Article

When to Ignore Advice: Invasion Predictions and Decision Theory

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Abstract

Organisms generally become pests at a low rate. As a consequence of this low base-rate probability, the large majority of organisms rejected in any random sample of potential introductions would probably be harmless, despite the fairly high accuracy of some recently proposed risk assessment systems for exotic introductions. Here we distinguish between a system's accuracy (the proportion of a group of known pest species that would be correctly identified as pests) and reliability (the rate of false positives and false negatives produced once the base-rate is taken into account). We next adapt a decision theory analysis of earthquake prediction to explore when we would be best advised to ignore the recommendations of a screening system for exotic introductions. In one scenario, we show that a pest risk assessment system with an accuracy of 85% would be better ignored, unless the damage caused by introducing a pest is eight times or more that caused by not introducing a harmless organism that is potentially useful. Furthermore, because of the base-rate effect, in certain situations it may be more efficient to focus on identifying potential invaders from amongst already naturalized species than from amongst species at the importation stage.

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... Species are then run through the WRA, omitting any data on the impacts of the species in the location of interest, to determine whether the WRA scores correctly predict that noninvaders are unlikely to invade ('accept' outcome), and that invaders are likely to invade ('reject' outcome). Accuracy is generally evaluated as the number of correct acceptances of non-invaders and correct rejections of invaders (Smith et al. 1999). ...
... This breakdown, however, does not refl ect the actual relative occurrence of invaders and non-invaders, where an estimated 0.1 to 1% of non-native species introduced become invasive ( Williamson and Fitter 1996, Groves et al. 2003, Mack 2005. If test species are selected to accurately represent the base-rate (sensu Smith et al. 1999) of invasive and non-invasive species, then families and life forms cannot be balanced. The Florida (Gordon et al. 2008b), Hawaii (Daehler and Carino 2000), and Bonin Islands (Kato et al. 2006) tests included roughly the same number of species in each a priori category, while Australia (Pheloung et al. 1999) and Japan (Nishida et al. 2009) used more invaders than non-invaders. ...
... The Czech Republic (Křivánek and Pyšek 2006) and the Hawaii and other Pacifi c Islands (Daehler et al. 2004) tests used a greater proportion of non-invaders than invaders, refl ecting the pattern (but not magnitude) of the natural base-rate. Since base-rate affects the reliability of predictions (Smith et al. 1999), or the proportion of accept or reject decisions that are correct, base-rate should be taken into consideration when comparing tests (Gordon et al. 2008a). ...
Article
Our test of the Australian Weed Risk Assessment system (WRA) in Florida and comparison of these results with those from tests of the system in other geographies reveal a number of areas where methodological variation may infl uence results. We demonstrate differences among the tests, such as variability in the base rate of test species and in the evidence required to answer WRA questions. We use the Florida dataset to explore the effects of elements of this variation on accuracy of the WRA and make recommendations to increase consistency in future WRA application and reporting. While we fi nd that the overall accuracy is relatively insensitive to the variation tested, the probability of accurate prediction and comparability of results from different geographies would increase if the system were more consistently and transparently applied.
... Following Smith et al. (1999), three measures of accuracy were defined, namely (i) for a priori invasive taxa, (ii) for a priori non-invasive taxa, and (iii) overall: ...
... causing some of them to fall below threshold) was also present in the WRA applications reviewed by Gordon et al. (2008), where only standard errors were reported. Overall, the low-to-very-low proportion of false positives and absence of false negatives across the FISK v1 and v2 applications, but also globally (Appendix Table A5 in Supplementary Material), is an indicator of the accuracy of this DS tool (Kumschick and Richardson 2013), as also measured explicitly by the corresponding A i , A n and A o values, which were in all cases close to or above 80% (Smith et al. 1999). ...
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Article
The freshwater Fish Invasiveness Screening Kit (FISK) has been applied in 35 risk assessment areas in 45 countries across the six inhabited continents (11 applications using FISK v1; 25 using FISK v2). The present study aimed: to assess the breadth of FISK applications and the confidence (certainty) levels associated with the decision-support tool’s 49 questions and its ability to distinguish between taxa of low-to-medium and high risk of becoming invasive, and thus provide climate-specific, generalised, calibrated thresholds for risk level categorisation; and to identify the most potentially invasive freshwater fish species on a global level. The 1973 risk assessments were carried out by 70+ experts on 372 taxa (47 of the 51 species listed as invasive in the Global Invasive Species Database www.iucngisd.org/gisd/), which in decreasing order of importance belonged to the taxonomic Orders Cypriniformes, Perciformes, Siluriformes, Characiformes, Salmoniformes, Cyprinodontiformes, with the remaining ≈8% of taxa distributed across an additional 13 orders. The most widely-screened species (in decreasing importance) were: grass carp Ctenopharyngodon idella, common carp Cyprinus carpio, rainbow trout Oncorhynchus mykiss, silver carp Hypophthalmichthys molitrix and topmouth gudgeon Pseudorasbora parva. Nine ‘globally’ high risk species were identified: common carp, black bullhead Ameiurus melas, round goby Neogobius melanostomus, Chinese (Amur) sleeper Perccottus glenii, brown bullhead Ameiurus nebulosus, eastern mosquitofish Gambusia holbrooki, largemouth (black) bass Micropterus salmoides, pumpkinseed Lepomis gibbosus and pikeperch Sander lucioperca. The relevance of this global review to policy, legislation, and risk assessment and management procedures is discussed.
... L'évaluation des risques liés aux végétaux (Weed Risk Assessment, WRA ; voir Sheppard et al., ce volume ;Smith et al., 1999) est normalement utilisée lors des contrôles aux frontières pour décider si une nouvelle espèce, dont l'introduction est proposée, est susceptible de devenir une future espèce envahissante et pour décider si elle doit ou non être importée. Cependant, l'évaluation des risques liés aux végétaux est également utilisée maintenant au-delà des frontières. ...
... Un système de notation ou de classement pour les évaluations internes des risques liés aux végétaux doit intégrer tous les principes d'un système d'évaluation de quarantaine (Smith et al., 1999), autres que l'exigence de satisfaction aux obligations internationales (sauf si elles sont susceptibles d'avoir un impact sur le commerce international). Un tel système doit être conçu de manière à proposer une échelle, ou toute autre forme de classification. ...
... Because some previous studies suggested that nonindigenous species spread and cause harm (i.e. become invasive) at a low base-rate, some authors have argued that attempts to predict the identity of invaders are unlikely to be sufficiently accurate to be worthwhile (Smith et al. 1999;Williamson 1999). ...
... Third, our model has shown that the value of protection based on predictions declines as the rate of invasion declines (from scenario 1 to scenario 4; Figure 5.2). This is an example of the base-rate effect (Matthews 1997;Smith et al. 1999) and occurs because the proportion of false positive predictions increases as the proportion of invaded lakes declines. For the present case, false positives are lakes that are protected although they are not at risk. ...
... Other questions relate to characteristics thought to enhance potential spread such as wind dispersal of seeds. Multiple tests of the AWRA tool [48][49][50][51] show that it generally has a high accuracy (>90%) in properly classifying current weeds or invasives. The tool poses a risk of circular reasoning, however, as existing botanical information sources for the questionnaire often describe species as weeds, pests, or invasives and, coupled with the knowledge of qualified botanists, invasion risks are likely to be characterized with good accuracy without the tool [51]. ...
... Thus, some species are falsely identified as invasive and excluded from introduction even when they may not cause economic or ecological damage. Smith et al. [49] conclude that a species should only be excluded if its potential control or damage costs exceed eight times the benefit of introducing it. ...
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Article
Short rotation woody crops (SRWC), fast growing tree species that are harvested on short, repeated intervals, can augment traditional fiber sources. These crops have economic and environmental benefits stemming from their capability of supplying fiber on a reduced land base in close proximity to users and when sensitive sites cannot be accessed. Eucalyptus and Populus appear to be genera with the greatest potential to provide supplemental fiber in the U. S. Optimal productivity can be achieved through practices that overcome site limitations and by choosing the most appropriate sites, species, and clones. Some Eucalyptus species are potentially invasive, yet field studies across multiple continents suggest they are slower to disperse than predicted by risk assessments. Some studies have found lower plant and animal diversity in SRWC systems compared to mature, native forests, but greater than some alterative land uses and strongly influenced by stand management, land use history, and landscape context. Eucalyptus established in place of grasslands, arable lands, and, in some cases, native forests can reduce streamflow and lower water tables due to higher interception and transpiration rates but results vary widely, are scale dependent, and are most evident in drier regions.
