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Deployment of mouse carcasses laced with acetaminophen has become a common management tool to control invasive brown tree snakes (Boiga irregularis; BTS) on Guam. Additionally, anticoagulant rodenticides may be used to control invasive rats (Rattus spp.) if their populations increase due to predator release in the wake of BTS eradication. However, there has been little research examining how scavengers on Guam could be incidentally exposed to toxicants by scavenging carcasses of animals that die from these population control strategies. Furthermore, there is a limited understanding of how the proliferation of invasive species on Guam has influenced the composition of the scavenger community. We investigated these topics by examining scavenger consumption of mouse, rat, and BTS carcasses on Guam in both a coastal and upland site during the wet (May–Aug 2016) and dry season (Jan–Apr 2017). We documented carcass consumption by 9 species, which scavenged 48% of carcasses. Interactions between season, habitat, and carcass type influenced probability of scavenging, and appeared to be driven by consumption by the two main scavenger species, BTS and cane toads (Rhinella marina), both of which are invasive on Guam. Baiting programs should consider the potential for toxin exposure to land crabs (Coenobita spp., Birgus latro), native species that scavenged at every combination of carcass type, habitat, and season. Overall, 60% of scavenging events were attributed to species considered pests that are recent introductions to Guam. Invasive species on Guam are the primary scavengers of small vertebrate carrion, suggesting a substantial role in trophic dynamics that extends beyond predation. [ABSTRACT FROM AUTHOR]

Invasive plants are one of the greatest threats leading to biodiversity loss and species extinction worldwide. Understanding the responses of liana and tree communities as well as liana-tree interactions to plant invasion could be important in biodiversity conservation and ecosystem functioning, but there is limited knowledge on this subject matter. We therefore sought to determine how the diversity, composition and structure of native liana and tree communities and liana-tree interaction networks responded to invasion by three tree species (Broussonetia papyrifera¸ Cedrela odorata, Tectona grandis) in two moist semi-deciduous forests in Ghana. Effects of plant invasion on native liana and tree community structure and liana-tree network structure were quantified by sampling liana species with diameter at 1.30 m from rooting base ≥ 1 cm, and tree species with diameter at breast height ≥ 5 cm in 20 20 × 20 m plots each in non-invaded and invaded sites. The findings of the study showed that plant invasion was associated with lower diversity and abundance of lianas and trees as well as shifts in species composition of the plants. Our results revealed that plant invasion influenced the patterns of liana-tree network structure, and tended to cause an increase in network connectance and nestedness, and a decrease in network modularity and specialisation. Plant invasion drove the topological roles of a few liana and tree species in the invaded sites. Generally, species abundance and specificity were important correlates of nestedness, and modularity and species roles of the networks. We conclude that the invasive tree species drove native liana and tree community structure, degree of liana-tree network structure, and species topological roles, all of which may have adverse consequences on biodiversity in the forests. [ABSTRACT FROM AUTHOR]

False mussels are recognized as the brackish water equivalent of zebra mussels, although the abiotic and habitat conditions that mediate these invaders' success are barely known. In this context, we aimed to evaluate the native and non-native geographical distribution of Mytilopsis species worldwide and assess biological traits, environmental condition, and habitat associated with false mussels in native and invaded systems. Our hypothesis is that Mytilopsis invasion is driven by species tolerance to environmental conditions and substrate use in brackish systems, where the colonization of non-native populations is favored by great availability of artificial substrates and tolerance to wide ranges of environmental conditions. In addition, this study provides the range and distribution patterns of Mytilopsis species within their introduced and native areas and documents the spread of introduced populations worldwide. Considering the five species evaluated, M. leucophaeata and M. sallei are the most widespread, while M. adamsi, M. trautwineana, and M. africana showed more restricted geographic distribution. In the last decades, M. leucophaeata and M. sallei consolidated and expanded their distributions. Environmental conditions were significantly different between native and non-native areas, where Mytilopsis populations presented significantly higher densities. Non-native populations exhibited remarkable plasticity concerning habitat colonization that was more frequent on artificial substrata. Mytilopsis populations presented significant differences in their biological traits, habitat environmental conditions, and substrate use between native and non-native areas. These species seem to adapt to the conditions of invaded systems, changing their preferences, which may reflect plasticity and a potential shift of their realized niches. [ABSTRACT FROM AUTHOR]

