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The information on the number of mammalian species introduced and established into the Neotropical Region and the knowledge on their history of introduction and ecological-genetic aspects are rather variable. To improve our understanding on these topics, we provide an updated list of mammalian species that have established wild populations in the Neotropics and, where possible, compare genetic variability between native and introduced populations in order to evaluate whether the genetic paradox of invasions (GPI) applies to these species. Our search exposed an evident lack of genetic data for most populations introduced in the Neotropics, which restricted our analysis to 10 out of the 51 mammalian species introduced and to only three neutral molecular markers. Losses of genetic variability were a frequent feature of introduced populations, suggesting that these populations have overcome low genetic variation and successfully established in the new environment adding support to the conditions needed to be considered paradoxical in the sense of the GPI. However, it was not possible to affirm that the magnitude of the loss is related to the number of introduction events or the number of individuals introduced or translocated. Alternative approaches to obtain better estimates of genetic diversity associated with the evolutionary potential of the species at the initial stages of invasion are needed. They will provide valuable insight into ecological and evolutionary processes involved in biological invasions, and useful information for species-based risk assessment of invasion. [ABSTRACT FROM AUTHOR]

We analysed the invasion history of two North American macrophytes (Elodea canadensis and E. nuttallii) in Italy, through an accurate census of all available herbarium and field records, dating between 1850 and 2019, and a rich literature collection describing the initial introduction and naturalisation phase that supports the results obtained by the occurrence records. Elodea canadensis arrived in Italy before 1866 and had two invasion phases, between the 1890s and 1920s and between the 1990s and 2000s; E. nuttallii, probably arrived in the 1970s, started invading in 2000 and the invasion is still ongoing. Botanical gardens and fish farming played a crucial role in dispersal and naturalisation of both species. The current invasion range of both species is centred in northern Italy, with scattered occurrences of E. canadensis in central and southern regions. River Po represents a dispersal barrier to the Mediterranean region and a strategic monitoring site to prevent the invasion in the peninsula. The study detects differences in the niches of the two species during the introduction and naturalisation phase and a habitat switch occurred after 1980 in E. canadensis and after 2000 in E. nuttallii, during their expansion phases. For E. canadensis the switch corresponds to the second invasion round. Further research can clarify whether the second invasion round is due to confusion of the recently introduced E. nuttallii with E. canadensis, to a cryptic introduction of a new genotype, to post-introduction evolution, or just to an increased scientific interest in biological invasions. [ABSTRACT FROM AUTHOR]

High community diversity may either prevent or promote the establishment of exotic species. The biotic resistance hypothesis holds that species-rich communities are more resistant to invasion than species-poor communities due to mechanisms including greater interspecific competition. Conversely, the invasional meltdown hypothesis proposes that greater exotic diversity increases invasibility via facilitative interactions between exotic species. To evaluate the degree to which biotic resistance or invasional meltdown influences marine community structure during the assembly period, we studied the development of marine epibenthic "fouling" communities at two southern California harbors. With a focus on sessile epibenthic species, we found that fewer exotic species established as total and exotic richness increased during community assembly and that this effect remained after accounting for space availability. We also found that changes in exotic abundance decreased over time. Throughout the assembly period, gains in exotic abundance were greatest when space was abundant and richness was low. Altogether, we found greater support for biotic resistance than invasional meltdown, suggesting that both native and exotic species contribute to biotic resistance during early development of these communities. However, our results indicate that biotic resistance may not always reduce the eventual dominance of exotic species. [ABSTRACT FROM AUTHOR]

Over the last few decades, rainfall has become more variable, with a worldwide increase in the frequency of extreme precipitation events. While increases in rainfall variability are expected to significantly affect plant species, the effects of precipitation dynamics on plant invasions remains understudied. We examined the growth response of Alternanthera philoxeroides to varying water availability at the community level when grown in a monoculture and mixed community with four commonly co-occurring native species. The native species were also grown together as a control to compare to the invasive species communities. Seven water treatments were applied to each community, including a 'normal' treatment (based on the average rainfall for the area), drought (water was one third of the normal treatment), flood (water was double the normal treatment), and other simulated extreme events (where water availability was more variable than the normal treatment). All plants were measured for growth (e.g., biomass and stolon length) and competitive traits (i.e., relative competitive dominance and relative interaction indices). Most growth traits in A. philoxeroides were enhanced with increased and/or more variable water availability in both the monoculture and mixed community. In contrast, differences in growth traits in the native plants were mostly non-significant across treatments in each plant community. Compared to the normal treatment, A. philoxeroides had higher relative competitive dominance (RDI) and interaction (RII) indices in response to flooding. Conversely, RII in the native species was not significantly different among treatments. Overall, our results suggest that A. philoxeroides is more responsive to flooding compared to the natives. Our study provides useful insights into growth response and competitiveness of A. philoxeroides to precipitation variability across different plant communities. [ABSTRACT FROM AUTHOR]

Humans are facilitating the introduction and range expansion of invasive alien species (IAS), which have negatively impacted ecological and socio-economic systems worldwide. Understanding the global diffusion of IAS is important for developing environmental policies and management strategies. We estimate the rate of increase and the doubling times of the number of new records of 178 IAS using a global dataset with c. 3.4 million records obtained over c. 100 years. Here, we show that the number of records of IAS have exponentially increased with a mean double time of c. 14 years across the Earth. For the most analysed species, the number of records increased faster in the non-native than native continents, suggesting that such IAS might be exponentially expanding their range size. We also found that each continent has a taxonomic group with a particular increase in IAS records. Governments and scientists should pay attention to these taxonomic groups to implement appropriate control or management actions. Our study provides an indication that the current local, regional and continental efforts to control invasions may be not sufficient at the global scale. This is a concerning situation given the great number of areas available for invasion worldwide. [ABSTRACT FROM AUTHOR]

