Thistle Species Research Articles

Characterisation of the vegetable rennets used for ‘Torta del Casar’ cheesemaking by a protein profile method

The purpose of this work was to develop a cheap, easy and fast procedure, based on protein analysis, that can be used in the characterisation of coagulants from thistle species, which can be used in Torta del Casar cheesemaking. Sodium dodecyl sulphate–polyacrylamide gel electrophoresis showed high efficiency in the identification of Cynara cardunculus from other thistle species and in discriminating between the technological properties, milk‐clotting and casein degradation activities of the vegetable rennets used in this study. This technique allowed for the grouping of aqueous extracts from the flowers of C. cardunculus into five different groups, which exhibited variable ability to degrade milk caseins.

Why close relatives make bad neighbours: phylogenetic conservatism in niche preferences and dispersal disproves Darwin's naturalization hypothesis in the thistle tribe.

The number of exotic plant species that have been introduced into the United States far exceeds that of other groups of organisms, and many of these have become invasive. As in many regions of the globe, invasive members of the thistle tribe, Cardueae, are highly problematic in the California Floristic Province, an established biodiversity hotspot. While Darwin's naturalization hypothesis posits that plant invaders closely related to native species would be at a disadvantage, evidence has been found that introduced thistles more closely related to native species are more likely to become invasive. To elucidate the mechanisms behind this pattern, we modelled the ecological niches of thistle species present in the province and compared niche similarity between taxa and their evolutionary relatedness, using fossil-calibrated molecular phylogenies of the tribe. The predicted niches of invasive species were found to have higher degrees of overlap with native species than noninvasive introduced species do, and pairwise niche distance was significantly correlated with phylogenetic distance, suggesting phylogenetic niche conservatism. Invasive thistles also displayed superior dispersal capabilities compared to noninvasive introduced species, and these capabilities exhibited a phylogenetic signal. By analysing the modelled ecological niches and dispersal capabilities of over a hundred thistle species, we demonstrate that exapted preferences to the invaded environment may explain why close exotic relatives may make bad neighbours in the thistle tribe.

Integral projection models show exotic thistle is more limited than native thistle by ambient competition and herbivory

Both competitors and natural enemies can limit plant population growth. However, demographic comparisons of the effects of these interactions on introduced versus co‐occurring, related native species are uncommon. We asked: (1) does plant competition, insect herbivory, or their combination reduce population growth rate, log λ, of the Eurasian thistle Cirsium vulgare sufficiently to explain its limited invasiveness in western tallgrass prairie; and (2) how do the effects of these interactions compare to those for C. altissimum, its co‐occurring, synchronously‐flowering native congener? We developed integral projection models (IPMs) to estimate log λ for both species, using parameter estimates from field experiments. Our models predicted that the growth potential (growth rate at minimal competition and herbivory) for the introduced thistle (log λ = 3.5 (2.5, 4.6)) was twice as large as for the native thistle (log λ = 1.6 (0.4, 3.1)); however, a high level of competition and ambient insect herbivory together reduced log λ to similar values for both thistle species (C. vulgare: log λ = −1.3 (−2.4, −0.3) vs C. altissimum: log λ = −0.9 (−1.4, −0.3)). This suggests that the introduced thistle was more affected by competition and insect herbivory. For the introduced thistle, neither competition nor insect herbivory alone led to negative log λ. In contrast, for the native thistle, high competition alone also led to negative population growth (log λ = −0.8, percentile limits do not overlap with zero). Ambient herbivory alone prevented the spread for both thistle species (percentile limits include zero). Overall, the results show that interspecific competition followed by ambient levels of insect herbivory strongly constrained log λ for both thistles, limiting C. vulgare invasiveness and C. altissimum abundance. The outcome highlights the importance of synergy between the two biological interactions in limiting plant population growth. Improved understanding of mechanisms limiting log λ for weedy plants enhances our ability to predict when biotic resistance will contribute to invasive plant species management.

