its potential to disperse noxious plant seeds along urban corridors and beyond. Indeed, the red‐vented bulbul is considered a vector of several introduced plant species in its alien range including Miconia calvescens, Lantana camara, and Schinus terebinthifolius. We conducted a quantitative assessment of the bulbul's fruits consumption by analyzing the gut contents of shot birds. We estimated gut passage times for four species of fruit found in gut contents (S. terebinthifolius, Myrtastrum rufopunctatum, Passiflora suberosa, and Ficus prolixa) and tested the effects of bird digestion on seed germination rates for two species. Finally, we monitored the movements of individual VHF radio‐tagged red‐vented bulbuls. All of the consumed fruit species we identified here have red fleshy diaspore, including fruit of the shrub M. rufopunctatum that occurred frequently (9.6%) in bulbul gut samples. Median gut passage times were short (15–41 min), corresponding to short‐distance seed transportation (77–92 m). The effect of gut passage was positive for the germination of the invasive S. terebinthifolius and negative for the endemic M. rufopunctatum, suggesting a potential bias in the contribution to the dispersal toward alien species. This study provides the first integrated assessment of mechanisms involved in the seed dispersal effectiveness of this high‐concern invasive bird species that is expected to face similar plant communities in most of its alien range in tropical islands. More generally, our results enhance knowledge of synergies between non‐native frugivores and plant species dispersal.

Gastropods alien to South Africa cause severe environmental harm in their global alien ranges across habitats.

Alien gastropods have caused extensive harm to biodiversity and socioeconomic systems like agriculture and horticulture worldwide. For conservation and management purposes, information on impacts needs to be easily interpretable and comparable, and the factors that determine impacts understood. This study aimed to assess gastropods alien to South Africa to compare impact severity between species and understand how they vary between habitats and mechanisms. Furthermore, we explore the relationship between environmental and socioeconomic impacts, and both impact measures with life‐history traits. We used the Environmental Impact Classification for Alien Taxa (EICAT) and Socio‐Economic Impact Classification for Alien Taxa (SEICAT) to assess impacts of 34 gastropods alien to South Africa including evidence of impact from their entire alien range. We tested for correlations between environmental and socioeconomic impacts per species, and with fecundity and native latitude range using Kendall's tau tests. Kruskal–Wallis tests were used to compare impact magnitude among mechanisms and habitats, respectively. This study presents the first application of EICAT and SEICAT for invertebrates. There was no correlation between environmental impacts and socioeconomic impacts. Habitats did not differ regarding the severity of impacts recorded, but impacts via disease transmission were lower than other mechanisms. Neither fecundity nor native range latitude was correlated with impact magnitude. Despite gastropods being agricultural and horticultural pests globally, resilience of socioeconomic systems makes high impacts uncommon. Environmental systems may be vulnerable to gastropod impacts across habitats, having experienced multiple local extinctions of wetland island snail fauna. South Africa stands out as the only continental country that follows this trend. The knowledge gained on severity and nature of gastropod impacts is useful in risk assessment, which can aid conservation management. To make impact assessments more realistic, we suggest alternative ways of reporting impacts classified under EICAT and SEICAT.

Maladaptive host choice by an alien leaf miner Phyllonorycter leucographella (Lepidoptera: Gracillariidae) has the potential to limit its invasiveness

Alien phytophagous insects are often introduced along with their host plants, creating opportunities for troublesome invasions. Yet, not all of them are able to successfully colonize novel host plants. In this study, we investigated host selection by the alien leaf miner Phyllonorycter leucographella (Zeller, 1850) on both its original host and novel host plants in the insect's alien range. We predicted that this insect's percentage infestation of the original host would be positively related to its specific leaf area (SLA), because high-SLA leaves are nutritious and have thin cuticles, traits related to high offspring developmental success. We further hypothesized that this host selection process would apply in the selection of novel host plants. Our results show that this leaf miner selects leaves of its original host plant, Pyracantha coccinea, according to their SLA values. The SLA value was also positively related to the probability of P. leucographella infesting and successfully developing on novel host plants. The selection of high-SLA plants by the moth leads to a high developmental success on novel host plants in the first (summer) generation, but it is likely to be maladaptive in the second (overwintering) generation, because in temperate Europe, high SLA values are associated with deciduous plants that shed their leaves in autumn. It is likely that the apparent maladaptive selection of novel host plants by P. leucographella reduces the invasiveness of this pest by preventing its establishment on native plants.