Peacock basses (genus Cichla) are Amazonian piscivorous fish that have been widely introduced into freshwater systems and caused great ecological impacts. Our goal was to assess the worldwide distribution of Cichla ocellaris and C. kelberi to delineate their niche and predict the most suitable areas for their invasion using data available in the scientific literature. We combined ecological niche models to identify hotspots of environmental suitability and invasion risk worldwide, in addition to niche similarity analysis in the geographic space, principal component analysis in the environmental space, and bias metric to assess niche changes between native and non-native ranges. We found 373 records (88 native and 285 non-native populations) for the occurrence of C. kelberi and C. ocellaris in several ecoregions around the world. Native populations were restricted to Amazonian and Tocantins-Araguaia ecoregions. Suitable areas for both species were concentrated within the tropical climatic zone. Amid the top 10 ecoregions more suitable for their occurrence there are four in Africa, one in Asia and also one in Brazil. The Upper Parana ecoregion deserves special highlight due to its prevalence in the number of non-native records and also of suitable areas for new invasions. There was a great increase in the Extent of Occurrence of non-native occurrences compared to native records. We found a moderate niche overlap in the geographical space and a high overlap in the environmental space between native and non-native ranges for both species, suggesting niche conservatism, but with some dissimilarity, higher for C. ocellaris. [ABSTRACT FROM AUTHOR]

Temperature is one of the most important factors governing the activity of ectothermic species, and it plays an important but less studied role in the manifestation of invasive species impacts. In this study, we investigated temperature-specific feeding and metabolic rates of invasive and native crayfish, and evaluated how temperature regulates their ecological impacts at present and in future according to different climatic scenarios by bioenergetics modelling. We conducted a series of maximum food consumption experiments and measured the metabolic rates of cold-adapted native noble crayfish (Astacus astacus) and invasive signal crayfish (Pacifastacus leniusculus) originally from a warmer environment over a temperature gradient resembling natural temperatures in Finland. The maximum feeding rates and routine metabolic rates (RMR) of native noble crayfish were significantly higher at low temperatures (< 10 °C than the rates of invasive signal crayfish. The RMRs of the species crossed at 18 °C, and the RMRs of signal crayfish were higher at temperatures above 18 °C. These findings indicate that the invader's thermal niche has remained stable, and the potential impacts per capita are lower at suboptimal cold temperatures than for the native species. Our bioenergetics modelling showed that the direct annual predation impact of noble and signal crayfish seem similar, although the seasonal dynamics of the predation differs considerably between species. Our results highlight that the temperature-specific metabolic and feeding rates of species need to be taken into account in the impact assessment instead of simple generalisations of the direction or magnitude of impacts. [ABSTRACT FROM AUTHOR]

The factors that determine patterns of non-native species richness and abundance are context dependent in both time and space. Global change has significantly boosted plant invasions in mountains, therefore, understanding which factors determine the invasion and at what scale they operate are fundamental for decision-making in the conservation of mountain ecosystems. Although much evidence has been gathered on the patterns of non-native species in mountain ecosystems, little is known about what specific abiotic, biotic, or anthropogenic factors are driven such patterns. Here, we assessed the importance of anthropogenic, biotic, and abiotic factors at two spatial scales as drivers of plant invasions along three roads in south-central Chile. We sampled non-native plant richness and abundance, and each of these explanatory factors, in-situ in 60 transects in disturbed areas and adjacent undisturbed vegetation. Low elevation areas were the most invaded, with patterns of richness and abundance driven mainly by anthropogenic factors, explaining between 20 and 50% of the variance for the three roads. Only for the abundance of non-native species along the road in the Malalcahuello National Reserve, biotic factors were more important (45% of the variance). At the regional scale, the abundance of non-native species was again explained best by anthropogenic factors (24% of the variance), yet non-native richness was driven most strongly by abiotic factors such as soil nitrogen content and pH (15% of the variance). Our results confirm the conclusions from experimental studies that anthropogenic factors override abiotic factors and are important drivers of non-native species at local and regional scales and that non-native plant invasion in mountains is currently not strongly limited by climate. [ABSTRACT FROM AUTHOR]

Investigating non-native species' impacts on recipient communities in the context of local habitat conditions is vital to understanding their potential invasiveness. This study used comparative functional response experiments to assess the potential predatory impacts of the non-native Oriental river prawn Macrobrachium nipponense compared to the native Malayan river prawn Macrobrachium malayanum in Singapore. Functional responses of these species were compared under different water temperature and pH conditions, representing Singapore's warmer, near-neutral artificial/modified fresh waters, and cooler, more acidic natural forest streams, where the two species are respectively abundant. Four water condition treatments of different temperature-pH permutations were tested: A (26 °C, pH 5.5), B (26 °C, pH 6.5), C (29 °C, pH 5.5) and D (29 °C, pH 6.5). Results found both species to exhibit Type II functional response across all treatments, but M. nipponense responses were significantly higher than those of M. malayanum in all of them. Overall, its functional response was also significantly amplified when water conditions resembled that of the artificial habitat, with higher attack rate, lower handling time, and higher maximum feeding rate. Results imply that M. nipponense can inflict ecological impact in Singapore in terms of predation on the invertebrate prey community. The predatory impact of M. nipponense can also be exacerbated by changes in water parameters (i.e. increasing temperature and/or pH) associated with anthropogenic change, highlighting the importance for conservation of natural freshwater habitats in Singapore. [ABSTRACT FROM AUTHOR]

The terrestrial invader hemlock woolly adelgid (Adelges tsugae) decimates eastern hemlock (Tsuga canadensis) stands that dominate riparian zones of Appalachian forest streams. However, the ecological consequences for linked aquatic-terrestrial ecosystems remain unknown. We measured stream-riparian trophic linkages at 21 sites of Ohio, West Virginia, and Virginia representing a chronosequence of T. canadensis decline. We measured reciprocal fluxes of basal resources (periphyton, terrestrial detritus), emerging aquatic insect flux rate and community composition, riparian orb-weaving spider density, and estimated spider trophic position and reliance on aquatically-derived energy using stable isotopes (13C, 15N, 2H) and Bayesian mixing models. Stream periphyton biomass was greater at uninvaded reference sites than at invaded sites and composition of the terrestrial-to-stream detritus flux changed with T. canadensis decline. Emergent aquatic insect community composition was partly explained by hemlock decline status, but the relative abundance of functional feeding groups was not. Riparian orb-weaving spider densities were highest at sites with severe hemlock decline (F = 4.27, p = 0.022), but were not linked to insect emergence flux rates (p > 0.10). Both trophic position ( x ¯ = 2.4) and relative reliance on aquatically-derived energy ( x ¯ = 83%) were comparable among spider families (Tetragnathidae, Araneidae, Pisauridae) and site decline status. Although spider δ13C signatures were unrelated to those of the most numerous emergent insect families, δ15N signatures of Araneidae and Pisauridae tracked emergent insect δ15N (r2 = 0.42 and 0.78, respectively), suggesting a trophic linkage. Overall, the ecological consequences of this invader were clearest at lower trophic levels, with more nuanced impacts on riparian spiders. [ABSTRACT FROM AUTHOR]

