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Human actions have led to large-scale shifts in the distributions of species, which have accelerated over recent decades. Two contributing factors include the introduction of non-native species to new regions, and more recently, the shift of species into new ranges to track a human-altered climate. While the context of these species redistributions is different, we argue here that scientists studying the effects of either invasion or range shifting are interested in the same underlying mechanistic questions: (1) What traits make a species likely to survive in a new location? and (2) Which recipient ecosystems are likely to support a newly arrived species? A survey of the theoretical literature surrounding these topics demonstrates the usefulness of this comparison and highlights key differences between range shifting and invasion in factors including genetic diversity, climatic tolerance, local adaptation, and coevolutionary history. This review does not support the blanket application of an invasion framework to climate change-induced range shifts. However, we suggest the use of modified invasion theories, experimental designs, and risk assessments could aid in predicting outcomes and prioritizing management resources for climate-threatened species., (© 2024 The Author(s). Global Change Biology published by John Wiley & Sons Ltd.)

Safeguarding aquatic ecosystems from invasive species requires a comprehensive understanding and quantification of their impacts, as this information is crucial for developing effective management strategies. In particular, aquatic invasive plants cause profound alterations to aquatic ecosystem composition, structure and productivity. Monetary cost assessments have, however, lacked at large scales for this group. Here, we synthesize the global economic impacts of aquatic and semi-aquatic invasive plants to describe the distributions of these costs across taxa, habitat types, environments, impacted sectors, cost typologies, and geographic regions. We also examine the development of recorded costs over time using linear and non-linear models and infer the geographical gaps of recorded costs by superimposing cost and species distribution data. Between 1975 and 2020, the total cost of aquatic and semi-aquatic invasive plants to the global economy exceeded US$ 32 billion, of which the majority of recorded costs (57 %) was attributable to multiple or unspecified taxa. Submerged plants had $8.4 billion (25.5 %) followed by floating plants $4.7 billion (14.5 %), emergent $684 million (2.1 %) and semi-aquatic $306 million (0.9 %). Recorded costs were disproportionately high towards freshwater ecosystems, which have received the greatest cost research effort compared to marine and brackish systems. Public and social welfare and fisheries were the sectors most affected, while agriculture and health were most underreported. Cost attributed to management (4.8 %; $1.6 billion) represented only a fraction of damages (85.8 %; $28.2 billion). While recorded costs are rising over time, reporting issues e.g., robustness of data, lack of higher taxonomic resolution and geographical gaps likely have led to a dampening of trajectories. In particular, invasive taxa currently occupy regions where monetary cost reports are lacking despite well-known impacts. More robust and timely cost estimates will enhance interpretation of current and future impacts of aquatic invasive plants, assisting the long-term sustainability of our aquatic ecosystems and associated economic activities., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have influenced the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

The ecological impacts of invasive alien species (IAS) are increasingly documented; however, they are usually studied through the lens of either the IAS or the affected species (IAS-threatened species). A clear understanding of how both protagonists of biological invasions are characterized is still lacking. We investigated the morphology, life history and ecology of birds involved in biological invasions. Evaluating the distribution of 450 IAS-threatened birds and 400 alien birds in a functional space, we found that both groups retained various strategies. Aliens had larger clutches and were more likely to be herbivores than IAS-threatened and worldwide birds, while IAS-threatened birds were more insular endemic from the Australia region than alien and worldwide birds. IAS-threatened species showed opposite strategies to aliens regarding traits related to diet, origin and reproduction. Further comparing traits associated with impact magnitude, we found that even if aliens were mostly herbivorous, those with high impact had more a generalist behaviour and an animal-based diet compared to aliens with low impact. By emphasizing differences relating to the distribution of bird groups in a functional space, we opened new opportunities to identify the role of birds in biological invasions.

Prey reconfigure their physiology to avoid costs of prolonged predator pressure. However, these changes might not occur under periodic predation risk, with repeating acute phases. To test the effect of predation risk continuity on changes in prey physiology, we exposed amphipods: Dikerogammarus villosus and Gammarus jazdzewskii to periodic and constant predation cue. After one week, we measured: cellular defence systems: total antioxidant status (TAS), heat shock proteins (Hsp70); intracellular damage marker: lipid peroxidation (TBARS); condition index: glycogen concentration. Predator presence reduced TAS level in G. jazdzewskii independent of its continuity and in D. villosus after periodic exposure. Amphipods showed downregulation of Hsp70 when exposed to periodic (D. villosus) or constant (G. jazdzewskii) predation risk. Exposure to predators reduced TBARS level in D. villosus (irrespective of the continuity) and G. jazdzewskii (periodic exposure). Glycogen concentration in both species was not affected by predator presence. Thus, the continuity of the predator cue shaped prey physiology reconfiguration, optimizing costs of physiological adjustments under challenging conditions. Nevertheless, the lack of negative consequences of the prolonged exposure to the predator cue, whether constant or periodic, shows that amphipods can thrive under chronic predation risk, which is a constant part of the wild environment.

