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Non-native plant species reliant on insect pollination must attract novel pollinators in their introduced habitat to reproduce. Indeed, pollination services provided by resident floral visitors may contribute to the spread of non-native species, which may then affect the pollination services received by native plants. To determine the mechanisms by which an invasive thistle attracts pollinators in its introduced range, and whether its presence changes the pollinator visitation to native plant species, we compared bee visitation to native plants in the presence or absence of the invader. We experimentally tested the effect of a thistle invasion into a native plant community. We found that the non-native thistle was the most attractive of the plant species to visiting bee species. However, there was no effect of experimental treatment (presence of thistle) on bee abundance or visitation rate (bees per unit floral area per sample) to native plant species. Across 68 bee and 6 plant species, we found a significant correlation between pollen protein content and bee abundance and visitation rate. Thistle pollen also had a similar protein: lipid ratio to legumes, which correlated with bumble bee visitation. The high protein content of the thistle pollen, as compared to four native asters, may allow it to attract pollinators in novel ecosystems, and potentially contribute to its success as an invader. At the same time, this high protein pollen may act as a novel resource to pollinators in the thistle’s invaded range.

The establishment and spread of invasive species are often facilitated by disturbance. Once established, however, individuals of invasive species are themselves subject to damage from disturbance; their responses to these perturbations could be an important component of invasive species' ability to persist in local environments. We quantified the impact of physical disturbances on individual invasive plants by conducting a field experiment to examine the effect of three physical disturbances (simulated hail, partial burial with gravel, and simulated trampling) interacting with two levels of warming (warmed and ambient) on the performance of two non‐native, invasive thistle species, Carduus nutans L. and Carduus acanthoides L. We found complete recovery from all three physical disturbance treatments, regardless of warming treatment, for both maximum plant height and number of stems (which can increase in response to physical damage due to loss of apical dominance). Physical disturbance and warming had no effect on the number of capitula produced by C. nutans ; however, simulated trampling interacted with warming to reduce the production of capitula by 45% in C. acanthoides . This was the lone significant change to any measured life history trait of either species in the entire experiment. While disturbance is generally considered to be both a cause and a consequence of invasion, our results demonstrate that established individuals of both species also have a strong capacity to rebound from subsequent disturbance. This suggests that within‐generation, individual response to disturbance could be an important component of an invasive species' ability to persist in the environment.

, commonly known as plumeless thistles, is a genus in the Asteraceae family that exhibits both medicinal value and invasive tendencies. However, the genomic data of (i.e., complete chloroplast genomes) have not been sequenced. We sequenced and assembled the chloroplast genome (cpDNA) sequences of three species using the Illumina Miseq sequencing system and Geneious Prime. Phylogenetic relationships between and related taxa were reconstructed using Maximum Likelihood and Bayesian Inference analyses. In addition, we used a single nucleotide polymorphism (SNP) in the protein coding region of the gene to develop molecular markers to distinguish from and . The cpDNA sequences of , and ranged from 152,342 bp to 152,617 bp in length. Comparative genomic analysis revealed high conservation in terms of gene content (including 80 protein-coding, 30 tRNA, and four rRNA genes) and gene order within the three focal species and members of subfamily Carduoideae. Despite their high similarity, the three species differed with respect to the number and content of repeats in the chloroplast genome. Additionally, eight hotspot regions, including , , , , , , , and , were identified in the study species. Phylogenetic analyses inferred from 78 protein-coding and non-coding regions indicated that is polyphyletic, suggesting the need for additional studies to reconstruct relationships between thistles and related taxa. Based on a SNP in , we successfully developed a molecular marker and protocol for distinguishing from the other two focal species. Our study provides preliminary chloroplast genome data for further studies on plastid genome evolution, phylogeny, and development of species-level markers in .

As the number of biological invasions increases, the potential for invader-invader interactions also rises. The effect of multiple invaders can be superadditive (invasional meltdown), additive, or subadditive (invasional interference); which of these situations occurs has critical implications for prioritization of management efforts. Carduus nutans and C. acanthoides , two congeneric invasive weeds, have a striking, segregated distribution in central Pennsylvania, USA. Possible hypotheses for this pattern include invasion history and chance, direct competition, or negative interactions mediated by other species, such as shared pollinators. To explore the role of resource competition in generating this pattern, we conducted three related experiments using a response-surface design throughout the life cycles of two cohorts. Although these species have similar niche requirements, we found no differential response to competition between conspecifics vs. congeners. The response to combined density was relatively weak for both species. While direct competitive interactions do not explain the segregated distributional patterns of these two species, we predict that invasions of either species singly, or both species together, would have similar impacts. When prioritizing which areas to target to prevent the spread of one of the species, it is better to focus on areas as yet unaffected by its congener; where the congener is already present, invasional interference makes it unlikely that the net effect will change.

Simultaneously flowering plant species may indirectly interact with each other by influencing the quantity of pollinator visitation and/or the quality of pollen that is transferred. These effects on pollination may depend on how pollinators respond to floral resources at multiple levels. In this study, we demonstrate pollinator‐mediated negative interactions between two invasive plants,Carduus acanthoidesandCarduus nutans. Using constructed arrays of the two species, alone and in mixture, we quantified pollinator visitation at the patch and individual plant levels and measured seed production. We found that co‐occurrence of our species led to a shift in pollinator services at both levels. Greater interference occurred when arrays were small and spacings between neighboring plants were large. A spatially explicit movement model suggests that pollinator foraging behavior, which mediates the interactions between plants, was driven by floral display size rather than species identity per se. Pollinator behavior significantly reduced the proportion of seed set for both species relative to that in single‐species arrays. Overall, the dependence of pollinator behavior on patch size, spacing between plants, and patch composition can lead to pollinator‐mediated plant interactions that range from facilitative to competitive.

