Projecting future expansion of invasive species: comparing and improving methodologies for species distribution modeling

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.     

Risk factors for helminth infections in a rural and a peri-urban setting of the Dongting Lake area, People's Republic of China

Schistosomiasis japonica and soil-transmitted helminthiasis are endemic parasitic diseases in the People’s Republic of China (PR China). As very few studies have reported on the distribution and interaction of multiple species helminth infections, we carried out a comparative study of households in a rural village and a peri-urban setting in the Dongting Lake area of Hunan province in November and December 2006 to determine the extent of single and multiple species infections, the underlying risk factors for infection, and the relationships with clinical manifestations and self-reported morbidity. In each household, stool samples were collected and subjected to the Kato-Katz method for identifying Schistosoma japonicum, Ascaris lumbricoides, hookworm and Trichuris trichiura infections. Clinical examinations were performed and questionnaire surveys conducted at both household and individual subject levels. Complete parasitological, clinical and questionnaire data were obtained for 1,298 inhabitants of the two settings. The overall prevalences of single infections of S. japonicum, A. lumbricoides, hookworm and T. trichiura were 6.5%, 5.5%, 3.0% and 0.8%, respectively; the majority of the infections were of light intensity. We found significant negative associations between wealth and infections with S. japonicum and A. lumbricoides. Clinical manifestations of splenomegaly, hepatomegaly and anaemia were prevalent (9.0%, 3.7% and 10.9%, respectively), the latter two being significantly (P < 0.05) associated with schistosomiasis. Self-reported symptoms were more common among females but there was considerable under-reporting in both sexes when relying only on spontaneous recall. Our findings may guide the design and targeting of a more equitable, comprehensive and integrated parasitic disease control programme in Hunan province and in other areas of PR China.     

Seed banks of invasive Australian Acacia species in South Africa: Role in invasiveness and options for management

Despite impressive efforts at clearing stands of invasive Australian Acacia species in South Africa, insufficient attention has been given to understanding the role of seed banks in the invasiveness and long-term persistence of populations. We review information on seeds of these species, considering seed production, seed rain, and the dynamics of seeds in three layers: leaf litter, and upper and lower seed banks in the soil. Many factors affect the accumulation and susceptibility to destruction of seed banks and thus the opportunities for intervention to reduce seed numbers for each of these components. Reduction of seed banks is crucial for the overall success of the multi-million dollar management initiatives against these species. Classical biological control of buds, flower and young pods has reduced the seed production of many Australian acacias in South Africa. Fire can be applied to reduce seed numbers in the leaf litter and upper seed bank in some cases, although there are serious problems associated with high fire intensities in dense acacia stands. Other options, e.g. soil inversion and solarisation, exist to exercise limited reduction of seed numbers in some situations. There is little prospect of meaningful reduction of seed numbers in the lower seed bank. Preventing the accumulation of seed banks by limiting seed production through biological control is by far the most effective means, and in almost all cases the only practical means, of reducing seed numbers. This must be an integral part of management strategies. Several invasive Australian acacias are already under effective biological control, and further work to identify additional potential agents for all the currently invasive species and potentially invasive alien species is the top priority for improving the efficiency of management programmes.     

Invasion dynamics and potential spread of the invasive alien plant species Ageratina adenophora (Asteraceae) in China

Ageratina adenophora (Sprengel) R. King & H. Robinson (=Eupatorium adenophorum Sprengel) is one of the worst invasive alien species in China. Since A. adenophora was first noticed in Yunnan Province of China in the 1940s, its rapid spread has caused an ecological problem in south‐western China. Understanding its historical invasion pattern and its potential for further spread is needed to plan the management of the species. We reconstructed the historical process of its invasion and analysed its ecological preferences in the invaded region. After a lag phase of 20 years (1940–60), A. adenophora spread rapidly throughout the south and middle subtropical zones in Yunnan, Guizhou, Sichuan, and Guangxi, China, with an average expansion rate of 20 km per year. It spread relatively slowly in north subtropical areas, with an average expansion rate of 6.8 km per year. It has not established in warm temperate areas within the invaded regions. Although range expansion in Yunnan stopped after 1990, the expansion of its range into neighbouring provinces indicates that A. adenophora has not reached the full potential of its distribution and its range is still rapidly expanding within China. We applied ecological niche modelling (GARP — Genetic Algorithm for Rule‐set Prediction) to predict potential invasion areas in mainland China on the basis of occurrence points within colonized areas where A. adenophora has reached equilibrium. The predictions, confirmed by the range of values of four key environmental parameters, generally match the parameters of the geography and ecology in the invaded region. Southern and south‐central China have climatic conditions suggestive of a high potential for invasion by A. adenophora. Climatic conditions in northern and western China appear unsuitable for A. adenophora. Urgent measures should be taken to prevent this species from further spreading into the vast areas of potential habitat in southern and south‐central China.     

