Extensive contiguous north–south range expansion of the original population of an invasive lizard in Florida

Florida has one of the two worst non-indigenous invasive species problems in the United States, and all such species are considered by statute to be a potential ecological problem. Unfortunately, little information is available about most of Florida's invasive species. Here, we provide information on range expansion of a population of one of the lesser-known species. The Palm Beach County, Florida, population of the northern curly-tailed lizard, Leiocephalus carinatus armouri, was examined for north–south expansion of its previously documented range. Observations were conducted as contiguous expansion outward from the previously known range. We found a substantial contiguous range expansion by a minimum of 46.3 km to the south and 34.1 km to the north. This species appears to be closely associated with coastal habitat degradation in the form of human infrastructure, especially ageing pavement, sea walls, buildings, and bridge bases.     

A model describing the effect of sex-reversed YY fish in an established wild population: The use of a Trojan Y chromosome to cause extinction of an introduced exotic species

A novel means of inducing extinction of an exotic fish population is proposed using a genetic approach to shift the ratio of male to females within a population. In the proposed strategy, sex-reversed fish containing two Y chromosomes are introduced into a normal fish population. These YY fish result in the production of a disproportionate number of male fish in subsequent generations. Mathematical modeling of the system following introduction of YY fish at a constant rate reveals that female fish decline in numbers over time, leading to eventual extinction of the population.     

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.     

Land use history, hurricane disturbance, and the fate of introduced species in a subtropical wet forest in Puerto Rico

Tropical forests are suffering from increasing intensities and frequency of disturbances. As a result, non-native species accidentally introduced or intentionally planted for farming, plantations, and ornamental purposes may spread and potentially invade undisturbed native forest. It is not known if these introduced species will become invasive, as a result of recurrent natural disturbances such as hurricanes. Using data from three censuses (spanning 15 years) of a 16-ha subtropical wet forest plot, we investigated the impact of two hurricanes on populations of plant species that were planted in farms and plantations that were then abandoned and from the natural spread of species introduced into Puerto Rico in the past. The populations of four species (Citrus paradis, Mangifera indica, Musa sp., and Simarouba glauca) changed little over time. Six species (Artocarpus altilis, Calophyllum calaba, Genipa americana, Hibiscus pernambucensis, Syzygium jambos, and Swietenia macrophylla) declined between the first two censuses after Hurricane Hugo, then increased again in Census 3 after Hurricane Georges. Spathodea campanulata gradually increased from census to census, while Coffea arabica declined. These introduced species represent only a small part of the forest basal area and few show signs of increasing over time. The number of stems per plant, new recruits, and the growth rates of these introduced species were within the ranges of those for native plant species. The mortality rates over both census intervals were significantly lower for introduced species (<5% year⁻¹) than for native ones (15% year⁻¹). Many new recruits established after Hurricane Hugo (prior to this study) had opened the forest canopy and these high mortality rates reflect their death as the canopy recovered. Only Swietenia macrophylla and Syzygium jambos showed an increase in stem numbers in the closed canopy area of forest that had suffered limited human disturbance in the past. A future increase in frequency of disturbance may enable greater stem numbers of introduced species to establish, while lower-mortality rates compared to native species, may allow them to persist during inter-hurricane intervals. An increase in the population of introduced species, especially for those that grow into large trees, may have an impact on this tropical forest in the future.     

Environmental tolerance of an invasive riparian tree and its potential for continued spread in the southwestern US

Questions: Exotic plant invasion may be aided by facilitation and broad tolerance of environmental conditions, yet these processes are poorly understood in species‐rich ecosystems such as riparian zones. In the southwestern United States (US) two plant species have invaded riparian zones: tamarisk (Tamarix ramosissima, T. chinensis, and their hybrids) and Russian olive (Elaeagnus angustifolia). We addressed the following questions: (1) is Russian olive able to tolerate drier and shadier conditions than cottonwood and tamarisk? (2) Can tamarisk and cottonwood facilitate Russian olive invasion? Location: Arid riparian zones, southwestern US. Methods: We analyzed riparian tree seedling requirements in a controlled experiment, performed empirical field studies, and analyzed stable oxygen isotopes to determine the water sources used by Russian olive. Results: Russian olive survival was significantly higher in dense shade and low moisture conditions than tamarisk and cottonwood. Field observations indicated Russian olive established where flooding cannot occur, and under dense canopies of tamarisk, cottonwood, and Russian olive. Tamarisk and native riparian plant species seedlings cannot establish in these dry, shaded habitats. Russian olive can rely on upper soil water until 15 years of age, before utilizing groundwater. Conclusions: We demonstrate that even though there is little evidence of facilitation by cottonwood and tamarisk, Russian olive is able to tolerate dense shade and low moisture conditions better than tamarisk and cottonwood. There is great potential for continued spread of Russian olive throughout the southwestern US because large areas of suitable habitat exist that are not yet inhabited by this species.     

