Search

Positive interactions such as mutualism and facilitation between invasive species can magnify their impact on invaded ecosystems. Yet, few studies have explicitly evaluated symbioses between invasive species that span the terrestrial–aquatic interface. We conducted two experiments to investigate the fitness outcomes (growth and germination) of frugivory and ichthyochory involving invasive channel catfish (Ictalurus punctatus) that consume fruits and pass seeds of invasive Russian olive (Elaeagnus angustifolia). Our results indicate that catfish frugivory of olive fruit provides an energy source that allows the catfish to maintain body mass and seeds passed by catfish were four times more likely to germinate than untreated seeds, suggesting catfish are viable olive seed dispersers. As such, we concluded that the interaction of frugivory of invasive olive fruits by invasive catfish and ichthyochory resulting from passed olive seeds constitute a facultative mutualism spanning the aquatic–terrestrial interface. The impact of the olive–catfish mutualism on the abundance, persistence and spread of both invasive species requires further study. Researchers and managers should consider the potential of positive interactions across ecotones to facilitate invasions [ABSTRACT FROM AUTHOR]

Invasive plants disrupt ecosystems by influencing species interactions, aiding co-invader integration, and worsening competition for native plants. Successful forest invasive species management relies on grasping these interaction patterns at the community level. This study aims to assess the community attributes of invasive plants in tropical forests of Northeast India, examining their dominance in various habitats, elucidating their influence at the community level and some species-specific effects on associated co-invaders and non-invasive groups. The present investigation recorded 101 invasive plant species mostly of neotropical origin, comprising of grasses, sedges, forbs, shrubs, trees, and vines. The findings revealed both positive and negative effects of invasive species richness and their percentage at community level and throughout different habitats. However, the presence of dominant invasive species caused a substantial decrease in species diversity of plant community in the study area, depicting a significant negative association with the non-invasive group and a notable positive association with the co-invasive group. These findings offer valuable insights by specifying the community-level impacts of exotic invaders on the natural plant population which will be very helpful in devising effective management plans to counter biotic invasion in the biodiversity rich tropical forested landscapes. [ABSTRACT FROM AUTHOR]

Aquatic neophytes are among the most harmful invasive species worldwide. Here we report the finding of the semi-aquatic invasive plant Crassula helmsii, naturalized in a freshwater reservoir that provides water to the large city of A Coruña, NW Spain. To better understand the extent and potential environmental correlates of C. helmsii invasion, we recorded the presence and frequency of C. helmsii in its emerged and floating mat forms at twelve sampling sites along the reservoir margins, and characterized the soil characteristics, plant community and environmental factors. Crassula helmsii is dispersed by fragmentation of the stems, potentially aided through shredding by local fauna such as the invasive crayfish Procambarus clarkii. We hypothesize that this could be a case of an invasional meltdown, when multiple invasive species facilitate one another and have synergistic effects on native ecosystems. The emerged form of C. helmsii was found in ten out of twelve sites with a mean cover value of 9.8 ± 10.4% (mean ± SD). We found no correlation between frequency of the emerged form of C. helmsii and abundance of Procambarus clarkii, but frequency of the emerged form of C. helmsii increased with higher soil nitrogen and vascular plant richness. We outline emergency actions for management of C. helmsii at this stage of the invasion, focusing on containment and avoiding spread to nearby water bodies. [ABSTRACT FROM AUTHOR]

ABSTRACT Invasive species affect ecosystems all over the world. Their impacts intensify when there are beneficial effects among different invasive species, an invasional meltdown. The Argentine black and white tegu lizard, Salvator merianae (Squamata: Teiidae), and the plant Eugenia uniflora (Myrtaceae) are native to mainland South America but behave as invasive species in other parts of the world. We tested the effectiveness of S. merianae as a seed disperser of E. uniflora. Tegu feces containing seeds of E. uniflora were collected to compare the seed germination of gut-passed seeds, manually de-pulped seeds, and seeds of whole fruits. Survival analysis indicated that Tegu lizards behave as seed dispersers of E. uniflora, and there was a tendency for gut-passed seeds to germinate faster than non-gut-passed seeds. Tegu lizards may carry seeds in their guts for considerable distances, facilitating the spread of E. uniflora where both species co-occur as native and invasive (e.g., southern USA). The results indicate a mutualistic interaction between the Tegu lizard and E. uniflora in their native range, which should be considered by initiatives to monitor and control the invasion of the lizard and the plant.

Introduction: Invasive species have been identified as a major threat to native biodiversity and ecosystem functioning worldwide due to their superiority in spread and growth. Such superiority is explained by the invasional meltdown phenomena, which suggests that invasive species facilitate the establishment of more invasive species rather than native species by modifying the plant-soil feedback (PSF). Methods: We conducted a two-phase plant-soil feedback experiment using the native Prosopis cineraria and the invasive Prosopis juliflora in Oman. Firstly, we conditioned the soil by planting seedlings of native species, invasive species, native and invasive species “mixed”, and unconditioned soil served as a control. Secondly, we tested the feedback of these four conditioned soil on the two species separately by measuring the productivity (total biomass) and the performance in the form of plant functional traits (plant height, specific leaf area (SLA), leaf nitrogen content (Nmass), leaf carbon content (Cmass) and specific root length (SRL) of native and invasive species as well as the nutrient availability in soil (soil organic carbon (SOC) and soil total nitrogen (STN)). Results and discussion: We found that the native species produced more biomass, best performance, and higher SOC and STN when grown in soil conditioned by native species, additionally, it gave lower biomass, reduced performance, and lower SOC and STN when grown in the soil conditioned by invasive and mixed species. These results suggest negative PSF for native species and positive PSF for invasive species in the soil conditioned by invasive species, which can be considered as red flag concerning the restoration of P. cineraria as an important native species in Oman, as such positive PSF of the invasive species P. juliflora will inhibit the regeneration of P. cineraria. [ABSTRACT FROM AUTHOR]

Copyright of Ecological Applications is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

IntroductionInvasive species have been identified as a major threat to native biodiversity and ecosystem functioning worldwide due to their superiority in spread and growth. Such superiority is explained by the invasional meltdown phenomena, which suggests that invasive species facilitate the establishment of more invasive species rather than native species by modifying the plant-soil feedback (PSF).MethodsWe conducted a two-phase plant-soil feedback experiment using the native Prosopis cineraria and the invasive Prosopis juliflora in Oman. Firstly, we conditioned the soil by planting seedlings of native species, invasive species, native and invasive species “mixed”, and unconditioned soil served as a control. Secondly, we tested the feedback of these four conditioned soil on the two species separately by measuring the productivity (total biomass) and the performance in the form of plant functional traits (plant height, specific leaf area (SLA), leaf nitrogen content (Nmass), leaf carbon content (Cmass) and specific root length (SRL) of native and invasive species as well as the nutrient availability in soil (soil organic carbon (SOC) and soil total nitrogen (STN)).Results and discussionWe found that the native species produced more biomass, best performance, and higher SOC and STN when grown in soil conditioned by native species, additionally, it gave lower biomass, reduced performance, and lower SOC and STN when grown in the soil conditioned by invasive and mixed species. These results suggest negative PSF for native species and positive PSF for invasive species in the soil conditioned by invasive species, which can be considered as red flag concerning the restoration of P. cineraria as an important native species in Oman, as such positive PSF of the invasive species P. juliflora will inhibit the regeneration of P. cineraria.

