Exotic Range Research Articles

Modelled distribution of an invasive alien plant species differs at different spatiotemporal scales under changing climate: a case study of Parthenium hysterophorus L.

Predicting the impact of climate change on species distribution at different spatial and temporal scales has emerged as one of the important areas of research in invasion ecology and conservation biology. We used MaxEnt (Maximum Entropy Algorithm) to predict the distribution of a highly invasive species, namely Parthenium hysterophorus L. under four Representative Concentration Pathway scenarios (RCPs 2.6, 4.5, 6.0 and 8.5) in 2050 and 2070 at global (world), regional (India) and local (Jammu & Kashmir State) spatial scales. Model predictions indicated differences in the extent of expansion in the distribution of this species under different climate change scenarios with marginal increase in moderately suitable area at the global scale but mostly a declining trend was noticed in its suitable and highly suitable area in future. More or less similar trend was predicted for India where increase in moderately suitable area was evident but decline in suitable and highly suitable areas was observed. In respect of Jammu & Kashmir, moderately suitable as well suitable area showed increase mostly under RCP scenarios of 6.0 and 8.5 in 2050 as well as 2070. Further analysis revealed that current centroid of P. hysterophorus is in south of Jammu and Kashmir and is predicted to shift by an average of 20.48 km in the north-west direction by 2050 and by 36.83 km by 2070. The future suitable area is likely to be around Hirapora Wildlife sanctuary in Kashmir. Pairwise comparison of the niche overlap and dynamics of P. hysterophorus between the native Americas and each of the regions (Africa, Asia, Australia and Oceania) where the species is introduced using Schoener’s D revealed variations in the niche overlap which was high between native Americas and Australia (0.70) and Africa (0.69), moderate between Americas and Asia (0.59) and low between Americas and Oceania (0.24). Exclusion of 25% of rare climatic conditions did not have any effect on the niche overlap index (D). Niche similarity test was not significant for any of the pairwise comparisons of native Americas and the continents in which the species is non-native indicating that the native niche is more similar to the exotic niche than any randomly sampled niche from the exotic range. But the niche equivalency tests showed that the environmental realized niche of P. hysterophorus in its invaded range was not totally equivalent to that in the native range indicating niche differentiation. The niche dynamic indices based on analogous and the entire climatic space in the native and introduced regions revealed a very high niche stability. A very limited niche expansion was noticed only in Asia and niche unfilling was evident in Oceania. Like niche overlap index (D), niche expansion and niche stability were not affected by the exclusion of 25% of rare climatic conditions but marginal change was noticed in niche unfilling in the Oceania. The above predictions have implications for formulation of policies at local, regional and global level for the management of this invasive species.

Abiotic conditions shape the relationship between indigenous and exotic species richness in a montane biodiversity hotspot

Montane ecosystems are more prone to invasions by exotic plant species than previously thought. Besides abiotic factors, such as climate and soil properties, plant-plant interactions within communities are likely to affect the performance of potential invaders in their exotic range. The biotic resistance hypothesis predicts that high indigenous species richness hampers plant invasions. The biotic acceptance hypothesis, on the other hand, predicts a positive relationship between indigenous and exotic species richness. We tested these two hypotheses using observational data along an elevational gradient in a southern African biodiversity hotspot. Species composition data of indigenous and exotic plants were recorded in 20 road verge plots along a gradient of 1775–2775 m a.s.l. in the Drakensberg, South Africa. Plots were 2 × 50 m in size and positioned at 50 m elevational intervals. We found a negative correlation between indigenous and exotic richness for locations with poorly developed mineral soils, suggesting biotic resistance through competitive interactions. A strong positive correlation for plots with very shallow soils at high elevations indicated a lack of biotic resistance and the possibility of facilitating interactions in harsher environments. These results suggest that biotic resistance is restricted to the lower and mid elevations while biotic acceptance prevails in presence of severe abiotic stress, potentially increasing the risk of plant invasions into montane biodiversity hotspots.

