Phenotypic plasticity of reproductive traits in response to food availability in invasive and native species of nematode

Invasive species cause severe ecological and economic damage; however, the mechanisms underlying their successful invasion often remain elusive. In the case of Bursaphelenchus xylophilus, a global quarantine pest which invaded Asia and Europe, it has been suggested that this species possesses highly competitive abilities, which promotes its establishment and rapid spread. To explore biological traits that may explain its highly competitive abilities, we focused on expression of phenotypic plasticity in response to the food conditions experienced by the females during their development as juveniles in the invasive species B. xylophilus and native species Bursaphelenchus mucronatus. We report an unexpected significant difference of phenotypic trade-off between egg number and egg size in the invasive species B. xylophilus and native species B. mucronatus. This leads to superior propagation ability of invasive species, under high and low food conditions in culture. These effects reflect adaptive optimal resource allocation where more eggs are produced in favorable environments to enhance population viability. Furthermore, we show that B. xylophilus eggs hatched earlier than B. mucronatus when their parents experienced high food availability. Thus, this study revealed, for the first time, phenotypic plasticity of reproductive traits in B. xylophilus which empowers the species a competitive advantage relative to their native counterpart B. mucronatus when they are under different range of food availability. These results are a step towards answering the vital question of how an exotic invasive species exclude a native species from its original niche.     

Bacteria associated with the pinewood nematode <Emphasis Type="Italic">Bursaphelenchus xylophilus</Emphasis> collected in Portugal

In this study, we report on the bacterial community associated with the pinewood nematode Bursaphelenchus xylophilus from symptomatic pine wilted trees, as well as from long-term preserved B. xylophilus laboratory collection specimens, emphasizing the close bacteria–nematode associations that may contribute to pine wilt disease development.     

Evolutionary change in a pine wilt system following the invasion of Japan by the pinewood nematode, <Emphasis Type="Italic">Bursaphelenchus</Emphasis><Emphasis Type="Italic">xylophilus</Emphasis>

Pinewood nematode (PWN), Bursaphelenchus xylophilus, is the causative agent of pine wilt disease (PWD) of pine trees and is transmitted by cerambycid beetles belonging to the genus Monochamus. PWN is believed to have been introduced into Japan from North America at the beginning of the 20th century. In this article, we first provide an outline of the PWD system and the range expansion of PWN in Japan and then review the literature, focusing on the virulence of PWN. Virulence is a heritable trait in PWN, with high virulence being closely related to a high rate of reproduction and within-tree dispersal. When two PWN isolates with different virulence levels are inoculated into pine seedlings, the more virulent nematodes always dominate in dead seedlings. In a laboratory setting, many more virulent nematodes board the insect vectors than avirulent ones. The age at which vectors transmit the most abundant PWNs to pine twigs changes during the course of a PWD epidemic. However, the relation between virulence and transmission of PWN remains as yet relatively unknown. Such information would enable ecologists to predict the evolution of the PWD system. In this review we also compare ecological traits between the PWN and the avirulent congener, B. mucronatus.     

Host specificity of <Emphasis Type="Italic">Ischnodemus variegatus</Emphasis>, an herbivore of West Indian marsh grass (<Emphasis Type="Italic">Hymenachne amplexicaulis</Emphasis>)

West Indian marsh grass, Hymenachne amplexicaulis Rudge (Nees) (Poaceae), is an emergent wetland plant that is native to South and Central America as well as portions of the Caribbean, but is considered invasive in Florida USA. The neotropical bug, Ischnodemus variegatus (Signoret) (Hemiptera: Lygaeoidea: Blissidae) was observed feeding on H. amplexicaulis in Florida in 2000. To assess whether this insect could be considered as a specialist biological control agent or potential threat to native and cultivated grasses, the host specificity of I. variegatus was studied under laboratory and field conditions. Developmental host range was examined on 57 plant species across seven plant families. Complete development was obtained on H. amplexicaulis (23.4% survivorship), Paspalum repens (0.4%), Panicum anceps (2.2%) and Thalia geniculata (0.3%). Adults survived 1.6 times longer and laid 6.6 times more eggs on H. amplexicaulis than the other species. Oviposition on suboptimal host species was positively related to I. variegatus density under multiple choice conditions. Results from field experiments indicated that H. amplexicaulis had higher densities of I. variegatus than other species. Spill-over to suboptimal hosts occurred in an area where H. amplexicaulis was growing in poor conditions and there was a high density of I. variegatus. Thus, laboratory and field studies demonstrate that I. variegatus had higher performance on H. amplexicaulis compared to any other host, and that suboptimal hosts could be colonized temporarily. Handling Editor: John Scott. An erratum to this article can be found at     