Non‐native ants can cause ecosystem‐wide ecological change, and these changes are generally assumed to be negative. Despite this, the evidence base has never been holistically synthesised to quantify whether and to what degree non‐native ants impact native species diversity.In this study, we performed a meta‐analysis of the effects of ant invasion on animal communities. We extracted data from 46 published articles investigating abundance (156 effect sizes) and richness (53 effect sizes) responses of animal taxa to ant invasion in locations relatively unimpacted by other stressors (e.g. human disturbance, other non‐native species) to help isolate the effects of invasion.Overall, local animal diversity declined severely, with species abundance and richness lower by 42.79% and 53.56%, respectively, in areas with non‐native ants compared with intact uninvaded sites. We then combined responses of individual animal taxa extracted from an article into a single response to represent the 'community' abundance (40 effect sizes) or richness (28 effect sizes) response to non‐native ants represented in each article. Local communities decreased substantially in total abundance (52.67%) and species richness (53.47%) in invaded sites.These results highlight non‐native ants as the drivers, rather than passengers, of large net‐negative reductions to animal community diversity in relatively undisturbed systems around the world, approximately halving local species abundance and richness in invaded areas. Improved international prevention processes, early detection systems harnessing emerging technologies, and well‐designed control measures deployable by conservation practitioners are urgently needed if these effects are to be mitigated, prevented or reversed. [ABSTRACT FROM AUTHOR]

Introduction: Phylogenetic relatedness is one of the important factors in the community assembly process. Here, we aimed to understand the large-scale phylogenetic relationship between alien plant species at different stages of the invasion process and how these relationships change in response to the environmental filtering process at multiple spatial scales and different phylogenetic extents. Methods: We identified the alien species in three invasion stages, namely invasive, naturalized, and introduced, in China. The occurrence records of the species were used to quantify two abundance-based phylogenetic metrics [the net relatedness index (NRI) and the nearest taxon index (NTI)] from a highly resolved phylogenetic tree. The metrics were compared between the three categories of alien species. Generalized linear models were used to test the effect of climate on the phylogenetic pattern. All analyses were conducted at four spatial scales and for three major angiosperm families. Results: We observed significantly higher NRI and NTI values at finer spatial scales, indicating the formation of more clustered assemblages of phylogenetically closely related species in response to the environmental filtering process. Positive NTI values for the invasive and naturalized aliens suggested that the presence of a close relative in the community may help the successful naturalization and invasion of the introduced alien species. In the twodimensional phylogenetic space, the invasive species communities significantly differed from the naturalized and introduced species, indicating that established alien species need to be phylogenetically different to become invasive. Positive phylogenetic measures for the invasive aliens across the spatial scales suggested that the presence of invasive aliens could facilitate the establishment of other invasive species. Phylogenetic relatedness was more influenced by temperature than precipitation, especially at a finer spatial scale. With decreased temperature, the invasive species showed a more clustered assemblage, indicating conservatism of their phylogenetic niche. The phylogenetic pattern was different at the family level, although there was a consistent tendency across families to form more clustered assemblages. Discussion: Overall, our study showed that the community assemblage became more clustered with the progression of the invasion process. The phylogenetic measures varied at spatial and taxonomic scales, thereby highlighting the importance of assessing phylogenetic patterns at different gradients of the community assembly process. [ABSTRACT FROM AUTHOR]

Indirect facilitation among exotic species may promote their establishment on ecosystems, causing biodiversity losses. However, few experimental studies have identified the mechanisms underlying the indirect facilitation among exotic species. In central-northern Chile, Mesembryanthemum crystallinum (Aizoaceae) is an exotic halophyte that increases soil salinity, while M. nodiflorum is another exotic halophyte –currently less dominant– that often co-occurs with M. crystallinum. In this study, we evaluated the indirect facilitation of M. nodiflorum by M. crystallinum which was mediated by the suppression of salt-susceptible native competitors via increased soil salinity. We further determined the relationship between salt-tolerance traits and the outcome of competitive interactions in saline soil. We included two native Asteraceae plants co-occurring with these Mesembryanthemum species: the –highly probable– salt-susceptible Helenium urmenetae and the salt-tolerant Amblyopappus pusillus. We combined field co-occurrence surveys with greenhouse germination and competition experiments. The Mesembryanthemum species tended to co-occur, which suggests facilitation. Further, the salinity level found under M. crystallinum significantly decreased germination and performance of H. urmenetae, but not of M. nodiflorum and A. pusillus. Accordingly, when in competition, the increased salinity counteracted the negative effect of H. urmenetae on M. nodiflorum biomass, giving M. nodiflorum a competitive advantage. These patterns were associated with decreased specific leaf area and crassulacean acid metabolism expression in M. nodiflorum. In contrast, A. pusillus and M. nodiflorum maintained a neutral interaction regardless of salinity. Overall, our results suggest that M. crystallinum, by increasing soil salinity, may reduce the performance of salt-susceptible competitors, indirectly facilitating the establishment of M. nodiflorum. [ABSTRACT FROM AUTHOR]

As alien invasive species are a key driver of biodiversity loss, understanding patterns of rapidly changing global species compositions depends upon knowledge of invasive species population dynamics and trends at large scales. Within this context, the Ponto-Caspian region is among the most notable donor regions for aquatic invasive species in Europe. Using macroinvertebrate time series collected over 52 years (1968–2020) at 265 sites across 11 central and western European countries, we examined the occurrences, invasion rates, and abundances of freshwater Ponto-Caspian fauna. We examined whether: (i) successive Ponto-Caspian invasions follow a consistent pattern of composition pioneered by the same species, and (ii) Ponto-Caspian invasion accelerates subsequent invasion rates. In our dataset, Ponto-Caspian macroinvertebrates increased from two species in 1972 to 29 species in 2012. This trend was parallelled by a non-significant increasing trend in the abundances of Ponto-Caspian taxa. Trends in Ponto-Caspian invader richness increased significantly over time. We found a relatively uniform distribution of Ponto-Caspian macroinvertebrates across Europe without any relation to the distance to their native region. The Ponto-Caspian species that arrived first were often bivalves (46.5% of cases), particularly Dreissena polymorpha, followed secondarily by amphipods (83.8%; primarily Chelicorophium curvispinum and Dikerogammarus villosus). The time between consecutive invasions decreased significantly at our coarse regional scale, suggesting that previous alien establishments may facilitate invasions of subsequent taxa. Should alien species continue to translocate from the Ponto-Caspian region, our results suggest a high potential for their future invasion success highly connected central and western European waters. However, each species' population may decline after an initial 'boom' phase or after the arrival of new invasive species, resulting in different alien species dominating over time. [ABSTRACT FROM AUTHOR]