Ecological theory on the trophic impacts of invasive fauna on native competitors is equivocal. Whilst increased interspecific competition can result in coexisting species having constricted and diverged trophic niches, the competing species might instead increase their niche sizes to maintain energy intakes. Empirical experiments can test invasion theory on competitive interactions and niche sizes across different spatial scales and complexity. The consequences of increased interspecific competition from a model alien fish Leuciscus idus were tested on two taxonomically and trophically similar native fishes, Squalius cephalus and Barbus barbus. Competitive interactions were tested in tank aquaria using comparative functional responses (CFRs) and cohabitation trials. The consequences of these competitive interactions for the trophic niche sizes and positions of the fishes were tested in pond mesocosms. Comparative functional responses revealed that compared to B. barbus, L. idus had significantly higher attack and consumption rates; cohabitation trials revealed B. barbus growth rates were depressed in sympatry with L. idus. For L. idus and S. cephalus, differences in their functional response parameters and growth rates were not significant. Pond mesocosms used stable isotope metrics to quantify shifts in the trophic niche sizes of the fishes between allopatry and sympatry using a substitutive experimental design. Isotopic niches were smaller and more divergent in sympatric paired species than predicted by their allopatric treatments, suggesting trophic impacts from interspecific competition. However, an all-species sympatric treatment revealed similar niche sizes with allopatry. This maintenance of niche sizes in the presence of all species potentially resulted from the buffering of direct competitive effects of the species pairs by indirect effects. Experimental predictions from tank aquaria assisted the interpretation of the constricted and diverged trophic niches detected in the paired-species sympatric treatments of the pond mesocosms. However, the all-species sympatric treatment of this experiment revealed greater complexity in the outcomes of the competitive interactions within and between the species. These results have important implications for understanding how alien species integrate into food webs and influence the trophic relationships between native species., (© 2019 The Authors. Journal of Animal Ecology © 2019 British Ecological Society.)

Biological invasions are occurring worldwide, causing enormous economic and ecological damage. Early detection and prediction of invasiveness are the most effective measures to reduce its damage. The Alexandra palm (Archontophoenix alexandrae) is a prolific seeder and an alien species widely planted in tropical China. To help understand the invasion risks posed by this species, lab and field experiments on seed germination were conducted. Results show that the seeds only germinate within a temperature range of 20-30 °C and are sensitive to desiccation and high temperature, with seedling inhibition at 35 °C and -0.8 MPa. Complete viability loss was observed after desiccation to water content of 0.17-0.21 g/g or heat treatment for 30 minutes at 60 °C and above. However, appropriate habitats such as the rainforest understory, forest gaps, forest edges, and a rubber plantation are present in Xishuangbanna. Seeds are also frequently consumed by animals; therefore, there is a high potential for Alexandra palm to become an invasive species in Xishuangbanna. Currently, the main barrier to invasion in Xishuangbanna is likely to be the need for seed dispersal into suitable moist, partly shaded, habitats. Understanding the requirements for germination of the Alexandra palm can better inform management strategies for the control of this species.

China's ambitious aspirations to build a modern Silk Road will open new avenues for species to spread into regions outside their native range. A new study identifies 14 hot spots of biological invasions falling along the planned economic corridors., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Evolution in harvested species has become a major concern for its potential to affect yield, sustainability, and recovery. However, the current singular focus on harvest-mediated evolution in target species overlooks the potential for evolution in non-target members of communities. Here we use an individual-based model to explore the scope and pattern of harvest-mediated evolution at non-target trophic levels and its potential feedbacks on abundance and yield of the harvested species. The model reveals an eco-evolutionary trophic cascade, in which harvest at top trophic levels drives evolution of greater defense or competitiveness at subsequently lower trophic levels, resulting in alternating feedbacks on the abundance and yield of the harvested species. The net abundance and yield effects of these feedbacks depends on the intensity of harvest and attributes of non-target species. Our results provide an impetus and framework to evaluate the role of non-target species evolution in determining fisheries yield and sustainability.

Successful microbial invasions are determined by a species' ability to occupy a niche in the new habitat whilst resisting competitive exclusion by the resident community. Despite the recognised importance of biotic factors in determining the invasiveness of microbial communities, the success and impact of multiple concurrent invaders on the resident community has not been examined. Simultaneous invasions might have synergistic effects, for example if resident species need to exhibit divergent phenotypes to compete with the invasive populations. We used three phylogenetically diverse bacterial species to invade two compositionally distinct communities in a controlled, naturalised in vitro system. By initiating the invader introductions at different stages of succession, we could disentangle the relative importance of resident community structure, invader diversity and time pre-invasion. Our results indicate that multiple invaders increase overall invasion success, but do not alter the successional trajectory of the whole community., (© 2018 The Authors Ecology Letters published by CNRS and John Wiley & Sons Ltd.)

Alien species can have major ecological and socioeconomic impacts in their novel ranges and so effective management actions are needed. However, management can be contentious and create conflicts, especially when stakeholders who benefit from alien species are different from those who incur costs. Such conflicts of interests mean that management strategies can often not be implemented. There is, therefore, increasing interest in engaging stakeholders affected by alien species or by their management. Through a facilitated workshop and consultation process including academics and managers working on a variety of organisms and in different areas (urban and rural) and ecosystems (terrestrial and aquatic), we developed a framework for engaging stakeholders in the management of alien species. The proposed framework for stakeholder engagement consists of 12 steps: (1) identify stakeholders; (2) select key stakeholders for engagement; (3) explore key stakeholders' perceptions and develop initial aims for management; (4) engage key stakeholders in the development of a draft management strategy; (5) re-explore key stakeholders' perceptions and revise the aims of the strategy; (6) co-design general aims, management objectives and time frames with key stakeholders; (7) co-design a management strategy; (8) facilitate stakeholders' ownership of the strategy and adapt as required; and (9) implement the strategy and monitor management actions to evaluate the need for additional or future actions. In case additional management is needed after these actions take place, some extra steps should be taken: (10) identify any new stakeholders, benefits, and costs; (11) monitor engagement; and (12) revise management strategy. Overall, we believe that our framework provides an effective approach to minimize the impact of conflicts created by alien species management., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Boom-bust dynamics - the rise of a population to outbreak levels, followed by a dramatic decline - have been associated with biological invasions and offered as a reason not to manage troublesome invaders. However, boom-bust dynamics rarely have been critically defined, analyzed, or interpreted. Here, we define boom-bust dynamics and provide specific suggestions for improving the application of the boom-bust concept. Boom-bust dynamics can arise from many causes, some closely associated with invasions, but others occurring across a wide range of ecological settings, especially when environmental conditions are changing rapidly. As a result, it is difficult to infer cause or predict future trajectories merely by observing the dynamic. We use tests with simulated data to show that a common metric for detecting and describing boom-bust dynamics, decline from an observed peak to a subsequent trough, tends to severely overestimate the frequency and severity of busts, and should be used cautiously if at all. We review and test other metrics that are better suited to describe boom-bust dynamics. Understanding the frequency and importance of boom-bust dynamics requires empirical studies of large, representative, long-term data sets that use clear definitions of boom-bust, appropriate analytical methods, and careful interpretations., (© 2017 John Wiley & Sons Ltd/CNRS.)

