Establishment Of Exotic Species Research Articles

Evaluation of Trichopria anastrephae performance as parasitoid of Drosophila suzukii and Zaprionus indianus, under controlled laboratory conditions

AbstractNative parasitoids are potential tools for the biological control of invasive exotic pests, such as the frugivorous flies spotted‐wing drosophila, Drosophila suzukii Matsumura, and African fig fly, Zaprionus indianus Gupta (both Diptera: Drosophilidae). Following biological invasions, the establishment of exotic species may be restricted, among other things, by their susceptibility to native or established natural enemies. The Neotropical‐native pupal endoparasitoid Trichopria anastrephae Costa Lima (Hymenoptera: Diapriidae), although primarily associated with hosts of the genus Anastrepha (Tephritidae), has also been described to attack Drosophilidae. There are few studies on the interaction between parasitoids native to Argentina and D. suzukii and/or Z. indianus. The present work evaluates the parasitism of T. anastrephae on both species of drosophilids under controlled conditions. Ten larvae (L3) of each host species were exposed separately to a couple of adult T. anastrephae for 72 h (n = 10). For both control and parasitoid treatment, 10 larvae (L3) of D. suzukii and Z. indianus were placed in 10 flasks (repetition) at the L3 stage. Host emergence, the infestation degree index (DI), and the parasitism success rate (SP) were calculated. Drosophila suzukii and Z. indianus emergence differed significantly in controlled conditions being 41% higher for Z. indianus than for D. suzukii. The DI was 100% in D. suzukii and 38% in Z. indianus, and the SP was 48% both in D. suzukii and in Z. indianus. These findings indicate that the native parasitoid T. anastrephae has a high potential as a biocontrol strategy against D. suzukii. In addition, the efficiency of T. anastrephae against Z. indianus, an invasive frugivorous widely spread in the Neotropical region, was evaluated for the first time.

Comparisons of body size for native and exotic Hymenoptera established in New Zealand

ABSTRACT Body size is a fundamental component of morphology, related to many physiological and ecological traits, and is influenced by a variety of biotic and abiotic factors. Body size may also have a role in influencing the establishment of exotic species. We compared the body size of New Zealand native species, accidentally introduced exotic species, and deliberately introduced species of Hymenoptera. Specimens in the New Zealand Arthropod Collection were used to measure body and forewing length. Linear mixed effects regression models were used to compare the overall body sizes between biostatus groups, and specifically between species within a genus and family. A total of 2231 specimens were measured from 740 species of Hymenoptera, comprising 503 native, 201 exotic, and 36 biocontrol species. There was a strong positive correlation between body length and forewing length (R 2 > 0.97). Overall, the average body size of species did not differ significantly between native and accidentally introduced exotic species, but deliberately introduced biocontrol species were significantly smaller than native species. Exotic species had greater interspecific variation in body size than either native or biocontrol species. There were no significant differences in the body sizes of native and exotic species within the same genus or same family. Levene’s tests revealed there was equal variance between biostatus groups at the genus level but unequal variance at the family level. This study provides a large dataset on a key morphological trait, body size, that can be used to further examine how morphology can be shaped by, and influence, ecological communities, and interactions between species.

Intervenciones para rehabilitar sistemas silvopastoriles degradados: Una oportunidad para las especies vegetales exóticas

Interventions needed for degraded natural ecosystems rehabilitation create an opportunity for the establishment of exotic species. In caldén woodland areas in the semi-arid Pampas region, proven techniques for grassland recovery generate disturbances of varying intensity, ranging from soil removal with the total elimination of plant cover to partial aerial phytomass reduction. The objective was to evaluate the exotic plants species entry in communities subjected to different interventions and their permanence at different times from the last intervention. Treatments included bulldozer with rake, roller, and a prescribed burn. For the bulldozer intervention, the control and disturbed treatments were defined. For the rest, the following were established: control, burned, rolled and rolled + burned. In each of them, a gradient from the edge to the interior of the community was considered. For the capped areas, evaluations were carried out after one year, at five for the rolled ones and at three for the burned and rolled + burned ones. Coverage of species in the grassy-herbaceous stratum, total cover of vegetation and brush, and proportion of soil without cover were determined. A total of 79 species were recorded, 23% were exotic. In the bulldozer intervened areas, its proportion reached 33% (23% in the control). In the other interventions, their contribution was 26% in rolling, 21% in burning, and 28% in rolled+burned (18% in the control). Regarding the intensity of the disturbance, in those rolled areas or intervened with a bulldozer, the exotic species proportion was higher. The areas towards inside community and without disturbance (or with low intensity disturbances [e.g., prescribed burns]) showed a lower invasion level. After five years the communities recovered the coverage of the perennial grasses of the grassland, but a high proportion of exotics that exceeds that registered in the control one.