Predicting the impacts of an introduced species from its invasion history: an empirical approach applied to zebra mussel invasions

1. Quantitative models of impact are lacking for the vast majority of known invasive species, particularly in aquatic ecosystems. Consequently, managers lack predictive tools to help them prioritise invasion threats and decide where they can most effectively allocate limited resources. Predictive tools would also enhance the accuracy of water quality assessments, so that impacts caused by an invader are not erroneously attributed to other anthropogenic stressors. 2. The invasion history of a species is a valuable guide for predicting the consequences of its introduction into a new environment. Regression analysis of data from multiple invaded sites can generate empirical models of impact, as is shown here for the zebra mussel Dreissena polymorpha. Dreissena's impacts on benthic invertebrate abundance and diversity follow predictable patterns that are robust across a range of habitat types and geographic regions. Similar empirical models could be developed for other invaders with a documented invasion history. 3. Because an invader's impact is correlated with its abundance, a surrogate model may be generated (when impact data are unavailable) by relating the invader's abundance to environmental variables. Such a model could help anticipate which habitats will be most affected by invasion. Lack of precision should not be a deterrent to developing predictive models where none exist. Crude predictions can be refined as additional data become available. Empirical modelling is a highly informative and inexpensive, but underused, approach in the management of aquatic invasive species.     

Resistance of an invasive gastropod to an indigenous trematode parasite in Lake Malawi

Successful establishment and spread of biological invaders may be promoted by the absence of population-regulating enemies such as pathogens, parasites or predators. This may come about when introduced taxa are missing enemies from their native habitats, or through immunity to enemies within invaded habitats. Here we provide field evidence that trematode parasites are absent in a highly invasive morph of the gastropod Melanoides tuberculata in Lake Malawi, and that the invasive morph is resistant to indigenous trematodes that castrate and induce gigantism in native M. tuberculata. Since helminth infections can strongly influence host population abundances in other host-parasite systems, this enemy release may have provided an advantage to the invasive morph in terms of reproductive capacity and survivorship.     

Population structure of an introduced species (Dreissena polymorpha) along a wave-swept disturbance gradient

The zebra mussel Dreissena polymorpha was introduced to North America during the mid-1980s, and is now a dominant member of many benthic communities in the lower Great Lakes. In this study, I explored the abundance, biomass, size structure and settlement of Dreissena inhabiting rocks along a wave-swept disturbance gradient near Middle Sister Island in western Lake Erie. Ten rocks were collected from quadrats at six sites along each of three transect lines oriented perpendicular to shore. Occurrence, abundance and biomass of Dreissena on smaller, movable rocks were positively associated with rock distance from shore (lake depth) and with rock area; rocks at nearshore sites supported little, if any, Dreissena, whereas those at offshore sites were heavily colonized. Mussel size distributions also differed in relation to shore distance. Large mussels (19 mm) were underrepresented or absent on rocks collected at nearshore sites, but were overrepresented at offshore locations (37 m). Settlement of larval mussels on settling pads was positively correlated with distance offshore and with time of exposure, though settlement was substantial even at a nearshore (10 m) location. Area-adjusted mussel dry mass increased more rapidly with distance offshore on large than on small rocks. Large rocks also required more force to displace and were significantly less likely to be disturbed when transplanted at the study site. Results from this study indicate that occurrence, abundance and size structure of Dreissena in nearshore waters of Lake Erie correspond with the frequency of habitat disturbance, though other factors including food limitation and larval supply may also contribute to these patterns. These patterns complement studies that established the significance of physical disturbance in other aquatic systems.     

对《重点管理外来入侵物种名录》中植物物种的解析与思考

《重点管理外来入侵物种名录》（简称《重点名录2023》）于2023年1月1日起正式施行,该名录对我国外来入侵物种防控管理具有重要的指导作用。本文梳理了我国外来入侵物种名录修订背景及概况,比较了《重点名录2023》和其他名录中外来入侵植物物种的差异,并分析了《重点名录2023》中33种外来入侵植物的危害性和扩散程度。《重点名录2023》与4批“中国外来入侵物种名单”和《国家重点管理外来入侵物种名录（第一批）》中的植物物种重合度较高。33种外来入侵植物对我国生态、农业、林业、人畜健康均有严重危害,且扩散范围广,但仍有值得商榷的问题。本文详述了《重点名录2023》在分类争议和前期评估上存在的问题和缺口,并对我国外来入侵植物物种名录的动态调整和分类管理提出了思考和建议。     

The effects of nitrate loading on the invasive macrophyte Hydrilla verticillata and two common, native macrophytes in Florida