Invasive species are increasing in number, extent and impact worldwide. Effective invasion management has thus become a core socio-ecological challenge. To tackle this challenge, integrating spatial-temporal dynamics of invasion processes with modelling approaches is a promising approach. The inclusion of dynamic processes in such modelling frameworks (i.e. dynamic or hybrid models, here defined as models that integrate both dynamic and static approaches) adds an explicit temporal dimension to the study and management of invasions, enabling the prediction of invasions and optimisation of multi-scale management and governance. However, the extent to which dynamic approaches have been used for that purpose is under-investigated. Based on a literature review, we examined the extent to which dynamic modelling has been used to address invasions worldwide. We then evaluated how the use of dynamic modelling has evolved through time in the scope of invasive species management. The results suggest that modelling, in particular dynamic modelling, has been increasingly applied to biological invasions, especially to support management decisions at local scales. Also, the combination of dynamic and static modelling approaches (hybrid models with a spatially explicit output) can be especially effective, not only to support management at early invasion stages (from prevention to early detection), but also to improve the monitoring of invasion processes and impact assessment. Further development and testing of such hybrid models may well be regarded as a priority for future research aiming to improve the management of invasions across scales., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

The number of invaders and the timing of invasion are recognized as key determinants of successful invasions. Despite the recognized importance of "propagule pressure," invasion ecology has largely focused on how characteristics of the native community confer invasion resistance. We simultaneously manipulated community composition and invader propagule pressure in microcosm communities of freshwater bacteria. We show that high propagule pressures can be necessary to establish an invader population, but that the influence of propagule pressure depends on the composition of the resident species. In particular, the number of individuals invading was most important to invasion success when one of the species in a resident community is a strong competitor against other species. By contrast, the timing of invasion was most important when communities had lower growth rates. The results suggest that the importance of propagule pressure varies both between communities and within the same community over time, and therefore have implications for the way we understand the relationship between biotic resistance and invasion success., (© 2017 The Authors. Ecology, published by Wiley Periodicals, Inc., on behalf of the Ecological Society of America.)

In this study, the invasive plant species from the riparian vegetation in 56 sampling sites of Luanhe Basin were identified, and the correlations between their composition, spatial distribution and environmental factors were explored. In the basin, a total of 26 invasive species were registered, which belonged to 19 genera and 12 families, and 73.1% of them were annual plants. Asteraceae and Amaranthaceae were the two dominant families with the most invasive species, attributing to 50% of the total invasive species. Amaranthus retroflexus, Bidens frondosa and Chenopodium serotinum appeared with the highest frequencies. The number of invasive species and the invasive intensity at each site were significantly negatively correlated with the altitude. The distribution of invasive plants was significantly influenced by the intensity of human activities. The invasive plants were mainly distributed in the plain area, shallow mountainous area with many reservoirs, and the mountainous area with developed tourism around Chengde City, meanwhile, only few species with broad ecological amplitude existed in the plateau area. In general, species with higher invasive grades were mainly distributed in low and medium altitude areas below 400 m. Except for A. retroflexus, no high-grade invasive plants were discovered in high altitude area so far.

Interdisciplinarity is needed to gain knowledge of the ecology of invasive species and invaded ecosystems, and of the human dimensions of biological invasions. We combine a quantitative literature review with a qualitative historical narrative to document the progress of interdisciplinarity in invasion science since 1950. Our review shows that 92.4% of interdisciplinary publications (out of 9192) focus on ecological questions, 4.4% on social ones, and 3.2% on social-ecological ones. The emergence of invasion science out of ecology might explain why interdisciplinarity has remained mostly within the natural sciences. Nevertheless, invasion science is attracting social-ecological collaborations to understand ecological challenges, and to develop novel approaches to address new ideas, concepts, and invasion-related questions between scholars and stakeholders. We discuss ways to reframe invasion science as a field centred on interlinked social-ecological dynamics to bring science, governance and society together in a common effort to deal with invasions.

Background: Rodents of the genus Rattus are among the most pervasive and successful invasive species, causing major vicissitudes in native ecological communities. A broad and flexible generalist diet has been suggested as key to the invasion success of Rattus spp. Here, we use an indirect approach to better understand foraging niche width, plasticity, and overlap within and between introduced Rattus spp. in anthropogenic habitats and natural humid forests of Madagascar., Results: Based on stable carbon and nitrogen isotope values measured in hair samples of 589 individual rodents, we found that Rattus rattus had an extremely wide foraging niche, encompassing the isotopic space covered by a complete endemic forest-dwelling Malagasy small mammal community. Comparisons of Bayesian standard ellipses, as well as (multivariate) mixed-modeling analyses, revealed that the stable isotope niche of R. rattus tended to change seasonally and differed between natural forests and anthropogenic habitats, indicating plasticity in feeding niches. In co-occurrence, R. rattus and Rattus norvegicus partitioned feeding niches. Isotopic mismatch of signatures of individual R. rattus and the habitat in which they were captured, indicate frequent dispersal movements for this species between natural forest and anthropogenic habitats., Conclusions: Since R. rattus are known to transmit a number of zoonoses, potentially affecting communities of endemic small mammals, as well as humans, these movements presumably increase transmission potential. Our results suggest that due to their generalist diet and potential movement between natural forest and anthropogenic habitats, Rattus spp. might affect native forest-dependent Malagasy rodents as competitors, predators, and disease vectors. The combination of these effects helps explain the invasion success of Rattus spp. and the detrimental effects of this genus on the endemic Malagasy rodent fauna.

