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1.
The Australian Weed Risk Assessment system (AWRA) is an effective pre-border weed-screening tool that has played an active role in preventing the introduction of alien weeds into Australia and has been utilized in several other countries worldwide. Here, we selected 131 species of naturalized exotic plants (including 76 species of given non-weeds and 55 species of given weeds) to evaluate the AWRA in China for the first time. The AWRA performed better for discriminating major weeds than non-weeds and minor weeds, as it correctly rejected 84% of major weeds and did not wrongly accept a major weed. Among non-weeds, 76% were correctly classified with the final outcome of “accept” and 7.9% were wrongly rejected by the AWRA. This system correctly rejected 56% of minor weeds but accepted only 2.8% of minor weeds. The remaining 23% of all alien plants tested were classified as “evaluate further” by the AWRA. The area under the ROC curve (AUC) was 0.944, suggesting that the AWRA would be highly efficient at discriminating alien plants in China. In addition, we compared the scores of seven attributes of the AWRA between prior plant categories and analyzed their correlation with weed status. The average score for each attribute differed significantly between the two prior categories (weed and non-weed), but the average scores of the attribute “undesirable traits” did not significantly differ between any two of the three categories (non-weeds, minor weeds, and major weeds). There was a significant positive correlation between the scores of each attribute of the AWRA and weed status. The correlation coefficient for “dispersal mechanisms” and weed status was the highest and that for “undesirable traits” was the lowest. We believe that the AWRA can serve as an important weed-screening tool for plant introduction management in China. 相似文献
2.
W. M. LONSDALE 《Austral ecology》1994,19(3):345-354
Abstract I surveyed the history of exotic pasture introductions in northern Australia to compare the rate of introduction of useful species with that of weeds. Between 1947 and 1985, 463 exotic grasses and legumes in at least 2033 accessions were intentionally introduced into the region, the grasses predominantly from Africa, and the legumes from Central and South America. Of these, only 21 (5%) came to be recommended as useful, while 60 (13%) became listed as weeds. Seventeen of the useful plants were in fact also weeds, leaving only 4 species (<1%) that were useful without causing weed problems. They were far outnumbered by the 43 species (9%) that were weeds but had no recorded use. Of the 60 weeds, 21 were weeds of cropping, 20 were weeds of conservation and 19 were weeds of both sectors. Thirteen were listed as major crop weeds. Growth rate, maximum height, seed size, and continent of origin were unrelated to weediness. Good predictors of weediness were whether a plant was useful, a good performer in trials, or persisted at a field site. In addition, grasses were more likely, and legumes less likely, to be weedy than expected. It is argued that a new form of assessment is required before an exotic plant species is released into the Australian environment as a pasture plant. This would recognize that a successful introduction is almost certain to become a weed in some situations, and would attempt to assess the net national benefit of the proposed introduction. 相似文献
3.
Using the Australian weed risk assessment (WRA) model as an example, we applied a combination of bootstrapping and Bayesian
techniques as a means for explicitly estimating the posterior probability of weediness as a function of an import risk assessment
model screening score. Our approach provides estimates of uncertainty around model predictions, after correcting for verification
bias arising from the original training dataset having a higher proportion of weed species than would be the norm, and incorporates
uncertainty in current knowledge of the prior (base-rate) probability of weediness. The results confirm the high sensitivity
of the posterior probability of weediness to the base-rate probability of weediness of plants proposed for importation, and
demonstrate how uncertainty in this base-rate probability manifests itself in uncertainty surrounding predicted probabilities
of weediness. This quantitative estimate of the weediness probability posed by taxa classified using the WRA model, including
estimates of uncertainty around this probability for a given WRA score, would enable bio-economic modelling to contribute
to the decision process, should this avenue be pursued. Regardless of whether or not this avenue is explored, the explicit
estimates of uncertainty around weed classifications will enable managers to make better informed decisions regarding risk.
When viewed in terms of likelihood of weed introduction, the current WRA model outcomes of ‘accept’, ‘further evaluate’, or
‘reject’, whilst not always accurate in terms of weed classification, appear consistent with a high expected cost of mistakenly
introducing a weed. The methods presented have wider application to the quantitative prediction of invasive species for situations
where the base-rate probability of invasiveness is subject to uncertainty, and the accuracy of the screening test imperfect 相似文献
4.
