Biological and ecological characteristics of invasive species: a gammarid study

Knowledge of characteristics helpful in screening potential invaders and in elaborating strategies to limit their success is highly desirable. We focused on gammarid amphipods from Western Europe and North America to discover biological and/or ecological traits that may explain successful invasion by these species. Two typologies were considered: an analytical one, with groups built on the basis of biological or ecological similarities, and an empirical one, with groups constituted a priori according to a species’ invasive status and its fresh or brackish water origin. The results obtained are discussed in the light of three hypotheses that may influence invasiveness: biotic potential, species size and euryoeciousness. The analysis revealed a particular ecological profile for invaders, with a strong influence of salinity tolerance, but no typology was found based on biological characteristics. Invasiveness cannot be predicted from a limited number of criteria, and is the result of a combination of several characteristics. Invasive species therefore exhibit a particular ecological profile rather than a biological one, contrary to most classical explanations.     

Phylogeography of the widespread marine invader Microcosmus squamiger (Ascidiacea) reveals high genetic diversity of introduced populations and non-independent colonizations

The spread of non-indigenous species into new marine habitats represents an increasing threat to global diversity. Genetic techniques provide basic understanding of the invasion processes. The ascidian Microcosmus squamiger is considered to be native to Australia, having been spread worldwide via transoceanic vessels. It has successfully invaded artificial and natural habitats where it has become a pest. We studied phylogeography and genetic structure of 12 M. squamiger populations, including samples from its native range (Australia) and introduced populations from the Indian, Pacific, and Atlantic oceans, as well as the Mediterranean Sea. We amplified 574 bp of the mitochondrial COI gene in 258 individuals and found a total of 52 haplotypes. A haplotype tree revealed two main groups of haplotypes. The relative frequency of each group of haplotypes, multidimensional scaling, and analysis of molecular variance showed important differences between the western Australia localities and the remaining ones (eastern Australia and introduced populations). Furthermore, we found that the colonization of the different areas by M. squamiger has not occurred independently, as many introduced populations shared some low frequency alleles. A nested clade analysis showed a global pattern of restricted gene flow with isolation by distance, although we found episodes of long-distance dispersal in some clades. A contiguous range expansion was detected between Australian populations. We conclude that M. squamiger is native to Australia and has most likely expanded its range of distribution sequentially through worldwide shipping, especially from the harbours of the more populated eastern Australia. In introduced populations, we found a high genetic diversity which suggests enhanced invasive potential. Consequently, there is a need to control this species, as it outcompetes local biota and is an economic threat.     

A rapid survey of the invasive plant species in western Angola

Angola is one of the most neglected African countries in terms of botanical research, in respect of both native and naturalized species. We conducted a rapid assessment of invasive plant species in western Angola during August 2014. In thirteen primary vegetation types, we recorded populations of 44 naturalized plant species, nineteen of which are conclusively invasive (spreading far from introduction sites). Dense invasive populations of Chromolaena odorata, Inga vera and Opuntia stricta pose the greatest environmental and economic threats. Some species with known taxonomic and/or biogeographic uncertainties (e.g. Chromolaena odorata and Ageratina adenophora) or which lacked key characteristics for identification such as flowers during our survey (e.g. Eucalyptus spp.) were subjected to DNA barcoding for comparisons with available genetic data from other studies. This approach allowed us to confirm the identity of taxonomically challenging taxa such as Inga vera, Opuntia stricta and Prosopis chilensis, to conclusively differentiate Chromolaena odorata from Ageratina adenophora, and identify the subspecific identity of Acacia saligna. Canonical correspondence analysis was used to assess the presence and abundance of invasive plant species with respect to the major abiotic factors and vegetation types. Three fairly distinct groups of species emerge from this analysis: (i) species of dry lowland habitats (Calotropis gigantea, Leucaena leucocephala and Opuntia stricta); (ii) species of relatively wet habitats at mid elevations (Ageratum conyzoides, Bidens pilosa, Cardiospermum grandiflorum, Chromolaena odorata, Solanum mauritianum and Tithonia diversifolia); and (iii) upland species (Ageratina adenophora, Galinsoga parviflora and Tagetes minuta). Several invasive species that are widespread in other tropical and subtropical African countries are currently either missing (e.g. many Australian Acacia species, Azolla filiculoides, Broussonetia papyrifera, Clidemia hirta, Parthenium hysterophorus, Rubus rosaefolius, Salvinia molesta), have only very localized populations in Angola (e.g. Lantana camara, Prosopis chilensis) or exist only as planted individuals (e.g. Acacia mearnsii and A. saligna subsp. saligna).     

