Exotic fishes that are phylogenetically close but functionally distant to native fishes are more likely to establish.

Since Darwin's time, degree of ecological similarity between exotic and native species has been assumed to affect the establishment success or failure of exotic species. However, a direct test of the effect of exotic-native similarity on establishment of exotics is scarce because of the difficulty in recognizing failures of species to establish in the field. Here, using a database on the establishment success and failure of exotic fish species introduced into 673 freshwater lakes, we evaluate the effect of similarity on the establishment of exotic fishes by combining phylogenetic and functional information. We illustrate that, relative to other biotic and abiotic factors, exotic-native phylogenetic and functional similarities were the most important correlates of exotic fish establishment. While phylogenetic similarity between exotic and resident fish species promoted successful establishment, functional similarity led to failure of exotics to become established. Those exotic species phylogenetically close to, but functionally distant from, native fishes were most likely to establish successfully. Our findings provide a perspective to reconcile Darwin's naturalization conundrum and suggest that, while phylogenetic relatedness allows exotic fish species to pre-adapt better to novel environments, they need to possess distinct functional traits to reduce competition with resident native fish species.

Smoke on the Water: Comparative Assessment of Combined Thermal Shock Treatments for Control of Invasive Asian Clam, Corbicula fluminea.

Suppression of established populations of invasive alien species can be a complex and expensive process, which is frequently unsuccessful. The Asian clam, Corbicula fluminea (Müller, 1774), is considered a high impact invader that can adversely alter freshwater ecosystems and decrease their socioeconomic value. To date, C. fluminea continues to spread and persist within freshwater environments worldwide, despite repeated management attempts to prevent dispersal and suppress established populations. As extensive C. fluminea beds can often become exposed during low-water conditions, the direct application of hot or cold thermal shock treatments has been proposed as suitable mechanism for their control. Further, mechanical substrate disturbance may enhance the efficacy of thermal shock treatments by facilitating exposures to multiple layers of buried clams. In the present study, we advanced these methods by assessing combined applications of both hot and cold thermal shock treatments for control of C. fluminea, using steam spray (≥100 °C; 350 kPa), low- or high-intensity open-flame burns (~1000 °C) and dry ice (-78 °C). In a direct comparison of raking combined with hot thermal shock applications, both steam and high-intensity open-flame treatments tended to be most effective, especially following multiple applications. In addition, when hot thermal treatments are followed by a final cold shock (i.e. dry ice), steam treatments tended to be most effective. Further, when dry ice was applied either alone or prior to an application of a hot shock treatment, substantial if not complete C. fluminea mortality was observed. Overall, this study demonstrated that combined applications of hot and cold thermal shock treatments, applied following the disruption of the substrate, can substantially increase C. fluminea mortality compared to separate hot or cold treatments.

Global determinants of prey naiveté to exotic predators.

Prey naiveté-the failure of prey to recognize novel predators as threats-is thought to exacerbate the impact that exotic predators exert on prey populations. Prey naiveté varies under the influence of eco-evolutionary mediating factors, such as biogeographic isolation and prey adaptation, although an overall quantification of their influence is lacking. We conducted a global meta-analysis to test the effects of several hypothesized mediating factors on the expression of prey naiveté. Prey were overall naive towards exotic predators in marine and freshwater systems but not in terrestrial systems. Prey naiveté was most pronounced towards exotic predators that did not have native congeneric relatives in the recipient community. Time since introduction was relevant, as prey naiveté declined with the number of generations since introduction; on average, around 200 generations may be required to erode naiveté sufficiently for prey to display antipredator behaviour towards exotic predators. Given that exotic predators are a major cause of extinction, the global predictors and trends of prey naiveté presented here can inform efforts to meet conservation targets.

Using structured eradication feasibility assessment to prioritize the management of new and emerging invasive alien species in Europe.