Using the Australian Weed Risk Assessment (WRA) model as an example, we applied a combination of bootstrapping and Bayesian
techniques as a means of explicitly estimating the posterior probability of weediness as a function of an import risk assessment
model screening score. Our approach provides estimates of uncertainty around model predictions, after correcting for verification
bias arising from the original training dataset having a higher proportion of weed species than would be the norm, and incorporates
uncertainty in current knowledge of the prior (base-rate) probability of weediness. The results confirm the high sensitivity
of the posterior probability of weediness to the base-rate probability of weediness of plants proposed for importation, and
demonstrate how uncertainty in this base-rate probability manifests itself in uncertainty surrounding predicted probabilities
of weediness. This quantitative estimate of the weediness probability posed by taxa classified using the WRA model, including
estimates of uncertainty around this probability for a given WRA score, would enable bio-economic modelling to contribute
to the decision process, should this avenue be pursued. Regardless of whether or not this avenue is explored, the explicit
estimates of uncertainty around weed classifications will enable managers to make better informed decisions regarding risk.
When viewed in terms of likelihood of weed introduction, the current WRA model outcomes of ‘accept’, ‘further evaluate’ or
‘reject’, whilst not always accurate in terms of weed classification, appear consistent with a high-expected cost of mistakenly
introducing a weed. The methods presented have wider application to the quantitative prediction of invasive species for situations
where the base-rate probability of invasiveness is subject to uncertainty, and the accuracy of the screening test imperfect. 相似文献
5.
Abstract Risk assessment systems for introduced species are being developed and applied globally, but methods for rigorously evaluating them are still in their infancy. We explore classification and regression tree models as an alternative to the current Australian Weed Risk Assessment system, and demonstrate how the performance of screening tests for unwanted alien species may be quantitatively compared using receiver operating characteristic (ROC) curve analysis. The optimal classification tree model for predicting weediness included just four out of a possible 44 attributes of introduced plants examined, namely: (i) intentional human dispersal of propagules; (ii) evidence of naturalization beyond native range; (iii) evidence of being a weed elsewhere; and (iv) a high level of domestication. Intentional human dispersal of propagules in combination with evidence of naturalization beyond a plants native range led to the strongest prediction of weediness. A high level of domestication in combination with no evidence of naturalization mitigated the likelihood of an introduced plant becoming a weed resulting from intentional human dispersal of propagules. Unlikely intentional human dispersal of propagules combined with no evidence of being a weed elsewhere led to the lowest predicted probability of weediness. The failure to include intrinsic plant attributes in the model suggests that either these attributes are not useful general predictors of weediness, or data and analysis were inadequate to elucidate the underlying relationship(s). This concurs with the historical pessimism that we will ever be able to accurately predict invasive plants. Given the apparent importance of propagule pressure (the number of individuals of an species released), future attempts at evaluating screening model performance for identifying unwanted plants need to account for propagule pressure when collating and/or analysing datasets. The classification tree had a cross‐validated sensitivity of 93.6% and specificity of 36.7%. Based on the area under the ROC curve, the performance of the classification tree in correctly classifying plants as weeds or non‐weeds was slightly inferior (Area under ROC curve = 0.83 ± 0.021 (±SE)) to that of the current risk assessment system in use (Area under ROC curve = 0.89 ± 0.018 (±SE)), although requires many fewer questions to be answered. 相似文献
6.
Not all weeds are created equal: A database approach uncovers differences in the sexual system of native and introduced weeds
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Megan L. Van Etten Jeffrey K. Conner Shu‐Mei Chang Regina S. Baucom 《Ecology and evolution》2017,7(8):2636-2642
Weedy species provide excellent opportunities to examine the process of successful colonization of novel environments. Despite the influence of the sexual system on a variety of processes from reproduction to genetic structure, how the sexual system of species influences weediness has received only limited consideration. We examined the hypothesis that weedy plants have an increased likelihood of being self‐compatible compared with nonweedy plants; this hypothesis is derived from Baker's law, which states that species that can reproduce uniparentally are more likely to successfully establish in a new habitat where mates are lacking. We combined a database of the weed (weedy/nonweedy) and introduction status (introduced/native) of plant species found in the USA with a database of plant sexual systems and determined whether native and introduced weeds varied in their sexual systems compared with native and introduced nonweeds. We found that introduced weeds are overrepresented by species with both male and female functions present within a single flower (hermaphrodites) whereas weeds native to the USA are overrepresented by species with male and female flowers present on a single plant (monoecious species). Overall, our results show that Baker's law is supported at the level of the sexual system, thus providing further evidence that uniparental reproduction is an important component of being either a native or introduced weed. 相似文献
7.
