Native ecosystem engineer facilitates recruitment of invasive crab and native invertebrates

Native ecosystem engineers that add physical structure to ecosystems can facilitate invasive species. In this study we determined the effects of the native tube-forming serpulid worm, Galeolaria caespitose on the recruitment of the invasive New Zealand porcelain crab, Petrolisthes elongatus, and whether invasive crab recruitment was related to the recruitment of native species. P. elongatus is abundant beneath intertidal rocks around Tasmania, southern Australia, and the underside of these rocks is usually covered with a calcareous matrix formed by the serpulid. We used an experimental approach to investigate whether rocks, serpulids on the underside of rocks and adult P. elongatus influenced the recruitment P. elongatus and native communities. P. elongatus and native invertebrates only recruited in the presence of rocks indicating the importance of rock as primary recruitment habitat. Moreover, the presence of serpulids on the underside of rocks significantly increased the recruitment of P. elongatus and native invertebrates compared to rocks without serpulids. Rocks with higher densities of adult P. elongatus at the end of the experiment also had higher densities of P. elongatus recruits. The density of P. elongatus recruits did not influence native species richness and abundance although there was some evidence that high P. elongatus recruitment was correlated with shifts in native community structure. We have shown that a native ecosystem engineer facilitates recruitment of an invasive crab but this does not appear to influence the recruitment of native species.     

Abundance and dispersion of the invasive Mediterranean annual, Centaurea melitensis in its native and non-native ranges

In general, invasive plants are assumed to behave more aggressively in their invasive ranges than in their native range, and studies of the mechanisms of invasion often assume these differences. However, comparisons of abundances between native and invasive ranges are rarely carried out. We compared density and dispersion of the invasive plant, Centaurea melitensis (Asteraceae) in its native range and two invasive ranges of similar mediterranean-climate type. The objective was to quantify the differences in its abundance among three distant regions. We surveyed six sites in the native range (Spain) and in each of two invaded ranges (California and central Chile) for population density, relative dominance and spatial distribution of Centaurea. Centaurea occurred at higher densities in invasive sites than in native ones, with a median of 100 plants per m² and 70 plants per m² in California and Chile, respectively, compared to only 4 plants per m² in Spain. Centaurea was more dominant in both invasive ranges than in the native range. Centaurea density and relative dominance were highly variable within regions. Plants in Spain were randomly dispersed, while those in both invasive ranges were more aggregated. Annual precipitation and mean annual temperature were the best predictors of Centaurea density. In California sites, density was negatively correlated with soil nutrients. The presence of at least one high-density population with near total dominance in Spain suggests that there might be ecological mechanisms for invasiveness in Centuarea that are not unique to invaded ranges.     

A comparison of native and invasive populations of three clonal plant species in Germany and New Zealand

Aim Our aim was to test for changes in growth patterns of three clonally growing plant species (Achillea millefolium, Hieracium pilosella and Hypericum perforatum) between native and invaded regions. We addressed the hypotheses that with differing important life‐history traits, invasive populations perform better than native populations, and that this expected better performance is linked to weakened trade‐offs between individual growth and sexual and clonal reproduction. Location Germany and New Zealand. Methods We conducted field surveys for the three above‐mentioned species in both native German and invasive New Zealand populations, and collected data at both population and individual levels. Results At the population level, the proportion of flowering plants, population size and population density were all higher in invasive populations. Similarly, at the individual level, the number of stolons per plant, stolon–biomass ratio and population crowdedness (local plant density in a specified area around a target plant) were significantly higher in New Zealand. Plant height did not differ between countries, and plant biomass was lower in New Zealand than in Germany for Achillea millefolium and Hypericum perforatum. These two species showed significant trade‐offs between individual growth and sexual and clonal reproduction. Achillea millefolium exhibited a weakened trade‐off in its invaded range, where the same proportion of flowering plants was sustained at much higher levels of population crowdedness than in its native range. Main conclusions The apparent invasion success of the three study species is generally due to better overall performance in their respective invaded ranges. In respect of both Achillea millefolium and Hypericum perforatum, this is driven primarily by increased vegetative reproduction. In contrast, Hieracium pilosella seems to benefit more from increased sexual reproduction in its invaded range. Shifts in trade‐offs as a general trend seem to be of minor importance.     