Mapping properties of fundamental harmonic analysis operators in the exotic Bessel framework

We prove sharp power-weighted Lp, weak type and restricted weak type inequalities for the heat semigroup maximal operator and Riesz transforms associated with the Bessel operator Bν in the exotic range of the parameter −∞<ν<1. Moreover, in the same framework, we characterize basic mapping properties for other fundamental harmonic analysis operators, including the heat semigroup based vertical g-function and fractional integrals (Riesz potential operators).

A fungus-eat-fungus world: Digitopodium, with particular reference to mycoparasites of the coffee leaf rust, Hemileia vastatrix

Digitopodium hemileiae was described originally in 1930 as Cladosporium hemileiae; growing as a mycoparasite of the coffee leaf rust (CLR), Hemileia vastatrix, in a sample of diseased leaves of Coffea canephora collected in the Democratic Republic of Congo. No cultures from this material exist. More recently, the type material was re-examined and, based on morphological features, considered to be incorrectly placed in Cladosporium. The new genus Digitopodium was erected to accommodate this species. Interest in fungal antagonists of H. vastarix, as potential biocontrol agents of CLR, led to comprehensive surveys for mycoparasites, both in the African centre of origin of the rust, as well as in its South American exotic range. Among the rust specimens from Ethiopia, one was found to be colonized by a fungus congeneric with, and similar to, D. hemileiae. Pure cultures obtained from the Ethiopian material enabled a molecular study and for its phylogenetic position to be elucidated, based on DNA sequence data from the ITS and LSU regions. Molecular data showed that two members of the recently erected genus Hyalocladosporiella (Herpotrichiellaceae: Chaetothyriales) are congeneric with Digitopodium from Ethiopia and morphologically similar to both D. hemileiae and the two Ethiopian isolates. These isolates were found to be morphologically and genetically identical to H. tectonae, described previously from Brazil. Thus, species of Hyalocladosporiella are re-allocated to Digitopodium here; including D. tectonae, and a novel species, D. canescens, recently found in Brazil growing as a mycoparasite of Puccinia thaliae. The potential use of D. hemileiae and D. tectonae for classical biological control of CLR is discussed.

Biogeographic differences in plant-soil biota relationships contribute to the exotic range expansion of Verbascum thapsus.

Exotic plant species can evolve adaptations to environmental conditions in the exotic range. Furthermore, soil biota can foster exotic spread in the absence of negative soil pathogen–plant interactions or because of increased positive soil biota–plant feedbacks in the exotic range. Little is known, however, about the evolutionary dimension of plant–soil biota interactions when comparing native and introduced ranges.To assess the role of soil microbes for rapid evolution in plant invasion, we subjected Verbascum thapsus, a species native to Europe, to a reciprocal transplant experiment with soil and seed material originating from Germany (native) and New Zealand (exotic). Soil samples were treated with biocides to distinguish between effects of soil fungi and bacteria. Seedlings from each of five native and exotic populations were transplanted into soil biota communities originating from all populations and subjected to treatments of soil biota reduction: application of (a) fungicide, (b) biocide, (c) a combination of the two, and (d) control.For most of the investigated traits, native populations showed higher performance than exotic populations; there was no effect of soil biota origin. However, plants developed longer leaves and larger rosettes when treated with their respective home soil communities, indicating that native and exotic plant populations differed in their interaction with soil biota origin. The absence of fungi and bacteria resulted in a higher specific root length, suggesting that V. thapsus may compensate the absence of mutualistic microbes by increasing its root–soil surface contact. Synthesis. Introduced plants can evolve adaptations to soil biota in their new distribution range. This demonstrates the importance of biogeographic differences in plant–soil biota relationships and suggests that future studies addressing evolutionary divergence should account for differential effects of soil biota from the home and exotic range on native and exotic populations of successful plant invaders.