... It may be that these estimates of accuracy are overly optimistic. Evaluations of screening systems have included biased sampling, the problem of dropouts, failure to carry out blind evaluation, and a failure to take account of the base rate effect (Lonsdale and Smith, in press;Smith et al., 1999). It is important that we improve weed risk analysis theory because, for example, the WRA may be used for GMO's, or for sleeper weeds, and so the consequences of over-optimism about screening methods may be disastrous. ...
Chapter
This publication consists of 22 papers which cover 18 different subject areas representing the most up-to-date description of the state of the art in the global rangeland situation.
... Following Smith et al. (1999), three measures of accuracy were defined: 1) for a priori invasive species: A i = (I r /I t ) × 100, where I r is the number of a priori invasive species rejected, and I t the total number of a priori invasive species screened; ...
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Article
The threat posed by invasive non-native species worldwide requires a global approach to identify which introduced species are likely to pose an elevated risk of impact to native species and ecosystems. To inform policy, stakeholders and management decisions on global threats to aquatic ecosystems, 195 assessors representing 120 risk assessment areas across all six inhabited continents screened 819 non-native species from 15 groups of aquatic organisms (freshwater, brackish, marine plants and animals) using the Aquatic Species Invasiveness Screening Kit. This multi-lingual decision-support tool for risk screening of aquatic organisms provides assessors with risk scores for a species under current and future climate change conditions that, following a statistically based calibration, permits the accurate classification of species into high-, medium- and low-risk categories under current and predicted climate conditions. The 1,730 screenings undertaken encompassed wide geographical areas (regions, political entities, parts thereof, water bodies, river basins, lake drainage basins, and marine regions), which permitted thresholds to be identified for almost all aquatic organismal groups screened as well as for tropical, temperate, and continental climate classes and for tropical and temperate marine ecoregions. In total, 33 species were identified as posing a ‘very high risk’ of being or becoming invasive in the study areas, and the scores of several of these species under current climate increased under future climate conditions, primarily due to their wide thermal tolerances. The risk thresholds determined for taxonomic groups and climate zones provide a basis against which area-specific or climate-based calibrated thresholds may be interpreted. In turn, the risk rankings help decision-makers identify which species require an immediate ‘rapid’ management action (e.g. eradication, control) to avoid or mitigate adverse impacts, which require a full risk assessment, and which are to be restricted or banned with regard to importation and/or sale as ornamental or aquarium/fishery enhancement.
... The introduction of species through ballast water (Vitousek, D'Antonio, Loope, Rejmánek, & Westbrooks, 1997) and through contaminated seeds or soil (Weber, 2003) are examples of this. In general, those species that are deliberately introduced are believed to be the most likely to establish in a new area, as they are usually selected for their tolerance of the new conditions (Smith, Lonsdale, & Fortune, 1999). ...
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Thesis
Crassula helmsii (Kirk) Cockayne is a non-native invasive plant species that occupies marginal areas of still water bodies in the UK. C. helmsii is known to be highly invasive, which makes management of this species problematic. C. helmsii can form dense stands of vegetation, which is thought to out-compete native plant species in habitats that it enters, however, evidence for this to date has remained largely anecdotal and based on untested observations. Additionally, C. helmsii has been implicated in the reduction of breeding success of urodele amphibians in UK ponds through reducing abundance of plants used for oviposition, which also remains untested. The aims of this study were to measure effects of C. helmsii, and its management, on plants occupying pond margins in the UK, particularly in the North West of England. This study also aimed to assess likely threats posed to native newt species by C. helmsii. Perceptions of the impacts of C. helmsii were compared against field-based measurements of impact. Perceptions of C. helmsii were largely negative, however, when historical pond species data were compared to recent survey findings, species richness and composition was not affected by C. helmsii presence. Species richness increased in ponds containing C. helmsii and decreased in ponds not containing C. helmsii, although other factors were believed to be driving these changes. An experimental approach was adopted to test for direct effects of C. helmsii on marginal plants used by newts for oviposition. The germination of six out of eleven species tested was significantly reduced by a covering of C. helmsii, however, adult plants of Mentha aquatica and Apium nodiflorum were apparently unaffected by C. helmsii as a neighbour. Additionally, soil seeds banks collected from six sites occupied by C. helmsii were not significantly impacted by its presence. In order to evaluate effectiveness of currently recommended control treatments, and assess their impact on non-target plant species, a 15-month experiment was conducted, involving two periods of treatment and monthly monitoring. Treatments were applied singly and in combination with one another. Clear differences in both effectiveness of C. helmsii removal and recovery of non-target vegetation existed between treatment regimes. Shading material was not effective and prevented rapid recovery of non-target plants, while herbicide, although effective, also prevented rapid re-growth of non-target vegetation. The use of turf removal proved to be both effective and allowed rapid restoration of the plant community. Finally, the effect of C. helmsii as an oviposition substrate for two newt species, Triturus vulgaris and Triturus cristatus, was evaluated. Developmental stage at hatching and post hatching developmental rate was determined when eggs where laid on C. helmsii and Rorippa nasturtium-aquaticum, a ‘preferred’ substrate. Larvae of T. vulgaris hatched at a significantly later developmental stage when laid on C. helmsii, whereas T. cristatus larvae hatched at the same developmental stage from both substrates. Post-hatching developmental rate was not affected by oviposition substrate in either newt species. This research has provided important information regarding the effects of C. helmsii on marginal plant assemblages, and has provided valuable data that can be used to more effectively manage C. helmsii in the North West of England. This will be particularly valuable for land managers attempting to protect or restore habitats important for newt breeding.
... However, the vast majority of naturalised species are benign with little recognisable impacts. Predicting and distinguishing potential invasive threats for species that have not yet arrived, or just have become established, has occupied scientists and policy makers for decades (Williamson and Fitter, 1996;Lonsdale, 1999;Smith et al., 1999;Sakai et al., 2001;Keller et al., 2007;Hayes and Barry, 2008;Elliott-Graves, 2016;Hulme and Bernard-Verdier, 2018;Divıśek et al., 2019;Fourniera et al., 2019;Muthukrishnan et al., 2019). Understanding each species' demography is at the core of separating major invasive plants that show rapid local population increase, establishment of local dominance or range expansions (Gurevitch et al., 2011) from those that become established but remain minor members of local plant communities. ...
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Article
While biological invasions have the potential for large negative impacts on local communities and ecological interactions, increasing evidence suggests that species once considered major problems can decline over time. Declines often appear driven by natural enemies, diseases or evolutionary adaptations that selectively reduce populations of naturalised species and their impacts. Using permanent long‐term monitoring locations, we document declines of Alliaria petiolata (garlic mustard) in eastern North America with distinct local and regional dynamics as a function of patch residence time. Projected site‐specific population growth rates initially indicated expanding populations, but projected population growth rates significantly decreased over time and at the majority of sites fell below 1, indicating declining populations. Negative soil feedback provides a potential mechanism for the reported disappearance of ecological dominance of A. petiolata in eastern North America.
... However, risk analysis methods are still being developed for IAS, and the inherent complexity may preclude accurate results (Lodge et al. 2016). The fact that such a small percentage of introduced species actually become invasive (Williamson 1996) is also a major limitation for prediction (Smith et al. 1999). ...
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Article
The precautionary nature of risk regulation in the European Union (EU) and the United States (US) is an ongoing debate. Theoretical contentions over ‘who is more precautionary’ confirm that the degree of relative precaution may lead to different levels of protection, but also suggest that precaution needs to be evaluated against different parts of the regulatory process. This paper addresses a new case of transatlantic split which has occurred with the adoption of the EU regulation on alien invasive species. This regulation aims to drive important changes at the trade–environment nexus and reflects Europe’s integrated policy approach to environmental, health, and safety risks. We have carried out a comparative analysis by examining parts of the regulatory process. We argue that differences in legal and policy frameworks, risk assessment, and risk management structures have left the EU and the US wide apart as to their risk governance ambitions. The EU exhibits more precautionary approach with regard to these parts, as compared to the US. Our finding suggests that policy divergence, as reflected in this case, is true for both stringency and regulatory process, expanding literature discussions on precaution in these systems. Yet, with the EU’s regulation being relatively new, there are still implementation issues up for debate.