Human management of ecological systems, including issues like fisheries, invasive species, and restoration, as well as others, often must be undertaken with limited information. This means that developing general principles and heuristic approaches is important. Here, I focus on one aspect, the importance of an explicit consideration of time, which arises because of the inherent limitations in the response of ecological systems. I focus mainly on simple systems and models, beginning with systems without density dependence, which are therefore linear. Even for these systems, it is important to recognize the necessary delays in the response of the ecological system to management. Here, I also provide details for optimization that show how general results emerge and emphasize how delays due to demography and life histories can change the optimal management approach. A brief discussion of systems with density dependence and tipping points shows that the same themes emerge, namely, that when considering issues of restoration or management to change the state of an ecological system, that timescales need explicit consideration and may change the optimal approach in important ways., Competing Interests: The author declares no conflict of interest.

Philosophers and scientists alike have suggested Akaike's Information Criterion (AIC), and other similar model selection methods, show predictive accuracy justifies a preference for simplicity in model selection. This epistemic justification of simplicity is limited by an assumption of AIC which requires that the same probability distribution must generate the data used to fit the model and the data about which predictions are made. This limitation has been previously noted but appears to often go unnoticed by philosophers and scientists and has not been analyzed in relation to complexity. If predictions are about future observations, we argue that this assumption is unlikely to hold for models of complex phenomena. That in turn creates a practical limitation for simplicity's AIC-based justification because scientists modeling such phenomena are often interested in predicting the future. We support our argument with an ecological case study concerning the reintroduction of wolves into Yellowstone National Park, U.S.A. We suggest that AIC might still lend epistemic support for simplicity by leading to better explanations of complex phenomena., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Invasions are one of the most easily identified spatial phenomena in ecology, and have inspired a rich variety of theories for ecologists' and naturalists' consideration. However, a number of arguments over the sensitivities of invasion rates to stochasticity, density-dependence, dimension, and discreteness persist in the literature. The standard mathematical approach to invasions is based on Fisher's analysis of traveling waves solutions for the spread of an advantageous allele. In this paper, we exploit an alternative theory based on Ellner's premise that species invasions are best interpreted not as waves, but as random walks, and that the discreteness of living organisms is fundamentally important. Using a density-dependent invasion model in a stationary environment with indivisible (atomic) individuals where reproduction and dispersal are stochastic and independent, we show 4 key properties of Ellner's invasions previously suggested by simulation analysis: (1) greater spatial dispersal stochasticity quickens invasions, (2) greater demographic stochasticity slows invasions, (3) negative density-dependence slows invasions, and (4) greater temporal dispersal stochasticity quickens invasions. We prove the first three results by using generating functions and stochastic-dominance methods to rank furthest-forward dispersal distributions. The fourth result is proven in the special case of atomless theory, but remains an open conjecture in atomic theory. In addition, we explain why, unlike atomless invasions, an infinitely wide atomic invasion in two-dimensions can travel faster than a finite-width invasion and a one-dimensional invasion. The paper concludes with a classification of invasion dynamics based on dispersal kernel tails., (Copyright © 2016 Elsevier Inc. All rights reserved.)

How should we model evolution in spatially structured populations? Here, I review an evolutionary ecology approach based on the technique of spatial moment equations. I first provide a mathematical underpinning to the derivation of equations for the densities of various spatial configurations in network-based models. I then show how this spatial ecological framework can be coupled with an adaptive dynamics approach to compute the invasion fitness of a rare mutant in a resident population at equilibrium. Under the additional assumption that mutations have small phenotypic effects, I show that the selection gradient can be expressed as a function of neutral measures of genetic and demographic structure. I discuss the connections between this approach and inclusive fitness theory, as well as the applicability and limits of this technique. My main message is that spatial moment equations can be used as a means to obtain compact qualitative arguments about the evolution of life-history traits for a variety of life cycles., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Plant traits can be used to understand a range of ecological processes, including competition with invasive species. The extent to which native and invasive species are competing via limiting similarity or trait hierarchies has important implications for the management of invaded communities. We screened 47 native species that co-occur with Festuca perennis, a dominant invader in California serpentine grassland, for traits pertaining to resource use and acquisition. We then grew F. perennis with 10 species spanning a range of functional similarity in pairwise competition trials. Functionally similar species did not have a strong adverse effect on F. perennis performance as would be expected by limiting similarity theory. Phylogenetic relatedness, which may integrate a number of functional traits, was also a poor predictor of competitive outcome. Instead, species with high specific root length, low root-to-shoot biomass ratio, and low leaf nitrogen concentration were more effective at suppressing the growth of F. perennis. Our results suggest that fitness differences (i.e., trait hierarchies) may be more important than niche differences (i.e., limiting similarity) in structuring competitive outcomes in this system and may be a promising approach for the restoration of invaded systems., (© 2016 by the Ecological Society of America.)

Investigating the effects of invasive species on native biodiversity is one of the most pressing challenges in ecology. Our goal in this study was to quantify the effects of invasive plants on butterfly and moth communities. In addition, we sought to elucidate the fitness consequences of non-native hosts on lepidopterans. We conducted a meta-analysis on a total of 76 studies which provided data on larval performance, survival, oviposition preference, abundance, and species richness of Lepidoptera on native and exotic plants. Overwhelmingly, we found that performance and survival were reduced for larvae developing on exotic hosts, relative to native hosts. At the community level, alien plant invasion was associated with a reduction in the overall abundance and richness of lepidopteran communities. We found that lepidopterans did not show strong oviposition preference for native hosts. This result suggests that many invasive plant species may decrease lepidopteran abundance by providing a target for oviposition where larvae have a relatively poor chance of survival. Among studies that tested both survival and preference on exotic hosts, 37.5 % found evidence for novel hosts that could function as ecological traps (the figure was 18 % when considering studies that only assayed larval performance). Thus, although the majority of novel hosts included in our analyses are not likely to act as ecological traps, the potential clearly exists for this effect, and the role of ecological traps should be considered along with other aspects of global change impacting natural communities.