The threat of invasive species to bats: a review

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Revisiting the use of the invasive species concept: An empirical approach

Invasion science has not been developed without controversies. Two questions that are still unsolved are: what is an invasive species?, and are invasive species an inherent conservation problem? These questions have led to discussions about effects versus origins. In contrast to the definitional problems, a unified framework describing invasion as a step‐by‐step process has been widely accepted. I conducted a bibliographic search with two separate databases searching for (i) evidence of less use of controversial terms over time; (ii) how many articles defined ‘invasive species’; (iii) the criteria used to define a species as invasive; and (iv) in which stage of the invasion continuum were species labelled as invasive located. My results show that controversial terms are widely used, that authors rarely define ‘invasive species’ and, often, it is very complicated to determine which criterion they used. In addition, only a fraction of the species labelled as invasive could be classified as such according to the unified framework of invasion stages. This is not a merely semantic issue, because invasive is a strong and value‐laden term that is used to guide environmental agendas. The uncritical use of a key concept could hamper research, complicate communication among peers and produce mixed results.     

Two colonisation stages generate two different patterns of genetic diversity within native and invasive ranges of Ulex europaeus

Genetic diversity and the way a species is introduced influence the capacity of populations of invasive species to persist in, and adapt to, their new environment. The diversity of introduced populations affects their evolutionary potential, which is particularly important for species that have invaded a wide range of habitats and climates, such as European gorse, Ulex europaeus. This species originated in the Iberian peninsula and colonised Europe in the Neolithic; over the course of the past two centuries it was introduced to, and has become invasive in, other continents. We characterised neutral genetic diversity and its structure in the native range and in invaded regions. By coupling these results with historical data, we have identified the way in which gorse populations were introduced and the consequences of introduction history on genetic diversity. Our study is based on the genotyping of individuals from 18 populations at six microsatellite loci. As U. europaeus is an allohexaploid species, we used recently developed tools that take into account genotypic ambiguity. Our results show that genetic diversity in gorse is very high and mainly contained within populations. We confirm that colonisation occurred in two stages. During the first stage, gorse spread out naturally from Spain towards northern Europe, losing some genetic diversity. During the second stage, gorse was introduced by humans into different regions of the world, from northern Europe. These introductions resulted in the loss of rare alleles but did not significantly reduce genetic diversity and thus the evolutionary potential of this invasive species.     

Contrasting patterns of genetic variation and structure in plant invasions of mountains

Aim To assess the population genetic consequences of the colonization of two species with contrasting mating systems, Solidago canadensis and Lactuca serriola, along altitudinal gradients in both their native and introduced ranges. Location Allegheny Mountains, West Virginia and Wallowa Mountains, Oregon, USA; Valais, southern Switzerland. Methods Leaf material was collected from populations along altitudinal gradients and genotyped at seven microsatellite loci for each species. Differences in variability between native and introduced areas and in relation to altitude were analysed using linear models. Differences in the genetic, geographical and altitudinal structure of populations between areas were analysed by AMOVA, cluster analysis and Mantel tests. Results Genetic variation within and across populations of S. canadensis was significantly reduced, while populations of L. serriola were significantly more variable, in the introduced area. Genetic diversity decreased significantly with altitude for S. canadensis but not L. serriola. Genetic structure of S. canadensis was similar in both areas, and populations were isolated by geographical but not altitudinal distance. By contrast, population structure of L. serriola was much weaker in the introduced area, and populations were not isolated by distance in either area. Main conclusions Solidago canadensis has experienced a strong genetic bottleneck on introduction to the Valais, but this has not prevented it from colonizing a wide altitudinal range. Variation in neutral markers is therefore not necessarily a good measure for judging the ecological behaviour of a species. By contrast, the greater variability of L. serriola in the introduced area, where it also occurs over a greater altitudinal range, can be explained by increased outcrossing among admixed populations. This suggests that the ecological amplitude of alien species might be enhanced after population admixture in the new range, especially for species with highly structured native populations. However, even genetically depauperate introduced populations can be expected to colonize the same environmental range that they occupy in the native area.     