... The effect of invasive Nypa palm is easily seen on the native mangrove macrophytes species as soon as it is established and spread along sheltered creeks (Smith et al., 1999). It is possible that thick Nypa establishment disturbs fish breeding in the Niger Delta thereby resulting to the subsequent decline of fish fauna throughout the area (Sunderland and Morakinyo, 2002;Choosak et al., 2015). ...
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Article
The invasion of mangroves forest by nypa palm is said to affect the ability of the mangroves to act as a spawning ground for fishes. It is thus hypothesized that nypa palm presence in mangrove forest will impact their fish spawning ability due to the reduction in plankton population. A total of four stations were chosen: station 1 (open water), Station 2 (nypa palm dominant), station 3 (Rhizophora and Avicennia dominant), Station 4 (Mixed forest). Results of water quality parameters include; pH (6.99 ± 0.16), temperature (28.20°C ± 0.05°C), DO (4.71 ± 0.18 mg/L), conductivity (19.52 ± 0.20 μm/s), salinity (10.76 ± 0.07 ppt) and TDS (13.45 ± 0.27 ppt). Mean values of the physico-chemical parameters were not significantly different from each other (P > 0.05). In all 737 zooplankton in eleven genera were collected. Copepoda dominated with 75.1%. Similarly, 4774 phytoplankton in six taxa were collected. Bacilliarophyceae dominated with 87.45%. Shannon Weiner index across the stations was highest in station 4 (0.36) and lowest in station 1 (0.33). Margalef’s index was highest in stations 2, 3, and 4 (3.48) and lowest in station 1 (2.67). Pielou’s index of evenness was highest in station 4 (0.099) and lowest in station 1 (0.089). The composition and abundance of plankton showed no significant difference across the four stations (P > 0.05). This implies that the presence of Nypa fruticans (Wurmb) did not have negative impact on the abundance and diversity of plankton.
... Our screening approach provides exactly such a probabilistic assessment of species invasiveness (table 1), and thus has the potential for being widely adopted. It is noteworthy that each country can select its own 'banning threshold' for compiling a black list according to transparent decisions relating to the cost-benefit balance in misclassification (i.e. the ratio of the costs of banning a species that is harmless and potentially useful, and the cost of introducing a future invader [48]). ...
Article
Biological invasions are on the rise globally. To reduce future invasions, it is imperative to determine the naturalization potential of species. Until now, screening approaches have relied largely on species-specific functional feature data. Such information is, however, time-consuming and expensive to collect, thwarting the screening of large numbers of potential invaders. We propose to resolve such data limitations by developing indicators of establishment success of alien species that can be readily derived from open-access databases. These indicators describe key features of successfully established aliens, including estimates of potential range size, niche overlap with human-disturbed environments, and proxies of species traits related to their palaeoinvasions and local dominance capacities. We demonstrate the utility of this new approach by applying it to two large and highly invasive plant groups: Australian acacias and eucalypts. Our results show that these indicators robustly predict establishment successes and failures in each clade independently, and that they can cross-predict establishment in these two clades. Interestingly, the indicator identified as most important was species potential range size on Earth, a variable too rarely considered as a predictor. By successfully identifying key features that predispose Australian plants to naturalize, we provide an objective and cost-effective protocol for flagging high-risk introductions.
... which are known to have strongly negative impacts and little or no commercial value, this seems eminently sensible. However, care should be taken to not adopt too conservative an approach for all taxa, as inappropriate rejection of species with considerable commercial value, due to overestimation of invasion risks, could have net negative effects (see Smith et al., 1999). As an example of the difficulty that can be faced when trying to a priori differentiate potentially invasive species, from those that are benign, Pseudorasbora elongata, as a close relative of P. parva (Yang et al., 2006), is similar in both biology and ecology, however is in decline in its native range and despite being associated with ornamental fish trade, is not recorded to be invasive (Chen, 2011). ...
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Thesis
In this thesis I set out to quantify the risk of invasion from the invasive freshwater fish, Pseudorasbora parva, at a global extent, using traditional correlative ecological niche modelling approaches with the integration of surrogate data representing introduction likelihood (Chapter I). These correlative approaches rely upon key assumptions relating to the presence or absence of local or regional adaptations, and so I subsequently tested for evidence of such adaptations in genetic lineages and in individual populations. This was achieved through analyzing climatic niche differentiation of key genetic lineages in the native and invasive ranges (Chapter II) and by conducting lab experiments comparing thermal responses of important life history traits in populations from contrasting climates (Chapter III). The initial risk assessment did not account for a key factor in invasions; namely, natural dispersal. Natural dispersal has been observed to be subject to selection in vanguard populations of invasive species, and adaptation of dispersal traits can infer additional invasive vigor, allowing the species to spread across the landscape quicker. For this reason, I quantified dispersal, activity and morphological differences, often associated with differential dispersal ability, in populations along a distance-gradient from an invasion front, in order to identify if P. parva is capable of such adaptations.The initial risk mapping study showed that large areas, beyond the current distribution of the species, are climatically suitable. These areas are mainly in North and South America, Australia and New Zealand, and constitute significant scope for spread and impact of this species. When introduction likelihood was included, N. America appears most at risk. I found no evidence to suggest that native genetic lineages represented local adaptations to their respective native climates - there was little or no differentiation of the lineages’ climatic niches in the invasive range. It was also apparent, from the niche comparisons, that the climatic niche in the invaded range constituted a significant shift, compared to the native range. The thermal responses of P. parva life history traits did not differ significantly between populations from a strongly seasonal continental climate and a mild temperate maritime climate. The overall reproductive output of females did not vary according to breeding season temperature, however, temporal reproductive strategy showed a strong response, with lower temperatures inducing a protracted breeding season and higher temperatures inducing rapid and intense reproductive output. The dispersal and morphology-related study identified a strong gradient of morphological change, corresponding with distance from invasion front. This demonstrates a high degree of plasticity in P. parva’s morphology in an invasion context, however this was not linked to either dispersal or activity levels, neither of which was significantly linked to distance from invasion front. Dispersal was best explained by body size, with larger fish more likely to disperse further.Whilst I found no evidence to suggest that the model predictions (Chapter I) were hampered by differentiation at either lineage or population levels, the findings of Chapter II do highlight the uncertainties surrounding the degree of conservatism in such predictions, mainly owing to the fact that past, native, distribution did not accurately predict the current invaded distribution. The results of Chapters II-IV show broad tolerances and great plasticity in P. parva, which likely underpin this species success as a pan-continental invader. The knowledge produced in this thesis provides a useful new resource for the development of management strategies for P. parva and could be usefully enhanced by the additional of analogous studies on native populations, which could help elucidate the source of the observed plasticity.
... parasites or pathogens (Kennedy 1975). Further, naturalisation of marine and freshwater invaders may be irreversible or unpredictable (ICES 2005) and it is arguable whether any intentional introductions are acceptable (Smith et al. 1999). ...
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Article
In this paper, the current state of non-indigenous fish species in the Greater Prespa Lake (Albanian side) is clarified. As in other big lakes on the Balkans, e.g. the Ohrid and Scadar Lakes, the Greater Prespa Lake is facing changes concerning fish biodiversity, including an increased presence of non-indigenous species. Following that, the native fish populations (well-known globally for their endemic and relict species) are seriously threatened by anthropogenic impacts. Although the Prespa Lakes region has been recognised as an European and global biodiversity hot spot because of the number of species and habitats, alien fish species are common inhabitants. The most abundant non-indigenous species are Pseudorasbora parva and Rhodeus amarus. Carassius gibelio, Lepomis gibbosus, Cyprinus carpio and Tinca tinca are represented with lower relative abundance. Six other aliens (recorded by previous studies), are not registered by the present study. The average relative non-indigenous species abundance was lower and their average relative biomass per m2 higher than the respective parameters of the indigenous species. Clear connection between their abundance and biomass could not be derived from the available data.