Anthony L. Koop Larry Fowler Leslie P. Newton Barney P. Caton 《Biological invasions》2012,14(2):273-294
The Australian weed risk assessment has been promoted as a simple and effective screening tool that can help prevent the entry
of weeds and invasive plants into new areas. On average, the Australian model identifies major-invaders more accurately than
it does non-invaders (90% vs. 70% accuracy). While this difference in performance emphasizes protection, the overall accuracy
of the model will be determined by its performance with non-invaders because the frequency of invasive species among new plant
introductions is relatively low. In this study, we develop a new weed risk assessment model for the entire United States that
increases non-invader accuracy. The new screening tool uses two elements of risk, establishment/spread potential and impact
potential, in a logistic regression model to evaluate the invasive/weedy potential of a species. We selected 204 non-invaders,
minor-invaders, and major-invaders to develop and validate the new model, and compare its performance to the Australian model
using the same set of species. Performing better than the Australian model, our new model accurately identified 94.1% of major-invaders
and 97.1% of non-invaders, without committing any false positives or false negatives. The new secondary screening tool we
developed reduced the number of species requiring secondary evaluation from 22 to 12%. We expect that the new weed risk assessment
model should significantly enhance the United State’s timeliness and accuracy in regulating potential weeds. 相似文献
8.
Consistent accuracy of the Australian weed risk assessment system across varied geographies 总被引:3,自引:1,他引:3
Doria R. Gordon Daphne A. Onderdonk Alison M. Fox Randall K. Stocker 《Diversity & distributions》2008,14(2):234-242
The ecological and economic advantages of preventing introduction of species likely to become invasive have increased interest in implementing effective screening tools. We compared the accuracy of the Australian Weed Risk Assessment (WRA) system with that across the six geographies in which it has been tested (New Zealand, Hawaii, Hawaii and Pacific Islands, Czech Republic, Bonin Islands and Florida). Inclusion in four of the tests of a secondary screening tool, developed to reduce the number of species requiring further evaluation, decreased the number of species with that outcome by over 60% on average. Averaging across all tests demonstrated that the WRA system accurately identified major invaders 90%, and non-invaders 70%, of the time. Examined differently, a species of unknown invasive potential is on average likely to be correctly accepted or rejected over 80% of the time for all of these geographies when minor invaders are categorized as invasive. Whereas increasing consistency in definitions and implementation would facilitate understanding of the general application of the WRA system, we believe that this tool functions similarly across islands and continents in tropical and temperate climates and has been sufficiently tested to be adopted as an initial screen for plant species proposed for introduction to a new geography. 相似文献
9.
Kwek Yan Chong Richard T. Corlett Darren C. J. Yeo Hugh T. W. Tan 《Biological invasions》2011,13(7):1571-1577
Worldwide spread and establishment of alien plant species continues to accelerate and damage ecological and agricultural systems.
Early warning and prevention of high-risk introductions is the most cost-effective approach to minimise losses while maximising
benefits, and the Australian Weed Risk Assessment (A-WRA) system has been the most well-developed and successful predictive
scheme. However, any system would be limited if the results or scores were confined to the locality of assessment. We compiled
A-WRA scores conducted in four tropical to sub-tropical regions and tested the accuracy of these scores for predicting naturalisations
for a separate well-documented, equatorial, exotic flora where weed risk assessments have never been conducted. Receiver Operating
Characteristic (ROC) curves reflect high accuracies of predictions, comparable to those in other studies. No significant differences
in accuracy were found between each regional subset and the compiled set of scores. Our results show that A-WRA scores assessed
at one locality can be used for others of similar climate, increasing the utility of every species’ assessment. A global database
of A-WRA scores would enable rapid local decision-making in border controls on imported plant species. A growing record of
species assessments would also facilitate monitoring evolutionary and ecological aspects of invasive species. 相似文献
10.