Leaf traits of congeneric host plants explain differences in performance of a specialist herbivore

1. Within the host range of herbivorous insects, performance hierarchies are often correlated with relatedness to a primary host plant, as plant traits are phylogenetically conserved. Therefore, it was hypothesised that differences in herbivore performance on closely related plant species are due to resistance traits that vary in magnitude, rather than in the nature of the traits.2. This hypothesis was tested by manipulating putative resistance traits of three congeneric thistle species (Cirsium arvense, Cirsium palustre, and Cirsium vulgare) and assessing the performance of the oligophagous, leaf‐feeding beetle, Cassida rubiginosa. Measurements were done of survival, weight gain, and development time of the beetle on its primary host, C. arvense, and two alternative hosts under low and high nutrient availability, and on shaved and unshaved leaves.3. Survival of C. rubiginosa was strongly dependent on plant species with final mean survival rates of 47%, 16%, and 8% on C. arvense, C. palustre, and C. vulgare, respectively. Survival was primarily explained by leaf trichome densities, and to a lesser extent by specific leaf area. Leaf flavonoid concentrations did not explain differences in beetle survival, and there were no differences in beetle weight gain or development time of individuals that survived to adulthood.4. No beetles survived on unshaved (hairy) C. vulgare plants, but manipulating leaf trichome densities of the thistle species by shaving the leaves moderated the plant‐specific resistance, and equalised the survival rates. Survival of C. rubiginosa on alternative congeneric hosts was explained by a common physical resistance trait that varied in magnitude.

Metabolite profiling to discriminate different species and genus from thistles in Korea using liquid chromatography with quadrupole time-of-flight mass spectrometry.

This study was designed to classify and identify closely related thistle species in the genus Cirsium, as well as Carduus and Cephalonoplos species, which are also thistles. The comprehensive and untargeted metabolite profiles of nine Korean thistles were determined using ultra high performance liquid chromatography combined with hybrid quadrupole time-of-flight mass spectrometry. The difference in metabolite profiles among species was explored using principal component analysis and hierarchical clustering analysis. The significantly different metabolites (Bonferroni-corrected P-value < 0.001) were used to construct a partial least squares discriminant analysis model to predict the species of thistle. Nine species were successfully classified using a partial least squares discriminant analysis model and confirmed using a cross-validation method. Species with similar features were grouped based on unique patterns in variable clusters. The present study suggests that liquid chromatography with quadrupole time-of-flight mass spectrometry untargeted metabolomic profiling with chemometric analysis is an efficient and powerful tool for discriminating between different species of medicinal herbs.

Establishment, dispersal, and prevalence of Rhinocyllus conicus (Coleoptera: Curculionidae), a biological control agent of thistles, Carduus species (Asteraceae), in Argentina, with experimental information on its damage

Use of the weevil, Rhinocyllus conicus Froelich, for classical biological control of Carduus species in Argentina has not been controversial, as it has been in Canada and the United States, because there are no native thistle species in the South American release areas. In this study, 30years after its first field release in Argentina, the Pampas region was surveyed to confirm the establishment of R. conicus, covering the original release sites and most of the overall area of distribution of its host thistles, Carduus species. Sites (n=121) were systematically selected and natural populations of thistles were examined to confirm the presence of the weevil. Twenty four sites with R. conicus were selected to record the weevil’s prevalence on Carduus thoermeri Weinman and Carduus acanthoides L. Additional opportunistic surveys were conducted in other regions of Argentina and Uruguay, more distant from the original release sites. Rhinocyllus conicus was found at 81% of the original release sites and at 69% of the total sites surveyed, an area of approximately 370.000km2. On average, 92% of the examined heads had damage in areas where the weevil was present, showing its high prevalence. A pilot study showed that the oviposition period of the weevils lasted 119days and seed production of C. acanthoides was reduced by 15.5%. These results encourage the implementation of an integrated management of thistles in Argentina, and maybe in other parts of South America.

Influence of Microsite Disturbance on the Establishment of Two Congeneric Invasive Thistles

The successful establishment of invasive species has been shown to depend on aspects of the invaded community, such as gap characteristics. Biotic resistance may be particularly critical for stopping invaders at early life history stages, but new species can often invade following disturbances, which may create microsites with very different characteristics than are usually present. We examine the response of two invasive thistle species, Carduus nutans L. and C. acanthoides L., to three different microsite characteristics: disturbance type, size, and water availability. The two species initially responded differently to the type of disturbance: C. acanthoides had higher emergence and survival in plots with both above- and belowground disturbance, whereas C. nutans had better early performance in large microsites with above-ground disturbance only. Later in their life cycle, C. nutans performed better in plots that had been disturbed both above- and belowground, whereas C. acanthoides was largely unaffected by disturbance type. Increased emergence and survival, larger size and a higher proportion flowering were observed in larger gaps for both species throughout the life cycle. Watering had a negative impact on C. nutans emergence and fall survival and on C. acanthoides survival to the following summer. Overall, these results suggest that disturbance-generated microsite characteristics (disturbance type and size) may have large impacts on establishment of these two Carduus species, which in turn may persist well beyond the initial stages of growth. Studying invader responses to disturbance can help us to understand under what circumstances they are likely to establish and create persistent problems; avoiding or ameliorating such situations will have significant management benefits.