Biotic resistance or invasional meltdown? Diversity reduces invasibility but not exotic dominance in southern California epibenthic communities

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.

Spatio-Temporal Variation in Soil Nutrients and Plant Recovery across a Fire-Severity Gradient in Old-Growth Araucaria-Nothofagus Forests of South-Central Chile

Forest fires can alter essential ecosystem processes, including soil nutrient cycling, potentially cascading into permanent vegetation changes. This is key to elucidate in ecosystems where fires are infrequent. We assessed the effects of fire severity on the spatio-temporal response of soil nutrients and plant diversity in old-growth forests of south-central Chile, 1, 2, and 3 years after a fire that occurred in 2015. Within ancient, old-growth Araucaria araucana (Mol.) K. Koch and Nothofagus pumilio (Poepp. and Endl.) Krasser forests, ranging from areas burned with fire of high severity to unburned forests, we evaluated nitrogen (N), phosphorus (P), potassium (K), and soil organic matter (SOM) content using spatial interpolation to predict their spatial distribution and assessed their availability over time. We also assessed plant species richness and abundance following the fire. The availability of N noticeably increased during the first year after fire but rapidly decreased in the following years, especially in areas of high fire severity. P, K, and SOM were less affected by the fire, remaining more constant over time. In the short term, plant species richness and diversity significantly decreased in severely burned areas, but over time, they became more similar to those of the unburned forests. The time since a fire and its severity determine a heterogeneous distribution of soil nutrients, with N shifting to a significantly lower availability after fire, which was more notable in areas of high fire severity. Here, vegetation exhibited a decrease in plant diversity and the establishment of exotic species, likely producing cascading effects at the community level.

Human-derived effects and failure in management drive coastal urban foredune degradation and novel vegetation structure

Urbanization can drive significant decay in species diversity and abundance; in dune ecosystems the composition changes at a pace with changes in spatial fragmentation. Infrastructure deployment and human activities may provoke synergistically a reduction in dune patch size and/or habitat loss and thus a potential for rapid establishment of exotic species, producing a ‘novel’ habitat configuration. In this study we examine the effects of coastal urbanization and associated human activities in foredune patch fragmentation and changes in floristic composition and abundance in an urban-rural gradient. Using samples from a recently bulldozed and managed urban foredune area, we assess the legacy of erroneous practices associated with planting of exotic species in urban settings. We found a significant increase in foredune fragmentation, estimated as the occurrence of marks left by vehicles (4WD, 2WD) and people in foredunes close to or within urban settings. A marked change from native to non-native plant species was found from rural to urban environments, with non-native species contributing to increase species richness in urban settings. A positive relationship of non-native species with level of foredunes fragmentation was found. Dominance of non-native species was persistent through time in altered foredune patches. Our findings showed that incorporation of non-native species for aesthetic or engineering purposes in bulldozed foredunes, could limit colonization of native species through rapid establishment and complete dominance of non-native ones. Historical activities associated with coastal infrastructure upgrades seem to configure the present foredune floristic pattern present in urbanized coasts. Management strategies correcting past erroneous actions and promoting foredune rehabilitation could help the conservation of services that these ‘novel’ habitats provide in coastal urban environments.