Prioritizing the management of invasive alien species (IAS) is of global importance and within Europe integral to the EU IAS regulation. To prioritize management effectively, the risks posed by IAS need to be assessed, but so too does the feasibility of their management. While the risk of IAS to the EU has been assessed, the feasibility of management has not. We assessed the feasibility of eradicating 60 new (not yet established) and 35 emerging (established with limited distribution) species that pose a threat to the EU, as identified by horizon scanning. The assessment was carried out by 34 experts in invasion management from across Europe, applying the Non-Native Risk Management scheme to defined invasion scenarios and eradication strategies for each species, assessing the feasibility of eradication using seven key risk management criteria. Management priorities were identified by combining scores for risk (derived from horizon scanning) and feasibility of eradication. The results show eradication feasibility score and risk score were not correlated, indicating that risk management criteria evaluate different information than risk assessment. In all, 17 new species were identified as particularly high priorities for eradication should they establish in the future, whereas 14 emerging species were identified as priorities for eradication now. A number of species considered highest priority for eradication were terrestrial vertebrates, a group that has been the focus of a number of eradication attempts in Europe. However, eradication priorities also included a diverse range of other taxa (plants, invertebrates and fish) suggesting there is scope to broaden the taxonomic range of attempted eradication in Europe. We demonstrate that broad scale structured assessments of management feasibility can help prioritize IAS for management. Such frameworks are needed to support evidence-based decision-making.

Salinity tolerance and geographical origin predict global alien amphipod invasions.

Invasive alien species are driving global biodiversity loss, compromising ecosystem function and service provision, and human, animal and plant health. Habitat characteristics and geographical origin may predict invasion success, and in aquatic environments could be mediated principally by salinity tolerance. Crustacean invaders are causing global problems and we urgently require better predictive power of their invasiveness. Here, we compiled global aquatic gammarid (Crustacea: Amphipoda: Gammaroidea) diversity and examined their salinity tolerances and regions of origin to test whether these factors predict invasion success. Across 918 aquatic species within this superfamily, relatively few gammarids (n = 27, 3%) were reported as aliens, despite extensive invasion opportunities and high numbers of published studies on amphipod invasions. However, reported alien species were disproportionately salt-tolerant (i.e. 32% of brackish-water species), with significantly lower proportions of aliens originating from freshwater and marine environments (both 1%). Alien gammarids also significantly disproportionally originated from the Ponto-Caspian (20% of these taxa) when compared with all 'other' grouped regions (1%), and principally invaded Eurasian waters, with translocations of salt-tolerant taxa to freshwaters being pervasive. This suggests habitat characteristics, alongside regional contexts, help predict invasibility. In particular, broad environmental tolerances to harsh environments and associated evolutionary history probably promote success of aliens globally.

Invasion costs, impacts, and human agency: response to Sagoff 2020.

Article impact statement: In an era of profound biodiversity crisis, invasion costs, invader impacts, and human agency should not be dismissed.

High Abundances of Microplastic Pollution in Deep-Sea Sediments: Evidence from Antarctica and the Southern Ocean.

Plastic pollution in Antarctica and the Southern Ocean has been recorded in scientific literature since the 1980s; however, the presence of microplastic particles (<5 mm) is less understood. Here, we aimed to determine whether microplastic accumulation would vary among Antarctic and Southern Ocean regions through studying 30 deep-sea sediment cores. Additionally, we aimed to highlight whether microplastic accumulation was related to sample depth or the sediment characteristics within each core. Sediment cores were digested and separated using a high-density sodium polytungstate solution (SPT) and microplastic particles were identified using micro-Fourier-transform infrared spectroscopy (µFTIR). Microplastic pollution was found in 93% of the sediment cores (28/30). The mean (±SE) microplastics per gram of sediment was 1.30 ± 0.51, 1.09 ± 0.22, and 1.04 ± 0.39 MP/g, for the Antarctic Peninsula, South Sandwich Islands, and South Georgia, respectively. Microplastic fragment accumulation correlated significantly with the percentage of clay within cores, suggesting that microplastics have similar dispersion behavior to low density sediments. Although no difference in microplastic abundance was found among regions, the values were much higher in comparison to less remote ecosystems, suggesting that the Antarctic and Southern Ocean deep-sea accumulates higher numbers of microplastic pollution than previously expected.