The invasive alien plant species Solidago gigantea alters ecosystem properties across habitats with differing fertility

Question: Invasive alien plants can affect biomass production and rates of biogeochemical cycling. Do the direction and intensity of such effects depend upon the functional traits of native and alien species and upon the properties of the invaded habitat, with the same alien species having differing impacts in different habitats? Location: Lowlands of Switzerland. Methods: Fourteen grassland and wetland sites invaded by Solidago gigantea and widely differing in biomass production and soil P availability were surveyed. To determine whether the impact of the species was related to site fertility, we compared the invaded and native vegetation in terms of biomass, species composition, plant traits and soil properties. Results: S. gigantea generally increased the above‐ground biomass production of the vegetation and soil C content, while reducing nutrient concentrations in biomass and N availability in the soil. However, it had no significant effect on plant species richness, soil respiration, soil pH and P availability. Leaves of S. gigantea had a greater C content than those of native species; other leaf traits and root phosphatase activity did not differ significantly. Conclusions: Our results suggest that a conservative nutrient‐use strategy allows S. gigantea to invade a broad range of habitats. The observed effects of invasion did not vary according to biomass production of the invaded sites, but some effects did depend on soil P availability, being more pronounced at more P‐rich sites. Thus, the full range of invaded habitats should be considered in studying the potential impact of plant invasions on ecosystem processes.     

Admixture between native and invasive populations may increase invasiveness of Mimulus guttatus

Self-fertilization and admixture of genotypes from different populations can have major fitness consequences in native species. However, few studies have addressed their potential roles in invasive species. Here, we used plants of Mimulus guttatus from seven native North American, three invasive Scottish and four invasive New Zealand populations to address this. We created seeds from self-fertilization, within-population outcrossing, between-population outcrossing within the same range, and outcrossing between the native and invasive ranges. A greenhouse experiment showed that native and invasive plants of M. guttatus suffered to similar degrees from inbreeding depression, in terms of asexual reproduction and biomass production. After outcrossing with plants from other populations, M. guttatus benefited from heterosis, in terms of asexual and sexual reproduction, and biomass production, particularly when plants from native and invasive populations were crossed. This suggests that, when novel genotypes of M. guttatus from the native North American range will be introduced to the invasive ranges, subsequent outcrossing with M. guttatus plants that are already there might further boost invasiveness of this species.     

Habitat utilization by an invasive herbivorous fish (<Emphasis Type="Italic">Siganus rivulatus</Emphasis>) in its native and invaded range

Movement is essential for understanding the distribution and abundance of animals. While it has been suggested that invasion success can be facilitated by species’ ability to adapt to novel environments, direct comparisons of movement patterns between native and invaded ranges of animals in their natural habitat are rare. The rivulated rabbitfish Siganus rivulatus was introduced from the Red Sea into the Mediterranean, where it is now found in extremely high abundances, and has overgrazed the coastal marine ecosystem in many locations. Through a continuous acoustic tracking system, we found that the movement of S. rivulatus individuals at a Mediterranean site differed substantially from those at a Red Sea site, with individuals in the Mediterranean having larger overall home ranges and lower site fidelity. However, no variation between sites was found in daily home range sizes. Results show that at the Mediterranean site S. rivulatus individuals have a larger spatial footprint, which may contribute to their impact and ability to expand their distribution. This study demonstrates a potential shift in individual movement of a marine invasive species between its native and invaded range, and highlights the role of movement in understanding biological invasions.     

Cuscuta australis restrains three exotic invasive plants and benefits native species

In this study we conducted field investigations to examine the effects of native Cuscuta australis on three exotic invasive plants (i.e. Ipomoea cairica, Mikania micrantha, and Wedelia trilobata) and on the invaded native communities. The results showed that C. australis produced high infection rates on the exotic invasive hosts but low ones on the native species. Furthermore, the results showed that C. australis exhibited vigorous growth and high reproduction when it grew on M. micrantha and W. trilobata, indicating that these exotic invasive plants are more rewarding hosts than are native plants for C. australis. C. australis infection was positively related to the growth traits (e.g. biomass, cover, and total leaf area) and nutrient contents (e.g. N, P, and K) of the exotic invasive plants. The infections of C. australis significantly decreased the growth and nutrient contents of exotic invasive hosts, and the host?Cparasite interactions benefited the native species with increased species richness and biodiversity, facilitating the recovery of invaded native communities. This study provides a model for a native agent to both resist exotic invasive plants and benefit other native species. Furthermore, it indicates that certain native agents in invaded regions can be an effective and environmentally benign alternative to traditional biological control.     