... parasites or pathogens (Kennedy 1975). Further, naturalisation of marine and freshwater invaders may be irreversible or unpredictable (ICES 2005) and it is arguable whether any intentional introductions are acceptable (Smith et al. 1999). ...
Full-text available
Article
In this paper, the current state of non-indigenous fish species in the Greater Prespa Lake (Albanian side) is clarified. As in other big lakes on the Balkans, e.g. the Ohrid and Scadar Lakes, the Greater Prespa Lake is facing changes concerning fish biodiversity, including an increased presence of non-indigenous species. Following that, the native fish populations (well-known globally for their endemic and relict species) are seriously threatened by anthropogenic impacts. Although the Prespa Lakes region has been recognised as an European and global biodiversity hot spot because of the number of species and habitats, alien fish species are common inhabitants. The most abundant non-indigenous species are Pseudorasbora parva and Rhodeus amarus. Carassius gibelio, Lepomis gibbosus, Cyprinus carpio and Tinca tinca are represented with lower relative abundance. Six other aliens (recorded by previous studies), are not registered by the present study. The average relative non-indigenous species abundance was lower and their average relative biomass per m2 higher than the respective parameters of the indigenous species. Clear connection between their abundance and biomass could not be derived from the available data.
... Ricciardi (2003) destaca que es posible la comparación de los resultados posteriores a la introducción de una especie en diferentes ecosistemas para determinar si los efectos son consistentes y predecibles en diferentes ambientes. Smith et al. (1999) señalan que el 10% de las EEI puede convertirse en plaga después de su establecimiento. Contrario a lo anterior, Bomford (2003), al realizar la evaluación del riesgo de importación y conservación de vertebrados exóticos en Australia, concluye que más del 50% de los vertebrados exóticos representan una plaga potencial. ...
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Article
The first record of tricolored munia (Lonchura malacca) is presented in the state of Oaxaca, a species introduced in the Caribbean and which has rapidly colonized wetlands and coastal areas of Mesoamerica. The tricolored munia has been sighted since 1993; in Yucatán (1993, 1998, 2005, 2014, 2015), Quintana Roo (2003, 2004, 2016), Campeche (2005, 2009, 2011, 2013- 2017), Chiapas (2007, 2010, 2013), 2015), Tabasco (2012, 2014, 2016), Veracruz (2014), Jalisco (2015) and Oaxaca State (2016). The evaluation of the distribution of this species in Mexican territory is important from an ecological and economic perspective, considering that this species can become a pest for rice and sorghum crops, 2 of the most important crops of the Isthmus of Tehuantepec.
... There are likely species that have been introduced and died without being recorded, and therefore, the calculated accuracies from our calibration dataset may not be the same as the expected accuracies when the model is applied to a new species. To account for the potential bias associated with this "base-rate problem" (Smith et al., 1999), we used the Receiver Operating Characteristic (ROC) curve as a metric to evaluate the performance of our risk assessment tool. between invasive and noninvasive species. ...
Preprint
The African Great Lakes system has high aquatic biodiversity but is increasingly threatened by anthropogenic stressors including the introduction of potentially invasive nonindigenous plant and animal species. Quantitative risk assessment models can be used to predict the potential impact of introduced species in a specific geographic region. We adapted an existing aquatic plant risk assessment model for use in the African Great Lakes region. Our assessment comprises 31 questions addressing species traits and enviro nmental tolerances with each response receiving a point value. These values are summed to give a total score for each species, with higher scores indicating higher probability of successful invasion. We evaluated the predictive ability of the model using records of nonindigenous species with known differing invasion success in t h e African Great Lakes region. The resulting model correctly distinguishes between known invasive and not established species with a maximum accuracy of 90%. Quantification of invasion risk using this assessment could inform voluntary or regulatory management actions to prevent the introduction and spread of potentially harmful aquatic plants in the multinational African Great Lakes and other wetland and aquatic habitats, thereby balancing human development and conservation of biodiversity.
... Non-native Planting Permit, Florida Department of Agriculture & Consumers Services (FDACS), Department of Plant Industry, 2013). The high economic and ecological costs associated with biological invasions (Hulme, 2012;Keller, Lodge, & Finnoff, 2007;Smith, Lonsdale, & Fortune, 1999) supports this precautionary, risk-assessment approach, particularly for long-lived, aggressive, rhizotomous, large stature grasses such as running bamboo species. ...
... Key components of any risk assessment used to set screening strategy are measures of propagule pressure such as propagule frequency and size (the number of arrivals of nonindigenous pest species, and the number of organisms in each arrival). While estimation of propagule pressure was thought for many years to be too subject to error due to the base rate effect to be reliable for devising guides for decision making (see for example [21]), recent work has shown measures of propagule pressure to be among the best predictors of invasion potential [5,[22][23][24][25][26][27]. Data from the Australian ornamental plant trade indicate that estimates of risk factorsincluding propagule pressure-measured with current accuracy rates can be used to devise screening strategies that generate positive net benefits in terms of avoided damage from invasive nonindigenous species relative to foregone trade value [18]. ...
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Article
The expansion of international trade in commodities increases the risk of alien species invasions. Invaders are difficult to detect on introduction, so prevention remains the preferred strategy for managing the threat of invasions. Propagule pressure has been shown to be a good predictor of invasion risk. Most studies to date, however, link potential invasive species arrivals with indirect measures of propagule pressure such as aggregate trade volumes. This paper estimates propagule pressure using data that measure actual arrivals. Specifically, it uses inspection data that covers almost all U.S. fruit and vegetable imports from 2005–2014 to estimate a logit model of the probability of potential invasive species arrival and expected propagule frequencies for 2,240 commodity/country of origin combinations. Clear patterns in the geographic origin and commodity pathways for potential pests are identified. The average probability of arrival is low, approximately 0.03, but is two to ten times higher for some commodities, most notably herbs. We identify commodities with a high number of expected arrivals due to either a large volume of trade, high interception rates, or a combination of both. Seven of the top ten countries of origin for propagule frequency are from the Western Hemisphere and further trade liberalization within the Western Hemisphere is likely to heighten challenges to enforcement of US phytosanitary standards. Patterns in the data can help identify the commodities and countries of origin in greatest need of technical assistance and guide targeting of surveillance for the pathways of greatest phytosanitary concern.
... Thus, the widespread use of an approved, efficient pre-border weed-screening tool will help China reduce the invasion of exotic plants in the future. In practice, no perfect weed-screening tool is available that can reject all weeds and accept all nonweeds due to the overlap between the characteristics of weeds and non-weeds (Caley and Kuhnert 2006;Reichard and Hamilton 1997) and the influences of the low base-rate that only a small percentage of the species introduced actually become invasive (Smith et al. 1999). Therefore, the primary tasks for plant management in China should be to prevent the introduction of major weeds and to ensure the introduction of most non-weeds. ...
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Article
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.
... The current rhythm of global tourism and trade greatly increases the risk and rate of new introductions (Williamson, 1996). However, only a small fraction of introduced species succeed in establishing themselves, and even fewer become widespread and recognized for their impact to natural ecosystems (Smith et al., 1999). Early identification of the invasive species is key for environmental management. ...
... The lack of knowledge and irresponsibility of many pet keepers lead to the introduction of exotic animals (Romagosa, 2015), a well-known problem in animal conservation. This is more serious considering that in many places trade in live animals is largely unregulated (Smith et al., 1999), and the number of introductions of nonnative species by this route continues to increase, and is expected, along with their associated impacts, to be of continued concern (Goss and Cumming, 2013;Kraus, 2009). The number of biological invasions associated with the practice of keeping exotic pets is very high. ...
... There have been several attempts at modelling invasions and developing modelling frameworks that accurately predict impending invasions (Williamson and Fitter 1996, Smith et al. 1999, Miller et al. 2007). In most cases, prevention and prediction are impeded by a lack of comprehensive data on previous invasions. ...