Effects of a non-native biocontrol weevil, Larinus planus, and other emerging threats on populations of the federally threatened Pitcher’s thistle, Cirsium pitcheri

Larinus planus Frabicius (Curculionidae), is a seed-eating weevil that was inadvertently introduced into the US and was subsequently distributed in the US and Canada for the control of noxious thistle species of rangelands. It has been detected recently in the federally threatened Pitcher’s thistle (Cirsium pitcheri). We assayed weevil damage in a natural population of Pitcher’s thistle at Whitefish Dunes State Park, Door County, WI and quantified the impact on fecundity. We then estimated the impact of this introduced weevil and other emerging threats on two natural, uninvaded populations of Pitcher’s thistle for which we have long-term demographic data for 16yr (Wilderness State Park, Emmet County, MI) and 23yr (Miller High Dunes, Indiana Dunes National Lakeshore, Porter County, IN). We used transition matrices to determine growth rates and project the potential effects of weevil damage, inbreeding, goldfinch predation, and vegetative succession on Pitcher’s thistle population viability. Based on our models, weevil seed predation reduced population growth rate by 10–12%, but this reduction was enough to reduce time to extinction from 24yr to 13yr and 8yr to 5yr in the MI and IN population, respectively. This impact is particularly severe, given most populations of Pitcher’s thistle throughout its range hover near or below replacement. This is the first report of unanticipated ecological impacts from a biocontrol agent on natural populations of Cirsium pitcheri.

Distribution and host specificity of the thistle‐feeding tortoise beetle Cassida vibex (Coleoptera: Chrysomelidae) in southwestern Hokkaido, northern Japan

AbstractThe thistle‐feeding tortoise beetle Cassida vibex (Coleoptera: Chrysomelidae) is widespread in the Palearctic region. In Japan, this species has been recorded only from the largest island, Honshu. Here we report the occurrence of this species on Hokkaido, the most northern main island of Japan, along with detailed distributional records from the southwestern part of the island (southern Oshima Peninsula) and information on host plants. We also present the results of laboratory experiments on adult feeding preference and larval developmental performance to determine the specificity of C. vibex for four thistle species (Cirsium grayanum, Cir. alpicola, Cir. yezoense and Cir. aomorense; Asteraceae) common in southwestern Hokkaido. Cassida vibex was detected at only four sites among 97 sites investigated on the Oshima Peninsula, in strong contrast to the common occurrence of the congeneric thistle feeder C. rubiginosa (74 of 97 sites). Cassida vibex was found mainly on Cir. alpicola in the wild, but adult beetles showed no feeding preference for this or three other thistle species when given a choice in the laboratory. Larval performance of C. vibex was similar on Cir. alpicola, Cir. yezoense and Cir. aomorense but significantly lower on Cir. grayanum. Since Cir. alpicola often forms large clumps of individual plants, whereas Cir. yezoense and Cir. aomorense are scattered in their habitats, and C. vibex was collected only at sites where there were dense patches of Cir. alpicola, we postulate that the persistence of C. vibex is possible only where a substantial amount of suitable host plants is available.

Coexistence patterns of two invasive thistle species, Carduus nutans and C. acanthoides, at three spatial scales

To better understand the competitive processes involved in invasion by congeners, we examine coexistence patterns of two invasive species, Carduus nutans and C. acanthoides, at three spatial scales. A roadside survey of 5 × 5 km blocks in a previously identified overlap zone provided information about the regional scale. At smaller scales, we surveyed four fields of natural co-occurrence, quantifying the spatial patterns at the field scale by randomly placed 1 × 1 m quadrats and at the smallest scale by detailing plant position within the quadrats. The patterns observed are strikingly different at the different scales. At the regional scale, there is positive local autocorrelation in both species but negative cross-correlation between them, consistent with previous surveys. However, at the field scale, there is positive local autocorrelation in both species, and we generally see a positive association between the two species. At the plot scale, when excluding areas of joint absence, there is again a negative association between the two species. This pattern can also be seen at the field scale when excluding plots with joint absence. These results suggest that, at the scale of a field, the strongest factor determining location is aggregation in favorable habitats, which is a stronger force than the competition-induced segregation evidenced at small scales. Lottery competition for spatially aggregated safe sites thus appears to drive the patterns observed at the field scale, while the regional scale pattern may be a result of restricted natural dispersal and invasion history.