The global invasion success of Central European plants is related to distribution characteristics in their native range and species traits

Aim Determining which traits predispose a species to become invasive is a fundamental question of invasion ecology, but traits affect invasiveness in concert with other factors that need to be controlled for. Here, we explore the relative effects of biological traits of plant species and their distributional characteristics in the native range on invasion success at two stages of invasion. Location Czech Republic (for native species); and the world (for alien species). Methods The source pool of 1218 species of seed plants native to Central Europe was derived from the flora of the Czech Republic, and their occurrence in 706 alien floras all over the world was recorded, distinguishing whether they were listed as an ‘alien’ or a ‘weed’ in the latest version of Randall’s ‘Global compendium of weeds’ database. The latter type of occurrence was considered to indicate species ability to invade and cause economic impact, i.e. a more advanced stage of invasion. Using the statistical technique of regression trees, we tested whether 19 biological traits and five distributional characteristics of the species in their native range can be used to predict species success in two stages of invasion. Results The probability of a species becoming alien outside its native distribution range is determined by the size of its native range, and its tolerance of a wide range of climates acquired in the region of origin. Biological traits play only an indirect role at this stage of invasion via determining the size of the native range. However, the ability of species to become a weed is determined not only by the above characteristics of native distribution, but also directly by biological traits (life form and strategy, early flowering, tall stature, generative reproduction, number of ploidy levels and opportunistic dispersal by a number of vectors). Species phylogenetic relatedness plays only a minor role; it is more important at the lowest taxonomic levels and at the later stage of invasion. Main conclusion The global success of Central European species as ‘weeds’ is determined by their distributional characteristics in the native ranges and by biological traits, but the relative importance of these determinants depends on the stage of invasion. Species which have large native ranges and are common within these ranges should be paid increased attention upon introductions, and the above biological traits should be taken into account in screening systems applied to evaluate deliberate introductions of alien plants to new regions.     

Phenotypic divergence during the invasion of Phyla canescens in Australia and France: evidence for selection-driven evolution

Rapid adaptive evolution has been advocated as a mechanism that promotes invasion. Demonstrating adaptive evolution in invasive species requires rigorous analysis of phenotypic shifts driven by selection. Here, we document selection-driven evolution of Phyla canescens , an Argentine weed, in two invaded regions (Australia and France). Invasive populations possessed similar or higher diversity than native populations, and displayed mixed lineages from different sources, suggesting that genetic bottlenecks in both countries might have been alleviated by multiple introductions. Compared to native populations, Australian populations displayed more investment in sexual reproduction, whereas French populations possessed enhanced vegetative reproduction and growth. We partitioned evolutionary forces (selection vs. stochastic events) using two independent methods. Results of both analyses suggest that the pattern of molecular and phenotypic variability among regions was consistent with selection-driven evolution, rather than stochastic events. Our findings indicate that selection has shaped the evolution of P . canescens in two different invaded regions.
Ecology Letters (2010) 13: 32–44     

我国“十三五”时期重要外来物种入侵防控科技进展与展望

随着经济全球化快速发展,外来物种入侵危害日益严重。“十三五”时期,我国针对当前面临的重大外来物种入侵威胁,按照基础前沿、共性关键技术与重大产品研发、典型应用示范研究3个层面,部署了一系列科技项目,取得了一批重大科研成果:阐明了入侵物种的入侵机理和进化机制,以及入侵植物与脆弱生态系统互作的调控机制;建立了潜在农业入侵生物信息分析平台,新发外来入侵物种的风险预测与评估模型,重大外来入侵物种的快速检测识别与监测预警技术,以及综合防控技术体系;围绕豚草、空心莲子草、苹果蠹蛾、番茄潜叶蛾、甜菜孢囊线虫等危害特点,开展全程防控技术应用示范。“十三五”期间,基本实现了潜在入侵物种数据量持续丰富完善,新发/突发入侵物种应急防控技术产品有效储备能力增强,重大入侵物种综合防控技术体系逐步健全的良好格局。面向“十四五”,建议继续支持外来物种入侵防控研究,推动“关口前移、疆域监控、灭除阻截、联控减灾”等核心技术的研发,实现有效防控生物入侵的重大目标。     

