Biological Invasions

Perera, Ana; Hernandez-Sastre, Pedro; Ayres, Cesar

doi: 10.1007/s10530-019-02076-9pmid: N/A

There is a massive gap in our knowledge of the distribution, ecology, and impacts of alien leeches. Here, we report the observation of two alien Helobdella species (H. europaea and H. octatestisaca) found during a long-term monitoring programme conducted in Northern and Western Spain. The alien leeches were attached to European pond turtles (Emys orbicularis) and Mediterranean pond turtles (Mauremys leprosa). In total, 29 European pond turtles and 29 Mediterranean pond turtles were trapped, 36% of which presented leeches attached to their shells or body. We amplified the COI gene region to confirm the identity of the leeches and trace their origins. Helobdella europaea leeches were identified in the two localities sampled, confirming the expansion of the species across the Iberian Peninsula. Moreover, their sequences were identical to the ones reported from Australia, Hungary, Taiwan, South Africa, USA and Spain. The other leech species, H. octatestisaca was detected attached to other leeches only in one of the localities sampled, and was genetically identical to sequences reported from South Africa and USA. This finding represents the first record of this species in Europe.

Eddy, Corey

doi: 10.1007/s10530-019-02078-7pmid: N/A

Invasive lionfishes have spread throughout the west central Atlantic Ocean, Gulf of Mexico and Caribbean Sea, with the potential to impact prey species populations as well as marine ecosystem structure and function. Lionfishes are known to be opportunistic predators with a broad, generalist diet, yet there has been little exploration of their trophic position, or of how this might vary between locations across the invaded range. Stable isotope analysis provides a means of comparing trophic position across locations with different suites of available prey species, but requires the calculation of species-specific trophic discrimination factors (TDFs) for proper interpretation. This study experimentally derived the TDFs for lionfish in Bermuda, where Δ15N = 2.7‰ and Δ13C = 2.4‰, providing an opportunity to calculate the trophic position of this invasive population. It also furthers our ability to compare lionfish trophic position across the many locations in the invaded range to help gauge their potential impacts as both predators and competitors.

Tobias, Vanessa; Conrad, J.; Mahardja, Brian; Khanna, Shruti

doi: 10.1007/s10530-019-02061-2pmid: N/A

Water hyacinth (Eichhornia crassipes) is an invasive species that has modified ecosystem functioning in the Sacramento-San Joaquin Delta (Delta), California, USA. Studies in lakes and rivers have shown that water hyacinth alters water quality. In tidal systems, such as the Delta, water moves back and forth through the water hyacinth patch so water quality directly outside the patch in either direction is likely to be impacted. In this study, we asked whether the presence or treatment of water hyacinth with herbicides resulted in changes in water quality in this tidal system. We combined existing datasets that were originally collected for permit compliance and long-term regional monitoring into a dataset that we analyzed with a before-after control-impact framework. This approach allowed us to describe effects of presence and treatment of water hyacinth, while accounting for seasonal patterns in water quality. We found that although effects of treatment were not detectable when compared with water immediately upstream, dissolved oxygen and turbidity became more similar to regional water quality averages after treatment. Temperature became less similar to the regional average after treatment, but the magnitude of the change was small. Taken together, these results suggest that tidal hydrology exports the effects of water hyacinth upstream, just as river flow is known to transport the effects downstream, creating a buffer of altered water chemistry around patches. It also suggests that although water hyacinth has an effect on dissolved oxygen and turbidity, these parameters recover to regional averages after treatment.

Coulin, Carolina; Vega, Gerardo; Chifflet, Lucila; Calcaterra, Luis; Schilman, Pablo

doi: 10.1007/s10530-019-02063-0pmid: N/A

Species distribution models based on the correlation of bioclimatic variables and presence spatial data-points are useful for recognizing species habitat suitability. However, they have limitations in predicting the introduced ranges of invasive species that could be overcome by using species eco-physiological traits. By combining bioclimatic variables with thermal tolerance plasticity of the highly invasive little fire ant, Wasmannia auropunctata, we intend to better understand the mechanism underlying its current and future distributions. To this end, we performed: (1) laboratory physiological experiments to assess thermal tolerances (CTmin and CTmax) and evaluate the effect of acclimation (laboratory) and acclimatization (nature) on these variables, (2) behavioral foraging observations in the field, (3) a correlative and a simple mechanistic SDM. Briefly, physiological results showed a modulation of the CTmax and CTmin by different acclimation temperatures and by seasonal thermal acclimatization. In the field, worker foraging activity begins at environmental temperatures just above (less than 1 °C) the lowest CTmin recorded in the laboratory. At the global scale, CTmin constitutes a key physiological trait that, when linked with the minimum temperature of the coldest month, could explain the southernmost limit of W. auropunctata native distribution and its physiological capacity to expand in the Mediterranean region. The eco-physiological approach carried out here may help explain the current distribution and predict potential spread of populations when there is no certain information about the whole distribution of the species or under a changing environment. The latter is of great importance especially when analyzing invasive insects, pests or disease vectors.