Recovery of herb‐layer vegetation and soil properties after pile burning in a Midwestern oak woodland

Thinning and removal of woody vegetation is the first step in restoring ecosystem structure to systems altered by woody encroachment. However, pile burning—a common method of eliminating woody residue at restoration sites—can promote the establishment of exotic species and adversely impact soils and native vegetation via extreme soil heating. Despite its widespread use, pile burning effects remain poorly understood in oak woodlands compared to coniferous forests. We examined how pile burning influenced soil properties and herb‐layer recovery in a Midwestern, U.S. oak woodland undergoing restoration via exotic shrub removal, tree thinning, and prescribed burning. We quantified soil properties and passive vegetation recovery inside and adjacent to pile burn scars after 3 years, and tested whether native seed additions in year 1 increased native cover and reduced exotic cover in year 3. Bare ground cover, soil pH, and concentrations of P and Ca remained elevated 3 years after pile burning. In contrast, native cover, native richness, and floristic quality recovered to levels similar to adjacent control locations. Pile burning did not promote exotic invasions, increase inorganic forms of N, or alter patterns of the native cover of most growth forms. However, Carex species failed to reestablish in burn scars. Compared to passive recovery, seed additions increased native cover in burn scars and reduced exotic cover in adjacent control locations. Our results indicate that burn scars can naturally recover in oak woodland, but native seed additions may accelerate this process and improve restoration outcomes.

Seagrass (Halophila stipulacea) invasion enhances carbon sequestration in the Mediterranean Sea.

The introduction and establishment of exotic species often result in significant changes in recipient communities and their associated ecosystem services. However, usually the magnitude and direction of the changes are difficult to quantify because there is no pre-introduction data. Specifically, little is known about the effect of marine exotic macrophytes on organic carbon sequestration and storage. Here, we combine dating sediment cores (210 Pb) with sediment eDNA fingerprinting to reconstruct the chronology of pre- and post-arrival of the Red Sea seagrass Halophila stipulacea spreading into the Eastern Mediterranean native seagrass meadows. We then compare sediment organic carbon storage and burial rates before and after the arrival of H. stipulacea and between exotic (H. stipulacea) and native (C. nodosa and P. oceanica) meadows since the time of arrival following a Before-After-Control-Impact (BACI) approach. This analysis revealed that H. stipulacea arrived at the areas of study in Limassol (Cyprus) and West Crete (Greece) in the 1930s and 1970s, respectively. Average sediment organic carbon after the arrival of H. stipulacea to the sites increased in the exotic meadows twofold, from 8.4±2.5gCorg m-2 year-1 to 14.7±3.6gCorg m-2 year-1 , and, since then, burial rates in the exotic seagrass meadows were higher than in native ones of Cymodocea nodosa and Posidonia oceanica. Carbon isotopic data indicated a 50% increase of the seagrass contribution to the total sediment Corg pool since the arrival of H. stipulacea. Our results demonstrate that the invasion of H. stipulacea may play an important role in maintaining the blue carbon sink capacity in the future warmer Mediterranean Sea, by developing new carbon sinks in bare sediments and colonizing areas previously occupied by the colder thermal affinity P. oceanica.

Beneficial rhizobacterium provides positive plant–soil feedback effects to Ageratina adenophora

Rhizosphere microbial communities play important roles in facilitating or inhibiting the establishment of exotic species. Since some invasive plants interact with soil microbial communities such as rhizosphere bacteria, changes triggered by rhizosphere bacteria may alter competitive interactions between exotic and native plants. This study compared the Bacillus cereus content in soils with different degrees of Ageratina adenophora invasion, and investigated the effects of A. adenophora allelochemicals on B. cereus growth and soil characteristics and the feedback effects of B. cereus on A. adenophora growth. Bacillus cereus content in the rhizosphere of A. adenophora increased with intensification of the invasion process, and newly invaded soil contained almost twice as much bacteria as noninvaded soil. When rhizosphere soil was added to the root exudates of A. adenophora, the contents of B. cereus were twice as much as the control, except on the first day. Certain soil parameters increased significantly, such as ammonium nitrogen (NH4+-N) and available phosphorus (AP), which were increased by 41 and 27%, respectively. Soil treatment with B. cereus promoted the degradation of two allelochemicals from the rhizosphere of A. adenophora, amorpha-4,7(11)-dien-8-one and 6-hydroxy-5-isopropy1-3,8-dimethyl-4a,5,6,7,8,8a-hexahydraphthalen-2(1H)-one, to varying degrees; and increased the germination rate by 50%, root length by 117%, shoot length by 48% and fresh weight by 81% for A. adenophora compared to those of untreated soil. Our results confirmed that the invasion of A. adenophora will promote an increase of B. cereus, a beneficial rhizosphere bacterium, which in turn induces a positive feedback effect on A. adenophora.