Rising nitrate concentrations in the water column and the spread of invasive, non-native macrophytes are two major threats to Florida's oligotrophic, freshwater ecosystems. We used a replicated mesocosm experiment to test the effects of elevated nitrate concentrations in the water on the growth of the invasive macrophyte Hydrilla verticillata and two common, native submerged macrophytes Vallisneria americana and Sagittaria kurziana. Results from this study indicate that nitrate concentrations of 1.0 mg L⁻¹ NO₃-N in the water increased the final dry-weight biomass of H. verticillata by 2.75 times, while having no statistical effect on the growth of the two native species. Additionally, H. verticillata grew at a faster rate than the two native species in the low nitrate treatments accounting for 82% of the total biomass, indicating that it may have the capacity to invade relatively pristine communities. In waters where nitrate concentrations continue to rise, the cost of control efforts for H. verticillata may substantially increase in the future.     

Ground-truthing the impact of invasive species: spatio-temporal overlap between native least chub and introduced western mosquitofish

Western mosquitofish (Gambusia affinis) are one of the most destructive introduced species in the American West. The negative impact of introduced species on native taxa depends on their spatio-temporal overlap, which will determine the availability of refugia for native species. Experiments on the mechanisms underlying the interactions between introduced and native species rarely address habitat use, overlap, and refugia because individuals are confined to enclosures. In a previous study we used cages, microcosms, and aquaria to show that mosquitofish could prey on and out-compete native least chub (Iotichthys phlegethontis). In this study, we examined the spatio-temporal overlap between mosquitofish and least chub under natural conditions. We found periods of overlap and partitioning in the seasonal and diel habitat use of these species. Both species used shallow habitats during the day and night throughout the spring when least chub were spawning. Predation by adult mosquitofish on young least chub during the spring likely explains the reduction in least chub recruitment in the presence of mosquitofish. During the summer least chub avoided mosquitofish by exclusively using cooler habitats, or by occupying deeper, cooler habitats during the day when mosquitofish were active, and shallower, warmer habitats at night when mosquitofish were inactive. A shift to cooler habitats in the presence of mosquitofish may result in decreased growth and fecundity of least chub. However, we suggest that a reduction of warm shallow habitat may have a disproportionately greater negative impact on mosquitofish than species native to temperate regions, such as least chub. Habitat manipulations that reduce or eliminate warm habitats may ameliorate the harmful effects of mosquitofish and promote the long-term persistence of native taxa.     

The natural decline of an introduced species following its initial increase in abundance; an explanation for Ommatoiulus moreletii in Australia

Summary The black Portuguese millipede, Ommatoiulus moreletii, an exotic species first reported in Australia in 1953, shows a pattern of initial eruption and subsequent decline in abundance following its introduction to sites in South Australia. Comparative sampling of new, erupted populations and older, declined populations was done in an attempt to find testable hypotheses to account for the decline. We report on laboratory and field experiments which show that a native rhabditid nematode appears to be the causal agent for the decline of populations of O. moreletii in South Australia. Implications for the biological control of introduced species are discussed in terms of this work.     

Probability models to facilitate a declaration that an exotic insect species has not yet invaded an area

A procedure is presented to facilitate a declaration that an area has not yet been invaded by a specific exotic insect pest following a trapping campaign to detect the pest species. For this we use a probability model to assess null trapping results and also a growth model to help verify that pests were not present at a given time in the past. The probability model is developed to calculate the probability of negative trapping results if in fact there were insects present, and then the hypothesis that insects are present can be rejected. The model depends on knowledge of the efficiency of the traps and also the area of attractiveness of the traps. If an incipient and undetected population does become established, then natural growth should eventually make it apparent. Using a growth model, the rate of increase of an insect population starting from one gravid female insect is calculated. For both the probability model and the growth model, the conclusion that no invaders were present relates to some period in the past, the lag being defined by the time interval during the trapping activity or the time taken for one fertilized female to produce a population detectable by trapping. If no insects are observed after a suitable waiting period, then a conclusion can be drawn that none were present. The methodology is applied to hypothetical insects with discrete or continuous reproduction.     

The impact of two introduced biocontrol agents, Phytomyza vitalbae and Phoma clematidina, on Clematis vitalba in New Zealand

Insecticide and fungicide exclusion experiments were performed to determine the impact of two biological control agents, an agromyzid leaf-mining fly Phytomyza vitalbae Kaltenbach and a coelomycete fungal pathogen Phoma clematidina (Thüm.) Boerema, on the growth and percentage cover of Clematis vitalba L. (Ranunculaceae) plants. Both insecticide and fungicide treatments significantly reduced control agent damage to C. vitalba leaves over one growing season at Blenheim, New Zealand. However, damage attributable to both agents was rather low and population peaks of both agents occurred in late fall, after the main period of stem growth. There was no significant impact of treatment on growth and only a minor (8–10%), but significant, reduction in percentage cover of C. vitalba was recorded. Disease symptoms were generally only expressed late in the growing season, when leaves were senescent, and were correlated with Py. vitalbae damage. Therefore, we tentatively conclude that alone, Ph. clematidina is insufficiently pathogenic to induce disease symptoms during the main growing season of C. vitalba. Selection criteria for any future potential biocontrol pathogen, therefore, need to evaluate inherent epidemiological factors before introduction, to ensure the candidate agent is an aggressive primary pathogen that can exert maximum disease attack on the target plant. Furthermore, the potential of Py. vitalbae to exist as an asymptomatic endophyte indicates that extra care may be required when assessing survey results for non-target attack, and when testing candidate pathogen biological control agents for host specificity.     