Introduced species can alter the dynamics and structure of a native community. Network analysis provides a tool to study host–parasite interactions that can help to predict the possible impact of biological invasions or other disturbances. In this study, we used weighted bipartite networks to assess differences in the interaction patterns between hosts and helminth parasites of native (Sea of Japan) and invasive (Black Sea and Sea of Azov) populations of Planiliza haematocheilus (Teleostei: Mugilidae). We employed three quantitative network descriptors, connectance, weighted nestedness and modularity, to gain insight into the structure of the host–parasite networks in the native and invaded areas. The role of parasite species in the networks was assessed using the betweenness centrality index. We analyzed networks encompassing the whole helminth community and subsets of species classified by their transmission strategy. The analyses were downscaled to host individual-level to consider intraspecific variation in parasite communities. We found significant differences between networks in the native and invaded areas. The latter presented a higher value of nestedness, which may indicate a co-occurrence between parasite species with many connections in the network and species with fewer interactions within the same individual-host. In addition, modularity was higher in the native area's networks than those of the invaded area, with subgroups of host individuals that interact more frequently with certain parasite species than with others. Only the networks composed of actively transmitted parasites and ectoparasites did not show significant differences in modularity between the Sea of Azov and the Sea of Japan, which could be due to the introduction of a part of the native community into the invaded environment, with a lower diversity and abundance of species. We show that network analysis provides a valuable tool to illuminate the changes that occur in host–parasite interactions when an invasive species and its parasite community are introduced into a new area. [ABSTRACT FROM AUTHOR]

Human activities have facilitated the introduction of invasive plants worldwide, altering habitat structure and leading to substantial effects on biodiversity. However, the effects of plant invasions on herbivore communities are understudied. Here, we examine factors influencing the occurrence of herbivores in ten coastal sites invaded by Carpobrotus edulis in the northwestern Iberian Peninsula. The aims were to evaluate the distribution and abundance of herbivorous invertebrates in different communities (invaded vs. non-invaded), explore the structure of plant–herbivore interaction networks, and assess whether the presence of herbivores affects the performance and fitness of C. edulis. Our results show that herbivore species composition was altered by the presence of C. edulis. Non-invaded plots had a higher number of plant–herbivore interactions and more specialized herbivore species, resulting in a greater degree of specialization. We also found an increase in the number of damaged flowers (florivory) of C. edulis by the native snails Theba pisana and Cornu aspersum. We conclude that C. edulis alters herbivore communities compared with non-invaded plots by changing plant–herbivore interactions and increasing the abundance of herbivores in invaded coastal sites. Snails might reduce seed production of C. edulis, acting as a natural biological control agent. Understanding the impacts of introduced species over invertebrate species at different community levels is crucial for implementing long-term management strategies that are key to reducing the impact of C. edulis on biodiversity. [ABSTRACT FROM AUTHOR]