Risk assessment schemes have been developed to identify potential invasive species, prevent their spread and reduce their
damaging effects. One of the most promising tools for detecting plant invaders is the weed risk assessment (WRA) scheme developed
for Australia. Our study explores whether the Australian WRA can satisfactorily predict the invasion status of alien plants
in the Mediterranean Basin by screening 100 invasive and 97 casual species in Spain. Furthermore, we analysed whether the
factors taken into account in the WRA are linked to invasion likelihood (i.e., invasion status) or to impacts. The outcome
was that 94% of the invasive species were rejected, 50% of the casual species were rejected and 29% of them required further
evaluation. The accuracy for casuals is lower than in other studies that have tested non-invasive (i.e., casuals or non-escaped)
alien species. We postulate that low accuracy for casual species could result from: (1) an incorrect “a priori” expert classification
of the species status, (2) a high weight of the WRA scores given to potential impacts, and (3) casual species being prone
to becoming invasive when reaching a minimum residence time threshold. Therefore, the WRA could be working as a precaution
early-warning system to identify casual species with potential to become invasive. 相似文献
11.
Tomoko Nishida Naoko Yamashita Motoaki Asai Shunji Kurokawa Takashi Enomoto Paul C. Pheloung Richard H. Groves 《Biological invasions》2009,11(6):1319-1333
We evaluated the applicability of the Australian Weed Risk Assessment (AWRA) system in Japan. Native weeds (n = 117) and introduced plants (n = 142), whose weed status was classified by 20 plant experts, were assessed using a slightly modified version of the AWRA
system designed to fit Japanese conditions. A receiver operating characteristic (ROC) curve for the system, when classifying
two-thirds of the 259 taxa as weeds or non-weeds, was plotted and the area under the ROC curve was calculated. The area was
0.88 and significantly greater than 0.5. Thus, the validity of the system to classify plants was proven. The best cut-off
level for the WRA score using Youden’s index was 10. When taxa whose AWRA scores were greater than 10 were regarded as weeds,
the sensitivity and specificity were 0.88 and 0.78, respectively. These values were verified with the remaining one-third
of the taxa. From these findings, the modified AWRA system was considered to be effective for use in Japan. However, further
studies are required to set the best cut-off level in terms of maximising the benefits gained from using the system. A second
screening test associated with the cut-off level also needs to be developed. 相似文献
12.
In order to better understand the relationship between reserve design and the species represented by such designs, we examined
the effectiveness of the Western Australian reserve system for conserving angiosperm diversity, and examined the characteristics
of those species conserved. We overlayed species distribution data for 14 plant lineages with the distribution of the reserve
system (8.5% of the State’s area) and identified the species that remained unprotected. We found that, depending upon the
method employed, between 174 (5.7%) and 570 (18.7%) of species were not included within the reserve system. Two main unprotected
regions were identified, one of which was also a centre of high diversity. Geographical range sizes of unprotected species
were six times smaller than those species that were protected, while species richness of small-ranged endemic species coincided
with general patterns of species richness. At the level of Western Australia’s bioregions we found that conservation effectiveness
was most dependent on characteristics of the reserve system rather than characteristics (size and positioning) of species
ranges. At this scale, the most effective way to conserve more species in Western Australia would be to conserve more land,
while conservation would be most successful in a uniformly dispersed reserve system. Our results highlight the fact that reserve
systems may take on two design approaches based on scale––at continental scales, reserves should be clustered around the hotspots
of endemic species, while within regions, an evenly distributed reserve system will most adequately sample species. 相似文献
13.
Jane Barton 《BioControl》2012,57(2):289-305
Before an exotic pathogen can be released as a classical biological control agent the likely positive and negative outcomes
of that introduction must be predicted. Host range testing is used to assess potential damage to non-target plants. To-date
28 species of fungi have been released as classical biological control agents against weeds world-wide. These pathogens have
been reported infecting only six non-target plant species outdoors and all of these incidents were predicted. Many more non-target
plant species developed disease symptoms in glasshouse tests than in the field. Consequently, data from other sources are
needed to ensure potential agents are not prematurely rejected. Predictions of pathogen host range to date have been sufficiently
accurate to prevent unpleasant surprises. Exotic pathogens are a safe and useful tool for weed control, especially in natural
areas rich in valued non-target species. 相似文献
14.