Tracking biological invasions in space and time: elucidating the invasive history of the green alga Codium fragile using old DNA

With the advent of 'ancient DNA' studies on preserved material of extant and extinct species, museums and herbaria now represent an important although still underutilized resource in molecular ecology. The ability to obtain sequence data from archived specimens can reveal the recent history of cryptic species and introductions. We have analysed extant and herbarium samples of the highly invasive green alga Codium fragile , many over 100 years old, to identify cryptic accessions of the invasive strain known as C. fragile ssp. tomentosoides , which can be identified by a unique haplotype. Molecular characterization of specimens previously identified as native in various regions shows that the invasive tomentosoides strain has been colonizing new habitats across the world for longer than records indicate, in some cases nearly 100 years before it was noticed. It can now be found in the ranges of all the other native haplotypes detected, several of which correspond to recognized subspecies. Within regions in the southern hemisphere there was a greater diversity of haplotypes than in the northern hemisphere, probably as a result of dispersal by the Antarctic Circumpolar Current. The findings of this study highlight the importance of herbaria in preserving contemporaneous records of invasions as they occur, especially when invasive taxa are cryptic.     

Genetic Diversities of Cymbidium mosaic virus and Odontoglossum ringspot virus Isolates Based on the Coat Protein Genes from Orchids in Guangdong Province,China

Orchids are some of the most important ornamental flowers. Cymbidium mosaic virus (CymMV) and Odontoglossum ringspot virus (ORSV) are the most prevalent and economically important viruses affecting orchids in China. In this study, 20 CymMV and 28 ORSV isolates were selected for genetic diversity analysis. The CymMV isolates shared 84.6–100% and 89.5–100% identities of coat protein (CP) at the nucleotide (nt) and amino acid (aa) levels, respectively. The identities of ORSV isolates were 96.4–100% (nt) and 92.5–99.4% (aa). The CP genes of CymMV were found to have genetic diversity, and the CP genes of ORSV were genetically conservative. These results can aid in designing effective disease‐control strategies.     

Occurrence of an invasive coral in the southwest Atlantic and comparison with a congener suggest potential niche expansion

Tubastraea tagusensis, a coral native to the Galapagos Archipelago, has successfully established and invaded the Brazilian coast where it modifies native tropical rocky shore and coral reef communities. In order to understand the processes underlying the establishment of T. tagusensis, we tested whether Maxent, a tool for species distribution modeling, based on the native range of T. tagusensis correctly forecasted the invasion range of this species in Brazil. The Maxent algorithm was unable to predict the Brazilian coast as a suitable environment for the establishment of T. tagusensis. A comparison between these models and a principal component analysis (PCA) allowed us to examine the environmental dissimilarity between the two occupied regions (native and invaded) and to assess the species' occupied niche breadth. According to the PCA results, lower levels of chlorophyll‐a and nitrate on the Atlantic coast segregate the Brazilian and Galapagos environments, implying that T. tagusensis may have expanded its realized niche during the invasion process. We tested the possible realized niche expansion in T. tagusensis by assuming that Tubastraea spp. have similar fundamental niches, which was supported by exploring the environmental space of T. coccinea, a tropical‐cosmopolitan congener of T. tagusensis. We believe that the usage of Maxent should be treated with caution, especially when applied to biological invasion (or climate change) scenarios where the target species has a highly localized native (original) distribution, which may represent only a small portion of its fundamental niche, and therefore a violation of a SDM assumption.     