Patterns of niche filling and expansion across the invaded ranges of an Australian lizard

Studies of realized niche shifts in alien species typically ignore the potential effects of intraspecific niche variation and different invaded‐range environments on niche lability. We incorporate our detailed knowledge of the native‐range source populations and global introduction history of the delicate skink Lampropholis delicata to examine intraspecific variation in realized niche expansion and unfilling, and investigate how alternative niche modelling approaches are affected by that variation. We analyzed the realized niche dynamics of L. delicata using an ordination method, ecological niche models (ENMs), and occurrence records from 1) Australia (native range), 2) New Zealand, 3) Hawaii, 4) the two distinct native‐range clades that were the sources for the New Zealand and Hawaii introductions, and 5) the species’ global range (including Lord Howe Island, Australia). We found a gradient of realized niche change across the invaded ranges of L. delicata: niche stasis on Lord Howe Island, niche unfilling in New Zealand (16%), and niche unfilling (87%) and expansion (14%) in Hawaii. ENMs fitted to native‐range data generally identified suitable climatic conditions at sites where the species has established non‐native populations, whereas ENMs based on native‐range source clades and non‐native populations had lower spatial transferability. Our results suggest that the extent to which realized niches are maintained during invasion does not depend on species‐level traits. When realized niche shifts are predominately due to niche unfilling, fully capturing species’ responses along climatic gradients by basing ENMs on native distributions may be more important for accurate invasion forecasts than incorporating phylogenetic differentiation, or integrating niche changes in the invaded range.     

No consistent association between changes in genetic diversity and adaptive responses of Australian acacias in novel ranges

Common garden studies comparing trait differences of exotic species between native and introduced ranges rarely incorporate an analysis of genetic variation, but simply infer that trait shifts between ranges are genetically determined. We compared four growth-related traits (total biomass, relative growth rate RGR, specific leaf area SLA, and root to shoot ratio R:S) of five invasive Fabaceae species (Acacia cyclops, A. longifolia, A. melanoxylon, A. saligna, Paraserianthes lophantha), grown in a common garden experiment using seeds from introduced and native ranges across Australia. Chloroplast microsatellite loci were used to compare genetic diversity of native and introduced populations to determine standing genetic diversity and infer introduction history. We asked whether shifts in traits associated with faster growth due to enemy release in the introduced range were associated with levels of genetic diversity associated with introduction history. We found differences in traits between ranges, although these traits varied among the species. Compared to native-range populations, introduced-range Acacia longifolia had greater biomass and larger SLA; A. cyclops had greater RGR; and A. melanoxylon displayed lower R:S. Genetic diversity in the introduced range was lower for one of those species, A. longifolia, and two others that did not show differences in traits, A. saligna and P. lophantha. Diversity was higher in the introduced range for A. melanoxylon and did not differ among ranges for A. cyclops. These patterns of genetic diversity suggest that a genetic bottleneck may have occurred following the introduction of A. longifolia, A. saligna and P. lophantha. In contrast greater or comparable genetic diversity in the introduced range for A. melanoxylon and A. cyclops suggests introductions from multiple sources. This study has shown that a reduction in genetic diversity in the introduced range is not necessarily associated with a reduced capacity for adaptive responses or invasion potential in the novel range.     

The influence of evolution and plasticity on the behavior of an invasive crayfish

Invasion success can be enhanced by evolution and behavioral plasticity, but the importance of these processes for most invasions is not well understood. Previous research suggests there is a genetic basis for differences in growth rate between native and invaded range rusty crayfish (Orconectes rusticus). We hypothesized that invaded range O. rusticus achieve faster growth by allocating more time to foraging and less to defense. We conducted a laboratory experiment to test the effects of range (native or invaded) and plasticity (as induced by exposure to predators) on crayfish behavior. We collected O. rusticus adults and eggs from both ranges, hatched eggs in the lab, and reared juveniles in common conditions either with or without predatory fish. We then quantified adult and juvenile crayfish activity in an experiment with and without predatory fish. In support of our hypothesis, invaded range adults displayed reduced antipredator behavior compared to native range adults. Further, invaded range juveniles were more active than native range juveniles without predators, but all juveniles were inactive with predators. In addition, invaded range juveniles had greater plasticity in behavior than native range juveniles. These results suggest that activity level in the absence of predators has diverged in the invaded range. Because active crayfish consume more prey, this change in behavior may be responsible for rapid growth in the invaded range of O. rusticus, a trait that contributes to the strong ecological impacts of this invasive crayfish.     