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Thesis
One of the world's most successful marine invaders, the European green crab (Carcinus maenas), continues to spread and invade the coastlines of Atlantic Canada. In Prince Edward Island in particular, populations have continued to expand since the late 1990s. In areas like these, there is a distinct need to document this species' expansion into new habitats, to monitor its impacts on important native species, and to develop innovative mitigation strategies to control some of its effects. This thesis addressed the large information gap that still exists on this species' effect in the Atlantic Canadian region by focusing on four main areas: First, I explored over a decade of green crab population expansion records along Prince Edward Island's main shorelines. Second, I surveyed and examined the effects of green crabs on vulnerable size classes of an important shellfish species, the American oyster (Crassostrea virginica). Third, I performed a preliminary study into the occurrence and synchrony of molting in green crabs, identifying suitable physical features of pre-molting crabs as a first step for developing a soft-shell crab industry. And fourth, I developed and tested a novel bycatch reduction device to be used with fyke nets to facilitate the implementation of the aforementioned directed fishery for this species. Samples collected during the years 2000-2013 indicated that green crab expansion rates on Prince Edward Island vary spatially and temporarily. Expansion rates were higher along the south shore than the north shore of the island, and it was hypothesized that this dissimilarity was possibly related to the higher availability of suitable habitat along the south shore. The speed of the spread was such that it seemed more likely related to the benthic movement of juvenile and adult crabs than associated to larval spread or new anthropogenic vectors. With regards to green crab impacts, multiple oyster bed surveys conducted in 2014 measured mortality levels of vulnerable size classes of oysters. These surveys revealed that the probability of mortality of small oysters was higher in areas where green crabs were present. This probability decreased in the presence of other food sources (i.e. mussel beds), a result likely linked to green crab prey iii preferences. Field experiments using inclusion/exclusion cages indicated that the odds of oyster mortality was higher in inclusion cages than in the open environment and exclusion cages. These results suggested that at least some of the mortality of oysters could be attributed to green crab predation. With the recent implementation of a fishery for green crab as a potential mitigation strategy, there is a need for a marketable product to prompt fishermen to harvest green crabs. A soft-shell green crab product modelled after the Venetian "moleche" is expected to provide a lucrative incentive beyond the existing hard shell bait market. The examination of the timing and characteristics of molting revealed that synchronized "molting windows" or times of increased molting occur in the early summer for male green crabs. Recorded molting rates in the laboratory and the field were as high as 75% and 60%, respectively. External physical characteristics such as the presence of a "halo" on the episternites of the carapace, were deemed a reliable indicator that a crab would molt within 3 weeks. Although these results were preliminary in nature, they were promising and suggested that further studies be performed on the potential scaling up of these results. Fyke nets are a natural choice for a directed fishery of green crabs, as this type of gear is readily available and used locally, primarily for American eel (Anguilla rostrata). These nets are also a variant of the fyke net used in Italy to fish for a similar species of crab (Carcinus aestuarii) during its molting season. However, before fyke nets can be used in a directed fishery for green crab in Atlantic Canada, bycatch must be reduced. A novel Bycatch Reduction Device (BRD) for fyke nets was therefore developed and evaluated. Bycatch numbers and diversity, including three key commercial species, were significantly lower in the BRD equipped nets. Overall, the results of this thesis advance green crab research in the region, especially with regards to the quantification of impacts and development of mitigation measures. Further research questions as a result of my thesis work are identified and briefly discussed.
... Rispetto a quelli terrestri, gli ambienti acquatici risultano particolarmente vulnerabili all'introduzione di NIS (Halpern et al., 2007;Ricciardi, 2015). Un fenomeno di invasione in ambiente acquatico è spesso un processo irreversibile poiché, una volta che la nuova specie si insedia, la sua eradicazione diventa estremamente diffi coltosa se non impossibile, e le probabilità di successo assai ridotte (Smith et al., 1999;Carpenter el al., 2011). La ricchezza di endemismi e la presenza di aree interne isolate, unite all'infl uenza di importanti attività antropiche, rendono gli ambienti d'acqua dolce particolarmente esposti e sensibili all'insediamento di NIS (Dudgeon et al., 2006;Gherardi, 2007). ...
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Article
Biological invasions are continuously expanding worldwide, including the aquatic environments in Italy, where non-indigenous inverte- brates represent the majority of non-indigenous taxa. Despite this, the public is not adequately aware of their potential impacts in aquatic environments, as concern is more focused on larger-sized species. From a thorough analysis of the scientific literature, the total number of non-indigenous invertebrate species in Italian marine, brackish and freshwater ecosystems was assessed: the most representative taxa are Crustaceans (29, 30 e 50% respectively) and Molluscs (27, 31 e 18% respectively). Furthermore, a few methodologies, which have been proposed in the literature and include the non-indigenous assemblage in the quality assessment of the aquatic environments, have been critically commented and compared to each other. So far, just a few indexes specifically addressing non-indigenous species have been proposed, and they have not yet reached a widespread consensus within the scientific community. Furthermore, some methods have been proposed to evaluate the risk of a non-indigenous species to become invasive and negatively impact existing communities and ecosystems. The weak point of these approaches lies in the fact that they need to be run with data on biological traits and impacts of non-indigenous species, but information of this sort is often unavailable. Environmental biologists, through the study of the species’ ecology and biology, may play an important role in the prevention of non- indigenous species introductions and in supporting implementation of existing legislation and methodologies.
... Biological invasions are a special type of range expansion [15] that can be defined by a series of discrete, consecutive phases which include: 'Arrival'-single or multiple arrivals of a nonindigenous species at one or more points of entry into a new locale/environment, and 'Establishment'-whereby arriving populations start to reproduce in situ, surpassing barriers of initial extinction (geographic, environment, reproductive, antagonists) [16][17][18]. ...
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Article
Biological invasions, resulting from deliberate and unintentional species transfers of insects, fungal and oomycete organisms, are a major consequence of globalization and pose a significant threat to biodiversity. Limiting damage by non-indigenous forest pathogens requires an understanding of their current and potential distributions, factors affecting disease spread, and development of appropriate management measures. In this review, we synthesize innate characteristics of invading organisms (notably mating system, reproduction type, and dispersal mechanisms) and key factors of the host population (namely host diversity, host connectivity, and host susceptibility) that govern spread and impact of invasive forest pathogens at various scales post-introduction and establishment. We examine spread dynamics for well-known invasive forest pathogens, Hymenoscyphus fraxineus (T. Kowalski) Baral, Queloz, Hosoya, comb. nov., causing ash dieback in Europe, and Cryphonectria parasitica, (Murr.) Barr, causing chestnut blight in both North America and Europe, illustrating the importance of host variability (diversity, connectivity, susceptibility) in their invasion success. While alien pathogen entry has proven difficult to control, and new biological introductions are indeed inevitable, elucidating the key processes underlying host variability is crucial for scientists and managers aimed at developing effective strategies to prevent future movement of organisms and preserve intact ecosystems.
... Early investments in invasive species control avoid potentially irreversible change to ecosystems. But avoiding investments in species predicted to become invasive, that in fact would not have, is desirable (Smith et al. 1999;Williamson 1999) and the information needed to make this determination is valuable. Third, the results speak to an ongoing and well-publicized debate among ecologists concerning the need for urgency in response to bioinvasions (Davis et al. 2011;Simberloff 2011). ...
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Article
Debate persists around the timing of risk reduction strategies for large-scale ecological change for three reasons: risks are difficult to predict, they involve irreversibilities, and they impact multiple jurisdictions. The combination of these three factors creates a general class of filterable spatial-dynamic externalities (FSDE) in which one person’s risk reduction investments reduce or filter undesirable events experienced by others and underestimates the option value placed on being able to respond to new information about the consequences of ecological change. By focusing on the optimal intervention decision, we illustrate how and when the opposing forces created by an FSDE will lead to a divergence in private and collective risk reduction strategies. We use bioinvasions as our motivating example. The bioinvasion first hits one jurisdiction, and that jurisdiction’s risk reduction investment reduces the risk faced by all other jurisdiction. We find that efforts to internalize the full benefits of risk reduction investments may have unintended consequences on the responsiveness of environmental policy. There is a social welfare gain from asking the first jurisdiction to delay a risk reduction investment to internalize the option values of all at-risk jurisdictions.