Sink trap: duckweed and dye attractant reduce mosquito populations.

Duckweeds, such as Lemna minor Linnaeus (Alismatales: Lemnaceae), are common in aquatic habitats and have been suggested to reduce larval mosquito survivorship via mechanical and chemical effects. Furthermore, pond dyes are used increasingly in aquatic habitats to enhance their aesthetics, although they have been shown to attract mosquito oviposition. The present study examined the coupled effects of L. minor and black pond dye on the oviposition selectivity of Culex pipiens Linnaeus (Diptera: Culicidae) mosquitoes in a series of laboratory choice tests. Subsequently, using outdoor mesocosms, the combined influence of duckweed and pond dye on mosquito abundances in aquatic habitats was quantified. Mosquitoes were strongly attracted to duckweed, and oviposited significantly greater numbers of egg rafts in duckweed-treated water compared with untreated controls, even when the duckweed was ground. The presence of pond dye interacted with the duckweed and further enhanced positive selectivity towards duckweed-treated water. The presence of duckweed caused significant and sustained reductions in larval mosquito numbers, whereas the relative effects of dye were not evident. The use of floating aquatic plants such as duckweed, combined with dye, may help reduce mosquito populations via the establishment of population sinks, characterized by high rates of oviposition coupled with high levels of larval mortality.

Using open-source software and digital imagery to efficiently and objectively quantify cover density of an invasive alien plant species.

The most commonly used method for measuring vegetation cover is visual estimation, which is highly subjective, potentially leading to measurement errors. This poses serious implications to the assessment and continued management of plant species cover, for example in the control of invasive plant species. Morphological analysis of digital imagery has, to date, been primarily applied in the classification of landscape features. Our novel application of morphological image analysis provides an objective method for detection and accurate cover assessment of an invasive alien plant species (IAS), giving reduced measurement errors when compared to visual estimation. Importantly, this method is entirely based on free software. Guidos Toolbox is a collection of generic raster image processing routines, including Morphological Spatial Pattern Analysis (MSPA), which classifies and quantifies features according to shape. MSPA was employed in this study to detect and quantify cover of invasive Petasites pyrenaicus (Winter heliotrope) in digital images of 1 m × 1 m plots. Its efficacy was compared to that of two other methods- GIS Digitisation (used as an accurate baseline) and Visual Estimation (standard method). We tested the limit of MSPA usability on images of varying complexity, i.e. "simple", intermediate" or "complex", depending on presence/absence of other vascular plant species and the species richness of plot. Our results show good agreement between all three methods. MSPA measurement of P. pyrenaicus cover was most closely aligned with the GIS Digitisation (concordance correlation coefficients of 0.966). Visual Estimation was less closely aligned with GIS Digitisation (concordance correlation coefficients of 0.888). However, image complexity resulted in differing levels of agreement; with the closest agreement being achieved between MSPA and GIS Digitisation when used on images of lower and higher complexity. MSPA consistently provides higher accuracy and precision for P. pyrenaicus cover measurement than the standard Visual Estimation method. Our methodology is applicable to a range of focal vegetation species, both herbaceous and graminoid. Future application of MSPA for larger-scale surveying and monitoring via remote sensing is discussed, potentially reducing resource demands and increasing cover measurement consistency and accuracy. We recommend this method forms part of vegetation management toolkits for not only environmental managers, but for anyone concerned with plant cover assessment, from agricultural systems to sustainable resource use.

Steam and Flame Applications as Novel Methods of Population Control for Invasive Asian Clam (Corbicula fluminea) and Zebra Mussel (Dreissena polymorpha).