Soil biota have strong effects on plants, but we have a poor understanding of how plant chemistry might modify these effects. We examined the effect of soil biota associated with an exotic invasive tree, Prosopis juliflora, versus that associated with native species, from seven sites across India on conspecifics and two other plant species. We then measured changes in species‐specific soil biota effects (identified as plant–soil feedbacks, PSFs) when leaf leachate from P. juliflora or from native plant species was added to soil containing respective live and sterile soil inoculum.We quantified the amino acid L‐tryptophan from leaf leachate of P. juliflora, Leucaena leucocephala (another invader), and two native species. We also tested effects of P. juliflora or native species soil inoculum amendment of tryptophan on P. juliflora, P. cineraria and L. leucocephala across seven sites. We then quantified the microbially metabolized derivatives of tryptophan, phytohormone indole‐3‐acetic acid (IAA) and intermediates after adding tryptophan into P. juliflora and native soils.Soil biota associated with P. juliflora generated positive effects on conspecifics and L. leucocephala, but negative effects on the native congener P. cineraria. When P. juliflora leaf leachate was added to soil with live P. juliflora inoculum, PSFs became more positive for P. juliflora and other species, compared to leaf leachate amended with sterile soil inoculum. Native leaf leachate interacted weakly with soil biota to impact biomass of conspecifics and heterospecifics.There was roughly 10× more tryptophan in the leaf leachate of P. juliflora than in the leaf leachate of other species. Tryptophan generally increased positive PSFs associated with P. juliflora relative to soil biota associated with other plant species. When tryptophan was added to live P. juliflora soil, IAA and its intermediates were produced at five of seven sites, and at four of these sites soil biota from P. juliflora had positive PSFs.Synthesis. These results provide the first experimental evidence that a chemical leached from the leaves of an invader regulates PSFs. Our results indicate that canopy effects and PSFs, which are usually studied independently, can interact in ways that strongly affect conspecifics and neighbouring species. [ABSTRACT FROM AUTHOR]

Monk Parakeets are considered one of the most invasive bird species given its unique capacity among psittacines to build their own communal nests. Originally introduced as pets in houses from where they escaped or were released, they are currently considered invasive in more than 20 countries worldwide. This is the case in Chile, where Monk Parakeets were introduced during the 1970s. Between 2016 and 2019 we searched Monk Parakeets’ nests structures in the Santiago metropolis region. We identified 1458 Monk Parakeets’ communal nests on 546 trees belonging to 34 tree species. Ninety-one percent of the occupied trees were also introduced. Paraná pine and cedar of Lebanon were the tree species with highest abundance of nests, averaging more than four nests/tree/species, with 23 and 18 maximum number of nests, respectively. Tasmanian blue gum and black locust were selected by parakeets more often than expected, based on availability. From all trees, 24.6% denoted health problems and 47.3% were pruned. The average nest height was 14.2 m and nests were observed mainly in secondary branches (59.3%). The occupancy rate was 89.7% and was associated to nest height and type of branch. During two reproductive seasons we quantified eggs and nestlings in chambers averaging 4.5 and 4.2, respectively. We provide a rough population size estimate and the characteristics of Monk Parakeets nest and tree selectivity, aiming to characterize several decades of a neglected urban invasion to warrant strategies for improved management measures.

Contemporary ecosystems commonly support multiple non‐native species, which can alter community structure and directly or indirectly interact with one another. Novel interactions between invasive species can result in the facilitation or suppression of one or both invaders, making it important to understand the underlying mechanisms that affect invasion outcomes.Goldfish Carassius auratus and Chinese mystery snails Cipangopaludina chinensis have been introduced widely through the aquarium trade and co‐occur in their non‐native ranges. We used an outdoor mesocosm experiment to assess separate and combined effects of goldfish and mystery snails on urban pond community structure and to investigate whether goldfish and mystery snails affected one another positively, neutrally or negatively. We predicted that the distinct trophic levels of each species and the anti‐predator traits of mystery snails would lead to positive interactions between invaders and synergistic effects on the aquatic community.Goldfish directly increased turbidity and decreased filamentous algae, zooplankton, juvenile native snails and survival of amphibians via consumptive effects. Goldfish indirectly increased periphyton, phytoplankton and body size of surviving native green frogs Lithobates clamitans through trophic cascades and/or release from competition. Mystery snails had more subtle effects including reducing growth rates of native grey tree frogs Hyla versicolor, likely through competitive interactions.With goldfish present, mystery snails showed increased reproductive success (higher biomass of juveniles), likely due to indirect competitive release from other herbivores. In contrast to their effects on native snails, goldfish did not consume juvenile mystery snails, likely due to their unique traits (e.g. large size and shell thickness). Mystery snails slightly reduced goldfish growth but did not affect their survival.These results suggest unidirectional facilitation between invaders via indirect changes in the food web. Overall, our study found strong direct and indirect effects of invasive aquarium species, particularly goldfish, and provides experimental support for the invasional meltdown hypothesis within urban waterbodies, which are especially prone to invasions. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

IntroductionPhylogenetic relatedness is one of the important factors in the community assembly process. Here, we aimed to understand the large-scale phylogenetic relationship between alien plant species at different stages of the invasion process and how these relationships change in response to the environmental filtering process at multiple spatial scales and different phylogenetic extents.MethodsWe identified the alien species in three invasion stages, namely invasive, naturalized, and introduced, in China. The occurrence records of the species were used to quantify two abundance-based phylogenetic metrics [the net relatedness index (NRI) and the nearest taxon index (NTI)] from a highly resolved phylogenetic tree. The metrics were compared between the three categories of alien species. Generalized linear models were used to test the effect of climate on the phylogenetic pattern. All analyses were conducted at four spatial scales and for three major angiosperm families.ResultsWe observed significantly higher NRI and NTI values at finer spatial scales, indicating the formation of more clustered assemblages of phylogenetically closely related species in response to the environmental filtering process. Positive NTI values for the invasive and naturalized aliens suggested that the presence of a close relative in the community may help the successful naturalization and invasion of the introduced alien species. In the two-dimensional phylogenetic space, the invasive species communities significantly differed from the naturalized and introduced species, indicating that established alien species need to be phylogenetically different to become invasive. Positive phylogenetic measures for the invasive aliens across the spatial scales suggested that the presence of invasive aliens could facilitate the establishment of other invasive species. Phylogenetic relatedness was more influenced by temperature than precipitation, especially at a finer spatial scale. With decreased temperature, the invasive species showed a more clustered assemblage, indicating conservatism of their phylogenetic niche. The phylogenetic pattern was different at the family level, although there was a consistent tendency across families to form more clustered assemblages.DiscussionOverall, our study showed that the community assemblage became more clustered with the progression of the invasion process. The phylogenetic measures varied at spatial and taxonomic scales, thereby highlighting the importance of assessing phylogenetic patterns at different gradients of the community assembly process.

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]

Simple Summary: Monk Parakeets are invasive birds globally. Through the construction of communal nests, they shape urban bird life. Monk Parakeets were introduced in Chile in 1972 and are now widely distributed in urban environments. Through the description of ecological parameters, we aim to assess the state of the Monk Parakeet in Santiago of Chile after 50 years of invasion. We characterized 1458 Monk Parakeets' nests on 546 trees, 91% of which were introduced species. Tasmanian blue gum and black locust were the trees preferred by parakeets for nesting. The average nest height was at 14.2 m with an occupancy rate of 89.7% and associated to nest height. During two reproductive seasons, chambers had an average of 4.5 eggs and 4.2 nestlings. Results and conclusions obtained will help in understanding the ecology of this avian invasion. Other urban metropolises such as Washington DC, Mexico City, Rome, Berlin, Paris, London, Tokyo, Nairobi, Casablanca and City of Singapore also suffer Monk Parakeet invasion. To aid in the understanding of Monk Parakeet invasive biology, we aim to contribute to better informed decisions in invasive synanthropic species management. Monk Parakeets are considered one of the most invasive bird species given its unique capacity among psittacines to build their own communal nests. Originally introduced as pets in houses from where they escaped or were released, they are currently considered invasive in more than 20 countries worldwide. This is the case in Chile, where Monk Parakeets were introduced during the 1970s. Between 2016 and 2019 we searched Monk Parakeets' nests structures in the Santiago metropolis region. We identified 1458 Monk Parakeets' communal nests on 546 trees belonging to 34 tree species. Ninety-one percent of the occupied trees were also introduced. Paraná pine and cedar of Lebanon were the tree species with highest abundance of nests, averaging more than four nests/tree/species, with 23 and 18 maximum number of nests, respectively. Tasmanian blue gum and black locust were selected by parakeets more often than expected, based on availability. From all trees, 24.6% denoted health problems and 47.3% were pruned. The average nest height was 14.2 m and nests were observed mainly in secondary branches (59.3%). The occupancy rate was 89.7% and was associated to nest height and type of branch. During two reproductive seasons we quantified eggs and nestlings in chambers averaging 4.5 and 4.2, respectively. We provide a rough population size estimate and the characteristics of Monk Parakeets nest and tree selectivity, aiming to characterize several decades of a neglected urban invasion to warrant strategies for improved management measures. [ABSTRACT FROM AUTHOR]