Islands harbor a considerable portion of global biodiversity and endemic biota, and also are the recipients of the largest proportional numbers of alien invaders. Such invaders may jeopardize the performance of native species, through either their direct or indirect effects. In this study, we investigated the reproductive ecology of the endemic scrambling perennial herb Canarina canariensis in remnants of the former thermosclerophyllous woodland of Tenerife (Canary Islands), assessing how two widespread alien invasive species, the honeybee (Apis mellifera) and the black rat (Rattus rattus), affect its reproductive success. Apis mellifera visits its flowers whereas the black rat consumes both its flowers and fruits. Here, we compared the pollination effectiveness of different animal guilds (vertebrates vs insects) by means of selective exclosures and determined the level of floral herbivory. Three bird species (Phylloscopus canariensis, Cyanistes teneriffae and Sylvia melanocephala), a lizard (Gallotia galloti) and two insects (A. mellifera and the butterfly Gonepteryx cleobule) were the main flower visitors. Phylloscopus canariensis was the most frequent visitor in the early flowering season whereas A. mellifera predominated in the flowers during mid and late flowering periods. Birds increased fruit set, whilst lizards and insects had a negligible effect. Rats consumed about 10% of the flowers and reduced fruit set to one third. Besides contributing little to plant reproduction, A. mellifera might interfere with bird pollination by depleting flowers of nectar. We conclude that both alien species can threaten C. canariensis reproduction and hence population sustainability in the thermosclerophyllous vegetation. Apis mellifera, in particular, may become especially detrimental if apiculture keeps expanding, or if this bee becomes active earlier in the season due to global warming. [ABSTRACT FROM AUTHOR]

The increased introduction of non-native species to habitats is a characteristic of globalisation. The impact of invading species on communities may be either linearly or non-linearly related to the invaders' abundance in a habitat. However, non-linear relationships with a threshold point at which the community can no longer tolerate the invasive species without loss of ecosystem functions remains poorly studied. We selected 31 wet meadow sites that encompassed the entire coverage spectrum of invasive goldenrods, and surveyed the abundance and diversity of pollinating insects (bees, butterflies and hover flies) and native plants. The species richness of native plants decreased linearly with goldenrod cover, whereas the abundance and species richness of bees and butterflies decreased non-linearly with increasing goldenrod cover. However, no statistically significant changes across goldenrod cover were noted for the abundance and species richness of hover flies. Because of the non-linear response, goldenrod had no visible impact on bees and butterflies until it reached cover in a habitat of about 50% and 30-40%, respectively. Moreover, changes driven by goldenrod in the plant and pollinator communities were related to species loss rather than species replacement. We demonstrated that the impact of goldenrod cover on a habitat is not instantaneous. Habit management aimed at preventing the invasion process and alleviating its impact should take into account that, for the non-linear relationships, the negative impact can appear rapidly after crossing the threshold point. [ABSTRACT FROM AUTHOR]

Forests play critical roles in global ecosystem processes and provide numerous services to society. But forests are increasingly affected by a variety of human influences, especially those resulting from biological invasions. Species invading forests include woody and herbaceous plants, many animal species including mammals and invertebrates, as well as a variety of microorganisms such as fungi, oomycetes, bacteria and viruses. These species have diverse ecological roles including primary producers, herbivores, predators, animal pathogens, plant pathogens, decomposers, pollinators and other mutualists. Although most non-native species have negligible effects on forests, a few have profound and often cascading impacts. These impacts include alteration of tree species composition, changes in forest succession, declines in biological diversity, and alteration of nutrient, carbon and water cycles. Many of these result from competition with native species but also trophic influences that may result in major changes in food web structure. Naturally regenerating forests around the world have been substantially altered by invading species but planted forests also are at risk. Non-native tree species are widely planted in many parts of the world for production of wood and fibre, and are chosen because of their frequently exceptional growth in their new environment. This greater growth is due, in part, to escape from herbivores and pathogens that exist in their native ranges. Over time, some pest species can 'catch-up' with their hosts, leading to subsequent declines in forest productivity. Other impacts result when native herbivores or pathogens adapt to exotic trees or when novel associations form between pathogens and vectors. Additionally, planted non-native trees are sometimes invasive and can have substantial adverse effects on adjacent natural areas. Management of invasions in forests includes prevention of arrival, eradication of nascent populations, biological control, selection for resistance in host trees, and the use of cultural practices (silviculture and restoration) to minimize invader impacts. In the future, the worlds' forests are likely to be subject to increasing numbers of invasions, and effective management will require greater international cooperation and interdisciplinary integration. [ABSTRACT FROM AUTHOR]