In aquatic systems, invasive submerged macrophytes considerably alter the structure and functioning of communities, thus potentially compromising ecosystem services. The prolific spread of invasive macrophytes is often aided by vegetative fragment propagation, yet the contributions of various commonly occurring invertebrates to such fragmentation are often unquantified. In the present study, we examine fragmentary spread of invasive macrophytes by a group of shredder-herbivores, larval caddisflies. Through novel application of the comparative functional response (FR; resource use as a function of density) approach to the native case-building species Limnephilus lunatus, we compared utilisation of non-native waterweeds Elodea canadensis and E. nuttallii in mono- and polycultures. Furthermore, we quantified de-cased and cased caddisfly-induced fragment production and length changes among non-native E. canadensis, E. nuttallii, Crassula helmsii and Lagarosiphon major under two different plant orientations: horizontal (floating) versus vertical (upright) growth forms. Larval caddisflies exhibited Type II (hyperbolic) FRs towards both Elodea species, and utilised each plant at similar rates when plants were provided separately. When plant species were presented in combination horizontally, E. canadensis was significantly less utilised compared to E. nuttallii, corroborating observations in the field. De-cased larvae produced new plant fragments for all four aquatic macrophytes, whereas cased larvae fragmented plants significantly less. Elodea nuttalii and C. helmsii were fragmented the most overall. Crassula helmsii was utilised to the greatest extent when plants were horizontally orientated, and Elodea species when vertically orientated. This study identifies and quantifies a mechanism from a novel species group that may contribute to the spread of invasive macrophytes in aquatic systems. Whilst exploititative interactions are thought to impede invasion success, here we demonstrate how resource utilisation by a resident species may exacerbate propagule pressure from an invasive species. [ABSTRACT FROM AUTHOR]

The European hare (Lepus europaeus) was introduced in the late 19th century in Argentina and has since rapidly expanded northwards, currently occupying the Brazilian south and southeast. Although European hare is known to be a farmland specialist in its native Europe, what habitat types or landscape features are facilitating its expansion in the Neotropics are not yet clear. Here we assessed support to the disturbance and biotic resistance hypotheses as general drivers of this invasion. We sampled with camera-traps and track surveys 205 sites in three landscapes in southeastern Brazil. We used occupancy models that corrected for both false positive and false negative errors. The disturbance hypothesis was the top-ranked (w = 0.66) with the amount of field, sugarcane, and managed forests all affecting strongly and positively hare occupancy. Support to the biotic resistance hypothesis was lower (ΔAICc = 2.14; w = 0.23) and partial, since only native forests showed a negative effect on hare occupancy. Our findings indicate that in the expansion front occupancy of this invader is mainly dictated by niche opportunities created by native habitat transformation into agricultural lands. The biotic resistance imposed by remaining native habitats seems to play a secondary role and only due to native forests. We conclude that hare geographical expansion should increase given the prominent role of Brazil as a commodity producer and exporter. Nevertheless, fomenting forested protected areas and improving adherence of rural owners to the Brazilian Forest Act, which protects forests in private rural properties, might help lessen this spread. [ABSTRACT FROM AUTHOR]

Introduced salmonids have invaded almost all Patagonian freshwater environments, and yet the effect they have had on native fish populations is difficult to evaluate due to a lack of data prior to their introduction. In this study we focused on evaluating trophic interactions during the juvenile period of Oncorhynchus mykiss, and the ecologically similar native Percichthys trucha. For this purpose, we evaluated the diet and size range of juveniles of both species in the Caleufu River over one yearly cycle. The functional response (FR: the relationship between prey density and consumption rate) and functional response ratio (FRR = attack rate/handling time) were estimated for each species, in mono-specific and multi-specific trials. Comparison of the diet of these species by season showed high similarity for spring and summer. It was also found that juvenile sizes of these species overlap during early ontogeny. Additionally, both species presented a type II FR in mono-specific trials, with similar functional curves. In multi-specific experiments O. mykiss juveniles were dominant, leading to a reduction in P. trucha food intake. FRR was higher for O. mykiss than for P. trucha in mono-specific experiments, a difference which increased in multi-specific experiments, indicating the high potential ecological impact of O. mykiss. Our results show it is very likely that O. mykiss and native P. trucha compete in lotic environments, O. mykiss being competitively superior, highlighting the potential detrimental effect they may have during the juvenile period, especially in habitats and seasons where food resources are scarce. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Invasion biology examines the process by which non-native species integrate into new habitats. Three species of buckeye butterflies (genus Junonia) currently occur in Florida, USA, including Junonia coenia (polyphagous and widely distributed), J. neildi (monophagous and restricted to coastal areas), and J. zonalis (polyphagous tropical species restricted to frost-free South Florida). Two species have long been resident in Florida, whereas J. zonalis was first detected in Florida in 1981. Diagnostic morphological and molecular markers exist for determining Junonia with Caribbean ancestry, allowing observation of the invasion and creation of a secondary contact zone over space and time. We developed techniques to quickly, inexpensively, and unambiguously determine mitochondrial genotypes from museum specimens collected in Florida and the Caribbean over the last 150 years. We reconstructed the invasion of J. zonalis as it colonized Florida using 816 Junonia museum specimens from 1866 to 2016, including some of the oldest insect museum specimens ever genotyped. Significant correlations were found between the presence of Caribbean genotypes and latitude, longitude, and time. Junonia zonalis likely colonized Florida from Cuba by the 1930s, followed by hybridization with resident species, with ongoing genetic exchange between Cuba and the Florida Keys. Episodic gene flow between Florida Keys and mainland populations of J. zonalis may also be occurring. Mainland mitochondrial genotypes appear to be more resilient to extreme high and low temperatures than Caribbean genotypes. This time series in Junonia can be used as a model for understanding the process of adaptation required for successful invasion of new habitats. [ABSTRACT FROM AUTHOR]