Positive interactions have been hypothesised to influence plant community dynamics and species invasions. However, their prevalence and importance relative to negative interactions remain unclear to understand community change and invasibility. We examined pairwise biotic interactions using over 50 years of successional data to assess the prevalence of positive interactions and their effects on each focal species (either native or exotic). We found that positive interactions were widespread and the relative frequency of positive and negative interactions varied with establishment stage and between native and exotic species. Specifically, positive interactions were more frequent during early establishment and less frequent at later stages. Positive interactions involving native species were more frequent and stronger than those between exotic species, reducing the importance of invasional meltdown on succession. Our study highlights the role of positive native interactions in shielding communities from biological invasion and enhancing the potential for long‐term resilience. [ABSTRACT FROM AUTHOR]

In altered communities, novel species' interactions may critically impact ecosystem functioning. One key ecosystem process, seed dispersal, often requires mutualistic interactions between frugivores and fruiting plants, and functional traits, such as seed width, may affect interaction outcomes. Forests of the Hawaiian Islands have experienced high species turnover, and introduced galliforms, the largest of the extant avian frugivores, consume fruit from both native and non-native plants. We investigated the roles of two galliform species as seed dispersers and seed predators in Hawaiian forests. Using captive Kalij Pheasants (Lophura leucomelanos) and Erckel's Francolins (Pternistis erckelii), we measured the probability of seed survival during gut passage and seed germination following gut passage. We also examined which seeds are being dispersed in forests on the islands of O'ahu and Hawai'i. We found that galliforms are major seed predators for both native and non-native plants, with less than 5% of seeds surviving gut passage for all plants tested and in both bird species. Gut passage by Kalij Pheasants significantly reduced the probability of seeds germinating, especially for the native plants. Further, larger-seeded plants were both less likely to survive gut passage and to germinate. In the wild, galliforms dispersed native and non-native seeds at similar rates. Overall, our results suggest the introduced galliforms are a double-edged sword in conservation efforts; they may help reduce the spread of non-native plants, but they also destroy the seeds of some native plants. Broadly, we show mutualism breakdown may occur following high species turnover, and that functional traits can be useful for predicting outcomes from novel species' interactions. [ABSTRACT FROM AUTHOR]

Non-native predators are known to cause ecological impacts through heightened consumption of resources and decimation of native species. One such species is Micropterus salmoides. Often introduced for sport fishing worldwide; it has been listed by International Union for Conservation of Nature and Natural Resources as one of the 100 of the world's worst invasive species. Whilst impacts conferred towards native prey are well known, its relationship with other non-native species has received much less attention. Therefore, the aim of this study was to experimentally investigate the feeding preference of M. salmoides towards native prey (Geophagus iporangensis) compared to non-native prey (Oreochromis niloticus and Coptodon rendalli) using comparative consumption and the Manly-Chesson selectivity index. We found a higher consumption by M. salmoides towards the non-native prey and a tendency for this non-native preference to increase when prey availability increased. Our results are in line with the hypothesis that the invasion of the non-native predator can be facilitated by the high abundance and reproductive rate of the non-native prey. This is relevant considering the interaction of multiple invaders in an ecosystem, in particular environments modified by humans. Interspecific relationships are complex and their understanding is necessary for environmental management decision-making. [ABSTRACT FROM AUTHOR]

Abstract Non-native predators are known to cause ecological impacts through heightened consumption of resources and decimation of native species. One such species is Micropterus salmoides. Often introduced for sport fishing worldwide; it has been listed by International Union for Conservation of Nature and Natural Resources as one of the 100 of the world’s worst invasive species. Whilst impacts conferred towards native prey are well known, its relationship with other non-native species has received much less attention. Therefore, the aim of this study was to experimentally investigate the feeding preference of M. salmoides towards native prey (Geophagus iporangensis) compared to non-native prey (Oreochromis niloticus and Coptodon rendalli) using comparative consumption and the Manly-Chesson selectivity index. We found a higher consumption by M. salmoides towards the non-native prey and a tendency for this non-native preference to increase when prey availability increased. Our results are in line with the hypothesis that the invasion of the non-native predator can be facilitated by the high abundance and reproductive rate of the non-native prey. This is relevant considering the interaction of multiple invaders in an ecosystem, in particular environments modified by humans. Interspecific relationships are complex and their understanding is necessary for environmental management decision-making.

Disturbances such as fire provide an opportunity for invasive plant species to exploit newly created niche space. Whether initial invaders facilitate, compete with, or do not affect later invaders is important to determine in communities affected by multiple invaders. This analysis focuses on the newer invaders Taeniatherum caput-medusae (medusahead) and Ventenata dubia (ventenata) in sagebrush-steppe communities previously invaded by Bromus tectorum (cheatgrass), during the first 5 years of recovery after wildfire. We combined probabilistic co-occurrence analysis and Getis-Ord spatial clustering analysis to assess relationships between different exotic annual grass species and native and introduced perennial bunchgrasses, then used Bayesian generalized linear models to determine if and how medusahead and ventenata differed in their environmental relationships and thus invasion niches. Medusahead presence was positively associated with both other exotic annual grasses, but ventenata presence was negatively associated with cheatgrass presence. Medusahead hotspots were more spatially similar to cheatgrass hotspots while ventenata hotspots were unique. Both invaders were negatively related to total perennial bunchgrass cover but disassociations between invaders and different perennial bunchgrasses were species-specific. Medusahead and ventenata occupied different niches; medusahead in low elevation, low precipitation areas and ventenata in higher elevation, higher precipitation areas. Despite seemingly similar ecology and growth requirements among these annual grasses and a tendency to be considered uniformly in both research and management, the species appeared to have different invasion niches. [ABSTRACT FROM AUTHOR]

Worldwide trade of the carnivorous snail Anentome helena may result in its chance dispersal from aquaria to the natural habitats. In course of consuming the invasive snail Physella acuta and the native snail Racesina luteola, selectively, A. helena can weaken the competitive interactions and elicit non-consumptive effects (NCEs) as well. To determine the NCEs on R. luteola and P. acuta, induced by the exotic A. helena, we observed the life-history trait variations due to competition, presence of A. helena and its cues. Since the prey snails were not exposed to such exotic predators, the resultant response will help to evaluate the prospective differences in the evasion and vulnerability of the interacting native and exotic snails. We initiated the experiment using freshly hatched R. luteola and P. acuta by placing them into intra and interspecific competitions. Furthermore, the experimental containers were divided into three treatment levels: control, presence of predator cues and A. helena. We did not find any alteration in the number of days required to attain the sexual maturity of both prey snails due to competition or predator treatments. Although R. luteola had no effects of competition; the body mass and fecundity were negatively affected by the presence of A. helena and its cues. However, the strong effect of intraspecific competition on P. acuta was weakened through increased length, body mass, and fecundity under the presence of A. helena. Therefore, the probable introduction of A. helena may indirectly affect the life-history parameters of both prey and favour P. acuta over R. luteola in the freshwater habitats of West Bengal, India. [ABSTRACT FROM AUTHOR]