The Asian tiger mosquito Aedes albopictus (Skuse), is one of the most invasive mosquito species worldwide. In Mexico it is now recorded in 12 states and represents a serious public health problem, given the recent introduction of Chikungunya on the southern border. The aim of this study was to analyze the population genetics of A. albopictus from all major recorded foci, and model its ecological niche. Niche similarity with that from its autochthonous distribution in Asia and other invaded countries were analyzed and its potential future expansion and potential human exposure in climate change scenarios measured. We analyzed 125 sequences of a 317 bp fragment of the cyt b gene from seven A. albopictus populations across Mexico. The samples belong to 25 haplotypes with moderate population structuring (Fst=0.081, p<0.02) and population expansion. The most prevalent haplotype, found in all principal sites, was shared with the USA, Brazil, France, Madagascar, and Reunion Island. The ecological niche model using Mexican occurrence records covers 79.7% of the country, and has an 83% overlap with the Asian niche projected to Mexico. Both Neotropical and Nearctic regions are included in the Mexican niche model. Currently in Mexico, 38.6 million inhabitants are exposed to A. albopictus, which is expected to increase to 45.6 million by 2070. Genetic evidence supports collection information that A. albopictus was introduced to Mexico principally by land from the USA and Central and South America. Prevalent haplotypes from Mexico are shared with most invasive regions across the world, just as there was high niche similarity with both natural and invaded regions. The important overlap with the Asian niche model suggests a high potential for the species to disperse to sylvatic regions in Mexico., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Denmark was considered not to have an established population of free-ranging wild boar. Today, sporadic observations of wild boar challenge that view. Due to its reservoir role for economic devastating swine diseases, wild boar represents a potential threat for Denmark's position as a large pig- and pork-exporting country. This study assessed the prospects of wild boar invasion in Denmark. Multi-source citizen science data of wild boar observations were integrated into a multi-modelling approach linking habitat suitability models with agent-based, spatially-explicit simulations. We tested whether the currently observed presence of wild boar is due to natural immigration across the Danish-German border, or whether it is more likely that wild boar escaped fenced premises. Five observational data sources served as evaluation data: (1) questionnaires sent to all 1625 registered owners of Danish farm land, located in the 60 parishes closest to the border, (2) an online questionnaire, (3) a mobile web-based GPS application, (4) reports in the media or by governmental agencies, and (5) geo-referenced locations of fenced wild boar populations. Data covering 2008-2013 included 195 observations of wild boar, including 16 observations of breeding sows. The data from the Danish Nature Agency and the mailed questionnaires were consistent regarding the location of wild boar observations, while data from the Danish Veterinary and Food Administration, the media and the electronic questionnaires documented individual scattered observations in the rest of Jutland. Most observations were made in the region bordering Germany. It is uncertain whether the relatively few observations represent an established population. Model outcomes suggested that the origin of wild boar in about half of the area with sporadic observations of wild boar could be attributed to spatial expansions from a local Danish population near the border and consisting of wild boar originally of German origin. However, the other half, located distant to the border, were likely a result of animals escaping fenced premises inside the country. The approach serves as a template to assess the status of an invading species and improve the knowledge base for risk assessment and management decision., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Modeling the distributions of species, especially of invasive species in non-native ranges, involves multiple challenges. Here, we developed some novel approaches to species distribution modeling aimed at reducing the influences of such challenges and improving the realism of projections. We estimated species-environment relationships for Parthenium hysterophorus L. (Asteraceae) with four modeling methods run with multiple scenarios of (i) sources of occurrences and geographically isolated background ranges for absences, (ii) approaches to drawing background (absence) points, and (iii) alternate sets of predictor variables. We further tested various quantitative metrics of model evaluation against biological insight. Model projections were very sensitive to the choice of training dataset. Model accuracy was much improved using a global dataset for model training, rather than restricting data input to the species' native range. AUC score was a poor metric for model evaluation and, if used alone, was not a useful criterion for assessing model performance. Projections away from the sampled space (i.e., into areas of potential future invasion) were very different depending on the modeling methods used, raising questions about the reliability of ensemble projections. Generalized linear models gave very unrealistic projections far away from the training region. Models that efficiently fit the dominant pattern, but exclude highly local patterns in the dataset and capture interactions as they appear in data (e.g., boosted regression trees), improved generalization of the models. Biological knowledge of the species and its distribution was important in refining choices about the best set of projections. A post hoc test conducted on a new Parthenium dataset from Nepal validated excellent predictive performance of our 'best' model. We showed that vast stretches of currently uninvaded geographic areas on multiple continents harbor highly suitable habitats for parthenium. However, discrepancies between model predictions and parthenium invasion in Australia indicate successful management for this globally significant weed., (© 2015 John Wiley & Sons Ltd.)

Wild pigs (Sus scrofa), also known as wild swine, feral pigs, or feral hogs, are one of the most widespread and successful invasive species around the world. Wild pigs have been linked to extensive and costly agricultural damage and present a serious threat to plant and animal communities due to their rooting behavior and omnivorous diet. We modeled the current distribution of wild pigs in the United States to better understand the physiological and ecological factors that may determine their invasive potential and to guide future study and eradication efforts. Using national-scale wild pig occurrence data reported between 1982 and 2012 by wildlife management professionals, we estimated the probability of wild pig occurrence across the United States using a logistic discrimination function and environmental covariates hypothesized to influence the distribution of the species. Our results suggest the distribution of wild pigs in the U.S. was most strongly limited by cold temperatures and availability of water, and that they were most likely to occur where potential home ranges had higher habitat heterogeneity, providing access to multiple key resources including water, forage, and cover. High probability of occurrence was also associated with frequent high temperatures, up to a high threshold. However, this pattern is driven by pigs' historic distribution in warm climates of the southern U.S. Further study of pigs' ability to persist in cold northern climates is needed to better understand whether low temperatures actually limit their distribution. Our model highlights areas at risk of invasion as those with habitat conditions similar to those found in pigs' current range that are also near current populations. This study provides a macro-scale approach to generalist species distribution modeling that is applicable to other generalist and invasive species.