Response of native and exotic longhorn beetles to common pheromone components provides partial support for the pheromone-free space hypothesis.

Longhorn beetles are among the most important groups of invasive forest insects worldwide. In parallel, they represent one of the most well-studied insect groups in terms of chemical ecology. Longhorn beetle aggregation-sex pheromones are commonly used as trap lures for specific and generic surveillance programs at points of entry and may play a key role in determining the success or failure of exotic species establishment. An exotic species might be more likely to establish in a novel habitat if it relies on a pheromone channel that is different to that of native species active at the same time of year and day, allowing for unhindered mate location (i.e., pheromone-free space hypothesis). In this study, we first tested the attractiveness of single pheromone components (i.e., racemic 3-hydroxyhexan-2-one, racemic 3-hydroxyoctan-2-one, and syn-2,3-hexanediol), and their binary and tertiary combinations, to native and exotic longhorn beetle species in Canada and Italy. Second, we exploited trap catches to determine their seasonal flight activity. Third, we used pheromone-baited "timer traps" to determine longhorn beetle daily flight activity. The response to single pheromones and their combinations was mostly species specific but the combination of more than one pheromone component allowed catch of multiple species simultaneously in Italy. The response of the exotic species to pheromone components, coupled with results on seasonal and daily flight activity, provided partial support for the pheromone-free space hypothesis. This study aids in the understanding of longhorn beetle chemical ecology and confirms that pheromones can play a key role in longhorn beetle invasions.

Historical legacies and ecological determinants of grass naturalizations worldwide

The global distribution of exotic species is the result of abiotic, biotic and dispersal filtering processes that shape the movement and success of species outside their native range. In this study we aim to understand how these filtering processes drive the fluxes of grass species among regions, the factors that influence which species establish outside of their native range, and where they do so.We used national and subnational checklists of native and introduced grass species to determine the extent to which each region was a source or recipient of exotic grass species. We asked how species traits may distinguish those grass species that have naturalized outside their native range from those that have not, and how environmental conditions are related to the distribution of exotic grass species.We found that exotic grass establishment is shaped by an array of factors including characteristics of regions, traits of species and their interactions. Regions with a longer history of human occupation and larger numbers of native grass species were generally the most important sources of exotic species. Global flows of species were mostly driven by a climate match between the native and exotic ranges, but were also highly asymmetric, with regions with recent human arrival being the major hosts of exotic grass species. Tall, annual and C4 grass species exhibited particularly high probabilities of establishment outside their native range.Despite the idiosyncrasy and stochasticity characteristic of exotic species establishment, this biogeographical analysis revealed important generalities across this large plant group. Our results suggest that grass species that have co‐occurred with humans for a longer time may be better adapted to living in anthropogenic landscapes, explaining the global asymmetry in species introductions.

Biological invasions in artificial habitats: factors that determine the presence of native and exotic peracarid Crustacea species in Southwestern Atlantic

ABSTRACT The aims of this study were to compare the richness and the population traits of exotic and native peracarid species in two ports of the Southwestern Atlantic (Mar del Plata: MDP, Puerto Madryn: PMY), in order to discuss the vulnerability of these environments to biological invasions, to explore the current status of these assemblages and to study the life history traits that could favour the establishment of exotic species in these ports. Five biofouling samples were taken each season from 2016 to 2017. The present study showed that exotic species were dominants in both ports but profound differences were registered between environments: MDP port is characterized by the absence of native species and highest richness of exotic species (n = 7 spp.); while in PMY port two native species were registered and exotic species (n = 2 spp.) showed lower richness than MDP port. The analysis of species assemblages and life history traits allows us to discuss the potential invasive pattern of peracarids in the Southwestern Atlantic, suggesting that factors, such as propagule pressure, port infrastructure, pollution levels are closely related to the differences in vulnerability of these artificial environments to biological invasions. In addition, the population dynamics and the reproductive traits of exotic species could explain their establishment and proliferation in the marine environments studied.