In their native range, Pacific salmon (Oncorhynchus spp.) have strong interactions with a multitude of species due to the annual pulse of marine‐derived nutrients that they deliver to streams and forests when they spawn and die. Over the past few decades, Chinook salmon (Oncorhynchus tshawytscha) has established non‐native populations throughout the Patagonia region of southern South America. Here, we provide the first assessment of the pathways through which salmon‐derived nutrients enter stream and forest food webs in Patagonia by surveying multiple streams in southern Chile to identify invertebrate and vertebrate consumers of salmon carcasses and summarizing all documented trophic interactions of Chinook salmon in Patagonia. Blowflies (Calliphoridae) were the dominant colonizer of carcasses in the riparian zone, and midge flies (Chironomidae) were the most common invertebrate on submerged carcasses. Camera trap monitoring in the riparian zone revealed consumption of carcasses or carcass‐associated invertebrates by the insectivorous passerine bird "chucao" (Scelorchilis rubecula), small rodents (black rat Rattus rattus, house mouse Mus musculus, and/or colilargo Oligoryzomys longicaudatus), the South American fox "culpeo" (Lycalopex culpaeus), and the invasive American mink (Neovison vison). A mink was filmed transferring a carcass from stream to streambank, indicating that vertebrate scavenging likely increases the degree to which marine‐derived nutrients enter terrestrial food webs. The native taxa that consume salmon are closely related to species that benefit from salmon consumption in North America, suggesting that the pathways of salmon nutrient incorporation in North American food webs have functionally re‐emerged in South America. Similarly, non‐native trout (Oncorhynchus mykiss and Salmo trutta) and mink consume salmon in Patagonia, and their eco‐evolutionary history of coexistence with salmon could mean that they are preadapted for salmon consumption and could thus be key beneficiaries of this invasion. Expanded monitoring of the abundance and impacts of salmon will be vital for understanding how these novel inputs of marine‐derived nutrients alter Patagonian food webs. [ABSTRACT FROM AUTHOR]

Abstract In their native range, Pacific salmon (Oncorhynchus spp.) have strong interactions with a multitude of species due to the annual pulse of marine‐derived nutrients that they deliver to streams and forests when they spawn and die. Over the past few decades, Chinook salmon (Oncorhynchus tshawytscha) has established non‐native populations throughout the Patagonia region of southern South America. Here, we provide the first assessment of the pathways through which salmon‐derived nutrients enter stream and forest food webs in Patagonia by surveying multiple streams in southern Chile to identify invertebrate and vertebrate consumers of salmon carcasses and summarizing all documented trophic interactions of Chinook salmon in Patagonia. Blowflies (Calliphoridae) were the dominant colonizer of carcasses in the riparian zone, and midge flies (Chironomidae) were the most common invertebrate on submerged carcasses. Camera trap monitoring in the riparian zone revealed consumption of carcasses or carcass‐associated invertebrates by the insectivorous passerine bird “chucao” (Scelorchilis rubecula), small rodents (black rat Rattus rattus, house mouse Mus musculus, and/or colilargo Oligoryzomys longicaudatus), the South American fox “culpeo” (Lycalopex culpaeus), and the invasive American mink (Neovison vison). A mink was filmed transferring a carcass from stream to streambank, indicating that vertebrate scavenging likely increases the degree to which marine‐derived nutrients enter terrestrial food webs. The native taxa that consume salmon are closely related to species that benefit from salmon consumption in North America, suggesting that the pathways of salmon nutrient incorporation in North American food webs have functionally re‐emerged in South America. Similarly, non‐native trout (Oncorhynchus mykiss and Salmo trutta) and mink consume salmon in Patagonia, and their eco‐evolutionary history of coexistence with salmon could mean that they are preadapted for salmon consumption and could thus be key beneficiaries of this invasion. Expanded monitoring of the abundance and impacts of salmon will be vital for understanding how these novel inputs of marine‐derived nutrients alter Patagonian food webs.

Multiple invasive species may interact, influencing one another and generating synergistic effects on food webs and ecosystem processes. We investigated the interaction between two non‐native species widespread in the western USA: common carp (Cyprinus carpio) and Russian olive (Elaeagnus angustifolia), an invasive riparian tree associated with di‐nitrogen fixation. Deep Creek, Idaho, was an International Biological Program site in the early 1970s; at that time, carp were rare and Russian olive was absent. Subsequently, Russian olive was introduced and established a dense stand, increasing allochthonous inputs and nitrogen‐rich benthic organic matter. Since 1971, carp density has increased ~4× (an increase our bioenergetic analysis suggests could not have been sustained in the absence of Russian olive). Carp gut contents in 2013–2014 revealed, on average, ~40% olives, and, similarly, stable isotope analyses revealed ~58% of carp tissues were derived from olives. A small‐scale, short‐term experimental exclusion of these subsidized carp caused ~3× increases in macrophytes and chlorophyll‐a, suggesting they may limit algae and macrophyte biomass. Moreover, carp that consumed olives excreted more nitrogen (~2× more ammonium, ~2× more total dissolved nitrogen, and ~3× more total nitrogen) compared to those that had not, which may amplify recycling and export from streams invaded by both species. This scenario is characteristic of an "invasional meltdown," with attendant changes in food webs and ecosystem processes. [ABSTRACT FROM AUTHOR]

Non-native species having high per capita impacts in invaded communities are those that modulate resource availability and alter disturbance regimes in ways that are biologically incompatible with the native biota. In areas where it has been introduced by humans, American beaver (Castor canadensis) is an iconic example of such species due to its capacity to alter trophic dynamics of entire ecosystems and create new invasional pathways for other non-native species. The species is problematic in several watersheds within the Southern California-Northern Baja California Coast Ecoregion, a recognized hotspot of biodiversity, due to its ability to modify habitat in ways that favor invasive predators and competitors over the region's native species and habitat. Beaver was deliberately introduced across California in the mid-1900s and generally accepted as non-native to the region up to the early 2000s; however, articles promoting the idea that beaver may be a natural resident have gained traction in recent years, due in large part to the species' charismatic nature rather than by presentation of sound evidence. Here, we discuss the problems associated with beaver disturbance and its effects on conserving the region's native fauna and flora. We refute arguments underlying the claim that beaver is native to the region, and review paleontological, zooarchaeological, and historical survey data from renowned field biologists and naturalists over the past ~160 years to show that no evidence exists that beaver arrived by any means other than deliberate human introduction. Managing this ecosystem engineer has potential to reduce the richness and abundance of other non-native species because the novel, engineered habitat now supporting these species would diminish in beaver-occupied watersheds. At the same time, hydrologic functionality would shift toward more natural, ephemeral conditions that favor the regions' native species while suppressing the dominance of the most insidious invaders.