Our ecological knowledge base is extensive, but the motivations for research are many and varied, leading to unequal species representation and coverage. As this evidence is used to support a wide range of conservation, management and policy actions, it is important that gaps and biases are identified and understood. In this paper we detail a method for quantifying research effort and impact at the individual species level, and go on to investigate the factors that best explain between-species differences in outputs. We do this using British breeding birds as a case study, producing a ranked list of species based on two scientific publication metrics: total number of papers (a measure of research quantity) and h-index (a measure of the number of highly cited papers on a topic--an indication of research quality). Widespread, populous species which are native, resident and in receipt of biodiversity action plans produced significantly higher publication metrics. Guild was also significant, birds of prey the most studied group, with pigeons and doves the least studied. The model outputs for both metrics were very similar, suggesting that, at least in this example, research quantity and quality were highly correlated. The results highlight three key gaps in the evidence base, with fewer citations and publications relating to migrant breeders, introduced species and species which have experienced contractions in distribution. We suggest that the use of publication metrics in this way provides a novel approach to understanding the scale and drivers of both research quantity and impact at a species level and could be widely applied, both taxonomically and geographically.

The process by which a species becomes a biological invader, at a location where it does not naturally occur, can be divided into a series of sequential stages (transport, introduction, establishment and spread). A species' success at passing through each of these stages depends, in a large part, on the number of individuals available to assist making each transition. Here, we review the evidence that numbers determine success at each stage of the invasion process and then discuss the likely mechanisms by which numbers affect success. We conclude that numbers of individuals affect transport and introduction by moderating the likelihood that abundant (and widespread) species are deliberately or accidentally translocated; affect establishment success by moderating the stochastic processes (demographic, environmental, genetic or Allee) to which small, introduced populations will be vulnerable; and affect invasive spread most likely because of persistent genetic effects determined by the numbers of individuals involved in the establishment phase. We finish by suggesting some further steps to advance our understanding of the influence of numbers on invasion success, particularly as they relate to the genetics of the process., (© 2015 John Wiley & Sons Ltd.)

Herbert Baker arguably initiated the search for species characteristics determining alien plant invasion success, with his formulation of the 'ideal weed'. Today, a profusion of studies has tested a myriad of traits for their importance in explaining success of alien plants, but the multiple, not always appropriate, approaches used have led to some confusion and criticism. We argue that a greater understanding of the characteristics explaining alien plant success requires a refined approach that respects the multistage, multiscale nature of the invasion process. We present a schema of questions we can ask regarding the success of alien species, with the answering of one question in the schema being conditional on the answer of preceding questions (thus acknowledging the nested nature of invasion stages). For each question, we identify traits and attributes of species we believe are likely to be most important in explaining species success, and we make predictions as to how we expect successful aliens to differ from natives and from unsuccessful aliens in their characteristics. We organize the findings of empirical studies according to the questions in our schema that they have addressed, to assess the extent to which they support our predictions. We believe that research on plant traits of alien species has already told us a lot about why some alien species become successful after introduction. However, if we ask the right questions at the appropriate scale and use appropriate comparators, research on traits may tell us whether they are really important or not, and if so under which conditions., (© 2014 John Wiley & Sons Ltd.)

Invasion genetics is a relatively new discipline that investigates patterns of genetic variation in populations of invasive species and their ecological and evolutionary consequences. Evolutionary biologists have a long-standing interest in colonizing species, owing to their short life cycles and widespread distributions, but not until publication of The Genetics of Colonizing Species (1965), edited by H.G. Baker and G.L. Stebbins, was a synthesis on the genetics and evolution of colonizers available. Here, I make the case that the Baker and Stebbins volume is the foundational document for invasion genetics, and in conjunction with the increased use of genetic markers and development of invasion biology, resulted in the birth of this new field over the past two decades. I consider the historical origins and legacy of the Baker and Stebbins volume and review some of the key issues that were addressed. I provide biographical sketches of the two editors, emphasizing their contrasting backgrounds and personalities. I review examples from my own work on plant invasions that are relevant to issues discussed by contributors to the volume. These include the following: determinants of invasion success, life history trade-offs, generalist vs. specialist strategies, general-purpose genotypes, adaptive phenotypic plasticity, mating systems and the influence of bottlenecks on genetic variation. I conclude by posing several key questions in invasion genetics and argue that one of the main challenges that the area faces is to integrate experimental field studies of the ecology and demography of populations with the largely descriptive approaches that have tended to dominate most research to date., (© 2014 John Wiley & Sons Ltd.)