Control strategies for established populations of invasive alien species can be costly and complex endeavours, which are frequently unsuccessful. Therefore, rapid-reaction techniques that are capable of maximising efficacy whilst minimising environmental damage are urgently required. The Asian clam (Corbicula fluminea Müller, 1774), and the zebra mussel (Dreissena polymorpha Pallas, 1771), are invaders capable of adversely affecting the functioning and biodiversity of freshwater ecosystems. Despite efforts to implement substantial population-control measures, both species continue to spread and persist within freshwater environments. As bivalve beds often become exposed during low-water conditions, this study examined the efficacy of steam-spray (≥100 °C, 350 kPa) and open-flame burn treatments (~1000 °C) to kill exposed individuals. Direct steam exposure lasting for 5 min caused 100% mortality of C. fluminea buried at a depth of 3 cm. Further, combined rake and thermal shock treatments, whereby the substrate is disturbed between each application of either a steam or open flame, caused 100% mortality of C. fluminea specimens residing within a 4-cm deep substrate patch, following three consecutive treatment applications. However, deeper 8-cm patches and water-saturated substrate reduced maximum bivalve species mortality rates to 77% and 70%, respectively. Finally, 100% of D. polymorpha specimens were killed following exposure to steam and open-flame treatments lasting for 30 s and 5 s, respectively. Overall, our results confirm the efficacy of thermal shock treatments as a potential tool for substantial control of low-water-exposed bivalves. Although promising, our results require validation through upscaling to field application, with consideration of other substrate types, increased substrate depth, greater bivalve densities, non-target and long-term treatment effects.

Parasites influence cannibalistic and predatory interactions within and between native and invasive amphipods.

In Northern Ireland, the amphipods Gammarus duebeni celticus (native) and G. pulex (invasive) coexist in some places, whilst in others the native species has been replaced by the invader. We explored the role of parasites in mediating interactions between these amphipods, which demonstrate mutual intraguild predation (IGP: predation between animals that also compete for prey). IGP and cannibalism can be important factors in structuring populations and communities. We investigated the effects of parasitism on rates of IGP between G. d. celticus and G. pulex and on cannibalism within each species by comparing functional responses (FRs: relationships between the use of a prey resource and its availability). Infection with the microsporidian Pleistophora mulleri caused an increase in IGP and cannibalism by G. d. celticus, which showed increased attack rates and reduced prey handling times. In contrast, infection with the acanthocephalan parasite Echinorhynchus truttae did not alter IGP or cannibalism by G. pulex. A prey preference experiment revealed that both amphipods were more likely to feed on heterospecific rather than conspecific prey, and this was also corroborated by the fact that overall IGP FRs were higher than cannibalism FRs. This may be selectively advantageous, as feeding on heterospecific prey removes possible competitors without the risk of consuming juvenile kin or acquiring parasites from infected conspecifics. Infection of the native G. d. celticus with P. mulleri enhanced IGP on the invasive G. pulex, which is likely to facilitate the coexistence of the 2 species.

Winning the arms race: host-parasite shared evolutionary history reduces infection risks in fish final hosts.

Parasite manipulation of intermediate hosts evolves to increase parasite trophic transmission to final hosts, yet counter selection should act on the final host to reduce infection risk and costs. However, determining who wins this arms race and to what extent is challenging. Here, for the first time, comparative functional response analysis quantified final host consumption patterns with respect to intermediate host parasite status. Experiments used two evolutionarily experienced fish hosts and two naive hosts, and their amphipod intermediate hosts of the acanthocephalan parasite Pomphorhynchus tereticollis The two experienced fish consumed significantly fewer infected than non-infected prey, with lower attack rates and higher handling times towards the former. Conversely, the two naive fish consumed similar numbers of infected and non-infected prey at most densities, with similar attack rates and handling times towards both. Thus, evolutionarily experienced final hosts can reduce their infection risks and costs via reduced intermediate host consumption, with this not apparent in naive hosts.

Detection of a novel gammaherpesvirus (genus Rhadinovirus) in wild muntjac deer in Northern Ireland.