Abstract Multiple invasive species may interact, influencing one another and generating synergistic effects on food webs and ecosystem processes. We investigated the interaction between two non‐native species widespread in the western USA: common carp (Cyprinus carpio) and Russian olive (Elaeagnus angustifolia), an invasive riparian tree associated with di‐nitrogen fixation. Deep Creek, Idaho, was an International Biological Program site in the early 1970s; at that time, carp were rare and Russian olive was absent. Subsequently, Russian olive was introduced and established a dense stand, increasing allochthonous inputs and nitrogen‐rich benthic organic matter. Since 1971, carp density has increased ~4× (an increase our bioenergetic analysis suggests could not have been sustained in the absence of Russian olive). Carp gut contents in 2013–2014 revealed, on average, ~40% olives, and, similarly, stable isotope analyses revealed ~58% of carp tissues were derived from olives. A small‐scale, short‐term experimental exclusion of these subsidized carp caused ~3× increases in macrophytes and chlorophyll‐a, suggesting they may limit algae and macrophyte biomass. Moreover, carp that consumed olives excreted more nitrogen (~2× more ammonium, ~2× more total dissolved nitrogen, and ~3× more total nitrogen) compared to those that had not, which may amplify recycling and export from streams invaded by both species. This scenario is characteristic of an “invasional meltdown,” with attendant changes in food webs and ecosystem processes.

Ongoing globalisation and climate change are causing plant species to invade new habitats and thereby alter biodiversity and ecosystem functioning. Since numbers of plant invasions continue to increase globally, it is crucial to investigate the effects of multiple co-occurring alien species on native communities. Furthermore, priority effects due to the earlier emergence of certain species affecting fitness of later arriving species can shape community structure and affect native species performance. We investigate in a common garden pot experiment the interactions among five alien-native species pairs. First we focus on the effect of growing with either one or two alien neighbour species on a native plant, second we alter the arrival time of the alien or native neighbour by 3 weeks. Generally, native species performance decreased when surrounded by two alien species compared to only one, although the magnitude of this effect varied depending on species, with one species even performing better with alien neighbours than in monoculture. Species performance greatly decreased when arriving second in the pot, for both native and alien species. In contrast, alien species tended to benefit more from arriving early. Given that we studied annual ruderal species, their potentially lower competitive ability might explain why we detected negative effects of late arrival. We highlight the need to further elucidate underlying mechanisms of small-scale invasion dynamics to achieve generalisations concerning the response of multiple alien and native plants given their species-specific differences in response to neighbour species and arrival time. [ABSTRACT FROM AUTHOR]

Apis species are a major component of pollinator faunas in their native and introduced habitats. A widespread concern is that non-native Apis mellifera may have negative effects on native pollinators and on plant reproduction. This is based on the assumptions that natural communities are at capacity, resource competition structures communities, native pollinators are more effective pollinators of native species, yet A. mellifera are superior competitors. The latter two assumptions are often true, but evidence from the Neotropics indicates that tropical communities are not tightly structured, and the foraging flexibilities of native bees maintain their populations. However, the less diverse and disharmonic biotas of islands may limit the buffering capacity of flexible behaviors. While few studies address these assumptions or the ecological and evolutionary consequences of A. mellifera to the flora and fauna of tropical islands, an accumulation of taxon-specific studies are suggesting that such effects run the spectrum from subtle and indirect to obvious and direct. A concerted research effort is needed to address the multitude of issues to develop strategies to ameliorate or enhance honey bee effects, or just let nature take its course.

The aim of the study is to present a complete and updated fish inventory of inland waters of the Emilia-Romagna region, Northern Italy, and to highlight the presence of fully exotic fish communities. Overall, based on 208 sampling locations, the observed fish fauna consisted of 45 species, 22 native and 23 exotics. A significant element of the inventory is the identification of xenodiversity hotspots (spatially clustered sites, one lowland and one upland region), where a complete substitution of native species by exotic species was observed (in total seven sites in the lowland and two sites in the upland with no native species presence). These xenodiversity hotspots were found to host specific combinations of exotic species, which may be able to constitute balanced exotic communities. The hotspots of the lowland region are located in the northeast lowland part of the territory, hosting exotic species combinations mainly composed by wels catfish (Silurus glanis Linnaeus, 1758, a large predator), common carp (Cyprinus carpio Linnaeus, 1758, a large benthivore), crucian carp (Carassius spp., a small-bodied generalist) and other less dominant exotic species. The hotspots in the upland region were located in the southwest part of the territory and were dominated by only one exotic species (rainbow trout, Oncorhynchus mykiss (Walbaum, 1792)). A difference between these xenodiversity hotspots is that in the lowland the introductions were mostly unintentional and are not continued, while in the upland the introduction of rainbow trout is intentional and currently carried out by local fishermen.

Increasing rates of invasions in ecosystems worldwide necessitate experiments to determine the role of biotic interactions in the success and impact of multiple alien species. Here, we examined competitive and facilitative interactions among various combinations of three widespread and often co‐occurring invaders: the zebra mussel Dreissena polymorpha, and the macrophytes Elodea canadensis and Elodea nuttallii.Using a mesocosm‐based, factorial experimental design, we assessed the effect of interspecific competition on macrophyte growth rates in the absence and presence at varying biomass of D. polymorpha.Growth rates (wet g/day) of E. canadensis and E. nuttallii were similar when grown in isolation. When grown together, in the absence of D. polymorpha, E. canadensis growth was not significantly reduced in the presence of E. nuttallii and vice versa. In the presence of D. polymorpha (26.0 ± 1 mm), monocultural growth of E. canadensis was largely unaffected, while E. nuttallii growth was strongly enhanced. Low (2.64 g) and medium (3.96 g) mussel biomass led to negative interspecific effects between E. canadensis and E. nuttallii; at high (5.28 g) mussel biomass, the effect of interspecific competition was negated.Overall, D. polymorpha alleviated competitive interactions between the two invasive macrophytes when all three species co‐occurred, and substantially enhanced growth of E. nuttallii with increasing mussel biomass, thereby suggesting a possible influence on the relative dominance of these macrophytes in the field.Our study demonstrates how facilitations can cause shifts in dominance among closely related invaders. The consequences of such facilitations for the structure and function of communities remain to be explored generally. [ABSTRACT FROM AUTHOR]

1. Interactions between invertebrate herbivores with different feeding modes are common on long‐lived woody plants. In cases where one herbivore facilitates the success of another, the consequences for their shared host plant may be severe. Eastern hemlock (Tsuga canadensis), a canopy‐dominant conifer native to the eastern U.S., is currently threatened with extirpation by the invasive stylet‐feeding hemlock woolly adelgid (Adelges tsugae). The effect of adelgid on invasive hemlock‐feeding folivores remains unknown. 2. This study evaluated the impact of feeding by hemlock woolly adelgid on gypsy moth (Lymantria dispar) larval preference for, and performance on, eastern hemlock. To assess preference, 245 field‐grown hemlocks were surveyed for gypsy moth herbivory damage and laboratory paired‐choice bioassays were conducted. To assess performance, gypsy moth larvae were reared to pupation on adelgid‐infested or uninfested hemlock foliage, and pupal weight, proportional weight gain, and larval period were analysed. 3. Adelgid‐infested hemlocks experienced more gypsy moth herbivory than did uninfested control trees, and laboratory tests confirmed that gypsy moth larvae preferentially feed on adelgid‐infested hemlock foliage. Gypsy moth larvae reared to pupation on adelgid‐infested foliage gained more weight than larvae reared on uninfested control foliage. 4. These results suggest that the synergistic effect of adelgid and gypsy moth poses an additional threat to eastern hemlock that may increase extirpation risk and ecological impact throughout most of its range. [ABSTRACT FROM AUTHOR]