The role of overseas genetic surveys to potentially accelerate biological control development for a new Hydrilla verticillata introduction in the USA

Documentation of fine-scale plant genetic identity in order to match weed genotypes between native and invasive ranges can be used to identify potential biological control agents from target genotypes in the hopes that they will be better adapted and thus more effective once introduced into the exotic range. However, the utility of this information for directing future exploration, for example upon introduction of a new weed genotype, is rarely considered. A cryptic introduction of the submersed aquatic weed, Hydrilla verticillata (L.f.) Royle (Alismatales: Hydrocharitaceae), was recently identified in the Connecticut River, which represents a new hydrilla haplotype not previously recorded in the USA. Because we have instituted concurrent plant genetic studies and biological control agent surveys during overseas exploration, potential herbivores of the cryptic introduction may already be known, requiring less resources if a biological control program of this haplotype is instigated. For the newly introduced haplotype and its closest relatives, we identified 22 herbivore taxa from China and Korea, including Bagous spp., Hydrellia spp., and a number of chironomids. This information may now be used to pursue agent development on the cryptic introduction without additional years and resources required to survey native hydrilla populations for new potential agents.

Ectomycorrhizal Plant-Fungal Co-invasions as Natural Experiments for Connecting Plant and Fungal Traits to Their Ecosystem Consequences

Introductions and invasions by fungi, especially pathogens and mycorrhizal fungi, are widespread and potentially highly consequential for native ecosystems, but may also offer opportunities for linking microbial traits to their ecosystem functions. In particular, treating ectomycorrhizal (EM) invasions, i.e., co-invasions by EM fungi and their EM host plants, as natural experiments may offer a powerful approach for testing how microbial traits influence critical ecosystem functions. Forests dominated by EM symbiosis have unique biogeochemistry whereby the extracellular compoundssecretions of EM plants and fungi may also alteraffect carbon (C) and nutrient cycling; moreover, particular lineages of EM fungi have unique functional traits. EM invasions may therefore alter the biogeochemistry of the native landscapes ecosystems they invade, especially nitrogen (N) and carbon (C) cycling. By identifying “response traits” that favor the success of fungi in introductions and invasions (e.g., spore dispersal and germination) and their correlations with “effect traits” (e.g., nutrient-cycling enzymes) that can alter N and C cycling (and affect other coupled elemental cycles), one may be able to predict the ecosystem functional consequences for ecosystems of fungal invasions using biogeochemistry models that incorporate fungal traits. Here, we review what is already known about how EM fungal community composition, traits, and ecosystem functions vary amongdiffer between native and exotic populations, focusing on the example of EM fungi associated with species of Pinus introduced from the Northern into the Southern Hemisphere. We develop hypotheses on how effects of introduced and invasive EM fungi may depend on interactions between exotic soil N availability in the exotic range and EM fungal traits. We discuss how such hypotheses could be tested by utilizing pine Pinus introductions and invasions as a model system, especially when combined with controlled laboratory experiments. Finally, we illustrate how ecosystem modeling can be used to link fungal traits to their consequences for ecosystem N and C cycling in the context of biological invasions, and we highlight exciting avenues for future directions in understanding EM invasion.

Native distribution characteristics rather than functional traits explain preadaptation of invasive species to high‐UV‐B environments