Contrasting trait responses to latitudinal climate variation in two lineages of an invasive grass

Plants are expected to respond to global environmental change through shifts in functional traits and in their ranges. These shifts could alter productivity and interactions among species or genetic lineages, ultimately leading to changes in distributions and abundance. In particular, cosmopolitan species are predicted to increase growth with decreasing latitude due to differences in climate and temperature. The pattern of changes in growth may vary among genotypes within species, leading to different responses with latitude. To evaluate whether climate can affect geographically distinct genotypes of cosmopolitan invasive species differently, we evaluated the trait responses of two lineages of the common reed, Phragmites australis, to variation in environmental conditions spanning North America’s Atlantic coast. Using three reciprocal transplant common gardens, we tested for the effects of garden location and plant lineage on traits related to biomass production, flowering frequency, leaf morphology, and leaf-level physiology. We found that aboveground biomass, stem density, and flowering frequency responded non-linearly to increasing latitude in one or both lineages. These results suggest that measures of plant traits over narrow latitudinal ranges may not accurately reflect organismal-level responses to global change at broad spatial scales. Given the responses to latitude that we observed in P. australis, we propose that feedbacks between growth and reproductive rate will influence range shifts in these two lineages. Such range shifts could lead to genetic admixtures, subsequently yielding more productive, locally-adapted genotypes.     

Native and invasive plant interactions in wetlands and the minimal role of invasiveness

The effects of invasive plants on plants native to areas that are being invaded can be quite variable, depending on the species of the invasive plant involved as well as the physical characteristics of the location being invaded. My study focuses on the effects of Phragmites australis Linnaeus (common reed) and Lythrum salicaria L. (purple loosestrife) on the same native plant community. Uninvaded plots dominated by native plants Typha angustifolia L. (narrowleaf cattail) and Typha latifolia L. (broadleaf cattail) served as the control. I surveyed percent cover of species during early summer and midsummer for 3 years in six Hudson River freshwater tidal wetlands (sites). Differences in species richness, composition and abundance were small, but significant among invaded and uninvaded plots and among sites. However, these differences remained significant when data for dominant species (invasive and native) were removed. Differences in native plant species abundance were attributed to invasive plant species-specific characteristics and differences in species richness and composition were attributed to physical location (zonation) in these freshwater tidal marshes. “Invasive” status of a dominant plant species was less important in invasive plant–native plant interactions than species-specific characteristics and zonation. Further research into the effects of site and land-use on invasive plant impacts is recommended.     

Local performance of six clonal alien species differs between native and invasive regions in Germany and New Zealand

Exotic plant invasions are widely observed to have strong biogeographic patterns with invasive species occurring at higher abundances in their introduced range when compared with their native range. However, only few field studies have validated this assumption by comparing plant populations of multiple species in their native and introduced ranges and have evaluated to what extent changes in sexual and clonal reproduction potentially have contributed to the success of plant invasions. Here, we present the results of a comparative field study in both the native (Germany) and the introduced (New Zealand, NZ) ranges of six clonal plant species with different invasive status: Achillea millefolium L., Pilosella officinarum Vaill., Hypericum perforatum L., Prunella vulgaris L., Leucanthemum vulgare Lam. and Lotus pedunculatus Cav. We hypothesized that all six species show better performance in introduced NZ than in native German populations and tested if population structures investigated at different scales provide a useful tool to identify differences between native and introduced occurrences. In 10 populations per species and country we assessed plant density and flowering proportion at the population scale and around individual plants, thereby identifying the ‘crowdedness’ of the populations. Furthermore, we collected individual plants and determined the number of attached clonal organs and plant biomass. For all six species crowdedness in NZ populations was higher than in German populations. Additionally, overall population density of four species and the production of clonal organs (expressed as total number or per biomass ratio) of three species were higher in NZ than in Germany. When measured around individual plants, the flowering proportion was higher in native German populations of Pilosella officinarum, Hypericum perforatum and Leucanthemum vulgare. Although the study species differed in their invasive status, our findings show that for all six species performance was better in introduced than in native populations. Furthermore, this study emphasizes that multiple measures of plant performance, different spatial scales and differences among species should be taken into account when trying to identify biogeographic differences in the performance of weed species.     