Thestrengthofbioticinteractions withinanecological communityaffectsthe susceptibility of the community to invasion by introduced taxa. In microbial communities, cross-feeding is a widespread type of biotic interaction that has the potential to affect community assembly and stability. Yet, there is little understanding of how the presence of cross-feeding within a community affects invasion risk. Here, I develop a metabolite-explicit model where native microbial taxa interact through both cross-feeding and competition for metabolites. I use this model to study how the strength of biotic interactions, especially cross-feeding, influence whether an introduced taxon can join the community. I found that stronger cross-feeding and competition led to much lower invasion risk, as both types of biotic interactions lead to greater metabolite scarcity for the invader. I also evaluated the impact of a successful invader on community composition and structure. The effect of invaders on the native community was greatest at intermediate levels of cross-feeding; at this ‘critical’ level of cross-feeding, successful invaders generally cause decreased diversity, decreased productivity, greater metabolite availability, and decreased quantities of metabolites exchanged among taxa. Furthermore, these changes resulting from a successful primary invader made communities further susceptible to future invaders. The increase in invasion risk was greatest when the network of metabolite exchange between taxa was minimally redundant. Thus, this model demonstrates a case of invasional meltdown that is mediated by initial invaders disrupting the metabolite exchange networks of the native community. [ABSTRACT FROM AUTHOR]

The global phenomenon of introduced species has caused serious, negative impacts on biodiversity and human productive activities. Often, introduced species become invasive and impact and modifies the availability of resources in native ecosystem. Cattle and wild boar are two species that have been introduced on all continents for food and sport hunting. Both species cause detrimental changes in ecosystem processes and biodiversity. Particularly in Patagonia, it has been shown in different studies that in isolation these species can cause damage to native plants, alter the structure of the soil and its processes. This study sought to assess and compare the ecosystem impacts of cattle and wild boar upon ecosystem structure and function in different scenarios with the presence of both, one or none of these focal species. Our study area is the Nahuel Huapi National Park where both species have significant presence on temperate forest. In order to evaluate the species impact we combined experimental and observational methods across sites with the presence of one species, both species, and sites without either species. Our data showed that sites with both species or only wild boar showed fewer impacts than expected. However, when cattle is presence, this species seriously threaten the native ecosystems by affecting plant biomass, reducing the shrub cover and number of native plants, and enhancing exotic plant species. Our study found no evidence to support of additive effects or impacts a between both species, but the presence of both cattle and wild boar could have an antagonistic effect or interactions through resource competition. Although cattle and wild boar are considered valuable socio-economic resources, we believe that the free-range populations of these mammals that inhabit temperate forests of Patagonia should have focused management plans that prioritize the control of cattle, to subsequently focus on the management of the wild boar. [ABSTRACT FROM AUTHOR]

Herbivore and plant invasions can modify the structure and functioning of ecosystems through positive interactions that facilitate their mutual establishment. An important consequence of the feeding behaviour of rabbits is that they can play a key role in seed dispersal by endozoochory. We examined the diet and potential for dispersing Rosa rubiginosa and R. canina (Rosa spp.) of European rabbits introduced in a semiarid protected area of Argentina. We found entire seeds in 100% of the samples of Rosa spp. analysed (n = 11, 187 pellets). Our results indicate that the passage of Rosa spp. seeds through the digestive tract of rabbits (64%) did not diminish their viability in comparison to the seeds taken directly from fruits (66%) (χ2 = 0.09, p > 0.05). This study has identified new positive interactions between an invasive mammal and two invasive plants, a finding that suggests that these invader complexes could have a reciprocal effect on one another, which would potentially aid their invasive process in a semiarid protected area of Argentina. [ABSTRACT FROM AUTHOR]

The availability of compatible mutualistic soil microbes could influence the invasion success of non‐native plant species. Specifically, there may be spatial variation in the distribution of compatible microbes, and species‐specific variation in plant host ability to associate with available microbes. Although either or both factors could promote or limit invasion, the scale over which most studies are conducted makes it difficult to examine these two possibilities simultaneously. However, this is critical to identifying a role of soil microbes in invasion.A series of recent research projects focused on interactions between Australian Acacia and nitrogen‐fixing bacteria (rhizobia) at multiple spatial scales, from the local to the inter‐continental, has allowed us to evaluate this question. Collectively, this research reveals that nodulation, performance and rhizobial community composition are all broadly similar across spatial scales and differentially invasive species.Synthesis and applications. We argue that current research provides convincing evidence that interactions with rhizobia do not determine invasion success in Acacia, but instead highlights key knowledge gaps that remain unfilled. Importantly, the ease with which non‐native Acacia species form mutualistic associations with rhizobia, regardless of invasive status, highlights the critical need to understand the impacts of all non‐native Acacia on native soil communities. [ABSTRACT FROM AUTHOR]

Widespread habitat-forming invaders inhabiting marinas, such as the spaghetti bryozoan Amathia verticillata, allow exploring facilitation processes across spatiotemporal contexts. Here we investigate the role of this bryozoan as habitat for native and exotic macrofaunal assemblages across different ecoregions of Western Mediterranean and East Atlantic coasts, and a monthly variation over a year. While only 7 (all peracarid crustaceans) of the 54 associated species were NIS, they dominated macrofaunal assemblages in terms of abundance, raising the potential for invasional meltdown. NIS richness and community structure differed among marinas but not among ecoregions, highlighting the importance of marina singularities in modulating facilitation at spatial scale. Despite facilitation did not depend on bryozoan abundance fluctuations, it was affected by its deciduous pattern, peaking in summer and disappearing in late winter. Monitoring A. verticillata in marinas, especially in summer periods, may improve the detection and management of multiple associated NIS. • Amathia verticillata host a diverse epifaunal community. • The bryozoan was prone to invasional meltdown. • Seven NIS found, all peracaridean crustaceans. • NIS richness and community structure differed among marinas but not among ecoregions. • Facilitation did not depend on bryozoan abundance. [ABSTRACT FROM AUTHOR]

Abstract Several dozen fish species have been introduced into Neotropical waters, causing significant biotic changes that include deterministic predation interactions with ecosystem effects. In general, reservoirs are preferred over lakes as places for stocking policies, due to their artificial aspect, consequently promoting fish introductions. In a meta‐analytic approach, we compared the biomass of plankton‐feeding (and top predators) with bottom‐feeding fish species between reservoirs and lakes, considering the influence of invaders and trophic levels. Among the 26 ecosystems (12 reservoirs and 14 lakes), there is a dominance of non‐native bottom‐feeding species in artificial environments. We revealed a mechanism behind this dominance in a study case, a tendency for trophic downgrading and biotic homogenization based on interactions between an expatriate invasive centrarchid (sunfish family) predator from North America (the largemouth bass Micropterus salmoides) and two omnivorous cichlids from Africa in novel environmental contexts in Brazil (the benthification process). Both juvenile and adult largemouth bass are keystone predators in aquatic food webs in both their native and introduced ranges. The omnivore–detritivore tilapiines Oreochromis spp. and the phytophagous–omnivorous Coptodon spp. are species that exhibits strong generalist tendencies. Such species feed on the omnivore and detritivore compartments, enhancing detritus cycling among a large variety of δ13C sources. Since their consumption is disproportionate, facilitation of other species occurs with multiplicative effects in the environment. Interactions between invasive species, that is, when an invasive predator (bird, fish, or invertebrate) eats an invasive prey (mainly fish and invertebrates), can serve to highlight biotic homogenization on fresh waters.