T. A. A. Speek J. A. R. Davies L. A. P. Lotz W. H. van der Putten 《Biological invasions》2013,15(6):1319-1330
The Weed Risk Assessment (WRA) has become an effective tool in predicting invasiveness of exotic plant species. In studies testing the WRA, exotic plant species are usually divided into major weeds, minor weeds and non-weeds. However, these divisions are qualitative, as the categories are assigned by experts. Many studies searching for plant traits that are indicative of plant invasiveness use quantitative estimates to measure invasiveness. We compared how quantitative and qualitative estimates of invasiveness may relate to WRA scores. As quantitative estimates we used regional frequency (spread), change in regional frequency and local dominance of naturalized exotic plant species in The Netherlands. To obtain a qualitative estimate we determined if the exotic plant species occurred on a black list in neighbouring regions. We related WRA scores of the exotic plant species to these qualitative and quantitative estimates of invasiveness. Our results reveal that the WRA predicted the qualitative (black list) estimate more accurately than the quantitative (dominance and spread) ones. The black list estimate matches with the overall impact of exotic species, which is assumed to incorporate regional spread, local dominance and noxiousness. Therefore, the WRA predicts the noxiousness component, but to a lesser extent the spatial components of impact of exotic species. On the other hand, studies that use regional spread and other quantitative estimates of invasiveness tend not to include the noxiousness component of impact. We propose that our analyses may also help to further solve the recent debate on whether or not performing research on exotic species. 相似文献
15.
Reproductive traits are tightly linked to plant fitness and may therefore be mechanisms driving biological invasions, including
the greater success of more phylogenetically novel introduced species in some systems. We present a phylogenetic comparative
analysis of “Baker’s law’’, that introduced plants with the ability to reproduce autogamous or asexually may be better able
to establish on introduction. We gathered data from both published and unpublished sources on pollen limitation of 141 species,
including 26 introduced species and 115 native species. Our analysis compared differences in the proportion of autonomous
autogamy, asexual reproduction, and pollen limitation among native, introduced noninvasive, and introduced invasive plant
species, and included the phylogenetic novelty of the introduced species to the native species in that community. Introduced
species were more likely to be autogamous than native species, consistent with Baker’s law. On the other hand, introduced
species were less likely to have the ability to reproduce asexually. Further, among species with no autonomous autogamy, pollen
limitation was greater for introduced compared to native species. Such a result is consistent with the idea that plants entering
a new continent receive lower quality or quantity of services from resident pollinators than species native to that continent.
Finally, more phylogenetically novel invasive species had lower pollen limitation than less novel invasive species, potentially
because they experience less competition for pollinators. This is the first evidence that enhanced pollination may be one
mechanism driving the greater invasiveness of phylogenetically novel introduced species observed in some systems. 相似文献
16.
Atsuko Miyagi Hideyuki Takahashi Kentaro Takahara Takayuki Hirabayashi Yoshiki Nishimura Takafumi Tezuka Maki Kawai-Yamada Hirofumi Uchimiya 《Metabolomics : Official journal of the Metabolomic Society》2010,6(1):146-155
Comprehensive analysis of metabolites using capillary electrophoresis–mass spectrometry was carried out in harmful weeds belonging
to Polygonaceae. A principal component analysis revealed clear distinctions among eight Rumex species and Fallopia japonica. Hierarchical clustering data showed that respective metabolites can be grouped due to species differences. There was a positive
relationship between oxalate and citrate, oxalate and ascorbate, and oxalate and glutamine. The amount of oxalate per leaf
fresh weight was not affected by increased concentrations of exogenously supplied nutrients from Hoagland’s formulation in
one of the most destructive weeds R. obtusifolius. The oxalate accumulation in this plant is independent of external nutrient level, where nutrient-rich environments apparently
stimulate internal constituents such as amino acids and other metabolites. 相似文献
17.
Rapid evolutionary divergence and ecotypic diversification of germination behavior in weedy rice populations 总被引:1,自引:0,他引:1
Feral plants have evolved from well-studied crops, providing good systems for elucidation of how weediness evolves. As yet, they have been largely neglected for this purpose. The evolution of weediness can occur by simple back mutations in domestication genes (domestication in reverse). Whether the evolutionary steps to weediness always occur in reverse remains largely unknown. We examined seed germination behavior in recently evolved weedy rice (Oryza sativa f. spontanea) populations and their coexisting cultivars in eastern and north-eastern China to address whether 'dedomestication' is the simple reverse of domestication. We found that these weedy populations did not diverge from their progenitors by reverting to the pre-domestication trait of seed dormancy. Instead, they have evolved a novel mechanism to avoid growing in inappropriate environments via changes in critical temperature cues for seed germination. Furthermore, we found evidence for subsequent ecotypic divergence of these populations such that the critical temperature for germination correlates with the local habitat temperature at latitudinal gradients. The origins of problematic plant species, weeds and invasives, have already been studied in detail. These plants can thus be used as systems for studying rapid evolution. To determine whether and how that evolution is adaptive, experiments such as those described here can be performed. 相似文献
18.