Invasive species often have higher functional responses than native analogs. A better understanding of the functional response of invasive species could help explain the effect of these species on native prey communities, and aid in the development of tools for predicting invasion impact. We investigated the role of population density and location along the invasion pathway in determining the functional response of an invasive fish. We used invasive round goby (Neogobius melanostomus) collected from the Trent-Severn Waterway in Ontario, Canada to test for differences in the functional response of fish from high and low density sites, and from different locations along the invasion pathway. We also compared the functional response of round goby with that of northern logperch (Percina caprodes), a native species occupying the same niche. The density of the invasive predator population influenced its functional response, with attack rate being significantly higher for fish from high-density sites compared to fish from low-density sites. Functional response of individuals living at the invasion front was not significantly different from those living in established areas. The higher functional response of round goby compared to its native analog was associated with shorter handling time. Patterns in functional response curves were not explained by differences in diet among wild populations. Our research demonstrates that population density influences the functional response of an invasive species, and therefore should be accounted for when evaluating the functional response of a potential invader. [ABSTRACT FROM AUTHOR]

Presently, it is debated if regional conservation efforts can alone resolve the ecological problems that global climatic changes could bring. Biological invasion is one of such concerns. In the present study, we modeled how change in global climate and regional anthropogenic pressure can impact the distribution of invasive Lantana camara in the Upper Ganga valley of the Western Himalaya (India). The forest in the study area was stratified into 1 km2 grid and two 15 m radius plot were located in each of the forest types in the grid, for recording Lantana presence. In total, 2221 plots were sampled covering 22% of forest. We used predictors representing the climate, forest patch size, fire and natural disaster variables for modeling the species distribution using maximum entropy algorithm. We further simulated 12 future landscape scenarios based on the global trends of these parameters. The present species—environment relationship was projected to these future landscape scenarios. Lantana was presently estimated to spread in 231 km2 of the study area. It invaded larger forest patches in the sub-tropical region, and smaller disturbed forest patches in the warm and cold temperate region. Increased distribution of Lantana was projected across all the future scenarios. The study revealed how global climate changes and regional anthropogenic pressure can have a synergistic effect on the expansion of invasive species in the future. It thus questions the efficiency of conducting only regional efforts in absence of global initiative to reduce the greenhouse gases emission. [ABSTRACT FROM AUTHOR]

Very little is known about how spatial effects influence invasive species throughout the invasion sequence. We propose here two mechanisms to explain the changes in spatial effects throughout the stages of invasion, using the soybean aphid (Aphis glycines) as a model. First, the “hierarchical spatial effect” hypothesis, based on a change in the relative importance of the spatial scales throughout the invasion process, with main effect at broad scale during the first years of invasion, and main effect at local scale during the subsequent years. Second, the “host-switching spatial effect” hypothesis, stating that the spatial effect is driven by a switch in the effect of the host/habitat throughout the invasion process, from effect of main summer host/habitat during the first years of invasion to effect of overwintering host/habitat during the subsequent years. Data from governmental archives and field samplings enabled to investigate the spatial effects on aphid density at three scales (regional, landscape, local) during a 7 year period (2006–2012). Our results demonstrate that the hierarchical spatial effect hypothesis is not an adequate model for the soybean aphid, aphid density being more affected by landscape-scale factors irrespective of years. In contrast, our results are in accordance with the host-switching spatial hypothesis, with positive effect of the main summer host/habitat (soybean) during the first steps of invasion (2006–2008), followed by a positive effect of overwintering habitats (buckthorn, woodland) during the subsequent years (2010–2012). Overall, investigating these hypotheses in other systems would determine whether the same tendency is observed for other invasive species. [ABSTRACT FROM AUTHOR]

We contend that invasion ecology requires a universal, measurable trait of species and their interactions with resources that predicts key elements of invasibility and ecological impact; here, we advocate that functional responses can help achieve this across taxonomic and trophic groups, among habitats and contexts, and can hence help unify disparate research interests in invasion ecology. [ABSTRACT FROM AUTHOR]

Aquatic macrophytes can successfully colonise and re-colonise areas separated by space and time. The mechanisms underlying such 'mobility' are not well understood, but it has often been hypothesised that epizoochory (external dispersal) plays an important role. Yet, there is only limited, and mostly anecdotal, evidence concerning successful epizoochorous dispersal of aquatic macrophytes, particularly in the case of short-distance dispersal. Here we examine in situ and ex situ dispersal of aquatic macrophytes, including three invasive alien species. A high frequency of Lemna minor Linnaeus dispersal was observed in situ, and this was linked to bird-mediated epizoochory. We concluded that wind had no effect on dispersal. Similarly, in an ex situ examination Lemna minuta Kunth and Azolla filiculoides Lamarck, were found to be dispersed with a high frequency by mallard ducks ( Anas platyrhynchos). No dispersal was measured for Elodea nuttalli (Planchon) H. St. John. It is concluded that short-distance or 'stepping-stone' dispersal via bird-mediated epizoochory can occur with high frequencies, and therefore can play an important role in facilitating colonisation, range expansion and biological invasion of macrophytes. [ABSTRACT FROM AUTHOR]