Background: Alliaria petiolata (garlic mustard) is a widespread allelopathic invasive species in North America, but despite extensive research we do not fully understand how it impacts plant communities. Aims: We tested the hypothesis that A. petiolata facilitates the introduction of additional alien species as predicted by the invasional meltdown hypothesis. Methods: We conducted co-occurrence surveys to compare the numbers of alien and native species in communities surrounding A. petiolata plants with those surrounding an allelopathic native species. We also conducted an experiment to compare recruitment of native and alien species in pots dominated by either A. petiolata or a native species. Results: A. petiolata plots in the co-occurrence surveys had relatively high proportions of bare ground, suggesting habitat modification, plus lower species richness and disproportionately fewer alien species. There was a greater tendency for native species than alien species to establish in A. petiolata pots. Conclusions: A. petiolata does not promote additional alien species, and in fact may be a more effective competitor against alien than native species in North America. This could help explain its invasive success in disturbed habitats, and illustrates the need to consider separately alien and native species when assessing the outcomes of competition. [ABSTRACT FROM AUTHOR]

Aim: Mutualisms are often disrupted for plants introduced to new ranges, yet many of these plants have managed to obtain effective mutualistic associations in their new ranges. There are two potential pathways for non‐native plants to reassemble mutualisms: cointroduction (i.e. familiar associations with cointroduced mutualists) or ecological fitting (i.e. forming or adapting novel associations with resident native mutualists). We assessed the importance of each pathway for mutualist reassembly in four Australian Acacia species (A. baileyana, A. dealbata, A. decurrens and A. melanoxylon) and their associated nitrogen‐fixing rhizobial symbionts in two non‐native locations. Location: Native ranges of acacias in south‐eastern Australia and two non‐native ranges in New Zealand and South Africa. Methods: Rhizobia associated with each acacia species in each country were isolated and identified based on DNA sequencing of the housekeeping recA gene and the symbiotic nodA gene. Separate phylogenies were reconstructed for each gene region to infer biogeographic histories of acacia‐associated rhizobia. Selected rhizobial strains for each acacia species by country combination were used as inocula in a glasshouse experiment and early growth kinetics and nitrogen fixation efficiency of acacia seedlings were compared between inoculum treatments to determine symbiotic effectiveness. Results: All isolated rhizobial strains belonged to the genus Bradyrhizobium. Phylogenetic analyses revealed almost no country‐ or species‐specific clusters of these strains for either gene region and indicated that most acacia‐associated bradyrhizobia in New Zealand and South Africa were cointroduced from Australia. These results were supported by little variation in the growth performances of acacia seedlings, irrespective of inoculum treatment. Main conclusions: This study revealed that cointroduction of Australian acacias and their rhizobia may be more prevalent than previously thought. Additionally, a single rhizobium cointroduction event may be sufficient to facilitate the establishment of effective mutualisms in numerous Acacia species, potentially leading to an invasion meltdown. [ABSTRACT FROM AUTHOR]

Positive interactions enhance biodiversity and ecosystem function, but can also exacerbate biological invasions. Facilitation of exotic invaders by exotic foundation species (invasional meltdown) has been studied extensively, but facilitation of exotic invaders by native foundation species has attracted less attention. Specifically, very few studies have examined the extent that native foundation species facilitate native and exotic competitors. Understanding the processes that mediate interactions between native and exotic species can help explain, predict, and improve management of biological invasions. Here, we examined the effects of native foundation shrubs on the relative abundance of the annual plant community - including native and exotic taxa - from 2015-2018 in a desert ecosystem at Carrizo Plain National Monument, California, USA (elevation: 723 m). Shrub effects varied by year and by the identity of annual species, but shrubs consistently enhanced the abundance of the annual plant community and facilitated both native (n=17 species) and exotic (n=4 species) taxa. However, at the provenance level, exotic annuals were facilitated 2.75 times stronger in abundance than native annuals, and exotic annuals were always more abundant than natives both near and away from shrubs. Our study reaffirms facilitation as an important process in the organisation of plant communities and confirms that both native and exotic species can form positive associations with native foundation species. However, facilitation by native foundation species can exacerbate biological invasions by increasing the local abundance of exotic invaders. Thus, the force of facilitation can have a dark side relevant to ecosystem function and management. [ABSTRACT FROM AUTHOR]

The aim of the study is to present a complete and updated fish inventory of inland waters of the Emilia-Romagna region, Northern Italy, and to highlight the presence of fully exotic fish communities. Overall, based on 208 sampling locations, the observed fish fauna consisted of 45 species, 22 native and 23 exotics. A significant element of the inventory is the identification of xenodiversity hotspots (spatially clustered sites, one lowland and one upland region), where a complete substitution of native species by exotic species was observed (in total seven sites in the lowland and two sites in the upland with no native species presence). These xenodiversity hotspots were found to host specific combinations of exotic species, which may be able to constitute balanced exotic communities. The hotspots of the lowland region are located in the northeast lowland part of the territory, hosting exotic species combinations mainly composed by wels catfish (Silurus glanis Linnaeus, 1758, a large predator), common carp (Cyprinus carpio Linnaeus, 1758, a large benthivore), crucian carp (Carassius spp., a small-bodied generalist) and other less dominant exotic species. The hotspots in the upland region were located in the southwest part of the territory and were dominated by only one exotic species (rainbow trout, Oncorhynchus mykiss (Walbaum, 1792)). A difference between these xenodiversity hotspots is that in the lowland the introductions were mostly unintentional and are not continued, while in the upland the introduction of rainbow trout is intentional and currently carried out by local fishermen. [ABSTRACT FROM AUTHOR]

The invasion paradox refers to the existence of biotic resistance and biotic acceptance hypotheses. According to the biotic resistance hypothesis, the higher the richness present in a community, the more resistant it is against invaders. In contrast, the biotic acceptance hypothesis states that if the environment is suitable for a high richness of native species, it will be similarly suitable for establishment of non-native species. Previous studies on terrestrial plant communities considered the scale-dependent nature of native and non-native relationships: the relationship tends to be negative at small scales (biotic resistance) and positive at broader scales (biotic acceptance). We tested the hypothesized role of spatial scale on the relationship between non-native and native species richness using a spatially nested design and a long-term dataset (146 communities sampled during 13 years) of fish species richness from the upper Paraná River floodplain, Brazil. Contrary to expectations, non-native fish species richness was positively correlated with native species richness at all spatial scales. Mobility of vertebrates, mode of invasion, and environmental disturbance may affect the role of spatial scale in potentially mediating relative importance of biotic acceptance versus resistance. In this context, the present study provides a unique contribution towards resolving the invasion paradox. [ABSTRACT FROM AUTHOR]

The impact of introduced fouling species and their associated epifauna in ports and marinas is potentially devastating for local biodiversity. The species composition of the epifauna on Tricellaria inopinata in Puerto América (Cádiz, Spain) was studied over a period of one year. Colonies were sampled bimonthly, and all associated mobile macrofauna was sorted and identified. A total of 19 species was found throughout the study period, including the introduced Caprella scaura and Monocorophium sextonae (Amphipoda) and Paracerceis sculpta (Isopoda). These three species represented over half of the individuals found throughout the study period, and there were significant differences between the abundance of native versus introduced species, though the direction of differences was not consistent. Whether the specific morphology and annual cycle of T. inopinata is favouring the establishment of other introduced species like those found here, and hindering other native species, is discussed, and future lines of research to address this phenomenon are proposed. [ABSTRACT FROM AUTHOR]