Invasion by alien plants results in serious adverse impacts on biodiversity, ecosystem services, economy and social welfare, and is an ever-increasing challenge for nature conservation. Control of established invasive species is frequently very difficult and costly. Therefore, predicting which species have risk of becoming invasive is crucial both to prevent introduction of new invaders and to target high risk species already present in order to avoid their spread, particularly to areas with high conservation value. In Portugal more than 600 alien plant species are present as casuals or naturalized, and decision support tools are needed to discriminate which of these have higher probability of becoming invasive. We aimed to assess the effectiveness of the Australian Weed Risk Assessment, adapted to the Portuguese conditions (P-WRA), by evaluating 172 plant species: 49 considered as invasive; and, 123 as non-invasive species. The results showed that the P-WRA correctly identified all invasive species. As for non-invasive species, 17% were accepted, 78% rejected and 5% required further evaluation. Receiver Operating Characteristic (ROC) curve reflected high accuracy of predictions despite lower than that found in other regions. The best cutoff level for P-WRA score, maximizing the ability for classification of the protocol, was 13 resulting in more non-invasive species accepted (46%). In the end, this assessment informed that in addition to the 49 species already invasive, a high number (66) of alien plant species have invasive risk. Amongst these, a list of 20 species is proposed for targeted priority management aiming to prevent their spread. Comparison of the scores obtained with A-WRA for other regions with Mediterranean climate revealed that 17% of the species compared (78) reached different outcomes, signaling the need to be careful when extrapolating the use of previous scores. The P-WRA can be a promising screening system post-border for predicting invasive species already present in Portugal and contribute to the targeting of species for priority intervention, particularly in natural areas with high conservation value. 相似文献
19.
The contributions of mycorrhizal fungi to the determination of plant community structure 总被引:10,自引:3,他引:7
While it is now widely accepted, even by ecologists, that most plants in the majority of ecosystems are infected by mycorrhizal
fungi, few experiments have been designed to investigate the function of the mutualism at the community level. Those involved
with mycorrhizal research have been largely preoccupied with questions of the mineral, particularly phosphorus, nutrition
of individual plants, while plant community ecologists have too often found it convenient, even when acknowledging the presence
of infection, to ignore its possible function in the ecosystem.
This presentation examines a selected number of seminal papers written by plant community ecologists and highlights some of
‘the most striking mysteries’ which they reveal. It describes experiments designed to determine whether knowledge of the presence
and activity of the mycorrhizal mycelium can help us to unravel the ‘mysteries’ which they define.
It is revealed that by having direct adverse effects upon seedlings of many ‘r’ selected species, while at the same time being
beneficial, if not essential, to those that are ‘K’ selected, the activities of the mycelium of VA fungi have a direct bearing
upon community composition. The extent to which ‘turf compatibility’ is actually a reflection of the compatibility of plant
species with the VA mycorrhizal mycelium is discussed and the possible role of the mycelium in consigning some species to
the ruderal habit is considered.
It is concluded that those attempting scientifically to understand, or managerially to manipulate, plant communities, without
recognizing the role of the mycorrhizal mycelium, do so at their peril, and it is recommended that scientists involved in
research on mycorrhiza extend their vision beyond the limited horizons which are currently so often defined by considerations
of the phosphorus nutrition of individual host plants. 相似文献
20.
Predictable risk to native plants in weed biological control 总被引:6,自引:0,他引:6
Robert W. Pemberton 《Oecologia》2000,125(4):489-494
Data on field host use of 112 insects, 3 fungi, 1 mite, and 1 nematode established for biological control of weeds in Hawaii, the continental United States, and the Caribbean indicate that the risk to native flora can be judged reliably before introduction. Virtually all risk is borne by native plant species that are closely related to target weeds. Fifteen species of insects introduced for biological control use 41 native plant species; 36 of which are congeneric with target weeds, while 4 others belong to two closely allied genera. Only 1 of 117 established biological organisms uses a native plant unrelated to the target weed. Thus the elements of protection for the native flora are the selection of weed targets that have few or no native congeners and the introduction of biological control organisms with suitably narrow diets. 相似文献