AbstractAimAlien species successfully colonize new ranges if they encounter favourable environmental conditions there and possess traits that match new challenges. Climate‐matching approaches comparing native and exotic ranges mostly consider temperature and precipitation niches of alien species, but have largely ignored UV‐B radiation. UV‐B fundamentally differs between hemispheres, with much higher levels at southern than at northern latitudes. Consequently, UV‐B might act at the global scale and present a so far neglected filter that species need to overcome when invading high‐UV‐B environments.LocationWe performed two multi‐species common garden experiments, conducted in the native European range (Germany) and the high‐UV‐B exotic range (New Zealand) to test for preadaptation to UV‐B.MethodsWe used 25 herbaceous species from open habitats, which we exposed in each range to three UV radiation treatments: (a) natural sunlight, (b) exclusion of UV‐B while allowing natural UV‐A, and (c) exclusion of UV‐B and UV‐A. We additionally used plant traits (TRY), global distribution data (GBIF, GloNAF) and global UV‐B satellite data (glUV) to determine species‐specific characteristics as fostering agents of UV‐B tolerance. The joint analysis of experimental and macroecological data allowed quantification of species plasticity and identification of beneficial species traits in high‐UV‐B environments.ResultsOur results showed an overall limiting effect of UV‐B in both common gardens but the UV‐stress response tended to be more pronounced in the invaded range. Across all species, we found little evidence for preadaptation by functional plant traits. In contrast, preadaptation to climatic conditions related to the species’ native UV‐B niche was of greater importance for plant performance in the presence of UV‐B radiation.Main conclusionsFor predicting alien species’ ability to expand into high‐UV‐B environments, macroclimatic niche characteristics of the species’ native range might be better predictors than functional traits and should be more considered in future projection models.

Allometric equations for the invasive vine air potato (Dioscorea bulbifera) in its exotic range in Florida

AbstractNondestructive means for estimating air potato (also known as air yam; Dioscorea bulbifera L.) biomass will help gauge its management efficacy over time. We developed allometric equations to estimate total and fractional biomass components and densities of aerial bulbils and underground tubers of field-grown D. bulbifera in Florida. We selected four naturally infested sites representing its southern, central, and northern distribution in Florida and measured three independent variables (vine densities, stem diameters, and top heights) of 84 (21 site−1) discrete D. bulbifera patches during late October to early December of 2012. We destructively harvested D. bulbifera biomass, sorted by tubers, stems, leaves, and bulbils; counted units of bulbils and underground tubers (dependent variables); and dried to a constant weight. Mean percentages of tuber, stem, leaf, and bulbil fractions in total biomass were 42.0, 15.6, 26.0, and 16.4, respectively. We developed a parameterized multiplicative prediction model and regression equation for each dependent variable. Slopes of relationships among independent and dependent variables varied by biomass and density (bulbil and tuber) of plant components. Multiplied values of independent variables: all three for total, tuber, stem, and leaf biomass; two (vine base diameter*patch height) for bulbil biomass; two (vine density*patch height) for bulbil density; and only one (stem density) for tuber density provided best (R2-based) prediction values. These models will provide nondestructive methods for estimating biomass components and density of vegetative propagules of naturally growing D. bulbifera. Models are critical for understanding the performance of D. bulbifera in its exotic range, estimating biomass to project control costs, and comparing biomass components and bulbil/tuber densities during pre- and postmanagement periods to gauge control efficacy.

&lt;p class="HeadingRunIn"&gt;&lt;strong&gt;North American Branchiobdellida (Annelida: Clitellata) or Crayfish Worms in France: the most diverse distribution of these exotic ectosymbionts in Europe&lt;/strong&gt;&lt;/p&gt;

Crayfishes and other invertebrates were collected during 2010 to 2016 from 519 sites located in the river basins of the Adour, Charente, Dordogne, Garonne, Loire, Seine, Rhône and Sélune in France. North American species included Pacifastacus leniusculus at 255 sites, Faxonius limosus at 206 sites, Procambarus clarkii at 56 sites, and the endemic Austropotamobius pallipes at two sites. However, branchiobdellidans were only recorded from 100 sites with 23 of these being sampled more than once, resulting in a total of 127 collections. The widely distributed western North American, P. leniusculus carried four of its endemic branchiobdellidan species: Cambarincola gracilis, C. okadai, Triannulata magna and Xironogiton victoriensis. X. victoriensis was found at the majority of sites, with C. okadai, C. gracilis, and T. magna at fewer locations. Although F. limosus was the second most numerous crayfish species collected, it did not carry any of its endemic North American branchiobdellidan species. However, it was found cohabiting with P. leniusculus at four sites but carried X. victoriensis at only one of these. European A. pallipes only occurred at two sites with individuals harboring X. victoriensis, although no cohabiting exotic crayfish were found. Crayfish were also absent from three sites where free-living X. victoriensis were recovered from substrate samples. Procambarus clarkii appeared at sites scattered across the country, while specimens with C. mesochoreus were restricted to the Adour drainage. This study has shown the widespread distribution of exotic branchiobdellidans in the wild and the virtual extinction of endemic species in France. In addition, we have provided the first European record of T. magna, and the first record of C. mesochoreus in France; the latter being only the second recording in Europe. With this comprehensive survey of their crayfish hosts in France, monitoring future exotic range expansions and endemic contraction or extinction can be traced. These data will be available to authorities for future planning in maintaining healthy freshwater bodies by reducing the damaging effects caused by exotic crayfishes.