Phenology in a warming world: differences between native and non‐native plant species

Phenology is a harbinger of climate change, with many species advancing flowering in response to rising temperatures. However, there is tremendous variation among species in phenological response to warming, and any phenological differences between native and non‐native species may influence invasion outcomes under global warming. We simulated global warming in the field and found that non‐native species flowered earlier and were more phenologically plastic to temperature than natives, which did not accelerate flowering in response to warming. Non‐native species' flowering also became more synchronous with other community members under warming. Earlier flowering was associated with greater geographic spread of non‐native species, implicating phenology as a potential trait associated with the successful establishment of non‐native species across large geographic regions. Such phenological differences in both timing and plasticity between native and non‐natives are hypothesised to promote invasion success and population persistence, potentially benefiting non‐native over native species under climate change.     

Recent behavioural and population genetic divergence of an invasive ant in a novel environment

Aim Invasive species frequently exhibit high temporal and spatial variation in abundance. Although ecological aspects undoubtedly affect this variation, genetic factors may also play a part. The invasive unicolonial yellow crazy ant Anoplolepis gracilipes exhibits considerable variation in abundance throughout its extensive distribution in Australia’s Northern Territory, where it was first detected in the 1980s. First, we aimed to determine whether A. gracilipes variation in abundance was associated with behavioural and genetic differentiation of the population and to determine whether one or more introductions occurred. Second, we investigated whether the A. gracilipes population was genetically and behaviourally heterogeneous to determine whether population divergence has occurred since introduction. Location Tropical monsoonal savanna in Arnhem Land, Northern Territory, Australia. Methods Ant abundances were assessed at 13 sites throughout the study region. We used mitochondrial DNA sequences and microsatellite molecular markers to determine population genetic structure, which we correlated with abundance. Behavioural differentiation was assayed using aggression trials and analysed together with genetic data to investigate population divergence. Results Although we found considerable variation in abundance, we found no association between population structure and differences in abundance. Our analyses suggest that A. gracilipes ants in Arnhem Land resulted from a single introduction. The population is not homogeneous, however, as aggression scores varied over both genetic and geographic distance. We also found a positive relationship between genetic and geographic distance. Main conclusions The variation in abundance in the Arnhem Land population of A. gracilipes is clearly not owing to invasion by ants from different sources. The genetic and behavioural differentiation we observed is suggestive of incipient genetic and behavioural divergence, which may be expected over time when an invasive species enters in a new environment.     

Discordant patterns of genetic and phenotypic differentiation in five grasshopper species codistributed across a microreserve network

Conservation plans can be greatly improved when information on the evolutionary and demographic consequences of habitat fragmentation is available for several codistributed species. Here, we study spatial patterns of phenotypic and genetic variation among five grasshopper species that are codistributed across a network of microreserves but show remarkable differences in dispersal‐related morphology (body size and wing length), degree of habitat specialization and extent of fragmentation of their respective habitats in the study region. In particular, we tested the hypothesis that species with preferences for highly fragmented microhabitats show stronger genetic and phenotypic structure than codistributed generalist taxa inhabiting a continuous matrix of suitable habitat. We also hypothesized a higher resemblance of spatial patterns of genetic and phenotypic variability among species that have experienced a higher degree of habitat fragmentation due to their more similar responses to the parallel large‐scale destruction of their natural habitats. In partial agreement with our first hypothesis, we found that genetic structure, but not phenotypic differentiation, was higher in species linked to highly fragmented habitats. We did not find support for congruent patterns of phenotypic and genetic variability among any studied species, indicating that they show idiosyncratic evolutionary trajectories and distinctive demographic responses to habitat fragmentation across a common landscape. This suggests that conservation practices in networks of protected areas require detailed ecological and evolutionary information on target species to focus management efforts on those taxa that are more sensitive to the effects of habitat fragmentation.     