Molecular identification and expression analysis of magnetic receptor in Spodoptera frugiperda (Lepidoptera: Noctuidae), an invasive species in China

The fall armyworm (FAW), Spodoptera frugiperda (Lepidoptera, Noctuidae), has emerged as a highly invasive pest globally in the past decade due to its remarkable migratory capabilities. Magnetic receptors play an important role in the migration and navigation of the animal, but little is known about the molecular mechanism of the magnetic receptors of S. frugiperda (SfMagR). In this study, we successfully cloned the cDNA encoding SfMagR, which has a 396 bp of open reading frame (ORF) encoding 132 amino acids. Phylogenetic analysis revealed a high conservation of magnetic receptors among various animal species, notably demonstrating a 98.4% sequence identity between S. frugiperda and Spodoptera litura, and a 70.3% identity with Homo sapiens, a vertebrate species. Expression analysis conducted across different developmental stages demonstrated SfMagR expression in the egg, larval, and pupal stages of the moth, but exhibited predominate expression in the adult stage, particularly in male adults. Moreover, the tissue expression profile indicated that SfMagR expression primarily occurred within the thorax of the moth, specifically in the thorax excluding the legs and wings. These findings not only provide fundamental data and a molecular foundation for future investigations into the function of SfMagR, but also offer valuable insights for the future management of invasive species.     

Trophic consequences of non‐native species for commercial fish in a backwater bay of the Three Gorges Reservoir,Southwest China

Trophic niche overlap in native and alien fish species can lead to competitive interactions whereby non‐native fishes outcompete indigenous individuals and eventually affect the viability of natural populations. The species Erythroculter mongolicus and Erythroculter ilishaeformis (belonging to the Culterinae), which are two commercially important fish species in the backwater bay of the Pengxi River in the Three Gorges Reservoir (TGR), were threatened by competition from the non‐native Coilia ectenes (lake anchovy). The latter is an alien species introduced into the lower reaches of the Yangtze River in China and now widespread in the TGR. The trophic consequences of non‐native lake anchovy invasion for E. mongolicus and E. ilishaeformis were assessed using stable isotope analysis (δ¹³C and δ¹⁵N) and associated metrics including the isotopic niche, measured as the standard ellipse area. The trophic niche of native E. mongolicus had little overlap (<15%) with the alien fish species and was significantly reduced in size after invasion by lake anchovy. This suggests that E. mongolicus shifted to a more specialized diet after invasion by lake anchovy. In contrast, the trophic niche overlap of native fish E. ilishaeformis with the alien fish species was larger (>50%) and the niche was obviously increased, implying that fish in this species exploited a wider dietary base to maintain their energetic requirements. Thus, marked changes for the native E. mongolicus and E. ilishaeformis were detected as the trophic consequences of invasion of non‐native lake anchovy.     

Predicting socio‐economic and biodiversity impacts of invasive species: Red Imported Fire Ant in the developing western Pacific

Effective biosecurity and pest management are fundamental to sustainable development. Invasive ants pose significant risks to the environment and economy, which are well‐managed by biosecurity agencies in developed countries. However, a comprehensive view of the potential impacts of invasive ants in developing Pacific Island Countries and Territories (PICTs) is lacking. We quantified the potential costs of the Red Imported Fire Ant (Solenopsis invicta Buren) across multiple sectors using an extrapolation analysis. Overall, we estimated that the impacts of Red Imported Fire Ant on developing PICTs could amount to over USD 329 million annually, corresponding to approximately 0.7% of combined GDP. Over half of the costs were predicted to result from impacts on the agriculture sector, a major source of employment and subsistence. We found that over 350 highly threatened species could be at risk from Red Imported Fire Ant. We would expect countries with Least Developed Country status and relatively low GDP to be least able to respond to an incursion of these ants, and as a result the costs could be higher than we have extrapolated. Red Imported Fire Ant could therefore potentially have considerable impact on the on‐going development of the region.     

Detection and Molecular Variability of Apple Stem Grooving Virus in Shaanxi,China

Apple stem grooving virus (ASGV) is one of the economically important latent viruses that are distributed in apple production areas worldwide. The presence of ASGV in apple trees was studied by serological assay and molecular biology methods. A total of 550 apple leaf samples from 14 different areas in Shaanxi were tested by DAS‐ELISA, and the results revealed an ASGV infection level of 55%. Those samples were also examined by RT‐PCR, and an infection level of 67% was found. Fourteen complete coat protein gene sequences of ASGV were obtained; phylogenetic analysis revealed that these 14 sequences separated into two clusters regardless of the geographic origin or host plants. To our knowledge, this is the first report of molecular variability analysis of ASGV in apple trees in China.     