Mother knows best: plant polyploidy affects feeding and oviposition preference of the alligator weed biological control agent, Agasicles hygrophila

Alligator weed (Alternanthera philoxeroides (Martius) Grisebach) is an amphibious invasive plant native to South America. It is an allopolyploid that, in Argentina, possess two cytotypes, tetraploids and hexaploids. In the exotic range, the plant is biologically controlled with flea beetle Agasicles hygrophila Selman and Vogt but with different levels of success. The genotype of host plant is an important factor that needs to be considered in biological control programs. We studied how alligator weed ploidy level affects the oviposition preferences of A. hygrophila and its relation with female feeding preference, egg survival and larval performance in its native range. Females recognized the different ploidy levels of alligator weed and preferred to lay eggs on hexaploids than tetraploids. This choice positively affected larval performance and may be explained by the preference–performance hypothesis in this case for different plant cytotypes. Polyploidy should be considered in evaluating and prioritising biological control agents.

Niche expansion of the invasive plant species Ageratina adenophora despite evolutionary constraints

AbstractAimEcological inferences drawn from studies on niche dynamics of invasive species are often limited due to difficulties in disentangling evolutionary adaptations of the fundamental niche from demographic and interspecific processes shaping the realized niche. We used Ageratina adenophora, an invasive plant with restricted evolutionary potential to investigate shifts in the realized climatic niche independent of potential evolutionary adaptations.LocationNative Mexican range; exotic ranges in Asia, the USA, the Canary Islands and Australia.TaxonInvasive Asteraceae A. adenophora (Spreng.) R.M.King &amp; H.Rob. Commonly known as Crofton weed.MethodsWe compiled a robust occurrence dataset of A. adenophora for its native Mexican range and four exotic ranges (Asia, USA, Canary Islands, and Australia) and quantified pairwise niche overlap (Schoener's D) and niche dynamic (stable, unfilling and expansion) indices between the native and exotic ranges in reduced climatic space using smoothed occurrence densities. Niche shift was statistically tested using niche equivalency tests.ResultsThe value of niche overlap (Schoener's D) differed considerably, ranging from relatively high between Mexico and Asia to low between Mexico and Australia. The niche dynamic indices indicated highest level of niche stability in Asia while highest degree of unstable niche was detected in Australia due to both niche expansion and unfilling. The niche similarity tests indicated that the native niche is more similar to the exotic niche than any randomly sampled niche from the exotic range. However, the niche equivalency tests showed evidence of niche differentiation as the observed niche overlap was lower than expected by chance for all pairwise comparisons. Jointly these tests indicate that despite the similarity, the native niche is not perfectly identical to any of the exotic niches.Main conclusionsThe current study has direct implications for understanding range expansion of invasive species even in the absence of evolutionary adaptation. Our study indicates that invasive species can occupy different, non‐consistent realized climatic niches in different parts of the world, thus limiting the transferability of species distribution models and corresponding risk assessments or future projections.

Exotic plant species are locally adapted but not to high ultraviolet-B radiation: a reciprocal multispecies experiment.