Environmental DNA (eDNA) methods are used to detect DNA that is shed into the aquatic environment by cryptic or low density species. Applied in eDNA studies, occupancy models can be used to estimate occurrence and detection probabilities and thereby account for imperfect detection. However, occupancy terminology has been applied inconsistently in eDNA studies, and many have calculated occurrence probabilities while not considering the effects of imperfect detection. Low detection of invasive giant constrictors using visual surveys and traps has hampered the estimation of occupancy and detection estimates needed for population management in southern Florida, USA. Giant constrictor snakes pose a threat to native species and the ecological restoration of the Florida Everglades. To assist with detection, we developed species-specific eDNA assays using quantitative PCR (qPCR) for the Burmese python (Python molurus bivittatus), Northern African python (P. sebae), boa constrictor (Boa constrictor), and the green (Eunectes murinus) and yellow anaconda (E. notaeus). Burmese pythons, Northern African pythons, and boa constrictors are established and reproducing, while the green and yellow anaconda have the potential to become established. We validated the python and boa constrictor assays using laboratory trials and tested all species in 21 field locations distributed in eight southern Florida regions. Burmese python eDNA was detected in 37 of 63 field sampling events; however, the other species were not detected. Although eDNA was heterogeneously distributed in the environment, occupancy models were able to provide the first estimates of detection probabilities, which were greater than 91%. Burmese python eDNA was detected along the leading northern edge of the known population boundary. The development of informative detection tools and eDNA occupancy models can improve conservation efforts in southern Florida and support more extensive studies of invasive constrictors. Generic sampling design and terminology are proposed to standardize and clarify interpretations of eDNA-based occupancy models.

The invasion of the giant Madagascar day gecko Phelsuma grandis has increased the threats to the four endemic Mauritian day geckos (Phelsuma spp.) that have survived on mainland Mauritius. We had two main aims: (i) to predict the spatial distribution and overlap of P. grandis and the endemic geckos at a landscape level; and (ii) to investigate the effects of P. grandis on the abundance and risks of extinction of the endemic geckos at a local scale. An ensemble forecasting approach was used to predict the spatial distribution and overlap of P. grandis and the endemic geckos. We used hierarchical binomial mixture models and repeated visual estimate surveys to calculate the abundance of the endemic geckos in sites with and without P. grandis. The predicted range of each species varied from 85 km2 to 376 km2. Sixty percent of the predicted range of P. grandis overlapped with the combined predicted ranges of the four endemic geckos; 15% of the combined predicted ranges of the four endemic geckos overlapped with P. grandis. Levin's niche breadth varied from 0.140 to 0.652 between P. grandis and the four endemic geckos. The abundance of endemic geckos was 89% lower in sites with P. grandis compared to sites without P. grandis, and the endemic geckos had been extirpated at four of ten sites we surveyed with P. grandis. Species Distribution Modelling, together with the breadth metrics, predicted that P. grandis can partly share the equivalent niche with endemic species and survive in a range of environmental conditions. We provide strong evidence that smaller endemic geckos are unlikely to survive in sympatry with P. grandis. This is a cause of concern in both Mauritius and other countries with endemic species of Phelsuma.

While the ecological impact of anthropogenically introduced exotic species is considered a major threat for biodiversity and ecosystems functioning, it is generally not accounted for in the environmental life cycle assessment (LCA) of products. In this article, we propose a framework that includes exotic species introduction in an LCA context. We derived characterization factors for exotic fish species introduction related to the transport of goods across the Rhine-Main-Danube canal. These characterization factors are expressed as the potentially disappeared fraction (PDF) of native freshwater fish species in the rivers Rhine and Danube integrated over space and time per amount of goods transported (PDF·m(3)·yr·kg(-1)). Furthermore, we quantified the relative importance of exotic fish species introduction compared to other anthropogenic stressors in the freshwater environment (i.e., eutrophication, ecotoxicity, greenhouse gases, and water consumption) for transport of goods through the Rhine-Main-Danube waterway. We found that the introduction of exotic fish species contributed to 70-85% of the total freshwater ecosystem impact, depending on the distance that goods were transported. Our analysis showed that it is relevant and feasible to include the introduction of exotic species in an LCA framework. The proposed framework can be further extended by including the impacts of other exotic species groups, types of water bodies and pathways for introduction.

Invasion science is a very active subdiscipline of ecology. However, some scientists contend that theoretical integration has been limited and that predictive power remains weak. This paper, focusing on plants, proposes a new multi-pronged research strategy that builds on recent advances in invasion science. More intensive studies on particular model organisms and ecosystems are needed to improve our understanding of the full suite of interacting factors that influence invasions ('model system research'). At the same time, comparative studies across many study systems are essential for unravelling the context-dependencies of insights that emerge from particular studies ('multi-site studies'); and quantitative synthesis based on large datasets should be constrained to well-defined theoretical domains ('focused meta-analysis'). We also suggest ways for better integration of information about species biology and ecosystem characteristics ('invasion syndromes'). We expect that a resulting theory of invasions will need to be conceived as a somewhat heterogeneous conglomerate of elements of varying generality and predictive power: laws that apply to well-specified domains, general concepts and theoretical frameworks that can guide thinking in research and management, and in-depth knowledge about the drivers of particular invasions., (© 2013 The Authors. New Phytologist © 2013 New Phytologist Trust.)

A major aim of invasion ecology is to identify characteristics of successful invaders. However, most plant groups studied in detail (e.g. pines and acacias) have a high percentage of invasive taxa. Here we examine the global introduction history and invasion ecology of Proteaceae--a large plant family with many taxa that have been widely disseminated by humans, but with few known invaders. To do this we compiled a global list of species and used boosted regression tree models to assess which factors are important in determining the status of a species (not introduced, introduced, naturalized or invasive). At least 402 of 1674 known species (24%) have been moved by humans out of their native ranges, 58 species (14%) have become naturalized but not invasive, and 8 species (2%) are invasive. The probability of naturalization was greatest for species with large native ranges, low susceptibility to Phytophthora root-rot fungus, large mammal-dispersed seeds, and with the capacity to resprout. The probability of naturalized species becoming invasive was greatest for species with large native ranges, those used as barrier plants, tall species, species with small seeds, and serotinous species. The traits driving invasiveness of Proteaceae were similar to those for acacias and pines. However, while some traits showed a consistent influence at introduction, naturalization and invasion, others appear to be influential at one stage only, and some have contrasting effects at different stages. Trait-based analyses therefore need to consider different invasion stages separately. On their own, these observations provide little predictive power for risk assessment, but when the causative mechanisms are understood (e.g. Phytophthora susceptibility) they provide valuable insights. As such there is considerable value in seeking the correlates and mechanisms underlying invasions for particular taxonomic or functional groups.