Assessing the vulnerability of riparian vegetation to invasion by Mimulus guttatus: relative importance of biotic and abiotic variables in determining species occurrence and abundance

Riparian habitats are particularly susceptible to invasion by non‐native plants. At present, attempts to build consensus as to what the primary drivers of plant invasion in riparian ecosystems might be is hindered by the absence of common standards for data collected on plant species (e.g. occurrence, or relative abundance). Mimulus guttatus L., a non‐native riparian plant species, was used as a model to determine how environmental drivers influence two aspects of invasibility: species occurrence and abundance (assessed in relation to three variables number of patches, patch area and number of stems per patch). Mimulus occurrence and abundance, together with 20 environmental variables, were surveyed in almost 700 contiguous 50‐m‐long riverbank segments within a catchment in north‐east Scotland. More than half of the segments had been colonized by Mimulus. Occurrence and number of patches responded to similar environmental gradients, particularly bare sediment, boulders, high soil moisture, short‐statured ruderal communities, and open canopies, and tended to be highest downstream where the river was widest. In contrast to occurrence and patch number, patch area and stem number per patch were higher in the upper reaches of the catchment and were positively associated with low tree canopy and vegetation dominated by light‐demanding species and smaller‐statured species. Patch area and stem number per patch were also positively related to grazing. This study has highlighted the importance of assessing more than one measure of invasion success (occurrence or patch number and either patch area or stem number per patch), as they are each determined by a different suite of environmental variables. Abiotic factors, such as sediment availability and presence of boulders, appeared to be the major determinants of occurrence and patch number, whereas biotic factors, such as interspecific competition and grazing, were more important ecological determinants underlying area and stem number per patch.     

Combined modelling of distribution and niche in invasion biology: a case study of two invasive Tetramorium ant species

Spatial modelling of species distributions has become an important tool in the study of biological invasions. Here, we examine the utility of combining distribution and ecological niche modelling for retrieving information on invasion processes, based on species occurrence data from native and introduced ranges. Specifically, we discuss questions, concerning (1) the global potential to spread to other ranges, (2) the potential to spread within established invasions, (3) the detectability of niche differences across ranges, and (4) the ability to infer invasion history through data from the introduced range. We apply this approach to two congeneric pavement ants, Tetramorium sp.E (formerly T. caespitum (Linnaeus 1758)) and T. tsushimae Emery 1925, both introduced to North America. We identify (1) the potential of both species to inhabit ranges worldwide, and (2) the potential of T. sp.E and T. tsushimae, to spread to 23 additional US states and to five provinces of Canada, and to 24 additional US states and to one province of Canada, respectively. We confirm that (3) niche modelling can be an effective tool to detect niche shifts, identifying an increased width of T. sp.E and a decreased width of T. tsushimae following introduction, with potential changes in niche position for both species. We make feasible that (4) combined modelling could become an auxiliary tool to reconstruct invasion history, hypothesizing admixture following multiple introductions in North America for T. sp.E, and a single introduction to North America from central Japan, for T. tsushimae. Combined modelling represents a rapid means to formulate testable explanatory hypotheses on invasion patterns and helps approach a standard in predictive invasion research.     

A new genus and species of freshwater monostiliferous hoplonemertean (Nemertea, Enopla) from the People's Republic of China

A new genus and species of freshwater monostiliferous hoplonemertean, Limnemertes poyangensis gen. et sp. nov., from Poyang Lake, People's Republic of China, is described and illustrated. The taxon is compared and contrasted with previously described freshwater hoplonemerteans. This is the fourth species of freshwater nemertean to be described from China and the first recorded from Poyang Lake.     

Athletic anurans: the impact of morphology,ecology and evolution on climbing ability in invasive cane toads

Although primarily terrestrial, cane toads (Rhinella marina) sometimes climb near‐vertical surfaces (tree‐trunks, cliffs, fences) during foraging or dispersal activities. We scored climbing ability (in laboratory trials) of 288 cane toads from four regions in Australia, plus two sites on the island of Hawai'i. We found strong divergence in climbing ability associated not only with sex and relative limb length, but also population of origin. Within each population, longer‐limbed individuals (and hence, males rather than females) were better climbers, although the geographical divergence in climbing ability remained significant even when sex and limb length were included in multivariate regression models. The geographical difference in climbing ability (but not morphology) disappeared when the progeny were raised in captivity under identical conditions, without climbing opportunities. Although influenced by morphology, climbing ability in wild‐caught cane toads appears to be driven primarily by local environmental conditions that facilitate and/or reward arboreal activity.