Niche conservatism is the tendency of related species to retain ancestral tolerances after geographic separation. We used Ecological Niche Modelling and Principal Components Analysis of bioclimatic and habitat variables to describe the extent of the species niche, and degrees of bioclimatic-habitat niche conservatism within the mountain hare ( L. timidus) clade. Mountain hare niche space was contrasted with that of the European hare ( L. europaeus), to shed light on species interactions in contact zones throughout Europe. All five subspecies of mountain hare had quantifiably distinct niches. Fennoscandian ( L.t. sylvaticus, L.t. timidus) and highland ( L.t. scoticus, L.t. varronis) subspecies, however, were most similar, exhibiting greatest apparent niche conservatism. They inhabit tundra, boreal forest and uplands, and, hence are presumed most similar to the ancestral form. The Irish hare was distinct, being consistently distinguished from other mountain hares in both 2D and nth dimensional (4D) niche space. The ecological distinctiveness of the Irish hare provides further evidence that it is an Evolutionarily Significant Unit, particularly vulnerable to displacement by introduced European hares with which it competes and hybridises. Projections under global climate change suggest that, by 2070, bioclimatic space for invasive European hares in Ireland will expand (by 79%) but contract for endemic Irish hares (by 75%), further facilitating their replacement. The near complete species replacement of the heath hare ( L.t. sylvaticus) in southern Sweden, where the European hare has also been introduced, may suggest a similar fate may be in store for the Irish hare. [ABSTRACT FROM AUTHOR]

A framework for identifying species that may become invasive under future climate conditions is presented, based on invader attributes and biogeography in combination with projections of future climate. We illustrate the framework using the CLIMEX niche model to identify future climate suitability for three species of Hawkweed that are currently present in the Australian Alps region and related species that are present in the neighbouring region. Potential source regions under future climate conditions are identified, and species from those emerging risk areas are identified. We use dynamically downscaled climate projections to complement global analyses and provide fine-scale projections of suitable climate for current and future (2070-2099) conditions at the regional scale. Changing climatic conditions may reduce the suitability for some invasive species and improve it for others. Invasive species with distributions strongly determined by climate, where the projected future climate is highly suitable, are those with the greatest potential to be future invasive species in the region. As the Alps region becomes warmer and drier, many more regions of the world become potential sources of invasive species, although only one additional species of Hawkweed is identified as an emerging risk. However, in the longer term, as the species in these areas respond to global climate change, the potential source areas contract again to match higher altitude regions. Knowledge of future climate suitability, based on species-specific climatic tolerances, is a useful step towards prioritising management responses such as targeted eradication and early intervention to prevent the spread of future invasive species. [ABSTRACT FROM AUTHOR]

Introduced mammalian predators have negatively affected native biota and ecological processes in ecosystems across the globe. The least weasel ( Mustela nivalis) is a Holarctic mustelid carnivore that has been considered one of the world's worst invasive alien species. It has been introduced to several islands in the Mediterranean Sea and Atlantic Ocean, and here we present a genetic analysis of these insular populations, based on mitochondrial DNA and microsatellites and building upon a previous Western Palearctic phylogeographic study, with the aim of inferring their origin and introduction history. This is essential information for ecological and evolutionary studies of those populations and our understanding of their impacts on the islands' biodiversity. Among the Mediterranean insular populations, a substantial mitochondrial subdivision between weasels in Sicily-Corsica and Malta-Sardinia-Balearics is best explained by a dual colonization originating from the Eastern Mediterranean. Given the correspondence between the observed genetic partition and the differential geographic distribution of Greek and Phoenician settlements and influence during the last millennium BC in those islands, we propose that weasels may have been introduced into the first group of islands by the Greeks and into the second group by the Phoenicians. There is strong support that the commercial and demographic expansions of Phoenicians and Greeks allowed the colonization of the western Mediterranean islands by the house mouse, and texts from Classical Antiquity show evidence that weasels were used for rodent control. Thus, weasels may have been intentionally introduced to the islands, with the aim of controlling commensal rodents. Besides indicating Eastern Mediterranean origins for weasels in Mediterranean islands, the mitochondrial data also revealed an unanticipated close genealogical connection between some of these populations and those from the Azores and São Tomé. The latter island populations showed no affinities with weasels from mainland Portugal, contrary to what might have been expected given that these Atlantic islands were settled by the Portuguese. The microsatellite data also supported the relationship between weasels in Atlantic and in Mediterranean islands. Considering geographic proximity and historical information, the most parsimonious explanation for the origin of the Atlantic weasels appears to be introduction from the Balearic Islands to the Azores and from there to São Tomé. [ABSTRACT FROM AUTHOR]

Identifying routes of invasion is a critical management strategy in controlling the spread of invasive species. This is challenging however in the absence of direct evidence. Therefore, indirect methodologies are used to infer possible invasion sources and routes, such as comparisons of genetic and morphological data from populations from invasive ranges and putative source areas. The greater white-toothed shrew ( Crocidura russula) was first discovered in Ireland from skeletal remains in the pellets of birds of prey collected in 2007 and is it is now sufficiently established that the species has a detrimental impact on Ireland's small mammal community. In this study, we address the uncertain origin(s) of the Irish population of C. russula. The cytochrome b gene of mitochondrial DNA was analysed from 143 individuals from throughout its range within a phylogenetic and approximate Bayesian computation framework. These analyses revealed that the Irish population stemmed from Europe as opposed to North Africa. Additionally, mandibles from 523 individuals from Ireland and 28 other European populations were subjected to multivariate and distance-based analyses, which demonstrated an association between the Irish population and those in France, Switzerland and Belgium. When the genetic and morphological analyses were considered together, an origin stemming from France was deemed the most likely scenario for the source of the invasive Irish population. This study has demonstrated the importance of utilising a multidisciplinary approach when attempting to identify the origins and invasion routes of invasive species. [ABSTRACT FROM AUTHOR]

Climate, land use and disturbances are well known drivers of invasion. However, their relative influence may change across spatial scales, where climate is expected to be the main filter at broad scales; land use is expected to have more influence at intermediate scales, and disturbance, at fine ones. Understanding the underlying processes that drive invasion patterns at different spatial scales is thus crucial to be able to anticipate the future spread of invaders. Here, we quantified the relative importance of climate, land use, and disturbance on the distribution of the invasive trees Ailanthus altissima and Robinia pseudoacacia, across three nested spatial scales, namely global, country (Spain) and riverbank (three riparian riverbanks). To do so, for each species and scale, we built ensemble species distribution models. We also identified their range filling and inferred the most suitable areas in Spain for them to spread. In general, our study confirms that climate acts as an initial coarse filter of species distribution, whilst both climate and land use were important at the country scale; at the riverbank scale human-mediated disturbances gained importance. However, R. pseudoacacia and A. altissima showed differences in their degree of range filling, where A. altissima has a higher potential for range expansion in the near future. Overall, the integration of different scales into invasion studies shows a great potential to enrich our understanding of species-habitat relationships, and to help anticipate their future dynamics. [ABSTRACT FROM AUTHOR]