Spatial Prediction of Habitat Overlap of Introduced and Native Thistles to Identify Potential Areas of Nontarget Activity of Biological Control Agents

Nontarget feeding of Rhinocyllus conicus Fröelich and Trichosirocalus horridus (Panzer) on native North American thistles in the genus Cirsium has been documented. Some species of these native thistles have shown greater infestation levels of R. conicus in populations that are in close proximity to the target plant species, Carduus nutans L. In 2005 a study was initiated to identify areas of potential nontarget feeding by R. conicus and T. horridus on thistle species by predicting habitats of two known introduced hosts [C. nutans and Cirsium vulgare (Savi) Tenore] and two native species [Cirsium carolinianum (Walter) Fernald and Schubert and C. discolor (Muhlenberg ex Willdenow) Sprengel] using Mahalanobis distance (D(2)). Cumulative frequency graphs showed that the D(2) models for all four plant species effectively identified site conditions that contribute to the presence of the respective species. Poisson regression showed an association between D(2) values and plant counts at field-test sites for C. nutans and C. carolinianum. However, negative binomial regression detected no association between D(2) values and plant counts for C. discolor or C. vulgare. Chi-square analysis indicated associations between both weevil species and sites where C. vulgare and Carduus nutans were found, but not between the weevil and native thistle species. Habitats of C. nutans and Cirsium carolinianum overlapped in ≈12% of the study area. Data-based habitat models may provide a powerful tool for land managers and scientists to monitor native plant populations for nontarget feeding by introduced biological control agents.

Host Utilization of Field-Caged Native and Introduced Thistle Species by Rhinocyllus conicus

Rhinocyllus conicus Fröelich was introduced from Europe into North America as a biological control agent of the exotic weed Carduus nutans L. Concern exists over the feeding of this weevil on at least 25 species of native Cirsium thistles. Beginning in 2008, cage studies isolating adults of R. conicus on buds and flower heads of all eight thistle species (native and introduced) recorded from Tennessee were conducted to test if R. conicus could use these species for reproduction and what impacts larval feeding of R. conicus may have on seed production. Larvae of R. conicus completed development in heads of the native species C. carolinianum (Walter) Fernald and Schubert. and C. horridulum Michaux, and significant reductions in seed numbers of both species occurred during 2008. Rhinocyllus conicus oviposited on both C. carolinianum and C. horridulum at significantly greater levels than the introduced species C. arvense (L.) Scopoli and C. vulgare (Savi) Tenore. Infested heads of C. carolinianum contained numbers of R. conicus per centimeter of plant head width similar to Ca. nutans in 2008, and both native species contained numbers of R. conicus per centimeter of plant head width similar to C. arvense and C. vulgare in 2009. Body length was similar between R. conicus reared on native thistles and its target host Ca. nutans. This report is the first documentation of R. conicus feeding and reproducing on C. carolinianum and C. horridulum. Although R. conicus has been observed only on introduced thistles in naturally occurring populations in this region, the utilization of C. carolinianum and C. horridulum as host species in controlled conditions warrants continued monitoring of field populations and further investigation into factors that may influence nontarget feeding in the future.

Plant spatial arrangement affects projected invasion speeds of two invasive thistles

The spatial arrangement of plants in a landscape influences wind flow, but the extent that differences in the density of conspecifics and the height of surrounding vegetation influence population spread rates of wind dispersed plants is unknown. Wind speeds were measured at the capitulum level in conspecific arrays of different sizes and densities in high and low surrounding vegetation to determine how these factors affect wind speeds and therefore population spread rates of two invasive thistle species of economic importance, Carduus acanthoides and C. nutans. Only the largest and highest density array reduced wind speeds at a central focal thistle plant. The heights of capitula and surrounding vegetation also had significant effects on wind speed. When population spread rates were projected using integrodifference equations coupling previously published demography data with WALD wind dispersal models, large differences in spread rates resulted from differences in average horizontal wind speeds at capitulum height caused by conspecific density and surrounding vegetation height. This result highlights the importance of spatial structure for the calculation of accurate spread rates. The management implication is that if a manager has time to remove a limited number of thistle plants, an isolated thistle growing in low surrounding vegetation should be targeted rather than a similar sized thistle in a high density population with high surrounding vegetation, if the objective is to reduce spread rates.