Asexual propagations of introduced exotic macrophytes <Emphasis Type="Italic">Elodea nuttallii</Emphasis>, <Emphasis Type="Italic">Myriophyllum aquaticum</Emphasis>, and <Emphasis Type="Italic">M. propinquum</Emphasis> are improved by nutrient-rich sediments in China

An increasing number of recent studies indicate that multiple interacting factors can affect the invasion of plants. However, few studies have focused on asexual propagation and the interaction of propagation with environmental factors that regulate the invasive potential of introduced exotic species in aquatic habitats. This study was designed to investigate the differences in asexual propagation between introduced exotic and non-invasive native aquatic macrophytes in nutrient-poor and nutrient-rich sediments and to test the hypothesis that differences in asexual propagation (stem fragment production) and propagule establishment between introduced exotic and non-invasive native macrophytes are driven by sediment nutrient levels. Three exotic aquatic macrophytes (Elodea nuttallii, Myriophyllum aquaticum, and M. propinquum) recently introduced to China and their non-invasive native counterparts (Hydrilla verticillata, M. oguraense, and M. ussuriense) were used for comparison in nutrient-poor (TN 0.59 and TP 0.03 mg g⁻¹) and nutrient-rich (TN 2.35 and TP 0.10 mg g⁻¹) sediments. After 8 weeks of growth, the exotic species tended to produce more total biomass, branch biomass and apical shoots and have higher relative growth rate (RGR) than their native counterparts in nutrient-rich sediment. Rooting efficiency and root growth of exotic fragments were higher than that of native counterparts in nutrient-rich sediment, although the survival rates of fragments did not differ between native and exotic species. In addition, superior traits (rooting efficiency and root growth) of exotic species were also observed in nutrient-poor sediment, but to a lesser degree than in nutrient-rich sediment. These results suggest that asexual propagation of these three introduced exotic macrophytes is more effective in nutrient-rich sediment than in nutrient-poor sediment in China.     

An exotic Australian <Emphasis Type="Italic">Acacia</Emphasis> fixes more N than a coexisting indigenous <Emphasis Type="Italic">Acacia</Emphasis> in a South African riparian zone

Acacia mearnsii is an introduced Australian acacia in South Africa and has invaded more than 2.5 million ha, primarily establishing in rangeland and riparian areas. Because acacias have the capability to fix N, A. mearnsii invasions may fundamentally change N dynamics in invaded systems. This study compares biological N₂-fixation in the alien invasive A. mearnsii and the native A. caffra growing in a grassland riparian zone in the Komati Gorge Reserve, Mpumalanga, South Africa. A ¹⁵N natural abundance field survey suggested that both mature alien and native acacias fix N under current conditions in the riparian zone. Significantly depleted δ¹⁵N was observed in both acacias relative to reference species, although variation in δ¹⁵N was not correlated with N concentrations. Calculated contributions of N₂-fixation (%Ndfa) suggest that alien acacias fix significantly more of their N than native acacias (~75 ± 5% SE and 53 ± 9% SE, respectively). There was a larger variation in δ¹⁵N and %Ndfa in the native acacia, suggesting relatively high plasticity in its N₂-fixation contributions. This plasticity was interpreted as a facultative N₂-fixation strategy for the native acacia, while the N₂-fixation strategy of the alien acacia remained unclear. Our results emphasize the importance of potentially elevated N inputs through N₂-fixation by invasive legumes in invaded landscapes. Furthermore, they suggest that N₂-fixation by invasive acacias may not respond to fine-scale patchiness in soil N in the same manner as native acacias, making them potential contributors to N excess in Southern Africa.     