Plant–soil biota interactions and spatial distribution of black cherry in its native and invasive ranges

One explanation for the higher abundance of invasive species in their non‐native than native ranges is the escape from natural enemies. But there are few experimental studies comparing the parallel impact of enemies (or competitors and mutualists) on a plant species in its native and invaded ranges, and release from soil pathogens has been rarely investigated. Here we present evidence showing that the invasion of black cherry (Prunus serotina) into north‐western Europe is facilitated by the soil community. In the native range in the USA, the soil community that develops near black cherry inhibits the establishment of neighbouring conspecifics and reduces seedling performance in the greenhouse. In contrast, in the non‐native range, black cherry readily establishes in close proximity to conspecifics, and the soil community enhances the growth of its seedlings. Understanding the effects of soil organisms on plant abundance will improve our ability to predict and counteract plant invasions.     

Changes in Diversity and Functional Gene Abundances of Microbial Communities Involved in Nitrogen Fixation, Nitrification, and Denitrification in a Tidal Wetland versus Paddy Soils Cultivated for Different Time Periods

In many areas of China, tidal wetlands have been converted into agricultural land for rice cultivation. However, the consequences of land use changes for soil microbial communities are poorly understood. Therefore, we investigated bacterial and archaeal communities involved in inorganic nitrogen turnover (nitrogen fixation, nitrification, and denitrification) based on abundances and relative species richness of the corresponding functional genes along a soil chronosequence ranging between 50 and 2,000 years of paddy soil management compared to findings for a tidal wetland. Changes in abundance and diversity of the functional groups could be observed, reflecting the different chemical and physical properties of the soils, which changed in terms of soil development. The tidal wetland was characterized by a low microbial biomass and relatively high abundances of ammonia-oxidizing microbes. Conversion of the tidal wetlands into paddy soils was followed by a significant increase in microbial biomass. Fifty years of paddy management resulted in a higher abundance of nitrogen-fixing microbes than was found in the tidal wetland, whereas dominant genes of nitrification and denitrification in the paddy soils showed no differences. With ongoing rice cultivation, copy numbers of archaeal ammonia oxidizers did not change, while that of their bacterial counterparts declined. The nirK gene, coding for nitrite reductase, increased with rice cultivation time and dominated its functionally redundant counterpart, nirS, at all sites under investigation. Relative species richness showed significant differences between all soils with the exception of the archaeal ammonia oxidizers in the paddy soils cultivated for 100 and 300 years. In general, changes in diversity patterns were more pronounced than those in functional gene abundances.     

Functional morphology underlies performance differences among invasive and non-invasive ruderal Rubus species

The ability of some introduced plant species to outperform native species under altered resource conditions makes them highly productive in ecosystems with surplus resources. However, ruderal native species are also productive when resources are available. The differences in abundance among invasive and non-invasive ruderal plants may be related to differences in ability to maintain access to or store resources for continual use. For a group of ruderal species in the Pacific Northwest of North America (invasive Rubus armeniacus; non-invasive R. ursinus, R. parviflorus, R. spectabilis, and Rosa nutkana), we sought to determine whether differences in functional morphological traits, especially metrics of water access and storage, were consistent with differences in water conductance and growth rate. We also investigated the changes in these traits in response to abundant vs. limited water availability. Rubus armeniacus had among the largest root systems and cane cross-sectional areas, the lowest cane tissue densities, and the most plastic ratios of leaf area to plant mass and of xylem area to leaf area, often sharing its rank with R. ursinus or Rosa nutkana. These three species had the highest water conductance and relative growth rates, though Rubus armeniacus grew the most rapidly when water was not limited. Our results suggest that water access and storage abilities vary with morphology among the ruderal species investigated, and that these abilities, in combination, are greatest in the invasive. In turn, functional morphological traits allow R. armeniacus to maintain rapid gas exchange rates during the dry summers in its invaded range, conferring on it high productivity.     

Longevity,growth and community ecology of invasive Poa annua across environmental gradients in the subantarctic

Poa annua is a cosmopolitan weed in turf grass. It is a widespread non-native species in the subantarctic and also occurs in the Antarctic Peninsula. It has highly variable morphology, longevity and reproductive capacity across both its invaded and native range. Little is known about the ecology of P. annua in the subantarctic, particularly its longevity, morphological variation across small spatial scales and competitive ability. We monitored individual P. annua plants on subantarctic Macquarie Island to assess their longevity; quantified morphology and biomass allocation across environmental gradients; and assessed community diversity indices in areas of varying P. annua density. We show that P. annua plants on Macquarie Island are perennial, and their morphology varies with elevation, animal disturbance and soil properties. At low altitude, coastal sites with high animal disturbance and deep, sandy soils, P. annua plants are larger and native plant diversity is low. Conversely, at high altitude sites P. annua plants are smaller and the diversity of native species is not reduced. This new information informs why P. annua is the most successful plant invader in the subantarctic and quantifies some key characteristics enabling an invasive species to function well beyond its natural range. Community ecology theory can also explain patterns in the ecology of P. annua on Macquarie Island.     