... From a socio-economic perspective alone, it is difficult to separate the impact of non-native species introductions from their direct benefit as prospects are short term and rarely globally evaluated. In effect, risk assessments need to be carried out independently by a panel of scientists and although these assessments are not one hundred per cent reliable (Smith et al., 1999;Gordon et al., 2008) they provide simple, bibliographic-based, objective tools in support of the decisionmaking process (Copp et al., 2009). A range of tools has been recently developed (Pheloung et al., 1999;EPPO, 2000) and some specific for aquatic species (Fish Invasive-ness Scoring Kit (FISK; Copp et al., 2005Copp et al., , 2009www.cefas.co.uk/4200.aspx). ...
Chapter
The introduction of non-native species in freshwater ecosystems is less the result of natural colonization than their association with lucrative ecosystem services. Although a large part of the world's inland human populations rely on fisheries essentially exploiting wild unmanaged fish populations, many also rely on aquaculture as a sustainable way of providing animal protein daily. Here, the current paradox that opposes economic drivers to conservation perspectives, referred to as the 'Janus syndrome' after the Roman god depicted as having two faces facing opposite directions, is put in perspective with cultural differences, economic parameters and current lack of scientific knowledge. This issue is a crying example of the current Anthropocene with inland aquatic systems being the most severely affected ecosystems in terms of magnitude, frequency and duration of human impacts. There is, unfortunately, no return to a biotic de-homogenization of our freshwater fisheries, but will the lessons learnt be of any use?
... Similarly, the AWRA system may also benefit from modification to reduce interdependence between some L and C questions, and could also include provision for variability and uncertainty around some parameters [13]. Hulme [16] has discussed shortcomings in assessment systems such as this (including the 'low base-rate' for true positives (about 2% [17]) and suggested that investments would be better directed towards detection, mitigation and management. However, risk assessment would still be required for the prioritization of species that are present. ...
... When a particular good is proposed for import, there can be a screening of whether the good should be allowed for import or not. There has been some discussion on whether we would be better off ignoring the advice of the screening process or not (Smith et al., 1999;Caley et al., 2006). An empirical application of a similar question is provided by Keller et al. (2007), who assess when risk assessment is worth it compared to letting all species in. ...
Chapter
Biosecurity is a concept that has important economic, social, ecological and health-related dimensions. By biosecurity we mean protection of production, ecosystems, health and the social infrastructure from external threats caused by pests, pathogens and diseases of various forms and origins. The fact that more goods, transport platforms and people are moving around the globe at increasing speeds provides unforeseen possibilities for rapid spread of different types of organisms. This is exacerbated by changes in the production structures and climate. As a result, both the benefits and the risks of changes in the food system cross borders more often, leading to an increased demand for biosecurity policies. Economics can be related to biosecurity in at least three fundamental ways. First, many of the ultimate or proximate causes of bioinvasions create economic welfare. Second, bioinvasions result in various types of impacts, many of which are economic by nature – or at least may be measured in economic terms. Third, the negative impacts of invasions or their probability of occurrence can often be either avoided or reduced. These biosecurity policies themselves have economic implications, which often may be quite different from those caused by the biological hazard itself. A few reviews of separate components of economics of biosecurity exist, but there have been no attempts to review the big picture. Instead, the previous reviews have concentrated on different components of biosecurity such as invasive species or animal diseases. Our aim is to look at the issue in broad terms, draw some commonalities from the research conducted, and identify areas in which economic analyses have primarily been conducted and in which areas there remainswork to do. The review includes about 230 studies from all areas of biosecurity up to the year 2008. The review finds that study of economics of biosecurity is growing steadily, but is still relatively concentrated on narrow questions, few countries, few species/diseases and few journals.
... At present, no comprehensive compilations from California Department of Food and Agriculture (CDFA) or the National Plant Diagnostic Network (NPND) exist to show new invasive species to target for a warmer climate (Richard M. Bostock, personal communication). Some literature suggests that it is more efficient to focus on the spread of already naturalized species rather than from new potential invasive species at the importation stage (Smith et al. 1999). Yet, the Yolo County Agricultural Commissioner, John Young (personal communication), notes that several recently arrived pests are becoming severe problems, such as the European grapevine moth in vineyards, spotted wing drosophila on cherries, and Japanese dodder on a wide range of cultivated and wildland plant species. ...
... First, the information gained in the above and similar studies has been used to develop methods to predict potential invaders, which have proven invaluable for informing management decisions where a precise mechanistic understanding of the underlying ecology is lacking [121,127,128]. However, the accuracy of such methods needs to be very high (e.g., >85%) for general usefulness [129]. Secondly, these large-scale studies allow researchers to uncover patterns, which the various mechanisms outlined in this chapter must ultimately explain. ...
Chapter
In this essay, we have provided a brief review of the rapidly expanding literature on biological invasions. Many of the hypotheses explored above are not mutually exclusive, and the processes that underlie them may act simultaneously, in concert or in opposition, to determine the ultimate success or failure of an invader at each invasion stage. Though we have tried to be thorough, experienced researchers in the field will no doubt formulate additional hypotheses that warrant investigation. To date, most experiments have focused on only a single hypothesis for a small subset of invasive species under particular environmental conditions. To arrive at a realistic understanding of the ecological processes underlying biological invasions, a more integrative approach is warranted — one that examines the relative importance of each processes for a variety of species under myriad environmental conditions. This will prove to be a daunting task indeed, but one that will perpetuate the expansion of the field of invasion ecology for years to come, thereby ensuring plenty of fruitful lines of research for the keen investigators of the future.
... Controlling propagule pressure, and particularly propagule size, is a broadly applicable and simple policy approach that can reduce the establishment of non-native species (see Reaser et al. (2008) for a review of how such policy might be implemented). These methods do not have to be based around the identification of already known invaders, which can prove more expensive and often less efficient (Smith et al. 1999), but instead on reducing the overall introduction rate of all propagules. A focus on decreasing the size of introduction vectors is a necessary step in slowing the rate of new invasions and preventing the future impacts of a broad array of nonnatives that have yet to establish and spread. ...
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Article
Propagule pressure has consistently been identified as a primary factor in invader success, and reducing it can be one of the most effective methods for preventing the establishment of non-native species. However, when policy is implemented to reduce propagule pressure it almost exclusively focuses on the size of individual introduction events (‘propagule size’), with little confirmation that controlling this single aspect of propagule pressure is the most effective strategy. The number of introduction events (‘propagule number’) can play as much, or more, of a role in invader success, yet only a small portion of propagule pressure research has studied the relative importance of size and number. We investigated the relative roles of propagule size and number in the establishment of a sexually reproducing species using a field mesocosm experiment that introduced Hemimysis anomala (a non-native mysid) across a range of propagule sizes and numbers. We found that single, large introductions had higher abundances and probabilities of survival than smaller, more frequent additions. This experiment illustrated that, for sexual reproducers, focusing on lowering propagule size can be the most effective method for reducing non-native establishment.
... Williamson (2006) and others (e.g. Smith et al. 1999, Floerl et al. 2005a have also pointed to the problem of low base rates in statistical modelling of invasions. The base rate is the prevalence or frequency of occurrence of the response in the data set. ...
... Historically, the native ranges of woody plant species have naturally expanded and contracted, but human actions have greatly accelerated their global expansion . Although many humanassisted plant introductions have been beneficial (Smith et al. 1999), others have led to naturalization (the ability of a plant to propagate and sustain a population outside of cultivation) or invasion (the ability of a naturalized plant to aggressively colonize and displace native plants) into new locations (Widrlechner et al. 2013). A recent update of a global database of trees and shrubs indicates that 751 species of woody plants (434 trees and 317 shrubs) are now considered invasive, alien species somewhere in the world . ...