Ultraviolet (UV) radiation intensities differ among global regions, with significantly higher levels in the southern hemisphere. UV-B may act as an environmental filter during plant invasions, which might particularly apply to plant species from Europe introduced to New Zealand. Just like for any other abiotic or biotic filter, successful invaders can cope with novel environmental conditions via plastic responses and/or through rapid adaptation by natural selection in the exotic range. We conducted a multispecies experiment with herbaceous plants in two common gardens located in the species' native and exotic ranges, in Germany and New Zealand, respectively. We used plants of German and New Zealand origin of eight species to test for adaptation to higher UV-B radiation in their new range. In each common garden, all plants were exposed to three radiation treatments: (1) ambient sunlight, (2) exclusion of UV-B while transmitting ambient UV-A, and (3) combined exclusion of UV-B and UV-A. Linear mixed-effect models revealed significant effects of UV-B on growth and leaf traits and an indication for UV-B-induced biomass reduction in both common gardens pointing to an impact of natural, ambient UV radiation intensities experienced by plants in the northern and in the southern hemisphere. In both common gardens, the respective local plants (i.e., German origins in Germany, New Zealand origins in New Zealand) displayed enhanced productivity and aboveground biomass allocation, thus providing evidence for recent evolutionary processes in the exotic range. Genetic differentiation between different origins in consequence of divergent local selection pressures was found for specific leaf area. This differentiation particularly hints at different selective forces in both ranges while only little evidence was found for an immediate selective effect of high UV-B intensities in the exotic range. However, reaction norm slopes across ranges revealed higher plasticity of exotic individuals in functional leaf traits that might allow for a more sensitive regulation of photoprotection measures in response to UV-B. During the colonization, New Zealand populations might have been selected for the observed higher phenotypic plasticity and a consequently increased ability to successfully spread in the exotic range.

The fickle activity of a fly and a moth: variation in activity of two biocontrol agents of Chrysanthemoides monilifera

Biocontrol agents released to control exotic pests may not have the same spatial distribution as the pest species and may therefore vary in efficacy across the exotic range. These changes in distribution are unlikely to be known until species have had time to fill all preferred niches in the invasive habitat. However, studies of post-release activity of biocontrol agents rarely assess longer-term patterns of establishment in the landscape. Comostolopsis germana and Mesoclanis polana were released to control Chrysanthemoides monilifera spp. rotundata (bitou bush) between 29 and 32 years ago. We assessed their activity in foredune and hinddune habitats of coastal beaches across the major distribution of bitou bush and experimentally assessed the effectiveness of C. germana at preventing flowering and seed set. Both biocontrol agents were found to be distributed along the 870 km of coastline, representing the core area of infestation. Tip damage by C. germana was highly variable but was consistently more effective in the foredune. Comostolopsis germana was found to reduce flower production from 15 to 59% with tip damage increasing with latitude. Mesoclanis polana did not show differences in activity with latitude and only showed a marginal increase in activity in hinddunes. Comostolopsis germana and M. polana are reducing the reproductive output of bitou bush but are unlikely to be effective as a sole management strategy particularly in warmer latitudes where more seeds are released.

The invasiveness of Hypochaeris glabra (Asteraceae): Responses in morphological and reproductive traits for exotic populations.

Scientists have been interested in many topics driven by biological invasions, such as shifts in the area of distribution of plant species and rapid evolution. Invasiveness of exotic plant species depends on variations on morphological and reproductive traits potentially associated with reproductive fitness and dispersal ability, which are expected to undergo changes during the invasion process. Numerous Asteraceae are invasive and display dimorphic fruits, resulting in a bet-hedging dispersal strategy –wind-dispersed fruits versus animal-dispersed fruits–. We explored phenotypic differentiation in seed morphology and reproductive traits of exotic (Chilean) and native (Spanish) populations of Hypochaeris glabra. We collected flower heads from five Spanish and five Chilean populations along rainfall gradients in both countries. We planted seeds from the ten populations in a common garden trial within the exotic range to explore their performance depending on the country of origin (native or exotic) and the environmental conditions at population origin (precipitation and nutrient availability). We scored plant biomass, reproductive traits and fruit dimorphism patterns. We observed a combination of bet-hedging strategy together with phenotypic differentiation. Native populations relied more on bet-hedging while exotic populations always displayed greater proportion of wind-dispersed fruits than native ones. This pattern may reflect a strategy that might entail a more efficient long distance dispersal of H. glabra seeds in the exotic range, which in turn can enhance the invasiveness of this species.