The success of a biological invasion is context dependent, and yet two key concepts-the invasiveness of species and the invasibility of recipient ecosystems-are often defined and considered separately. We propose a framework that can elucidate the complex relationship between invasibility and invasiveness. It is based on trait-mediated interactions between species and depicts the response of an ecological network to the intrusion of an alien species, drawing on the concept of community saturation. Here, invasiveness of an introduced species with a particular trait is measured by its per capita population growth rate when the initial propagule pressure of the introduced species is very low. The invasibility of the recipient habitat or ecosystem is dependent on the structure of the resident ecological network and is defined as the total width of an opportunity niche in the trait space susceptible to invasion. Invasibility is thus a measure of network instability. We also correlate invasibility with the asymptotic stability of resident ecological network, measured by the leading eigenvalue of the interaction matrix that depicts trait-based interaction intensity multiplied by encounter rate (a pairwise product of propagule pressure of all members in a community). We further examine the relationship between invasibility and network architecture, including network connectance, nestedness and modularity. We exemplify this framework with a trait-based assembly model under perturbations in ways to emulate fluctuating resources and random trait composition in ecological networks. The maximum invasiveness of a potential invader (greatest intrinsic population growth rate) was found to be positively correlated with invasibility of the recipient ecological network. Additionally, ecosystems with high network modularity and high ecological stability tend to exhibit high invasibility. Where quantitative data are lacking we propose using a qualitative interaction matrix of the ecological network perceived by a potential invader so that the structural network stability and invasibility can be estimated from the literature or from expert opinion. This approach links network structure, invasiveness and invasibility in the context of trait-mediated interactions, such as the invasion of insects into mutualistic and antagonistic networks. [ABSTRACT FROM AUTHOR]

The spread of non-native invasive plants is closely linked to land use changes imposed by human activities such as the expansion of urbanizations and agricultural activities that result in the loss and fragmentation of native forests. While the conditions generated in fragmented forests may provide suitable new habitat for the arrival and establishment of invasive plant propagules, we know little about the reproductive performance of established invasive populations growing in fragmented conditions. We assess sexual reproduction of Ligustrum lucidum in continuous and fragmented forests across 2 years. We also measure soil quality parameters in 1 year to determine their relative influence in shaping its reproduction in both landscape conditions. We observed a strong decrease in reproductive success at the population level in fragmented habitats. However, reproduction at the individual level showed no differences in seed production per tree between landscape conditions, implying no changes in pollination service. Simultaneously, soils of continuous forests had higher water content, total nitrogen, organic matter and carbon. These soil quality parameters were positively correlated with seed production and seedling number per plot within the same year. Thus, reproductive failure in fragmented forests would not be the result of Allee effects but the consequence of less favorable abiotic soil conditions. In current dynamic and changing climatic scenarios imposed by human activities, water and nutrient demanding invasive plants like L. lucidum might be as likely as or even more susceptible to these changes than native ones. Climatic shifts acting in concert with land use changes may either ameliorate invasion spread in abiotically eroded fragmented habitats or boost invasion into novel environments, resulting in new distribution spread patterns. [ABSTRACT FROM AUTHOR]

The Africanized honeybee Apis mellifera (AHB) is an invasive species spread over all Brazilian biomes, which has negative impacts on native bee populations, but whose impacts on native plants are still controversial. In order to understand how its impacts extend to the pollination service at the community level, we studied the AHB and its interactions in a multi-species context using network theory. We analyzed six pollination networks from the Brazilian Caatinga, a xeric biome where beekeeping is increasing very quickly. The AHB occupied a central position in all networks, as it was responsible for a large share of the interactions observed (14 ± 7 %) and bound together different modules. By simulating the removal of the AHB from each network, we observed no effects on connectance, but a strong decrease in nestedness (−23 ± 19 %) and an increase in modularity (8 ± 5 %). The robustness of networks to cumulative random extinctions was on average not affected. In summary, our evidence points out that the AHB induces significant changes in the structure of native pollination networks, mainly by making them more cohesive and monopolizing many interactions. Although the AHB did not affect network robustness, its net impact on the pollination service may be negative, because this invasive species is very generalistic and may not be an efficient pollinator for some native plants. [ABSTRACT FROM AUTHOR]