Article
Numerous predictive models have been developed to determine the likelihood that non-native plants will escape from cultivation and potentially become invasive. Given the substantial biological and economic costs that can result from the introduction of a new invasive plant and the unending pressures of world trade and transport, the creation and implementation of effective predictive models are becoming increasingly important. One key question in the development of such models focuses on the geographic scope at which models can best be developed and applied. We have developed models to predict woody-plant naturalization in five local areas within the Upper Midwest (United States). Herein, we consider whether naturalization can be reasonably predicted from a single model for the entire region or whether local models are required for each specific area. We develop a random forest model to predict the probability of naturalization in the region and compare out-of-sample prediction errors between the regional and local models. The regional model makes better predictions of the probability of naturalization for those species observed to naturalize but worse predictions for those not currently observed to naturalize. This model development process has given us an opportunity (not previously addressed in the literature) to examine the strengths and weaknesses of local and regional approaches, with the ultimate intent of optimizing geographic scope.
... Par ailleurs, la probabilité d'implantation d'une espèce allochtone introduite intentionnellement est supérieure à celle d'une espèce introduite de façon non intentionnelle. Cette différence résulte du comportement des agents qui introduisent volontairement des espèces sélectionnées pour leur capacité à survivre dans leur nouvel environnement (Smith et al., 1999). Un autre élément de différence entre les probabilités d'implantation tient au caractère plus ou moins répétitif des introductions (Enserink, 1999). ...
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Article
Biological invasions are nowadays an important challenge to biodiversity and human welfare. Managing biological invasions, which encompasses both prevention and control, is a public good and, as such, falls within the scope of cost-benefit analysis. The thesis deals with the control of an invasive species void of market value, and acting as a space competitor for a native valuable harvested species. Its first part is dedicated to a theoretical bioeconomic model describing the interacting dynamics of the two species and accounting for the undesirable consequences native stock harvesters behaviour have on the spread of invasion. In the model, control variables are the levels of harvesting effort of each species, and the target-function maximises the resource rent provided by harvesting the native stock, minus the cost of harvesting the invasive species. Static equilibrium analysis of the model provides a clear-cut alternative between asymptotic quasi-eradication of the invasive species and complete laisser-faire. Dynamic optimisation of the model displays the existence of a time-path leading to an optimal steady-state equilibrium where the native species is sustainable harvested and the invasive species is kept under control, provided units costs of native species harvesting and invaded areas cleaning, natural and anthropogenic invasive species dispersal coefficients and time-discount rate are moderate, and the problem is addressed early enough. The second part of the thesis is dedicated to the case-study of the invasion of the bay of St-Brieuc scallop fishery by an alien shellfish, the slipper-limpet. Cost-benefit analysis of the bay of Saint-Brieuc case makes use of an age-structured bioeconomic model of harvesting common scallop combined with a spatial invasion model, on which an invasion control program is studied.
... The general criticism for system-or model-based assessment of IAS for their invasiveness is the accuracy and reliability of information derived from the system or model. As Smith et al. (1999) have defined, the probability of correct classification of invasive species will determine the accuracy of the system. Any sample of species rejected because of being an IAS by a screening system will include a proportion of non-invasive species inappropriately classified as invaders, depending on the reliability of the system/model used. ...
... Similarly, the AWRA system may also benefit from modification to reduce interdependence between some L and C questions, and could also include provision for variability and uncertainty around some parameters [13]. Hulme [16] has discussed shortcomings in assessment systems such as this (including the 'low base-rate' for true positives (about 2% [17]) and suggested that investments would be better directed towards detection, mitigation and management. However, risk assessment would still be required for the prioritization of species that are present. ...
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Article
A number of policies, strategies and tools are available for the management of invasive alien plants. This review considers these and their suitability in the light of developing theory and practical experience. Policies range from quarantine and eradication to containment and asset protection. While there is scope for modelling the potential spread and impact of invasive plants, these factors are invariably species-specific and a land manager is typically faced with the problem of dealing with several species simultaneously. Weed risk management systems have been developed to prioritize species management actions. These systems will be improved by further efforts to encompass uncertainty. Most management actions require long time-frames, and institutional commitment, as well as stakeholder involvement for successful outcomes. Review Methodology: For this review we surveyed the recent literature on invasive plant species management as well as earlier relevant publications, considering the range of policies and strategies related to this topic, before condensing these into a logical sequence for a wide readership. There is some bias in the review towards natural ecosystems, reflecting the emphasis in recent literature. The review considers, in turn, strategies from quarantine through to asset protection. In practice, management of alien plants is rarely conducted on single species and there is some emphasis on weed risk management systems which are used to categorize and prioritize species management actions. Tools for the control of invasive alien plants are also briefly considered.
... Exposure analysis quantitatively assesses the likelihood that each identified hazard or benefit will occur and the consequences should it occur. Such analyses can generate a field of risk for each hazard or benefit, based on the probability of the hazard or benefit occurring (i.e. the base rate) at different levels of importance or consequence (Smith et al., 1999). Exposure analysis includes associated uncertainty bounds to such predictions while recognizing that the capacity to predict an occurrence decreases with the probability of it occurring. ...
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Article
Risks of non-target effects resulting from releases of exotic organisms for the biological control of alien pests are a growing major concern because: (a) previous releases (<1%) are having significant negative impacts on rare native species, (b) alien organisms are a recognized global threat to sustainable agriculture and biodiversity, (c) risk analysis, as applied to environmental threats of species invasions and harmful effects of releases of genetically modified organisms, is a burgeoning field, and (d) biological control is increasingly being used in complex natural ecosystems where indirect impacts are harder to predict. As a result, governments are adopting a more risk-averse attitude to biological control as they assess such releases from an environmental and an economic standpoint. This is leading to more expensive and fewer successful release applications. In this paper we review the processes of risk analysis used by regulatory bodies around the world to prejudge biological control releases against weeds. The aim is to publicize both strengths and weaknesses and to help encourage existing assessments to be fair to all without blunting the value of biological control as an effective tool against invasive alien weeds. The review, based around the five components of formal risk analysis (comparative analysis, risk assessment, risk management, risk evaluation, and risk communication), also focuses on how well the benefits and costs of biological control releases are evaluated in addition to the traditional analysis of the hazards. Currently only the New Zealand approach closely matches a full ecological risk-benefit-cost analysis of biological control releases with a precautionary approach, open consultation, a broad hazard/benefit definition in the release application and a judicial basis to the decision, but it comes at a high cost. Improving the analytical approaches used by countries runs a high risk of grinding biological control releases to a halt in a world where the precautionary approach has been adopted with respect to threats from exotic organisms on biodiversity (in line with the 'precautionary approach' set forth in principle 15 of the 1992 Rio Declaration on Environment and Development). The benefits of biological control remain poorly understood by the public, allowing the risks to attain disproportionate attention. We make recommendations to address this crisis in the making and discuss the outcomes of the review with respect to the inherent social risks of making analysis of biological control releases an overly protracted process.
... While the above system is an improvement over earlier assessment methods, the statistics for success are somewhat misleading because serious invasive and damaging weed species are relatively rare and the system is unlikely to be perfectly efficient in the future. Substantial risks remain in species that are already naturalised and that continue to spread to the full extent of their potential range (Smith et al. 1999). ...
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Article
Despite the fact that the most changes in lists of threatened species reflect changes in knowledge rather than changes in conservation status, the lists continue to provide social and legal mandates for conservation; they are used to report on the state of the environment and to guide the allocation of scarce resources. There is a substantial under-representation of non-vascular species in threatened plant lists, reflected in an absence of documented extinctions among fungi and algae. Turnover in the composition of extinct flora lists in Australia suggests that the lists of threatened species may not be sufficiently reliable to form the basis for reporting on the state of the environment. They are of limited use in distinguishing between levels of threat and may not be a reliable guide for the allocation of scarce conservation resources among plant species. Systems for listing threatened species create a feedback loop, responsive to the subjective preferences of scientists, largely unresponsive to underlying true threats, self-perpetuating and accentuating bias with each iteration. Other tools, including formal decision approaches and the acquisition of new kinds of data, are needed to fill the roles.
... In addition, introduced birds have major economic impacts in many locations (Lever 1994, Bomford & Sinclair 2002. Defining and measuring precisely what we mean by impact remains a challenging task, but one that is critical to setting priorities for managing invasive species (Parker et al. 1999;Smith et al. 1999;Williamson 1999Williamson , 2001Ricciardi et al. 2000). Assuming that we can quantify impacts, we can, in principle, apply comparative methods to identify why some species have greater impact than others, as has been done for other invasion transitions, and use this information in explanatory models. ...