Living with the enemy: parasites and pathogens of the ladybird <Emphasis Type="Italic">Harmonia axyridis</Emphasis>

Harmonia axyridis is an invasive alien predator in many countries across the world. The rapid establishment and spread of this species is of concern because of the threat it poses to biodiversity as a generalist predator. Understanding the mechanisms that contribute to the success of this species as an invader is not only intriguing but also critical to our understanding of the processes governing such invasions. The enemy release hypothesis (ERH) could explain the rapid population growth of many invasive alien species. However, empirical evidence in support of the ERH is lacking. An alternative hypothesis that could explain rapid population growth is evolution of increased competitive ability (EICA). Here we provide an overview of the parasites and pathogens of coccinellids with a particular focus on H. axyridis as a host. We examine the differential susceptibility of host species and highlight the resilience of H. axyridis in comparison to other coccinellids. We recognise the paucity and limitations of available information and suggest that studies, within a life-table framework, comparing life history traits of H. axyridis in both the native and introduced ranges are necessary. We predict that H. axyridis could benefit from both enemy release and EICA within the introduced range but require further empirical evidence.     

Parasites of <Emphasis Type="Italic">Harmonia axyridis</Emphasis>: current research and perspectives

Harmonia axyridis (Coleoptera: Coccinellidae) has been introduced widely for biological control of agricultural pests. Harmonia axyridis has established in four continents outside of its native range in Asia and it is considered an invasive alien species (IAS). Despite a large body of work on invasion ecology, establishment mechanisms of IAS and their interactions with natural enemies remain open questions. Parasites, defined as multicellular organisms that do not directly kill the host, could potentially play an important role in regulating host populations. This study presents a review of the parasites of H. axyridis, discussing their distributions and effects on host populations across the host’s native and invasive range. These parasites are: Hesperomyces virescens Thaxt. fungi, Coccipolipus hippodamiae (McDaniel and Morrill) mites, and Parasitylenchus bifurcatus Poinar and Steenberg nematodes.     

Potential allelopathic effects of the tropical legume <Emphasis Type="Italic">Sesbania virgata</Emphasis> on the alien <Emphasis Type="Italic">Leucaena leucocephala</Emphasis> related to seed carbohydrate metabolism

Allelopathy has been considered a key mechanism to explain the invasiveness of some species. It is well known that invasive plants can affect native plants by producing novel allelochemicals but some exotic plant species may be also sensitive to allelochemicals released by native species, providing a tool to reduce growth and impacts of invasive exotic species. Here, using growth chamber experiments we tested the mutual potential allelopathic effects of Sesbania virgata (a native dominant species) and the alien Leucaena leucocephala seeds. S. virgata was unaffected by seed leachates of L. leucocephala, indicating that, under lab conditions, this legume presents resistance to the phytotoxic compounds produced by seeds of this alien species. In contrast, germination and seedling growth of L. leucocephala were strongly affected by the phytochemicals produced by seeds of S. virgata. A delay in endospermic mobilization of storage carbohydrates (raffinose-family oligosaccharides and galactomannan) was observed in the alien species. These potential allelopathic effects could not be attributed sole to the presence neither of the phytoxic catechin nor of ABA in seed leachates of S. virgata. Our findings indicate that the in vitro behavior of S. virgata is consistent with its aggressiveness in natural environment and suggest sesbanimide as a potential candidate as implicated in the noxious effects of S. virgata on the alien species.     

<Emphasis Type="Italic">Acroptilon repens</Emphasis>, an Asian invader,has stronger competitive effects on species from America than species from its native range

The ability to competitively suppress native species is key to successful invasion. Since invasions involve an increase in abundance or dominance of a species in its non-native range, competitive effects might be expected to be stronger in the non-native range of an invader; however, there have been few comparisons of the competitive effects of invasive plants on species from invaded ranges versus species from native ranges. We compared the competitive and allelopathic effects of Acroptilon repens on native North American species to effects on related species from the native range of Acroptilon in Uzbekistan. We also compared the competitive interactions among these North American and Eurasian species, in the absence of Acroptilon, examining the hypothesis that particular regional species pools may show differences in competitive ability. The results showed that Acroptilon had stronger competitive effects against native North American species than against species native to Uzbekistan. There was no difference in the competitive effects among Eurasians and North Americans. The effects of leachates collected from Acroptilon roots were weak but more negative on species from North America than on species from Uzbekistan. Our results suggest that inherently stronger competitive and allelopathic effects of Acroptilon on North American plants than on plants from its native range may contribute to its invasive success.     