The alien predatory lizard, Anolis carolinensis, has reduced the insect fauna on the two main islands of the Ogasawara archipelago in Japan. As a result of this disturbance, introduced honeybees are now the dominant visitors to flowers instead of endemic bees on these islands. On the other hand, satellite islands not invaded by alien anoles have retained the native flower visitors. The effects of pollinator change on plant reproduction were surveyed on these contrasting island groups. The total visitation rates and the number of interacting visitor groups on main islands were 63% and 30% lower than that on satellite islands, respectively. On the main islands, the honeybees preferred to visit alien flowers, whereas the dominant endemic bees on satellite islands tended to visit native flowers more frequently than alien flowers. These results suggest that alien anoles destroy the endemic pollination system and caused shift to alien mutualism. On the main islands, the natural fruit set of alien plants was significantly higher than that of native plants. In addition, the natural fruit set was positively correlated with the visitation rate of honeybees. Pollen limitation was observed in 53.3% of endemic species but only 16.7% of alien species. These data suggest that reproduction of alien plants was facilitated by the floral preference of introduced honeybees. [ABSTRACT FROM AUTHOR]

Abstract  A literature survey identified 403 primary research publications that investigated the ecological effects of invasive alien insects and/or the mechanisms underlying these effects. The majority of these studies were published in the last 8 years and nearly two-thirds were carried out in North America. These publications concerned 72 invasive insect species, of which two ant species, Solenopsis invicta and Linepithema humile, accounted for 18% and 14% of the studies, respectively. Most publications investigated effects on native biodiversity at population or community level. Genetic effects and, to a lesser extent, effects on ecosystem services and processes were rarely explored. We review the effects caused by different insect invaders according to: their ecosystem roles, i.e. herbivores, predators, parasites, parasitoids and pollinators; the level of biological organisation at which they occur; and the direct and indirect mechanisms underlying these effects. The best documented effects occur in invasive ants, Eurasian forest herbivores invasive in North America, and honeybees. Impacts may occur through simple trophic interactions such as herbivory, predation or parasitism. Alien species may also affect native species and communities through more complex mechanisms such as competition for resources, disease transmission, apparent competition, or pollination disruption, among others. Finally, some invasive insects, particularly forest herbivores and ants, are known to affect ecosystem processes through cascading effects. We identify biases and gaps in our knowledge of ecological effects of invasive insects and suggest further opportunities for research. [ABSTRACT FROM AUTHOR]

Abstract  Invasion by alien organisms is a common worldwide phenomenon, and many alien species invade native communities. Invasion by alien species is especially likely to occur on oceanic islands. To determine how alien species become integrated into island plant–insect associations, we analyzed the structure of tree–beetle associations using host plant records for larval feeding by wood-feeding beetles (Coleoptera: Cerambycidae) on the oceanic Ogasawara Islands in the northwestern Pacific Ocean. The host plant records comprised 109 associations among 28 tree (including 8 alien) and 26 cerambycid (including 5 alien) species. Of these associations, 41.3% involved at least one alien species. Most native cerambycid species feed on host trees that have recently died. Alien trees were used by as many native cerambycid species (but by significantly more alien cerambycid species) as were native trees. Native cerambycid species used as many alien tree species (but significantly more native tree species) as did alien cerambycids. Thus, we observed many types of interactions among native and alien species. A network analysis revealed a significant nested structure in tree–cerambycid associations regardless of whether alien species were excluded from the analysis. The original nested associations on the Ogasawara Islands may thus have accepted alien species. [ABSTRACT FROM AUTHOR]