Any despot at my table? Competition among native and introduced bird species at garden birdfeeders in winter

Garden bird feeding constitutes a massive provision of food that can support bird communities, but there is a growing concern it might favour the establishment of exotic species that could be detrimental to others. How bird species compete with novel species for this anthropogenic food resources needs to be assessed.Here, we investigated competition in wintering bird communities at garden birdfeeders. We evaluated whether – and how much – bird access to resources is hampered by the presence of putative superior competing species, among which the Rose-ringed parakeet, the most abundant introduced species across Europe.Using the nation-wide citizen science scheme BirdLab, in which volunteers record in real-time bird attendance on a pair of birdfeeders during 5-minute sessions, we tested whether i) cumulative bird presence time and richness at birdfeeders, and ii) species probability of presence at birdfeeders, were influenced by three large species (the Eurasian magpie, the Eurasian collared-dove, and the Rose-ringed parakeet). Additionally, we assessed whether the Rose-ringed parakeet occupied resources significantly more than others.Presence of the Rose-ringed parakeet or the Eurasian collared-dove similarly reduced community cumulative presence time at birdfeeders, but only the dove reduced community richness. Each of the three large species influenced the presence of at least one of the six smaller species that could be separately modelled, but effects varied in strength and direction. The Rose-ringed parakeet and the Eurasian collared-dove were among the three species monopolising birdfeeders the longest, substantially more than the Eurasian magpie.Our findings confirm the competitive abilities of the large species studied, but do not suggest that garden bird feeding may alarmingly favour introduced species with detrimental effects on native species. Given the variability of large species' effects on small passerines, direct and indirect interactions among all species must be examined to fully understand the ecological net effects at stake.

Early warning: detection of exotic coho salmon (Oncorhynchus kisutch) by environmental DNA and evidence of establishment at the extreme south of Patagonia

The global expansion of aquaculture is a constant propagule pressure that enables the establishment of exotic species in freshwater and marine environments. Here, we provide the first report on the presence of exotic coho salmon (Oncorhynchus kisutch) at the extreme south of Patagonia, in the island of Tierra del Fuego (TDF). During the last 6 years, 43 juvenile coho salmon were captured along the Beagle Channel, while one adult was captured in fresh water. Scale analysis showed that migration from fresh water as smolt would occur during their first winter of life. Mitochondrial DNA analyses revealed two haplotypes previously reported in North America and a new haplotype not reported before. We developed an environmental DNA assay for detecting coho salmon DNA from fresh water, obtaining positive results in three rivers. Additionally, one of these rivers was monitored monthly for a year, and we detected coho salmon DNA over 7 months, revealing the probable occurrence of coho salmon juveniles in fresh water. These results suggest the potential establishment of self-sustaining populations of coho salmon in TDF.

Lista florística del bosque de galería del río Metztitlán, Hidalgo, México

Antecedentes y Objetivos: El bosque de galería (BG) del río Metztitlán tiene importancia ecológica en la Reserva de la Biosfera Barranca de Metztitlán y contribuye al sostenimiento de la biodiversidad y al desarrollo de numerosos procesos biológicos. Los objetivos del estudio fueron realizar la lista florística del BG en la Reserva y determinar la composición de especies nativas y exóticas, su capacidad de distribución, hábitat y estado de riesgo según la NOM-059-SEMARNAT-2010 y la Lista Roja de Especies Amenazadas (IUCN).Métodos: Las colectas botánicas se realizaron en la época de lluvia (2013) y de estiaje (2014), en ambos márgenes del río. La identificación taxonómica se efectuó con base en la Flora Fanerogámica del Valle de México y la Flora del Bajío y de regiones adyacentes y se confirmó con especialistas, y en el Herbario-Hortorio (CHAPA) del Colegio de Postgraduados. Mediante revisiones bibliográficas se determinó la capacidad de distribución de las especies así como su hábitat y estado de riesgo (NOM-059-SEMARNAT-2010 e IUCN).Resultados clave: Se identificaron 122 especies de plantas vasculares pertenecientes a 38 familias y 102 géneros. Las familias representativas fueron Asteraceae (21 géneros y 24 especies) y Poaceae (12 y 17); los géneros con mayor número de especies fueron Cyperus (4) y Eragrostis (4). Del total de especies, 81 son nativas; cinco probablemente nativas de México; 34 exóticas; una de origen incierto; tres endémicas de México. Ninguno de los taxones se encontró en estado de riesgo.Conclusiones: El BG en la Reserva de la Biosfera Barranca de Metztitlán presenta alteraciones de origen antrópico, que favorecen el establecimiento de especies exóticas, las cuales integran 27% de la lista florística con predominancia en la cobertura vegetal.