Identification and comparative analysis of microRNAs in <Emphasis Type="Italic">Pinus massoniana</Emphasis> infected by <Emphasis Type="Italic">Bursaphelenchus xylophilus</Emphasis>

Pine wilt disease seriously endangers pine tree growth and can lead to wilting and death. In this study, Masson pine (Pinus massoniana) was used as the donor plant to study miRNA expression by high-throughput sequencing in needle leaves of trees during the first 3 days after infection by Bursaphelenchus xylophilus. The results showed that the number of differentially expressed miRNAs first increased and then decreased in samples within 3 days of infection, with the highest expression in samples collected on day 2. Analysis of miRNA target genes in needles on different days after infection revealed enrichment in two pathways: plant hormone signal transduction and RNA transport. Further comparison of the samples indicated differential expression of 10 miRNAs on different days after infection, and the corresponding target genes, such as those participating in plant hormone signal transduction, were also significantly enriched. In addition, the concentrations of zeatin and indole acetic acid in needle tissues were significantly lower after infection than in the control sample. The above results indicated that B. xylophilus infection influenced the expression of miRNAs related to plant hormone signal transduction in P. massoniana, decreasing plant hormone synthesis and ultimately affecting the growth of Masson pine.     

Nematicidal activity of <Emphasis Type="Italic">Paecilomyces</Emphasis> spp. and isolation of a novel active compound

Many species of Paecilomyces are entomogenous fungi and several are efficacious toward nematodes. To study the potential of Paecilomyces species in controlling nematodes, fungal extracts of 40 Paecilomyces spp. were evaluated for their nematicidal activity against Bursaphelenchus xylophilus and Panagrellus redivivus. The extracts of six Paecilomyces spp. exhibited the nematicidal activity against P. redivivus, and 11 species exhibited the nematicidal activity against B. xylophilus. The methanol extract of strain 1.01761 incubating on Czapek solid medium killed more than 95% P. redivivus in 24 h at 5 mg/ml, and the filtrate of strain 1.01788 cultured in Sabouraud’s broth medium resulted in 90% mortality of B. xylophilus in 24 h at 5 mg/ml. A novel nematicidal compound 4-(4′-carboxy-2′-ethyl-hydroxypentyl)-5,6-dihydro-6-methylcyclobuta[b]pyridine-3,6-dicarboxylic acid, was isolated from Paecilomyces sp. YMF1.01761. The LD₅₀ value of the compound within 24 h against P. redivivus was 50.86 mg/L, against Meloidogyne incognita was 47.1 mg/L, and against B. xylophilus was 167.7 mg/L.     

New Insights into the Phylogeny and Worldwide Dispersion of Two Closely Related Nematode Species,Bursaphelenchus xylophilus and Bursaphelenchus mucronatus

The pinewood nematode, Bursaphelenchus xylophilus, is one of the greatest threats to coniferous forests worldwide, causing severe ecological damage and economic loss. The biology of B. xylophilus is similar to that of its closest relative, B. mucronatus, as both species share food resources and insect vectors, and have very similar morphological characteristics, although little pathogenicity to conifers has been associated with B. mucronatus. Using both nuclear and mitochondrial DNA markers, we show that B. xylophilus and B. mucronatus form distinct phylogenetic groups with contrasting phylogeographic patterns. B. xylophilus presents lower levels of intraspecific diversity than B. mucronatus, as expected for a species that evolved relatively recently through geographical or reproductive isolation. Genetic diversity was particularly low in recently colonised areas, such as in southwestern Europe. By contrast, B. mucronatus displays high levels of genetic diversity and two well-differentiated clades in both mitochondrial and nuclear DNA phylogenies. The lack of correlation between genetic and geographic distances in B. mucronatus suggests intense gene flow among distant regions, a phenomenon that may have remained unnoticed due to the reduced pathogenicity of the species. Overall, our findings suggest that B. xylophilus and B. mucronatus have different demographic histories despite their morphological resemblance and ecological overlap. These results suggest that Bursaphelenchus species are a valuable model for understanding the dispersion of invasive species and the risks posed to native biodiversity and ecosystems.     