BACKGROUND AND AIMS: Although many methods exist for quantifying the number of pollen grains in a sample, there are few standard methods that are user-friendly, inexpensive and reliable. The present contribution describes a new method of counting pollen using readily available, free image processing and analysis software. METHODS: Pollen was collected from anthers of two species, Carduus acanthoides and C. nutans (Asteraceae), then illuminated on slides and digitally photographed through a stereomicroscope. Using ImageJ (NIH), these digital images were processed to remove noise and sharpen individual pollen grains, then analysed to obtain a reliable total count of the number of grains present in the image. A macro was developed to analyse multiple images together. To assess the accuracy and consistency of pollen counting by ImageJ analysis, counts were compared with those made by the human eye. KEY RESULTS AND CONCLUSIONS: Image analysis produced pollen counts in 60 s or less per image, considerably faster than counting with the human eye (5-68 min). In addition, counts produced with the ImageJ procedure were similar to those obtained by eye. Because count parameters are adjustable, this image analysis protocol may be used for many other plant species. Thus, the method provides a quick, inexpensive and reliable solution to counting pollen from digital images, not only reducing the chance of error but also substantially lowering labour requirements.

AIM: Although the negative effects of invasive species are globally recognized, little is known about the potential positive impacts they can have on other species in the ecosystems they invade. However, the persistence of invaders in a wide range of ecological communities may mean that they provide resources and refuge for threatened native species, or supplement ecosystem services. LOCATION: Agroecosystems in the USA. METHODS: We use a 2‐year field experiment to explore the potential positive and negative impacts of an invasive thistle (Carduus acanthoides) on the composition of the resident community of foraging insects. The presence or absence of the thistle was the only difference in experimental and control plots comprising a background community of ten flowering annual species. RESULTS: We demonstrate that the invasive thistle is both highly visited and strongly preferred by bees relative to other flowering species. Bee abundance was 302% higher and bee species richness 35% higher in habitat patches where the thistle was present compared to where it was absent. In addition, the abundance of Bombus species, a native group recently found to be in decline, was 479% higher when the thistle was present. MAIN CONCLUSIONS: Our results suggest that, despite causing significant problems, the invasion of this non‐native species may also provide crucial benefits via floral resources for pollinators. Benefits, such as the floral resources that invaders provide to pollinators, should also be taken into account in conservation and invader management plans. Eradication or complete removal of invasive species which provision insects with floral resources could have unintended negative impacts on the associated pollinator community.

Understanding and predicting population spread rates is an important problem in basic and applied ecology. In this article, we link estimates of invasion wave speeds to species traits and environmental conditions. We present detailed field studies of wind dispersal and compare nonparametric (i.e., data‐based) and mechanistic (fluid dynamics model–based) dispersal kernel and spread rate estimates for two important invasive weeds,Carduus nutansandCarduus acanthoides. A high‐effort trapping design revealed highly leptokurtic dispersal distributions, with seeds caught up to 96 m from the source, far further than mean dispersal distances (approx. 2 m). Nonparametric wave speed estimates are highly sensitive to sampling effort. Mechanistic estimates are insensitive to sampling because they are obtained from independent data and more useful because they are based on the dispersal mechanism. Over a wide range of realistic conditions, mechanistic spread rate estimates were most sensitive to high winds and low seed settling velocities. The combination of integrodifference equations and mechanistic dispersal models is a powerful tool for estimating invasion spread rates and for linking these estimates to characteristics of the species and the environment.

The present paper discusses the analysis of flavonoids in the methanol extract from the flowering herbs of Carduus acanthoides (L.), where flavonois were indentified by TLC and SPE HPLC. The quantitative analysis was performed using spectrophotometric Christ-Müller’s method. The samples containing flavonoids and those released after acid hydrolysis were investigated by 1D TLC on silica gel and polyamide. After purification by SPE, the samples were also analyzed by RP-HPLC. Apigenin-7-glucoside, luteolin-7-glucoside, kaempferol-3-rhamnoglucoside, kaempferol-3-glucoside, apigenin, luteolin and chlorogenic acid and p-coumaric acid were detected in the fractions of methanol extracts obtained from the plant. This method is very simple for the analysis and suitable for rapid screening of flavonoids in plants.

As the number of biological invasions increases, the potential for invader-invader interactions also rises. The effect of multiple invaders can be superadditive (invasional meltdown), additive, or subadditive (invasional interference); which of these situations occurs has critical implications for prioritization of management efforts. Carduus nutans and C. acanthoides , two congeneric invasive weeds, have a striking, segregated distribution in central Pennsylvania, USA. Possible hypotheses for this pattern include invasion history and chance, direct competition, or negative interactions mediated by other species, such as shared pollinators. To explore the role of resource competition in generating this pattern, we conducted three related experiments using a response-surface design throughout the life cycles of two cohorts. Although these species have similar niche requirements, we found no differential response to competition between conspecifics vs. congeners. The response to combined density was relatively weak for both species. While direct competitive interactions do not explain the segregated distributional patterns of these two species, we predict that invasions of either species singly, or both species together, would have similar impacts. When prioritizing which areas to target to prevent the spread of one of the species, it is better to focus on areas as yet unaffected by its congener; where the congener is already present, invasional interference makes it unlikely that the net effect will change.