This study represents the initial part of an investigation into the potential for non-native, wild, free-living muntjac deer (Muntiacus reevesi) to carry viruses that could be a threat to livestock. A degenerate PCR assay was used to screen a range of tissues from muntjac deer culled in Northern Ireland for the presence of herpesviral nucleic acids. This was followed by sequencing of PCR amplicons and phylogenetic analysis. We report the detection of a novel gammaherpesvirus most closely related to a type 2 ruminant rhadinovirus from mule deer. It remains to be determined if this new virus is pathogenic to deer or presents a risk to food security through the susceptibility of domestic livestock.

On the context-dependent scaling of consumer feeding rates.

The stability of consumer-resource systems can depend on the form of feeding interactions (i.e. functional responses). Size-based models predict interactions - and thus stability - based on consumer-resource size ratios. However, little is known about how interaction contexts (e.g. simple or complex habitats) might alter scaling relationships. Addressing this, we experimentally measured interactions between a large size range of aquatic predators (4-6400 mg over 1347 feeding trials) and an invasive prey that transitions among habitats: from the water column (3D interactions) to simple and complex benthic substrates (2D interactions). Simple and complex substrates mediated successive reductions in capture rates - particularly around the unimodal optimum - and promoted prey population stability in model simulations. Many real consumer-resource systems transition between 2D and 3D interactions, and along complexity gradients. Thus, Context-Dependent Scaling (CDS) of feeding interactions could represent an unrecognised aspect of food webs, and quantifying the extent of CDS might enhance predictive ecology.

Ecological impacts of invasive alien species along temperature gradients: testing the role of environmental matching.

Invasive alien species (IAS) can cause substantive ecological impacts, and the role of temperature in mediating these impacts may become increasingly significant in a changing climate. Habitat conditions and physiological optima offer predictive information for IAS impacts in novel environments. Here, using meta-analysis and laboratory experiments, we tested the hypothesis that the impacts of IAS in the field are inversely correlated with the difference in their ambient and optimal temperatures. A meta-analysis of 29 studies of consumptive impacts of IAS in inland waters revealed that the impacts of fishes and crustaceans are higher at temperatures that more closely match their thermal growth optima. In particular, the maximum impact potential was constrained by increased differences between ambient and optimal temperatures, as indicated by the steeper slope of a quantile regression on the upper 25th percentile of impact data compared to that of a weighted linear regression on all data with measured variances. We complemented this study with an experimental analysis of the functional response (the relationship between predation rate and prey supply) of two invasive predators (freshwater mysid shrimp, Hemimysis anomala and Mysis diluviana) across. relevant temperature gradients; both of these species have previously been found to exert strong community-level impacts that are corroborated by their functional responses to different prey items. The functional response experiments showed that maximum feeding rates of H. anomala and M. diluviana have distinct peaks near their respective thermal optima. Although variation in impacts may be caused by numerous abiotic or biotic habitat characteristics, both our analyses point to temperature as a key mediator of IAS impact levels in inland waters and suggest that IAS management should prioritize habitats in the invaded range that more closely match the thermal optima of targeted invaders.

Predicting invasive species impacts: a community module functional response approach reveals context dependencies.

Predatory functional responses play integral roles in predator-prey dynamics, and their assessment promises greater understanding and prediction of the predatory impacts of invasive species. Other interspecific interactions, however, such as parasitism and higher-order predation, have the potential to modify predator-prey interactions and thus the predictive capability of the comparative functional response approach. We used a four-species community module (higher-order predator; focal native or invasive predators; parasites of focal predators; native prey) to compare the predatory functional responses of native Gammarus duebeni celticus and invasive Gammarus pulex amphipods towards three invertebrate prey species (Asellus aquaticus, Simulium spp., Baetis rhodani), thus, quantifying the context dependencies of parasitism and a higher-order fish predator on these functional responses. Our functional response experiments demonstrated that the invasive amphipod had a higher predatory impact (lower handling time) on two of three prey species, which reflects patterns of impact observed in the field. The community module also revealed that parasitism had context-dependent influences, for one prey species, with the potential to further reduce the predatory impact of the invasive amphipod or increase the predatory impact of the native amphipod in the presence of a higher-order fish predator. Partial consumption of prey was similar for both predators and occurred increasingly in the order A. aquaticus, Simulium spp. and B. rhodani. This was associated with increasing prey densities, but showed no context dependencies with parasitism or higher-order fish predator. This study supports the applicability of comparative functional responses as a tool to predict and assess invasive species impacts incorporating multiple context dependencies.