Biological control of the pinewood nematode <Emphasis Type="Italic">Bursaphelenchus xylophilus</Emphasis> by application of the endoparasitic fungus <Emphasis Type="Italic">Esteya vermicola</Emphasis>

Esteya vermicola (Ophiostomataceae) is the first reported endoparasitic fungus of the pinewood nematode (PWN), Bursaphelenchus xylophilus (Nematoda: Aphelenchoidoidea). It has high in vitro infectivity. In this study, the nematocidal effect of E. vermicola in logs was investigated and evaluated. Two months after inoculation of pine wilt-killed Pinus densiflora logs with E. vermicola conidia suspensions of 3 × 10⁸ and 3 × 10⁶ ml⁻¹, the density of nematodes decreased by approximately 79% and 47%, respectively. When the fungus was sprayed on to four-year-old pine seedlings one month before PWN inoculation, the survival index of seedlings reached 0.67 compared with only 0.067 for control seedlings without fungal spraying. These results suggest that conidia spraying of E. vermicola can, to some extent, protect pine trees from wilt disease. Moreover, infected nematodes and hyphae of E. vermicola were observed in the treated wood sections.     

Molecular evidence for hybridization between invasive <Emphasis Type="Italic">Solidago canadensis</Emphasis> and native <Emphasis Type="Italic">S</Emphasis>. <Emphasis Type="Italic">virgaurea</Emphasis>

Hybridization between alien and native species is biologically very important and could lead to genetic erosion of native taxa. Solidago × niederederi was discovered over a century ago in Austria and described by Khek as a natural hybrid between the alien (nowadays regarded also as invasive) S. canadensis and native S. virgaurea. Although interspecific hybridization in the genus Solidago is considered to be relatively common, hybrid nature of S. × niederederi has not been independently proven using molecular tools, to date. Because proper identification of the parentage for the hybrid Solidago individuals solely based on morphological features can be misleading, in this paper we report an additive polymorphism pattern expressed in the ITS sequences obtained from individuals representing S. × niederederi, and confirm the previous hypothesis that the parental species of this hybrid are S. canadensis and S. virgaurea. Additionally, based on variability at the cpDNA rpl32-trnL locus, we showed that in natural populations hybridization occurs in both directions.     

Palatability to a generalist herbivore,defence and growth of invasive and native <Emphasis Type="Italic">Senecio</Emphasis> species: testing the evolution of increased competitive ability hypothesis

This paper tests the prediction that introduced plants may become successful invaders because they experience evolutionary changes in growth and defence in their new range [evolution of increased competitive ability hypothesis (EICA)]. Interspecific and intraspecific binary feeding choices were offered to the snail Helix aspersa. The choices were between: (1) plants of the invasive Senecio inaequidens and Senecio pterophorus derived from populations in the introduced range (Europe) and plants of three indigenous species (Senecio jacobea, Senecio vulgaris and Senecio malacitanus) from populations in Europe; (2) plants of the invasive S. inaequidens and S. pterophorus from populations in the introduced range (Europe) and from populations in the native range (South Africa). We did not find a clear pattern of preference for indigenous or alien species of Senecio. However, we found that European invasive populations of S. inaequidens and S. pterophorus were less palatable than South African native populations. Moreover, in contrast to the predictions of the EICA hypothesis, the invasive genotypes of both species also showed a higher total concentration of pyrrolizidine alkaloids, and in the case of S. inaequidens we also found higher growth than in native genotypes. Our results are discussed with respect to the refinement of the EICA hypothesis that takes into account the difference between specialist and generalist herbivores and between qualitative and quantitative defences. We conclude that invasive populations of S. inaequidens and S. pterophorus are less palatable than native populations, suggesting that genetic differentiation associated with founding may occur and contribute to the plants’ invasion success by selecting the best-defended genotypes in the introduced range.     

Molecular detection of <Emphasis Type="Italic">Rickettsia</Emphasis>, <Emphasis Type="Italic">Coxiella</Emphasis> and <Emphasis Type="Italic">Rickettsiella</Emphasis> DNA in three native Australian tick species

Three Australian native animal species yielded 60 samples composed of three indigenous ticks. Hosts included twelve koalas, two echidnas and one wombat from Victoria, and ticks were of the species Ixodes tasmani (n = 42), Bothriocroton concolor (n = 8) and B. auruginans (n = 10), respectively. PCR screening and sequencing detected a species of Coxiella, sharing closest sequence identity to C. burnetii (>98%), in all B. auruginans, as well as a species of Rickettsia, matching closest to R. massiliae, in 70% of the same samples. A genotype sharing closest similarity to Rickettsia bellii (>99%) was identified in three female B. concolor collected from one of the echidnas. Three samples of I. tasmani, taken from three koalas, yielded different genotypes of Rickettsiella. These results represent the first detection of the three genera in each tick species and identify a high level of previously undetected bacterial diversity in Australian ticks.     