Russo, L.; Albert, R.; Campbell, C.; Shea, K.

doi: 10.1007/s10530-019-02064-zpmid: N/A

Invasive species that form mutualistic interactions can perturb resident communities by creating new interactions, or weakening the strength of existing interactions via competition. We hypothesized that introducing a super-generalist plant species to bee-plant networks would lead to (1) increases in the weighted and unweighted average degree, nestedness, and connectance and (2) decreases in the modularity. We constructed visitation networks of bees to five native plant species in experimental research plots, in the presence and absence of an invasive thistle and while varying thistle abundance and time/duration of introduction. Species introduction did not change the visitation rate of bees to co-occurring native plants, or the interaction structure between the native plant species and bee visitors; seed set of a focal native plant species was also unaffected. We found the number of bee species with which the introduced species interacted (generality) correlated with significant increases in unweighted and weighted average degree, nestedness, and connectance, but not modularity. When comparing the impact of the introduced species either early or late in the season, we found similar relationships between introduced species generality and weighted and unweighted average degree and connectance; there was a significant negative relationship between introduced species generality and modularity early in the season, and a significant positive relationship with nestedness late in the season, suggesting introduction timing within a season may affect some measures differently. Overall, the native community was robust to the introduction of the super-generalist; our experimental test of network theory predictions demonstrates an improving mechanistic understanding of how mutualistic networks respond to ecological perturbations.

Fukano, Yuya; Soga, Masashi

doi: 10.1007/s10530-019-02065-ypmid: N/A

Understanding the dynamics of public interest in invasive alien species (IAS) is important for the establishment of effective strategies to prevent their spread and mitigate the negative social impacts thereof. Our knowledge of this topic is still limited, however, largely because of the difficulty in collecting data regarding public interest in IAS at a sufficiently large scale and for a long period. Here, we use relative search volume (RSV) on Google as a proxy of the general public’s interest in IAS and investigate its spatio-temporal distributions and drivers in Japan. We analyzed the data for 31 major IAS in Japan and found that the spatial distribution of RSV was predicted by both the actual distribution of IAS and the number of news articles featuring these species. Path analyses revealed that the presence of IAS increased RSV both directly and indirectly thorough an increase in the total number of news articles in local newspapers. Also, time-series analysis of the RSV for serial invasion of Solenopsis invicta, a recently detected IAS in Japan, demonstrated that the local RSV for this species increased sharply after the official announcement of its invasion was made. Overall, our study demonstrates that public interest in IAS varies greatly both spatially and temporally, and this variation was predicted by both ecological and social factors associated with IAS. Understanding the patterns of variation in public interest in IAS and its key drivers should help us to design more responsive and effective strategies to control these species.

Weterings, Robbie; Barbetti, Mike; Buckley, Hannah

doi: 10.1007/s10530-019-02066-xpmid: N/A

Dengue fever is a mosquito-borne disease that has undergone a marked rise in incidence since the 1950s, throughout the world’s tropical regions. Here, we present a hypothesis that this rise in incidence may have been exacerbated by the invasion of house geckos, due to their role in the mosquito vector food web. Previous research has shown that in the absence of a top predator, house geckos reach high densities, directly affecting spider densities and indirectly resulting in higher Aedes-mosquito densities. Hence, we expect that in areas where house geckos are invasive and an effective top predator is lacking, Aedes densities will be higher, resulting in a higher dengue fever incidence rate. We perform a preliminary test of this hypothesis by looking for patterns in secondary country-level data to estimate the global range of invasive house gecko species over time. We related these estimated ranges to variation in the number of per capita dengue cases in 80 different countries. The incidence of dengue was significantly higher in countries where house geckos were introduced, when compared with countries where it was either native or absent. In addition, in countries where house geckos were introduced earlier and had time to become naturalized, dengue fever incidence rates were higher than for countries where house geckos were introduced more recently. These results suggest that house geckos could indeed have played a role in the rise of dengue in tropical countries. Here, we present a framework for the required experimental research to test the mechanism underlying these observations.