The invasive Ponto-Caspian amphipod Dikerogammarus villosus strongly impairs the structure of recipient freshwater communities, mostly through predation of a wide range of invertebrates. Useful insights on the ecological impact of an invader can be provided by comparing its functional response (FR)-namely the relationship between resource use and resource availability-to that of trophic analogs from the recipient communities. We applied this method and derived the FR of D. villosus, the native Gammarus pulex, and Echinogammarus berilloni, another gammarid that is also undergoing range expansion, feeding on live dipteran larvae. We tested a range of predator densities to account for mutual interference among predators, assuming that predators do not forage alone in their natural environment. We also analysed the predators' spatial distribution to investigate whether spatial behaviour might be at the origin of interference. For the three gammarid species, the per capita predation rate was a function of the prey-to-predator ratio and showed a decelerating rise to an asymptote. There was no difference in searching efficiency between the three species while prey handling time was significantly lower in G. pulex than in D. villosus and E. berilloni, leading to a higher food intake for the native at high prey densities. Differences in morphology and behaviour between the three gammarids might explain our results. Indeed, D. villosus tended to aggregate more than the other two gammarid species, which promotes conspecific interactions. Our findings suggest that mutual interference between conspecifics is a fundamental shaper of gammarid predation. Time spent interacting with conspecifics is likely to decrease the biotic pressure of the Killer shrimp D. villosus. From a broader perspective, in addition to higher predation risk, parasitism, habitat complexity or climatic variables, the presence of conspecifics of the predator (i.e. predator density) is another factor that has the potential to alter FR comparisons. [ABSTRACT FROM AUTHOR]

Ecological impacts of invasive species are mediated by the environmental characteristics of the invaded habitats. The invasive round goby Neogobius melanostomus is a brackish-water adapted invader with high predatory and competitive impacts on native communities. We test the hypothesis that both body mass gain and predation rates of the round goby are reduced in low-dissolved ion waters in which they can establish, using calcium (Ca) as a focal ion of great importance to the physiology of aquatic animals. Round gobies were first acclimated for 36 days on a diet of shrimp pellets in either high (35 mg L) or low (12 mg L) Ca concentration [Ca]. We then assessed the functional response (FR)-the relationship between predation rate and prey supply-of the round goby from high and low [Ca] on amphipod prey in either condition. Round gobies in high [Ca] consumed more pellets during the acclimation period and gained more mass compared to fish in low-[Ca] conditions. Functional response experiments revealed that round gobies at high-[Ca] levels for both acclimation and FR experiments had the highest predatory impact, whereas fish in low-[Ca] FR treatments had similarly low predation rates regardless of acclimation [Ca]. In a second experiment, non-acclimated round gobies had a higher FR on mayfly nymph prey at high [Ca] than fish at low-[Ca] levels. Our results indicate that the round goby has stronger ecological impacts in conditions that are more physiologically optimal for the species. Identifying key physico-chemical factors that mediate impacts of invaders would help prioritize habitats for management attention. [ABSTRACT FROM AUTHOR]

Mutualism between invaders may alter a key characteristic of the recipient community, leading to the entry or in situ release of other exotic species. We considered whether mutualism between invasive yellow crazy ant Anoplolepis gracilipes and exotic honeydew-producing scale insects indirectly facilitated land snails (exotic and native) via the removal of a native omnivore, the red land crab Gecarcoidea natalis. In plateau rainforest on Christmas Island, Indian Ocean, the land snail community was surveyed at 28 sites representing four forest states that differed in the density of red crabs, the abundance of yellow crazy ants and management history. One-way ANOVAs and multivariate analyses were used to determine differences in land snail species abundance and composition between forest states. Sample-based rarefaction was used to determine differences in species richness. The removal of the red land crab by supercolonies of yellow crazy ants was associated with a significant increase in the abundance of both invasive (14 species) and native (four species) land snails. Compositional differences in the land snail community were driven most strongly by the significantly greater abundance of a few common species in forest states devoid of red crabs. In forest where the crab population had recovered following management for ants, the land snail assemblage did not differ from intact, uninvaded forest. The land snail community was dominated by exotic species that can coexist alongside red crabs in rainforest uninvaded by exotic ants and scale insects. However, the ant-scale mutualism significantly increased land snail abundance and altered their composition indirectly though the alteration of the recipient community. We suggest these constitute 'population-release' secondary invasion in which the impacts of previously successful invaders facilitate a significant increase in abundance of other exotic species already established at low density within the community. Understanding facilitative interactions between invaders and indirect consequences of impacts will provide invaluable insights for conservation in heavily invaded ecosystems. [ABSTRACT FROM AUTHOR]

The invasive aquatic plant species Elodea nuttallii could pose a considerable risk to European freshwater ecosystems based on its current distribution, rate of spread and potential for high biomass. However, little research has been conducted on the impacts of this species on native biota. This study takes an ecosystem-wide approach and examines the impact of E. nuttallii on selected physicochemical parameters (dissolved oxygen and pH), algae, invertebrate and macrophyte communities. Elodea nuttallii had small but significant impacts on plant, invertebrate and algal species. The richness of algal periphyton was lower on E. nuttallii than on native macrophytes. The taxonomic composition of invertebrate communities associated with E. nuttallii differed from that associated with similar native plant species, but did not differ in terms of total biomass or species richness. Macrophyte species richness and total cover were positively correlated with percentage cover of E. nuttallii. Not all macrophyte species responded in the same way to E. nuttallii invasion; cover of the low-growing species, Elodea canadensis and charophytes were negatively correlated with E. nuttallii cover, whilst floating-rooted plants were positively correlated with E. nuttallii cover. All observed differences in the macrophyte community were small relative to other factors such as nutrient levels, inter-annual variation and differences between sites. Despite this, the observed negative association between E. nuttallii and charophytes is a key concern due to the rarity and endangered status of many charophyte species. [ABSTRACT FROM AUTHOR]