Higher genetic diversity in introduced than in native populations of the mussel Mytella charruana: evidence of population admixture at introduction sites

Aim  Levels of genetic diversity can be used to determine haplotype frequency, population size and patterns of invasive species distribution. In this study, we sought to investigate the genetic structure of the invasive marine mussel Mytella charruana and compare variation from invasive populations with variation found within three native populations.
Location  Invaded areas in the USA (Florida, Georgia); native areas in Ecuador, Colombia and Brazil.
Methods  We sequenced 722 bp of the mitochondrial COI gene from 83 M. charruana samples from four invasive populations (USA) and 71 samples from two natural populations (Ecuador, Columbia). In addition, we sequenced 31 individuals of a congeneric species, Mytella guyanensis , from Salvador, Brazil. We constructed the phylogenetic relationship among all haplotypes and compared diversity measures among all populations.
Results  We found significantly higher levels of nucleotide diversity in invasive populations than in native populations, although the number of haplotypes was greater in the native populations. Moreover, mismatch distribution analyses resulted in a pattern indicative of population admixture for the invasive populations. Conversely, mismatch distributions of native populations resulted in a pattern indicative of populations in static equilibrium.
Main conclusion  Our data present compelling evidence that the M. charruana invasion resulted from admixture of at least two populations, which combined to form higher levels of genetic diversity in invasive populations. Moreover, our data suggest that one of these populations originated from the Caribbean coast of South America. Overall, this study provides an analysis of genetic diversity within invasive populations and explores how that diversity may be influenced by the genetic structure of native populations and how mass dispersal may lead to invasion success.     

中国外来入侵物种的分布与传入路径分析

外来物种入侵已成为全球性的环境问题,本文采用文献调研,实地考察与专家咨询相结合的方式,调查了全国陆生,淡水水生生态系统中外来入侵微生物,无脊椎动物,两栖爬行类,鱼类,鸟类,哺乳类,杂草,树木和海洋生态系统中外来入侵物种的种类及分类地位,起源,引入路径和环境影响等内容。查明我国共有283种外来入侵物种,其中外来入侵微生物,水生植物,陆生植物,水生无脊椎动物,陆生无脊椎动物,两栖爬行类,鱼类,哺乳类分别为19种,18种,170种,25种,33种,3种,10种和5种,来源于美洲,欧洲,亚洲,非洲,大洋洲的外来入侵物种分别占55.1%,21.7%,9.9%.8.1%和0.6%。我国对外来物种的引进存在一定程度的盲目性;50.%的外来入侵植物是作为牧草或饲料,观赏植物,纤维植物,药用植物,蔬菜,草坪模特而引进的;25%的外来入侵动物是用于养殖,观赏,生物防治的引种,对外来物种只重引进,疏于管理,也可能导致外来物种逃逸到自然环境中,造成潜在的环境意传入的;76.3%的外来入侵动物是由于检查不严,随贸易物品或运输工具传入我国的。因此,我国既要加强检疫工作,又要对外来物种的有意引进进行严格管理,实行外来物种引进的风险评估制度。     

Capwire: a R package for estimating population census size from non‐invasive genetic sampling

Non‐invasive genetic sampling is an increasingly popular approach for investigating the demographics of natural populations. This has also become a useful tool for managers and conservation biologists, especially for those species for which traditional mark–recapture studies are not practical. However, the consequence of collecting DNA indirectly is that an individual may be sampled multiple times per sampling session. This requires alternative statistical approaches to those used in traditional mark–recapture studies. Here we present the R package capwire , an implementation of the population size estimators of Miller et al. (Molecular Ecology 2005; 14 : 1991), which were designed to deal specifically with this type of sampling. The aim of this project is to enable users across platforms to easily manipulate their data and interact with existing R packages. We have also provided functions to simulate data under a variety of scenarios to allow for rigorous testing of the robustness of the method and to facilitate further development of this approach.     

Threat and management strategies of potentially invasive insects in China

The Global Invasive Species Database, GISD, comprises 27 species of the most significant invasive alien insects in the world (through November, 2005), 6 of which are originally native to China, 11 are established in China, and 10 have a potential invasion threat to China. This paper discusses these species in terms of distribution, harmfulness and dispersal ways, and finds that: (i) Information regarding invasive insects in the GISD remains inadequate. Such harmful invasive species as Opogona sacchari (Bojer), Oracella acuta (Lobdell), and Dendroctonus valens LeConte are not included. (ii) Ten species of invasive insects, particularly Lasius neglectus Van Loon and Linepithema humile (Mayr) which become established in areas near China, have the potential to become established in China. (iii) Special attention should be paid to species from Asia and the Americas because of their greater likelihood of becoming established in China. Finally, some management strategies including legislation, quarantine, early warning, prevention and control are suggested.