Fincham, William; Dunn, Alison; Brown, Lee; Hesketh, Helen; Roy, Helen

doi: 10.1007/s10530-019-02067-wpmid: N/A

Invasive alien species (IAS) can drive community change through ecological interactions. Parasites and pathogens can play an important role in community function including mitigating or enhancing IAS impacts. Despite this, the degree to which pathogen pressure influences IAS impacts remains poorly understood. We quantified the predatory behaviour of the highly invasive alien harlequin ladybird (Harmonia axyridis) and two UK native species, the 7-spot (Coccinella septempunctata) and 2-spot (Adalia bipunctata) ladybirds, using comparative functional response experiments. We investigated the impacts of pathogen infection on the predatory ability of the ladybirds by exposing individuals to Beauveria bassiana, a widespread entomopathogen. Invasive H. axyridis was a more efficient predator than both the native A. bipunctata and C. septempunctata, often having higher attack and/or lower prey handling time coefficients, whereas native A. bipunctata were the least efficient predators. These differences were found in both adult and larval life-stages. Beauveria bassiana infection significantly altered the predatory efficiency of adult and larval ladybird predators. The effects of pathogenic infection differed between species and life-stage but in many cases infection resulted in a reduced predatory ability. We suggest that the interactions between IAS and pathogens are integral to determining invasion success and impact.

Hegel, C.; Santos, L.; Marinho, J.; Marini, M.

doi: 10.1007/s10530-019-02068-9pmid: N/A

The wild pig (Sus scrofa) is an invasive species that negatively impacts new areas into which it is introduced. In this study, we evaluated the effects of wild pig presence on the estimated occupancy and detection probabilities of native mammals in the Brazilian Atlantic Forest. We used camera traps at 100 different points for 8 days (800 trap-days) to collect data and two-species conditional occupancy models to estimate the probability of occupancy (ψ) and the probability of detection (p) of mammal species. We detected a total of 23 native mammal species and two non-native mammal species [wild pig and European hare (Lepus europaeus)] and generated 21 models to evaluate the effects of wild pig occupancy on the European hare and the following 13 native mammals: Cerdocyon thous, Pseudalopex gymnocercus, Hydrochoerus hydrochaeris, Mazama americana, Mazama gouazoubira, Mazama nana, Dasyprocta aguti, Dasypus novemcinctus, Leopardus wiedii, Puma yagouaroundi, Didelphis albiventris, Conepatus chinga, and Procyon cancrivorus. Overall, the presence of wild pig had a range of negative effects on the occupancy and detection of the other mammals, which were less likely to occupy areas that were occupied by wild pig. In addition, we observed lower occurrence and richness of native mammal species in sampling points where wild pig were present compared with locations where wild pig were not present. These results highlight the importance of wild pig management and control for the conservation of native mammals in the Atlantic Forest, a region that is already threatened by a high degree of fragmentation.

Casso, Maria; Turon, Xavier; Pascual, Marta

doi: 10.1007/s10530-019-02069-8pmid: N/A

Assessing genomic diversity and population structure of non-indigenous species is crucial to develop adequate management strategies. However, in species with scarce material for DNA extraction, applying genomic techniques can be a difficult task. Here we set a protocol for small DNA samples combining whole genome amplification (WGA) and genotyping-by-sequencing (GBS). This protocol was applied to the worldwide invasive colonial ascidian Didemnum vexillum using a single zooid per colony. WGA–GBS performance was tested using half zooids, providing empirical demonstration for genotyping reliability. We analysed 296 individuals from 12 localities worldwide including native and the main invaded areas. Polymorphic loci datasets generated by locality, area and globally, identified genetic differentiation at all levels. The two groups found in Japan, the native area, matched Cytochrome Oxidase I clades and were strongly differentiated at the genomic level suggesting reproductive isolation. Our genomic analyses confirmed that only one clade spread worldwide. We also detected some clones, always within the same locality. Genetic diversity was high in both the introduced and in the native area. Three independent colonisation events determined the global distribution of the species, although population pairwise comparisons within each introduced genetic cluster were significant. Human-mediated transportation seems to drive the distribution pattern of this species worldwide and regionally, as there is a lack of isolation by distance within introduced areas. Diverse and well differentiated populations point to a high expansion potential of this worrisome worldwide invader.