Predicting the ecological impacts of damaging invasive species under relevant environmental contexts is a major challenge, for which comparative functional responses (the relationship between resource availability and consumer uptake rate) have great potential. Here, the functional responses of Gammarus pulex, an ecologically damaging invader in freshwaters in Ireland and other islands, were compared with those of a native trophic equivalent Gammarus duebeni celticus. Experiments were conducted at two dissolved oxygen concentrations (80 and 50 % saturation), representative of anthropogenic water quality changes, using two larval prey, blackfly (Simuliidae spp.) and mayfly ( Baetis rhodani). Overall, G. pulex had higher Type II functional responses and hence predatory impacts than G. d. celticus and the functional responses of both predators were reduced by lowered oxygen concentration. However, this reduction was of lower magnitude for the invader as compared to the native. Further, the invader functional response at low oxygen was comparable to that of the native at high oxygen. Attack rates of the two predators were similar, with low oxygen reducing these attack rates, but this effect occurred more strongly for blackfly than mayfly prey. Handling times were significantly lower for the invader compared with the native, and significantly higher at low oxygen, however, the effect of lowered oxygen on handling times was minimal for the invader and pronounced for the native. Maximum feeding rates were significantly greater for the invader compared with the native, and significantly reduced at low oxygen, with this effect again lesser for the invader as compared to the native. The greater functional responses of the invader corroborate with its impacts on recipient macroinvertebrate communities when it replaces the native. Further, our experiments predict that the impact of the invader will be less affected than the native under altered oxygen regimes driven by anthropogenic influences. [ABSTRACT FROM AUTHOR]

Biological invasions continue to exert pressure on ecosystems worldwide and we thus require methods that can help understand and predict the impacts of invasive species, on both native species and previously established invaders. Comparing laboratory derived functional responses among invasive and native predators has emerged as one such method, providing a robust proxy for field impacts. We used this method to examine the likely impacts of the Ponto-Caspian amphipod Dikerogammarus haemobaphes, known as the 'demon shrimp', a little investigated invader in European freshwaters that has recently established in the British Isles. We compared the functional responses on two prey species of D. haemobaphes with two other amphipod species: Dikerogammarus villosus, a congeneric invasive with well-documented impacts on macro-invertebrate communities and a native amphipod, Gammarus pulex. Prey species were native Chironomus sp. and the invasive Chelicorophium curvispinum, a tube-building amphipod also originating from the Ponto-Caspian region. D. villosus showed higher Type II functional responses towards both prey species than did D. haemobaphes and G. pulex, with the latter two predators exhibiting similar impacts on the native prey. However, D. haemobaphes had higher functional responses towards the invasive C. curvispinum than did G. pulex, both when prey individuals were tubeless and resident in their protective mud tubes. Thus, we demonstrate that functionally equivalent invasive congeners can show significantly different impacts on prey, regardless of shared evolutionary history. We also show that some predatory invaders can have impacts on native prey equivalent to native predator impacts, but that they can also exert significant impacts on previously introduced prey. We discuss the importance of invasion history and prey identity when attempting to understand and predict the impacts of new invaders. [ABSTRACT FROM AUTHOR]

The European hare ( Lepus europaeus) has declined throughout its native range but invaded numerous regions where it has negatively impacted native wildlife. In southern Sweden, it replaces the native mountain hare ( L. timidus) through competition and hybridisation. We investigated temporal change in the invasive range of the European hare in Ireland, and compared its habitat use with the endemic Irish hare ( L. timidus hibernicus). The range of the European hare was three times larger and its core range twice as large in 2012-2013 than in 2005. Its rate of radial range expansion was 0.73 km year with its introduction estimated to have occurred ca. 1970. Both species utilised improved and rough grasslands and exhibited markedly similar regression coefficients with almost every land cover variable examined. Irish hares were associated with low fibre and high sugar content grass (good quality grazing) whilst the invader had a greater tolerance for low quality forage. European hares were associated with habitat patch edge density, suggesting it may be more suited to using hedgerows as diurnal resting sites than the Irish hare. Consequently, the invader had a wider niche breadth than the native but their niche overlap was virtually complete. Given the impact of the European hare on native species elsewhere, and its apparent pre-adaption for improved grasslands interspersed with arable land (a habitat that covers 70 % of Ireland), its establishment and range expansion poses a significant threat to the ecological security of the endemic Irish hare, particularly given their ecological similarities. [ABSTRACT FROM AUTHOR]

The impact of invasive bank vole ( Myodes glareolus) and greater white-toothed shrew ( Crocidura russula) on indigenous Irish small mammals, varies with season and habitat. We caught bank voles in deciduous woodland, young coniferous plantations and open habitats such as rank grass. The greater white-toothed shrew was absent from deciduous woods and plantations but did use open habitats with low level cover in addition to field margins. Numbers of both invasive species in field margins during summer were higher than in the previous spring. The indigenous wood mouse ( Apodemus sylvaticus) and pygmy shrew ( Sorex minutus), differed in degrees of negative response to invasive species. Wood mice with bank voles in hedgerows had reduced recruitment and lower peak abundance. This effect was less extreme where both invasive species were present. Wood mice numbers along field margins and open habitats were significantly depressed by the presence of the bank vole with no such effect in deciduous woodland or coniferous plantations. Summer recruitment in pygmy shrews was reduced in hedgerows with bank voles. Where greater white-toothed shrew was present, the pygmy shrew was entirely absent from field margins. Species replacement due to invasive small mammals is occurring in their major habitat i.e. field margins and open habitats where there is good ground cover. Pygmy shrew will probably disappear from these habitats throughout Ireland. Wood mice and possibly pygmy shrew may survive in deciduous woodland and conifer plantations. Mitigation of impacts of invasive species should include expansion of woodland in which native species can survive. [ABSTRACT FROM AUTHOR]