Invasion ecology has much advanced since its early beginnings. Nevertheless, explanation, prediction, and management of biological invasions remain difficult. We argue that progress in invasion research can be accelerated by, first, pointing out difficulties this field is currently facing and, second, looking for measures to overcome them. We see basic and applied research in invasion ecology confronted with difficulties arising from (A) societal issues, e.g., disparate perceptions of invasive species; (B) the peculiarity of the invasion process, e.g., its complexity and context dependency; and (C) the scientific methodology, e.g., imprecise hypotheses. To overcome these difficulties, we propose three key measures: (1) a checklist for definitions to encourage explicit definitions; (2) implementation of a hierarchy of hypotheses (HoH), where general hypotheses branch into specific and precisely testable hypotheses; and (3) platforms for improved communication. These measures may significantly increase conceptual clarity and enhance communication, thus advancing invasion ecology.

Humans are altering the global distributional ranges of plants, while their co-evolved herbivores are frequently left behind. Native herbivores often colonise non-native plants, potentially reducing invasion success or causing economic loss to introduced agricultural crops. We developed a predictive model to forecast novel interactions and verified it with a data set containing hundreds of observed novel plant-insect interactions. Using a food network of 900 native European butterfly and moth species and 1944 native plants, we built an herbivore host-use model. By extrapolating host use from the native herbivore-plant food network, we accurately forecasted the observed novel use of 459 non-native plant species by native herbivores. Patterns that governed herbivore host breadth on co-evolved native plants were equally important in determining non-native hosts. Our results make the forecasting of novel herbivore communities feasible in order to better understand the fate and impact of introduced plants., (© 2013 John Wiley & Sons Ltd/CNRS.)

This Special Issue of Ecology Letters presents contributions from an international meeting organised by Centre National de la Recherche Scientifique (CNRS) and Ecology Letters on the broad theme of ecological effects of global environmental change. The objectives of these articles are to synthesise, hypothesise and illustrate the ecological effects of environmental change drivers and their interactions, including habitat loss and fragmentation, pollution, invasive species and climate change. A range of disciplines is represented, including stoichiometry, cell biology, genetics, evolution and biodiversity conservation. The authors emphasise the need to account for several key ecological factors and different spatial and temporal scales in global change research. They also stress the importance of ecosystem complexity through approaches such as functional group and network analyses, and of mechanisms and predictive models with respect to environmental responses to global change across an ecological continuum: population, communities and ecosystems. Lastly, these articles provide important insights and recommendations for environmental conservation and management, as well as highlighting future research priorities., (© 2013 John Wiley & Sons Ltd/CNRS.)

Genetic and fossil data often lack the spatial and temporal precision for tracing the recent biogeographic history of species. Data with finer resolution are needed for studying distributional changes during modern human history. Here, I show that printed wormholes in rare books and artwork are trace fossils of wood-boring species with unusually accurate locations and dates. Analyses of wormholes printed in western Europe since the fifteenth century document the detailed biogeographic history of two putative species of invasive wood-boring beetles. Their distributions now overlap broadly, as an outcome of twentieth century globalization. However, the wormhole record revealed, unexpectedly, that their original ranges were contiguous and formed a stable line across central Europe, apparently a result of competition. Extension of the wormhole record, globally, will probably reveal other species and evolutionary insights. These data also provide evidence for historians in determining the place of origin or movement of a woodblock, book, document or art print.

In many North American rivers, populations of multiple species of non-native cyprinid fishes are present, including black carp (Mylpharyngodon piceus), grass carp (Ctenopharyngodon idella), bighead carp (Hypophthalmichthys nobilis), silver carp (Hypophthalmichthys molitrix), common carp (Cyprinus carpio), and goldfish (Carassius auratus). All six of these species are found in the Mississippi River basin and tracking their invasion has proven difficult, particularly where abundance is low. Knowledge of the location of the invasion front is valuable to natural resource managers because future ecological and economic damages can be most effectively prevented when populations are low. To test the accuracy of environmental DNA (eDNA) as an early indicator of species occurrence and relative abundance, we applied eDNA technology to the six non-native cyprinid species putatively present in a 2.6 river mile stretch of the Chicago (IL, USA) canal system that was subsequently treated with piscicide. The proportion of water samples yielding positive detections increased with relative abundance of the six species, as indicated by the number of carcasses recovered after poisoning. New markers for black carp, grass carp, and a common carp/goldfish are reported and details of the marker testing to ensure specificity are provided.

One source of potential harm from the cultivation of transgenic crops is their dispersal, persistence and spread in non-agricultural land. Ecological damage may result from such spread if the abundance of valued species is reduced. The ability of a plant to spread in non-agricultural habitats is called its invasiveness potential. The risks posed by the invasiveness potential of transgenic crops are assessed by comparing in agronomic field trials the phenotypes of the crops with the phenotypes of genetically similar non-transgenic crops known to have low invasiveness potential. If the transgenic and non-transgenic crops are similar in traits believed to control invasiveness potential, it may be concluded that the transgenic crop has low invasiveness potential and poses negligible ecological risk via persistence and spread in non-agricultural habitats. If the phenotype of the transgenic crop is outside the range of the non-transgenic comparators for the traits controlling invasiveness potential, or if the comparative approach is regarded as inadequate for reasons of risk perception or risk communication, experiments that simulate the dispersal of the crop into non-agricultural habitats may be necessary. We describe such an experiment for several commercial insect-resistant transgenic maize events in conditions similar to those found in maize-growing regions of Mexico. As expected from comparative risk assessments, the transgenic maize was found to behave similarly to non-transgenic maize and to be non-invasive. The value of this experiment in assessing and communicating the negligible ecological risk posed by the low invasiveness potential of insect-resistant transgenic maize in Mexico is discussed.