Influence of invasion history on rapid morphological divergence across island populations of an exotic bird.

There is increasing evidence that exotic populations may rapidly differentiate from those in their native range and that differences also arise among populations within the exotic range. Using morphological and DNA‐based analyses, we document the extent of trait divergence among native North American and exotic Hawaiian populations of northern cardinal (Cardinalis cardinalis). Furthermore, using a combination of historical records and DNA‐based analyses, we evaluate the role of founder effects in producing observed trait differences. We measured and compared key morphological traits across northern cardinal populations in the native and exotic ranges to assess whether trait divergence across the Hawaiian Islands, where this species was introduced between 1929 and 1931, reflected observed variation across native phylogeographic clades in its native North America. We used and added to prior phylogenetic analyses based on a mitochondrial locus to identify the most likely native source clade(s) for the Hawaiian cardinal populations. We then used Approximate Bayesian Computation (ABC) to evaluate the role of founder effects in producing the observed differences in body size and bill morphology across native and exotic populations. We found cardinal populations on the Hawaiian Islands had morphological traits that diverged substantially across islands and overlapped the trait space of all measured native North American clades. The phylogeographic analysis identified the eastern North American clade (C. cardinalis cardinalis) as the most likely and sole native source for all the Hawaiian cardinal populations. The ABC analyses supported written accounts of the cardinal's introduction that indicate the original 300 cardinals shipped to Hawaii were simultaneously and evenly released across Hawaii, Kauai, and Oahu. Populations on each island likely experienced bottlenecks followed by expansion, with cardinals from the island of Hawaii eventually colonizing Maui unaided. Overall, our results suggest that founder effects had limited impact on morphological trait divergence of exotic cardinal populations in the Hawaiian archipelago, which instead reflect postintroduction events.

Estimating the potential geographical range of Sirex noctilio: comparison with an existing model and relationship with field severity

The Sirex woodwasp, Sirex noctilio, is a significant pest of exotic stands of Pinus species in the southern hemisphere, and an emerging threat in north-eastern America. The potential global distribution of S. noctilio was assessed using the process-oriented niche modelling software CLIMEX. Model parameters were inferred from S. noctilio’s known native distribution in Eurasia and northern Africa, its exotic range in Brazil, New Zealand and South Africa, and from ecophysiological laboratory observations of both S. noctilio and its symbiotic wood-decay fungus, Amylostereum areolatum. Model predictions were validated using independent distribution data from Australia, New Zealand, South Africa and the Americas. Damage significance and spatial distribution data of S. noctilio infestations in New Zealand were compared with growth and suitability outputs of the model, to explore if the impact of S. noctilio could be related to climate. However, no correlation between modelled climate suitability and field infestation severity were found. The resulting model indicated that S. noctilio is currently occupying a fraction of its potential climatic niche in the regions it has invaded. Taking into account areas where suitable hosts occur, results suggest that S. noctilio could further extend its range into additional plantations in southern Queensland in Australia and central Brazil, and into native and exotic stands of Pinus throughout north-east America. Stands of Pinus that are isolated at present from current S. noctilio infestations, such as those in California, Central America and Western Australia, may also be at risk if control measures are ineffective in preventing its spread. Differences in parameter selection and risk projections of our model and a previously published CLIMEX model of S. noctilio are discussed.