Short-Term Vegetation Responses to Invasive Shrub Control Techniques for Amur Honeysuckle (Lonicera maackii [Rupr.] Herder)

Invasive shrubs in forest understories threaten biodiversity and forest regeneration in the eastern United States. Controlling these extensive monotypic shrub thickets is a protracted process that slows the restoration of degraded forest land. Invasive shrub removal can be accelerated by using forestry mulching heads, but evidence from the western United States indicates that mulching heads can promote exotic species establishment and mulch deposition can reduce native plant species abundance. We compared the effectiveness of the mulching head and the “cut-stump” method for controlling the invasive shrub Amur honeysuckle (Lonicera maackii), as well as their impacts on native plant community recovery, in mixed-hardwood forests of Indiana. After two growing seasons, mulching head treatment resulted in greater L. maackii regrowth and regeneration. The recovery of native plant abundance and diversity following shrub removal did not differ between the two methods. However, mulch deposition was associated with increased abundance of garlic mustard (Alliaria petiolata), an invasive forb. Increasing mulching head treatment depth reduced L. maackii regrowth, but additional study is needed to determine how it affects plant community responses. The mulching head is a promising technique for invasive shrub control and investigating tradeoffs between reducing landscape-scale propagule pressure and increased local establishment will further inform its utility.

Limiting similarity, biotic resistance, nutrient supply, or enemies? What accounts for the invasion success of an exotic legume?

Models for community invasion can inform grassland management if patterns involving the environment, other species, and invader success are evident. We evaluated unplanned invasion by Lespedeza cuneata into an experiment on a reconstructed tallgrass prairie. Our goal was to determine whether the pattern of invasion by this exotic legume was consistent with either the limiting similarity hypothesis (LSH), which predicts poorer establishment of exotic species in communities with related species, or the biotic resistance hypothesis, which predicts a negative association between species richness and invasion. We also examined how the abiotic environment and hemiparasite abundance affect spread of L. cuneata. From 2006 to 2015 we manipulated fertilizer and presence of the hemiparasitic plant, Pedicularis canadensis, in 1-m2 plots, and manipulated shade for the first 5 years. We found greater support for the LSH. Biomasses of legumes and other forbs in 2008 were negatively associated with change in L. cuneata biomass over the next 7 years but species richness was not a significant effect. Lespedeza cuneata cover in 2015 was lower in fertilized plots relative to unfertilized plots and was negatively associated with a composite variable that described the number and combined cover of legume species and number of exotic species currently in the plots. Shading for five seasons reduced L. cuneata growth, but only significantly in fertilized plots from which the hemiparasite had been removed. Other analysis suggested that L. cuneata increased more as the hemiparasite abundance increased. Prairie management that increases the kinds and abundances of native legume species and increases soil fertility may slow the spread of L. cuneata, but we caution against adding P. canadensis to large areas without greater knowledge of site-specific effects.

Secondary invasion: When invasion success is contingent on other invaders altering the properties of recipient ecosystems.