Impact of drought on plant populations of native and invasive origins

Invasive populations often shift phenotypically during introduction. Moreover, they are postulated to show an increased phenotypic plasticity compared with their native counterparts, which could be advantageous. However, less is known about trait selection across populations along the invasion gradient in response to environmental factors, such as increasing drought caused by climate change. In this study, we investigated the impacts of drought on growth, regrowth, and various leaf traits in plants of different origin. Therefore, seeds of 18 populations of the perennial Tanacetum vulgare were collected along the invasion gradient (North America, invasive; West Europe, archaeophyte; East Europe, native) and grown in competition with the grass Poa pratensis under control or dry conditions in a common garden. Above-ground biomass was cut once and the regrowth was measured as an indicator for tolerance over a second growth period. Initially, drought had little effects on growth of T. vulgare, but after cutting, plants grew more vigorously. Against expectations, phenotypic plasticity was not higher in invasive populations, but even reduced in one trait, which may be attributable to ecological constraints imposed by multiple stress conditions. Trait responses reflected the range expansion and invasion gradient and were influenced by the latitudinal origin of populations. Populations of invaded ranges may be subject to faster and more extensive genetic mixing or had less time to undergo and reflect selective processes.     

A New (Old), Invasive Ant in the Hardwood Forests of Eastern North America and Its Potentially Widespread Impacts

Biological invasions represent a serious threat for the conservation of biodiversity in many ecosystems. While many social insect species and in particular ant species have been introduced outside their native ranges, few species have been successful at invading temperate forests. In this study, we document for the first time the relationship between the abundance of the introduced ant, Pachycondyla chinensis, in mature forests of North Carolina and the composition, abundance and diversity of native ant species using both a matched pair approach and generalized linear models. Where present, P. chinensis was more abundant than all native species combined. The diversity and abundance of native ants in general and many individual species were negatively associated with the presence and abundance of P. chinensis. These patterns held regardless of our statistical approach and across spatial scales. Interestingly, while the majority of ant species was strongly and negatively correlated with the abundance and presence of P. chinensis, a small subset of ant species larger than P. chinensis was either as abundant or even more abundant in invaded than in uninvaded sites. The large geographic range of this ant species combined with its apparent impact on native species make it likely to have cascading consequences on eastern forests in years to come, effects mediated by the specifics of its life history which is very different from those of other invasive ants. The apparent ecological impacts of P. chinensis are in addition to public health concerns associated with this species due to its sometimes, deadly sting.     

Disruption of ant-seed dispersal mutualisms by the invasive Asian needle ant (<Emphasis Type="Italic">Pachycondyla chinensis</Emphasis>)

By disrupting the structure of native ant assemblages, invasive ants can have effects across trophic levels. Most studies to date, however, have focused on the impacts just two species (Linepithema humile and Solenopsis invicta). The impacts of many other invasive ant species on ecological processes in their introduced range are unknown. In this study we tested the hypothesis that the invasive ant Pachycondyla chinensis disrupts ant-seed dispersal mutualisms by displacing native ant species, especially the keystone mutualist Aphaenogaster rudis, while failing to disperse seeds itself. In a paired design we measured the impact of P. chinensis on the native ant-plant seed dispersal mutualism. The number of A. rudis workers was 96% lower in invaded than in intact plots, and the number of seeds removed was 70% lower in these plots. Finally, in invaded plots the abundance of Hexastylis arifolia, a locally abundant myrmecochorous plant, was 50% lower than in plots where P. chinensis was absent. A parsimonious interpretation of our results is that P. chinensis causes precipitous declines in the abundance of A. rudis within invaded communities, thereby disrupting the ant-plant seed dispersal mutualisms and reducing abundances of ant-dispersed plants. In sum, the magnitude of the effects of P. chinensis on seed dispersal is quantitatively similar to that documented for the intensively studied invasive Argentine ant. We suggest that more studies on the impacts of less-studied invasive ant species on seed dispersal mutualisms may increase our knowledge of the effects of these invaders on ecosystem function.