Local variation in the thistle species Cirsium grayanum affects its utilization by the herbivorous ladybird beetle Henosepilachna niponica

AbstractHost plants are the most critical environmental factor for phytophagous arthropods. Adaptation to a novel host will alter the distributional range of an herbivore to include the area the novel host covers, and might promote divergence between populations utilizing the old and new hosts. On the Oshima Peninsula, Hokkaido Island, northern Japan, the ladybird beetle Henosepilachna niponica (Lewis) (Coleoptera: Coccinellidae) usually occurs exclusively on the thistle Cirsium alpicola Nakai (Asteraceae), which is distributed in the southernmost part of the island, although some other Cirsium species often grow in sympatry. At least at one site (Assabu), however, H. niponica depends on another thistle, Cirsium grayanum (Maxim.) Nakai, the most abundant and widely distributed thistle species on the Oshima Peninsula. We examined adult feeding acceptance and preference, and larval performance, in two populations of H. niponica that utilize different species of thistles (the Assabu population occurs on C. grayanum; the Shiriuchi population, on C. alpicola) by testing three kinds of thistles (C. grayanum from Assabu, C. grayanum from Shiriuchi, and C. alpicola from Shiriuchi). Results strongly suggested that among the three plants tested, C. grayanum from Assabu was the most suitable host for H. niponica. We concluded that local differences in C. grayanum mainly explain why it is not used at Shiriuchi, but that there are also local differences in host use among the beetle populations, suggesting some degree of local adaptation. This suggests that different selective regimes associated with different host plants might promote divergence among beetle populations. We conclude that H. niponica is at present unlikely to expand its range to the whole range of C. grayanum.

Classical biological control of weeds with Curculionidae.

Abstract The intentional use of insects to control weeds has been in practice for more than 150 years. Historically, species from the orders Lepidoptera and Coleoptera have shown the greatest success. Among the Coleoptera, the weevils (family Curculionidae) have played an integral role in the suppression of more than 50% of targeted weed programmes in various regions of the world. Notable successes using Curculionidae are in the control of waterhyacinth, Australian Acacia spp. and several thistle species. Published records indicate that of the 67 weed species targeted for control with Curculionidae worldwide, most are terrestrial-herbaceous weeds (65.7%). Curculionidae used for most of the targeted terrestrial-herbaceous ( n =44) and aquatic/semi-aquatic weeds ( n =6) are in North America, while the majority of the terrestrial-arborescent weeds ( n =17) are in Africa. Of the 75 species of Curculionidae used to control these weeds worldwide, 34 are in North America. Success, as defined by the establishment of a biological control agent that has a detrimental impact on the target weed, is dependent on the number of programmes implemented and the resources for follow-through. This review provides insight into the successful establishment of some selected weevil species and their impact on their target weeds.

First documentation of adult Trichosirocalus horridus on several non-target native Cirsium species in Tennessee

Releases of Trichosirocalus horridus (Panzer) (Coleoptera: Curculionidae), native to Europe, began in Tennessee in 1989 as part of a biological control program against musk thistle (Carduus nutans L.). In surveys conducted to investigate non-target feeding of T. horridus on native Cirsium thistle species from 2005 to 2008, adults of T. horridus were observed on all five native Cirsium thistles. These adult occurrences are the first documentation of T. horridus occurring on three of these native species [C. carolinianum (Walt.) Fern & Schub., C. horridulum Michx. and C. muticum Michx.], and the first record of T. horridus occurring in the Great Smoky Mountains National Park. While C. carolinianum and C. horridulum did not show symptoms of larval feeding in the meristematic tissues, C. altissimum, C. discolor, and C. muticum all had damaged meristems and possible oviposition scars on the midribs of the leaves. However, the impact of feeding by larvae of T. horridus on the reproductive potential of native plants is uncertain, because even in the target species (musk thistle and other introduced Cirsium species) plant death only sometimes occurs, and seed production continues.