Positive interactions between exotic species may increase ecosystem‐level impacts and potentially facilitate the entry and spread of other exotic species. Invader‐facilitated invasion success—”secondary invasion”—is a key conceptual aspect of the well‐known invasional meltdown hypothesis, but remains poorly defined and empirically underexplored. Drawing from heuristic models and published empirical studies, we explore this form of “secondary invasion” and discuss the phenomenon within the recognized conceptual framework of the determinants of invasion success. The term “secondary invasion” has been used haphazardly in the literature to refer to multiple invasion phenomena, most of which have other more accepted titles. Our usage of the term secondary invasion is akin to “invader‐facilitated invasion,” which we define as the phenomenon in which the invasion success of one exotic species is contingent on the presence, influence, and impacts of one or more other exotic species. We present case studies of secondary invasion whereby primary invaders facilitate the entry or establishment of exotic species into communities where they were previously excluded from becoming invasive. Our synthesis, discussion, and conceptual framework of this type of secondary invasion provides a useful reference to better explain how invasive species can alter key properties of recipient ecosystems that can ultimately determine the invasion success of other species. This study increases our appreciation for complex interactions following invasion and highlights the impacts of invasive species themselves as possible determinants of invasion success. We anticipate that highlighting “secondary invasion” in this way will enable studies reporting similar phenomena to be identified and linked through consistent terminology.

Third-party mutualists have contrasting effects on host invasion under the enemy-release and biotic-resistance hypotheses

Plants engage in complex multipartite interactions with mutualists and antagonists, but these interactions are rarely included in studies that explore plant invasiveness. When considered in isolation, we know that beneficial microbes can enhance an exotic plant’s invasive ability and that herbivorous insects often decrease an exotic plant’s likeliness of success. However, the effect of these partners on plant fitness has not been well characterized when all three species coevolve. We use computational evolutionary modeling of a trait-based system to test how microbes and herbivores simultaneously coevolving with an invading plant affect the invaders’ probability of becoming established. Specifically, we designed a model that explores how a beneficial microbe would influence the outcome of an interaction between a plant and herbivore. To model novel interactions, we included a phenotypic trait shared by each species. Making this trait continuous and selectable allows us to explore how trait similarities between coevolving plants, herbivores and microbes affect fitness. Using this model, we answer the following questions: (1) Can a beneficial plant-microbe interaction influence the evolutionary outcome of antagonistic interactions between plants and herbivores? (2) How does the initial trait similarity between interacting organisms affect the likelihood of plant survival in novel locations? (3) Does the effect of tripartite interactions on the invasion success of a plant depend on whether organisms interact through trait similarity [Enemy Release Hypothesis (ERH)] or dissimilarity (Biotic Resistance Hypothesis)? We found that it was much more difficult for plants to invade under the ERH but that beneficial microbes increase the probability of plant survival in a novel range under both hypotheses. To our knowledge, this model is the first to use tripartite interactions to explore novel species introductions. It represents a step towards gaining a better understanding of the factors influencing establishment of exotic species to prevent future invasions.

Agroforestry systems reduce invasive species richness and diversity in the surroundings of protected areas

The Serra do Brigadeiro State Park (PESB) is one of the largest fragments of Brazilian Atlantic Rainforest, and it is relevant for native species conservation. However, monocultures settled around the Park resulted in extensive open areas that facilitate the establishment of alien species on the PESB perimeter, which may threaten native species conservation therein, since biological invasion is the second main cause of global biodiversity loss. In this region, there are also farmers planting agroforestry systems (AFS), characterized by tree-based intercropping, which are structurally more similar to the Atlantic Rainforest reminiscent fragments present in the region and may limit local occurrence of potentially invasive exotic weeds for several reasons, such as the high levels of shade provided by trees, the groundcover that result from loss of tree leaves and the increased competition for belowground resources. This study aimed to test whether AFS limit exotic species establishment when compared to monoculture systems. Accordingly, three coffee monocultures and three agroforestry coffee plantations around the PESB were studied. In each of the six study areas, 30 plots of 1 m2 were established between the lines of coffee plantation, where all species present were surveyed. In both treatments, rarefaction curves were constructed to evaluate native and exotic richness, and diversity of these two categories was estimated through Simpson index inverse (1/D). All 13 sampled exotic species were present in monocultures, but only three of them occurred in AFS. Besides, alien diversity in monocultures ( $$1/D$$ = 2.173 ± 0.011) was significantly higher than in AFS ( $$1/D$$ = 1.031 ± 0.001). Such changes in alien plant community between land-use show that AFSs limit invasive species establishment. Therefore, when planted around protected areas, AFS may contribute to the control of biological invasions and to biodiversity conservation.