Interspecific displacement mechanisms by the invasive little fire ant <Emphasis Type="Italic">Wasmannia auropunctata</Emphasis>

Competition between invasive species and native ones in the new environment was found to be significant and to affect both animal and plant species. Invasive ants are notorious for displacing local ant species through competition. Competitive displacement of native species can occur through interference and or resource competition. However, for invasive ants, little is known about the relative importance of competitive displacement. We studied competitive interactions of the little fire ant, Wasmannia auropunctata, one of the most destructive invasive ant species, with two other ant species, Monomorium subopacum and Pheidole teneriffana. We compared the species’ foraging behavior and studied their aggressive interactions around food baits for the short (2 h) and long (21 days) term in the laboratory. Surprisingly we found that in short term experiments W. auropunctata had the poorest foraging abilities of the three species studied: it took the workers the longest to locate the bait and retrieve it; in addition they retrieved the lowest amount of food. When both W. auropunctata and M. subopacum were foraging the same bait, in the short term competition experiment, W. auropunctata workers did not defend the bait, and ceased foraging when encountered with competition. The long-term experiments revealed that W. auropunctata had the advantage in aggressive interactions over time; they eliminated seven of nine M. subopacum’s nests while consuming some of the workers and brood. According to our laboratory studies, W. auropunctata cannot be considered an extirpator species, unless it has a substantial numerical advantage, in contrast with previous assumptions. Otherwise it may behave as an insinuator species, i.e. the workers do not initiate aggression and by staying undetected they can continue foraging adjacent to dominant species.     

Understanding the influence of urbanization on invasibility: <Emphasis Type="Italic">Carpobrotus edulis</Emphasis> as an exemplar

Coastal dune areas are valuable ecosystems, generally impacted by habitat destruction and invasive alien species. In this study, we assessed how human disturbance and invasion by Carpobrotus edulis impact the soils and the establishment of native flora in the north-western coastal regions of Spain. We compared soil characteristics (pH, conductivity, water content, nutrients and enzymatic activities) and native plant as well as C. edulis fitness correlates (germination and early growth) between uninvaded and invaded soils from urban and natural coastal dune areas. We found that human disturbance impacts coastal soils by increasing organic matter and water content, modifying soil nutrients and cycles, and reducing the pH in urban soils. The presence of invasive C. edulis further increases these impacts. These changes in soil characteristics allow for the establishment of the native, but ruderal, Scolymus hispanicus and non-native C. edulis, both of which are not adapted to the typically limiting conditions of coastal dunes. In some instances, the coastal dune endemic, Malcolmia littorea, showed no fitness effects in response to urbanization or the presence of C. edulis. These results suggest that human disturbed coastal areas might be more easily invaded than natural areas. More broadly, our findings of differential responses of different native species to disturbance and invasion, illustrate the need for multi-taxon approaches when assessing the impacts of invasive species.     

Plant zonation at salt marshes of the endangered cordgrass <Emphasis Type="Italic">Spartina maritima</Emphasis> invaded by <Emphasis Type="Italic">Spartina densiflora</Emphasis>

The South American cordgrass Spartina densiflora is invading European salt marshes getting into contact with the indigenous and endangered low-marsh dominant, Spartina maritima. This work describes the evolution of the plant zonation during 7 years in a marsh of S. maritima invaded by S. densiflora. S. maritima appeared throughout the whole intertidal gradient from 1.72 to 3.33 m over Spanish Hydrographic Zero (SHZ), showing its higher biomasses and shoot densities at low elevations. In contrast, S. densiflora only invaded upper areas (>+2.59 m SHZ) at the centre of circular tussocks of S. maritima. Above-ground biomass of S. maritima dropped drastically at maximum occupation of space by the alien, and its shoot density and above-ground biomass decreased at S. densiflora zone during the study. The competitive potential of S. densiflora was reflected in high above- and below-ground biomass and shoot densities, accompanied by elevated wrack accumulation and the absence of other marsh plants presented together with S. maritima from areas dominated by S. densiflora. S. densiflora altered the native vegetational zonation pattern through the invasion of the centre of S. maritima tussocks; however, the alien invasion may be limited by the presence of the autochthonous cordgrass at lower elevations. Handling editor: Luis Mauricio Bini