Fortune favours the bold: a higher predator reduces the impact of a native but not an invasive intermediate predator.

Emergent multiple predator effects (MPEs) might radically alter predictions of predatory impact that are based solely on the impact of individuals. In the context of biological invasions, determining if and how the individual-level impacts of invasive predators relates to their impacts in multiple-individual situations will inform understanding of how such impacts might propagate through recipient communities. Here, we use functional responses (the relationship between prey consumption rate and prey density) to compare the impacts of the invasive freshwater mysid crustacean Hemimysis anomala with a native counterpart Mysis salemaai when feeding on basal cladoceran prey (i) as individuals, (ii) in conspecific groups and (iii) in conspecific groups in the presence of a higher fish predator, Gasterosteus aculeatus. In the absence of the higher predator, the invader consumed significantly more basal prey than the native, and consumption was additive for both mysid species - that is, group consumption was predictable from individual-level consumption. Invaders and natives were themselves equally susceptible to predation when feeding with the higher fish predator, but an MPE occurred only between the natives and higher predator, where consumption of basal prey was significantly reduced. In contrast, consumption by the invaders and higher predator remained additive. The presence of a higher predator serves to exacerbate the existing difference in individual-level consumption between invasive and native mysids. We attribute the mechanism responsible for the MPE associated with the native to a trait-mediated indirect interaction, and further suggest that the relative indifference to predator threat on the part of the invader contributes to its success and impacts within invaded communities.

The enemy of my enemy is my friend: intraguild predation between invaders and natives facilitates coexistence with shared invasive prey.

Understanding and predicting the outcomes of biological invasions is challenging where multiple invader and native species interact. We hypothesize that antagonistic interactions between invaders and natives could divert their impact on subsequent invasive species, thus facilitating coexistence. From field data, we found that, when existing together in freshwater sites, the native amphipod Gammarus duebeni celticus and a previous invader G. pulex appear to facilitate the establishment of a second invader, their shared prey Crangonyx pseudogracilis. Indeed, the latter species was rarely found at sites where each Gammarus species was present on its own. Experiments indicated that this may be the result of G. d. celticus and G. pulex engaging in more intraguild predation (IGP) than cannibalism; when the 'enemy' of either Gammarus species was present, that is, the other Gammarus species, C. pseudogracilis significantly more often escaped predation. Thus, the presence of mutual enemies and the stronger inter- than intraspecific interactions they engage in can facilitate other invaders. With some invasive species such as C. pseudogracilis having no known detrimental effects on native species, and indeed having some positive ecological effects, we also conclude that some invasions could promote biodiversity and ecosystem functioning.

Parasites that change predator or prey behaviour can have keystone effects on community composition.

Parasites play pivotal roles in structuring communities, often via indirect interactions with non-host species. These effects can be density-mediated (through mortality) or trait-mediated (behavioural, physiological and developmental), and may be crucial to population interactions, including biological invasions. For instance, parasitism can alter intraguild predation (IGP) between native and invasive crustaceans, reversing invasion outcomes. Here, we use mathematical models to examine how parasite-induced trait changes influence the population dynamics of hosts that interact via IGP. We show that trait-mediated indirect interactions impart keystone effects, promoting or inhibiting host coexistence. Parasites can thus have strong ecological impacts, even if they have negligible virulence, underscoring the need to consider trait-mediated effects when predicting effects of parasites on community structure in general and biological invasions in particular.