Shipment and storage effects on the terminal velocity of seeds

AbstractMechanistic models of seed dispersal by wind include terminal velocity as the main seed characteristic that influences the dispersal process and hence the resulting dispersal kernels and spread rates. Accurate measurement of the terminal velocity of seeds is therefore pivotal. However, compression during shipment through the post or during storage between collection in the field and terminal velocity measurements in the lab may affect these measurements. To evaluate the effects of shipment and storage on terminal velocity measurements, capitula of Carduus nutans, an invasive thistle species from Eurasia, were stored for 1–5 years and subjected to three different packing treatments. Seeds from capitula were then assessed for terminal velocity values, plume area, seed mass, wing loading, number of filaments per pappus, qualitative assessments of pappus damage, and number of intact dispersal units per capitulum. Compression significantly increased seed terminal velocity. However, storage duration for 1–5 years did not cause a significant increase or decrease in any of the response variables. The compression treatment was validated by shipment of seeds from New Zealand to the United States. When capitula that are to be used for terminal velocity measurements are stored or shipped, they should be packaged in incompressible containers to avoid damage to the fragile dispersal structures. Studies using capitula that were originally collected and stored for other purposes, such as transcontinental demographic studies, should rescale observed terminal velocity values to take into account possible damage.

Occurrence ofTrichosirocalus horridus(Coleoptera: Curculionidae) on NativeCirsium altissimumVersus ExoticC. vulgarein North American Tallgrass Prairie

Postrelease studies can provide data with which to evaluate expectations based on prerelease tests of biological control insects. In 2004, we observed Trichosirocalus horridus Panzer (Coleoptera: Curculionidae), the rosette weevil introduced into North America against Eurasian thistles, feeding on native tall thistle, Cirsium altissimum L. Spreng., in tallgrass prairie. In this study, we examined the rosette weevil's use of tall thistle, compared with its use of the co-occurring exotic bull thistle, C. vulgare (Savi) Tenore. For both thistle species, we quantified weevil frequency, abundance, and seasonal variation in incidence, using both timed observations at two sites over two growing seasons (2004, 2005) and dissections of thistle flowering shoots from 13 sites (2005). Based on prerelease information, we expected the Eurasian thistle to be the quantitatively preferred host plant for this Eurasian weevil. Instead, we found that both the frequency of infestation and the mean number of adult rosette weevils per plant were at least as high, and sometimes higher, on the native thistle as on the exotic thistle. Furthermore, adult weevil phenology coincided on the two host species. This study provides new quantitative evidence of nontarget feeding by another weevil released for thistle biological control; and it raises important questions for further research. We conclude that continued new releases, as well as augmentation of existing populations, of T. horridus should wait until more research is done on the impact of the nontarget occurrence now reported for this biological control insect.

Host races inChaetostomella cylindrica(Diptera: Tephritidae): genetic and behavioural evidence

The highly oligophagous tephritid Chaetostomella cylindrica infests the flower heads of six genera and ten species of thistles in Lebanon. It predominantly utilizes two hosts occurring in sympatry, Notobasis syriaca and Onopordum illyricum. Previous work showed that adult flies emerging from N. syriaca fit more closely the description of the species, particularly with respect to the colour and pattern on the mesonotum; furthermore, significant differences were observed between the aculeus shape and length. This study investigates the biology of the immatures and compares adults from the two host races behaviourally and genetically. Larvae of both races fed in a similar way, with each larva destroying 3-10 achenes; however, the oviposition behaviour of females differed. Females of the Onopordum-associated flies laid an average of three eggs per head, and deposited the eggs glued to each others in a cluster, while females of the Notobasis-associated flies deposited their eggs unattached, usually with one egg per head. Subtle differences were also observed in the post-mating behaviour of adult males. DNA sequencing of an amplified fragment of the mitochondrial NADH-dehydrogenase subunit 1 gene revealed 44 single nucleotide polymorphisms in 622 base pairs. A PCR-RFLP method was developed to distinguish the two host-associated populations. Together with previously published morphometric studies, our data show that C. cylindrica consists of distinct host races, which seem to be reproductively isolated as two separate genetic lineages were observed.

Predicting Potential Occurrence and Spread of Invasive Plant Species along the North Platte River, Nebraska

AbstractRiparian habitats are important components of an ecosystem; however, their hydrology combined with anthropogenic effects facilitates the establishment and spread of invasive plant species. We used a maximum-entropy predictive habitat model, MAXENT, to predict the distributions of five invasive plant species (Canada thistle, musk thistle, Russian olive, phragmites, and saltcedar) along the North Platte River in Nebraska. Projections for each species were highly accurate. Elevation and distance from river were most important variables for each species. Saltcedar and phragmites appear to have restricted distributions in the study area, whereas Russian olive and thistle species were broadly distributed. Results from this study hold promise for the development of proactive management approaches to identify and control areas of high abundance and prevent further spread of invasive plants along the North Platte River.