Growth and competition of Cytisus scoparius,an invasive shrub,and Australian native shrubs

English broom (Cytisus scoparius) is an aggressive invasive shrub in native sclerophyll forests of South Australia. We studied its relative growth rate (RGR) and competitive ability in soils from invaded and uninvaded woodlands, in comparison to three native species it commonly displaces:Hakea rostrata, Acacia verniciflua, and A. myrtifolia. Hakea was the slowest growing species throughout the year. Both native species had their highest RGR during spring. The RGR of broom was higher than that of both hakea and acacia in the winter and spring. Despite losing its leaves in the summer, the RGR of broom through the year was higher than that of either of the native species. Soil from the invaded stands had higher organic C, N and soluble P than that from uninvaded sites. Broom and acacia grew better in the higher nutrient soil than in the lower nutrient soil. Competition did not decrease the final biomass of any of the species in low nutrient soil. In the higher nutrient soil the biomass of broom was reduced by competition with acacia, but not by competition with hakea. Competition by broom reduced the biomass of hakea but not that of acacia. Broom's earlier and higher RGR, high competitiveness in nutrient rich soils, and probably its ability to change nutrient availability could be important contributors to the mechanisms by which it invades native woodlands.     

A native species does not prevent the colonization success of an introduced submerged macrophyte,even at low propagule pressure

Hydrobiologia - Invasions are a threat to biodiversity because non-native species are generally more competitive than native species. Hydrilla verticillata is an invasive macrophyte that causes...     

Assessing the areas under risk of invasion within islands through potential distribution modelling: The case of Pittosporum undulatum in São Miguel, Azores

Non-indigenous plant species have been frequently reported as successful invaders in island environments, changing plant community composition and structure. This is the case of the sweet pittosporum (Pittosporum undulatum), native from Australia, which is one of the most successful plant invaders in the Azores archipelago. Data extracted from recent forestry inventories were used to model and map the potential distribution of P. undulatum in São Miguel, the larger island of the Azores. Current distribution of P. undulatum is related to climate, altitude and some human activity effects. Further analysis of the areas under risk of invasion showed that protected areas are under potential threat, although only a few native forest remnants seem to be threatened due to future expansion of P. undulatum, since the current distribution of these native communities has been reduced due to clearing and competition with invasive plants. We discuss the threats that any further expansion of the species will represent for low-altitude native forests, as well as the utility of species distribution models in the assessment of the areas under risk of invasion.     

The fate of an intentional introduction of Formica lugubris to North America from Europe

Red wood ants (Formica s.str.) are not prevalent in the forests of North America, but commonly occur in conifer and mixed conifer forests in northern Europe and Asia. In 1971, a European red wood ant species, Formica lugubris, was intentionally established in a 35‐year‐old predominantly mixed conifer plantation approximately 30 km north of QC, Canada. The purpose of its introduction was to evaluate the potential of this species as a biological control agent against conifer‐defoliating Lepidoptera species. This red wood ant introduction was monitored periodically for about 5 years after establishment, but its long‐term fate has not been reported. We visited this field site in 2005 and found that this species was well established, and we could locate some of the nests that resulted from the original release. We mapped and measured over 100 nests around the site of original release, which ranged from 5 cm in height to over 1 m. We estimated the population of introduced ants to have grown to over 8 million in the last 34 years. Significant clustering of nests suggests that these nests may be one supercolony. F. lugubris has become a dominant understory arthropod in this mixed forest, and is likely to have ecological impacts, including effects at the community and ecosystem level.     

Establishing a beachhead: a stochastic population model with an Allee effect applied to species invasion

We formulated a spatially explicit stochastic population model with an Allee effect in order to explore how invasive species may become established. In our model, we varied the degree of migration between local populations and used an Allee effect with variable birth and death rates. Because of the stochastic component, population sizes below the Allee effect threshold may still have a positive probability for successful invasion. The larger the network of populations, the greater the probability of an invasion occurring when initial population sizes are close to or above the Allee threshold. Furthermore, if migration rates are low, one or more than one patch may be successfully invaded, while if migration rates are high all patches are invaded.