Unexplained variability among spatial replicates in transient elasticity: implications for evolutionary ecology and management of invasive species

AbstractUnderstanding actual and potential selection on traits of invasive species requires an assessment of the sources of variation in demographic rates. While some of this variation is assignable to environmental, biotic or historical factors, unexplained demographic variation also may play an important role. Even when sites and populations are chosen as replicates, the residual variation in demographic rates can lead to unexplained divergence of asymptotic and transient population dynamics. This kind of divergence could be important for understanding long‐ and short‐ term differences among populations of invasive species, but little is known about it. We investigated the demography of a small invasive tree Psidium cattleianum Sabine in the rainforest of Hawaiʻi at four sites chosen for their ecological similarity. Specifically, we parameterized and analyzed integral projection models (IPM) to investigate projected variability among replicate populations in: (1) total population size and annual per capita population growth rate during the transient and asymptotic periods; (2) population structure initially and asymptotically; (3) three key parameters that characterize transient dynamics (the weighted distance of the structure at each time step from the asymptotic structure, the strength of the sub‐dominant relative to the dominant dynamics, and inherent cyclicity in the subdominant); and (4) proportional sensitivity (elasticity) of population growth rates (both asymptotic and transient) to perturbations of various components of the life cycle. We found substantial variability among replicate populations in all these aspects of the dynamics. We discuss potential consequences of variability across ecologically similar sites for management and evolutionary ecology in the exotic range of invasive species.

Exotic plant species receive adequate pollinator service despite variable integration into plant-pollinator networks.

Both exotic and native plant species rely on insect pollinators for reproductive success, and yet few studies have evaluated whether and how exotic plant species receive services from native pollinators for successful reproduction in their introduced range. Plant species are expected to successfully reproduce in their exotic range if they have low reliance on animal pollinators or if they successfully integrate themselves into resident plant-pollinator networks. Here, we quantify the breeding system, network integration, and pollen limitation for ten focal exotic plant species in North America. Most exotic plant species relied on animal pollinators for reproduction, and these species varied in their network integration. However, plant reproduction was limited by pollen receipt for only one plant species. Our results demonstrate that even poorly integrated exotic plant species can still have high pollination service and high reproductive success. The comprehensive framework considered here provides a method to consider the contribution of plant breeding systems and the pollinator community to pollen limitation, and can be applied to future studies to provide a more synthetic understanding of the factors that determine reproductive success of exotic plant species.

Invasive legumes can associate with many mutualists of native legumes, but usually do not

Mutualistic interactions can strongly influence species invasions, as the inability to form successful mutualisms in an exotic range could hamper a host's invasion success. This barrier to invasion may be overcome if an invader either forms novel mutualistic associations or finds and associates with familiar mutualists in the exotic range. Here, we ask (1) does the community of rhizobial mutualists associated with invasive legumes in their exotic range overlap with that of local native legumes and (2) can any differences be explained by fundamental incompatibilities with particular rhizobial genotypes? To address these questions, we first characterized the rhizobial communities naturally associating with three invasive and six native legumes growing in the San Francisco Bay Area. We then conducted a greenhouse experiment to test whether the invasive legume could nodulate with any of a broad array of rhizobia found in their exotic range. There was little overlap between the Bradyrhizobium communities associated with wild‐grown invasive and native legumes, yet the invasive legumes could nodulate with a broad range of rhizobial strains under greenhouse conditions. These observations suggest that under field conditions in their exotic range, these invasive legumes are not currently associating with the mutualists of local native legumes, despite their potential to form such associations. However, the promiscuity with which these invading legumes can form mutualistic associations could be an important factor early in the invasion process if mutualist scarcity limits range expansion. Overall, the observation that invasive legumes have a community of rhizobia distinct from that of native legumes, despite their ability to associate with many rhizobial strains, challenges existing assumptions about how invading species obtain their mutualists. These results can therefore inform current and future efforts to prevent and remove invasive species.