Identifying the factors that determine the severity and type of alien bird impacts

AbstractAimTo identify traits related to the severity and type of environmental impacts generated by alien bird species, in order to improve our ability to predict which species may have the most damaging impacts.LocationGlobal.MethodsInformation on traits hypothesized to influence the severity and type of alien bird impacts was collated for 113 bird species. These data were analysed using mixed effects models accounting for phylogenetic non‐independence of species.ResultsThe severity and type of impacts generated by alien bird species are not randomly distributed with respect to their traits. Alien range size and habitat breadth were strongly associated with impact severity. Predation impacts were strongly associated with dietary preference, but also with alien range size, relative brain size and residence time. Impacts mediated by interactions with other alien species were related to alien range size and diet breadth.Main conclusionsWidely distributed generalist alien birds have the most severe environmental impacts. This may be because these species have greater opportunity to cause environmental impacts through their sheer number and ubiquity, but this could also be because they are more likely to be identified and studied. Our study found little evidence for an effect of per capita impact on impact severity.

Determinants of data deficiency in the impacts of alien bird species

To identify the factors that influence the availability of data on the negative impacts of alien bird species, in order to understand why more than 70% are currently classified as Data Deficient (DD) by the Environmental Impact Classification of Alien Taxa (EICAT) protocol.Information on factors hypothesised to influence the availability of impact data were collated for 344 alien bird species (107 with impact data and 237 DD). These data were analysed using mixed effects models accounting for phylogenetic non‐independence of species (MCMCglmm).Data deficiency in the negative impacts of alien birds is not randomly distributed. Residence time, relative brain size and alien range size were found to be strongly related to the availability of data on impacts.The availability of data on the negative impacts of alien birds is mainly influenced by the spatial and temporal extents of their alien ranges. The results of this study suggest that the impacts of some DD alien birds are likely to be minor (e.g. species with comparatively long residence times as aliens, such as the common waxbill Estrilda astrild and the Java sparrow Padda oryzivora). However, the results also suggest that some DD alien birds may have damaging impacts (e.g. species from orders of alien birds known for their impacts to biodiversity but with comparatively small alien ranges, such as the New Caledonian crow Corvus moneduloides). This implies that at least some DD alien birds may have impacts that are being overlooked. Studies examining the traits that influence the severity of alien bird impacts are needed to help to predict which DD species are more likely to impact upon biodiversity.

Effects of UV-B radiation on leaf hair traits of invasive plants-Combining historical herbarium records with novel remote sensing data.

Ultraviolet-B (UV-B) radiation is a key but under-researched environmental factor that initiates diverse responses in plants, potentially affecting their distribution. To date, only a few macroecological studies have examined adaptations of plant species to different levels of UV-B. Here, we combined herbarium specimens of Hieracium pilosella L. and Echium vulgare L. with a novel UV-B dataset to examine differences in leaf hair traits between the plants’ native and alien ranges. We analysed scans of 336 herbarium specimens using standardized measurements of leaf area, hair density (both species) and hair length (H. pilosella only). While accounting for other bioclimatic variables (i.e. temperature, precipitation) and effects of herbivory, we examined whether UV-B exposure explains the variability and geographical distribution of these traits in the native (Northern Hemisphere) vs. the alien (Southern Hemisphere) range. UV-B explained the largest proportion of the variability and geographical distribution of hair length in H. pilosella (relative influence 67.1%), and hair density in E. vulgare (66.2%). Corresponding with higher UV-B, foliar hairs were 25% longer for H. pilosella and 25% denser for E. vulgare in records from the Southern as compared to those from the Northern Hemisphere. However, focusing on each hemisphere separately or controlling for its effect in a regression analysis, we found no apparent influence of UV-B radiation on hair traits. Thus, our findings did not confirm previous experimental studies which suggested that foliar hairs may respond to higher UV-B intensities, presumably offering protection against detrimental levels of radiation. We cannot rule out UV-B radiation as a possible driver because UV-B radiation was the only considered variable that differed substantially between the hemispheres, while bioclimatic conditions (e.g. temperature, precipitation) and other considered variables (herbivory damage, collection date) were at similar levels. However, given that either non-significant or inconclusive relationships were detected within hemispheres, alternative explanations of the differences in foliar hairs are more likely, including the effects of environment, genotypes or herbivory.

Geographical range expansion of alien birds and environmental matching

The international wildlife trade is a significant source of introduced alien species, some of which proceed to become invasive and cause negative environmental and economic effects. However, not all introduced aliens establish viable populations, and it is important to identify the factors that determine establishment success. We explore the role of environmental suitability (including anthropogenic influences, climate and habitat types) in the establishment success of alien bird species introduced to Taiwan. Using maximum entropy modelling, we employed a recursive feature elimination and Akaike information criterion (AIC)‐based stepwise model selection approach to assess whether the environmental suitability, native range size, body size, residence time and the numbers of birds for sale in the shops affect variation in the extent of alien bird range size in Taiwan. We show that species with larger native range sizes and larger body sizes tend to have larger alien range sizes in Taiwan. There was no effect of environmental suitability on alien range size in Taiwan, but environmental suitability influenced the establishment success of bird species there.