As the number of introductions of non-indigenous species (NIS) continues to rise, ecologists are faced with new and unique opportunities to observe interactions between species that do not naturally co-exist. These interactions can have important implications on the invasion process, potentially determining whether NIS become widespread and abundant, survive in small numbers, or fail to establish and disappear. Although many studies have naturally focused on the interactions between NIS and native species to examine their effects and the biological resistance of the recipient community to invasion, few have examined the effects that NIS have on each other. In some cases, interactions can facilitate the invasion process of one or both species (i.e., 'invasional meltdowns'), but competition or predation can lead to negative interactions as well. The introduction of the vase tunicate, Ciona intestinalis, in Prince Edward Island (Canada) has harmed mussel aquaculture via heavy biofouling of equipment and mussels. Through both a broad-scale survey and small-scale field experiments, we show that Ciona recruitment is drastically reduced by caprellid amphipods, including the NIS Caprella mutica. This study provides an exciting example of how established invasive species can negatively impact the recruitment of a secondary invader, highlighting the potential for non-additive effects of multiple invasions. [ABSTRACT FROM AUTHOR]

Invasion ecology urgently requires predictive methodologies that can forecast the ecological impacts of existing, emerging and potential invasive species. We argue that many ecologically damaging invaders are characterised by their more efficient use of resources. Consequently, comparison of the classical 'functional response' (relationship between resource use and availability) between invasive and trophically analogous native species may allow prediction of invader ecological impact. We review the utility of species trait comparisons and the history and context of the use of functional responses in invasion ecology, then present our framework for the use of comparative functional responses. We show that functional response analyses, by describing the resource use of species over a range of resource availabilities, avoids many pitfalls of 'snapshot' assessments of resource use. Our framework demonstrates how comparisons of invader and native functional responses, within and between Type II and III functional responses, allow testing of the likely population-level outcomes of invasions for affected species. Furthermore, we describe how recent studies support the predictive capacity of this method; for example, the invasive 'bloody red shrimp' Hemimysis anomala shows higher Type II functional responses than native mysids and this corroborates, and could have predicted, actual invader impacts in the field. The comparative functional response method can also be used to examine differences in the impact of two or more invaders, two or more populations of the same invader, and the abiotic (e.g. temperature) and biotic (e.g. parasitism) context-dependencies of invader impacts. Our framework may also address the previous lack of rigour in testing major hypotheses in invasion ecology, such as the 'enemy release' and 'biotic resistance' hypotheses, as our approach explicitly considers demographic consequences for impacted resources, such as native and invasive prey species. We also identify potential challenges in the application of comparative functional responses in invasion ecology. These include incorporation of numerical responses, multiple predator effects and trait-mediated indirect interactions, replacement versus non-replacement study designs and the inclusion of functional responses in risk assessment frameworks. In future, the generation of sufficient case studies for a meta-analysis could test the overall hypothesis that comparative functional responses can indeed predict invasive species impacts. [ABSTRACT FROM AUTHOR]

Invasive species pose a major threat to biodiversity but provide an opportunity to describe the processes that lead to changes in a species' range. The bank vole ( Myodes glareolus) is an invasive rodent that was introduced to Ireland in the early twentieth century. Given its continuing range expansion, the substantial empirical data on its spread thus far, and the absence of any eradication program, the bank vole in Ireland represents a unique model system for studying the mechanisms influencing the rate of range expansion in invasive small mammals. We described the invasion using a reaction-diffusion model informed by empirical data on life history traits and demographic parameters. We subsequently modelled the processes involved in its range expansion using a rule-based spatially explicit simulation. Habitat suitability interacted with density-dependent parameters to influence dispersal, most notably the density at which local populations started to donate emigrating individuals, the number of dispersing individuals and the direction of dispersal. Whilst local habitat variability influenced the rate of spread, on a larger scale the invasion resembled a simple reaction-diffusion process. Our results suggest a Type 1 range expansion where the rate of expansion is generally constant over time, but with some evidence for a lag period following introduction. We demonstrate that a two-parameter empirical model and a rule-based spatially explicit simulation are sufficient to accurately describe the invasion history of a species that exhibits a complex, density-dependent pattern of dispersal. [ABSTRACT FROM AUTHOR]

Empirical support for 'invasional meltdown', where the presence of one invading species facilitates another and compounds negative impacts on indigenous species, is equivocal with few convincing studies. In Ireland, the bank vole was introduced 80 years ago and now occupies a third of the island. The greater white-toothed shrew arrived more recently within the invasive range of the bank vole. We surveyed the abundance of both invasive species and two indigenous species, the wood mouse and pygmy shrew, throughout their respective ranges. The negative effects of invasive on indigenous species were strong and cumulative bringing about species replacement. The greater white-toothed shrew, the second invader, had a positive and synergistic effect on the abundance of the bank vole, the first invader, but a negative and compounding effect on the abundance of the wood mouse and occurrence of the pygmy shrew. The gradual replacement of the wood mouse by the bank vole decreased with distance from the point of the bank vole's introduction whilst no pygmy shrews were captured where both invasive species were present. Such interactions may not be unique to invasions but characteristic of all multispecies communities. Small mammals are central in terrestrial food webs and compositional changes to this community in Ireland are likely to reverberate throughout the ecosystem. Vegetation composition and structure, invertebrate communities and the productivity of avian and mammalian predators are likely to be affected. Control of these invasive species may only be effected through landscape and habitat management. [ABSTRACT FROM AUTHOR]

European hare Lepus europaeus populations have undergone recent declines but the species has successfully naturalised in many countries outside its native range. It was introduced to Ireland during the mid-late nineteenth century for field sport and is now well established in Northern Ireland. The native Irish hare Lepus timidus hibernicus is an endemic subspecies of mountain hare L. timidus and has attracted major conservation concern following a long-term population decline during the twentieth century and is one of the highest priority species for conservation action in Ireland. Little is known about the European hare in Ireland or whether it poses a significant threat to the native mountain hare subspecies by compromising its ecological security or genetic integrity. We review the invasion ecology of the European hare and examine evidence for interspecific competition with the mountain hare for habitat space and food resources, interspecific hybridisation, disease and parasite transmission and possible impacts of climate change. We also examine the impact that introduced hares can have on native non-lagomorph species. We conclude that the European hare is an emerging and significant threat to the conservation status of the native Irish hare. Invasive mammal species have been successfully eradicated from Ireland before and immediate action is often the only opportunity for cost-effective eradication. An urgent call is issued for further research whilst the need for a European hare invasive Species Action Plan (iSAP) and Eradication strategy are discussed. [ABSTRACT FROM AUTHOR]