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Article
▪ Abstract A growing number of species have been transported and introduced by humans to new locations and have established self-sustaining wild populations beyond their natural range limits. Many of these species go on to have significant environmental or economic impacts. However, not all species transported and introduced to new locations succeed in establishing wild populations, and of the established species only some become widespread and abundant. What factors underlie this variation in invasion success? Here, we review progress that has been made in identifying factors underpinning invasion success from studies of bird introductions. We review what is known about the introduction, establishment, and spread of introduced bird species, focusing on comparative studies that use historical records to test hypotheses about what factors determine success at different stages in the invasion process. We close with suggestions for future research.
Article
The selection, introduction, and cultivation of non-native woody plants beyond their native ranges can have great benefits, but also unintended consequences. Among these consequences is the tendency for some species to naturalize and become invasive pests in new environments to which they were introduced. In lieu of lengthy and costly field trials, risk-assessment models can be used to predict the likelihood of naturalization. We compared the relative performance of five established risk-assessment models on species datasets from two previously untested areas: southern Minnesota and northern Missouri. Model classification rates ranged from 64.2 to 90.5%, biologically significant errors ranged from 4.4 to 9.3%, and horticulturally limiting errors ranged from 6.6 to 30.4%. For the random forest model, we investigated the importance of variables used to predict naturalization by examining datasets for five distinct study areas across the Upper Midwest. Geographic-risk ratios were the most important predictors of species' tendency to naturalize. Other factors, such as quick maturity, record of invading elsewhere, and production of fleshy, bird-dispersed fruit were also important in the random forest models. Although some models tested need additional refinement, the random forest models maintain robustness and provide additional information on plant-specific characteristics that contribute to naturalization.
Article
Accurate methods to predict the naturalization of non-native woody plants are key components of risk-management programs being considered by nursery and landscape professionals. The objective of this study was to evaluate four decision-tree models to predict naturalization (first tested in Iowa) on two new sets of data for non-native woody plants cultivated in the Chicago region. We identified life-history traits and native ranges for 193 species (52 known to naturalize and 141 not known to naturalize) in two study areas within the Chicago region. We used these datasets to test four models (one continental-scale and three regional-scale) as a form of external validation. Application of the continental-scale model resulted in classification rates of 72–76%, horticulturally limiting (false positive) error rates of 20–24%, and biologically significant (false negative) error rates of 5–6%. Two regional modifications to the continental model gave increased classification rates (85–93%) and generally lower horticulturally limiting error rates (16–22%), but similar biologically significant error rates (5–8%). A simpler method, the CART model developed from the Iowa data, resulted in lower classification rates (70–72%) and higher biologically significant error rates (8–10%), but, to its credit, it also had much lower horticulturally limiting error rates (5–10%). A combination of models to capture both high classification rates and low error rates will likely be the most effective until improved protocols based on multiple regional datasets can be developed and validated.
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Barrow Island, north-west coast of Australia, is one of the world’s significant conservation areas, harboring marsupials that have become extinct or threatened on mainland Australia as well as a rich diversity of plants and animals, some endemic. Access to construct a Liquefied Natural Gas (LNG) plant, Australia’s largest infrastructure development, on the island was conditional on no non-indigenous species (NIS) becoming established. We developed a comprehensive biosecurity system to protect the island’s biodiversity. From 2009 to 2015 more than 0.5 million passengers and 12.2 million tonnes of freight were transported to the island under the biosecurity system, requiring 1.5 million hrs of inspections. No establishments of NIS were detected. We made four observations that will assist development of biosecurity systems. Firstly, the frequency of detections of organisms corresponded best to a mixture log-normal distribution including the high number of zero inspections and extreme values involving rare incursions. Secondly, comprehensive knowledge of the island’s biota allowed estimation of false positive detections (62% native species). Thirdly, detections at the border did not predict incursions on the island. Fourthly, the workforce detected more than half post-border incursions (59%). Similar approaches can and should be implemented for all areas of significant conservation value.
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In general, environmental stressors are chemical, physical, or biological agents capable of causing adverse effects on human health, safety, or the environment. Historically, the field of environmental risk assessment has focused primarily on the human health effects of chemical toxicants. The environmental risks posed by physical stressors, such as radiation, flood, drought, and fire, have also been assessed to a significant extent. Formal, quantitative risk assessment for biological stressors, however, is a nascent field of scientific analysis. Although the bounds of scientific uncertainty for risk assessment of chemical contaminants may span multiple orders of magnitude, the underlying principles, methods, data, and conventions for chemical risk assessment are far more developed than are those for the assessment of biological stressors. The main difference between chemical and biological stressors are that biological organisms: (a) grow, reproduce, and may multiply; (b) disperse both actively and passively, often in “jumps” that are hard to predict; (c) interact with ecosystems in ways that can be complex and are hard, if not impossible, to predict; and (d) evolve, and this evolution is largely random [1]. Some biological hazards combine elements of both biological and chemical risks. Staphylococcal food poisoning, for example, is not an infection but results from the production of a heat-stable chemical toxin by Staphylococcus aureus. The quantity of the toxin present in food, however, is a function of staphylococcal growth. To appreciate the novel risk assessment challenges posed by biological stressors, consider that chemical contaminants present below analytical detection limits typically pose negligible risks.
Article
This paper presents a literature review on the economic analysis of biological invasions control. Invasive species are mainly human induced and could generate important damages, thus many economic analyses have focussed on biological invasions control policies. This paper summarizes a high number of recent studies to analyze conditions under which the control is efficiency.
Article
The European Food Safety Authority (EFSA) requested the Panel on Plant Health (PLH Panel) to provide guidance for the evaluation of the effectiveness of the options for plants and plant products for reducing the risk of introduction and spread of harmful organisms in the European Union territory. Two operational tools are presented: a checklist for evaluating a proposed risk reduction option (RRO) and a database of references corresponding to published guidance documents or experimental assessments of RROs. The checklist can be used by the Panel or the dossier-submitting parties to verify whether all required information is provided in support of a RRO, to quickly describe information supplied to EFSA and to identify major gaps in the data. Four types of RRO assessments are distinguished in the proposed checklist according to their purposes and characteristics: experimental assessment of the effectiveness of the option to reduce pest infestation in plant material/products under laboratory/controlled conditions; experimental assessment of the effectiveness of the option to reduce pest infestation in plant material/products under operational conditions; analysis of the applicability of the RRO; and assessment of the effectiveness of the option to reduce the risk of pest entry from an infested area to a pest-free area. The database of references is intended to assist the Panel in (i) identifying potential RROs for a given pest and plant material, and (ii) quickly retrieving relevant experimental data and guidance documents for assessing a proposed RRO. In addition, the current document provides recommendations for assessing RROs, specifically: on experimental design; on the use of statistical methods including approaches for studying uncertainty; on the use of quantitative pathway analysis and spread models describing their advantages and limitations; and on recommendations for general surveillance and specific surveys.
Article
Question: The use of plant traits to predict weed impact is a long-standing goal in weed ecology. In particular, trait plasticity, i.e. the variability of a trait response to environmental change, is widely considered to contribute to weed success. However, the generality of the role of trait plasticity in determining weed impacts has never been systematically tested. Methods and location: We tested the hypothesis that high-impact environmental weeds have greater plasticity in growth responses to nutrient availability than low-impact species. In a glasshouse experiment, we supplied a complete nutrient solution at five different concentrations to seedlings of 24 species of high- and low-impact environmental weeds from south east Queensland, Australia. Results: Almost all species showed plasticity in biomass accumulation in response to the nutrient treatments, but plasticity in biomass accumulation did not differ between related high- and low-impact species. There was no evidence of nutrient-related plasticity in root:shoot allocation. Seedling survival was greater at higher nutrient concentrations, and also differed greatly between families. Survival among low-impact species was marginally (p = 0.0610) lower than among high-impact species. Conclusion: We conclude that the impact of environmental weeds in south east Queensland cannot be predicted from nutrient-related plasticity in seedling growth. The effects of nutrients on seedling survival warrant further research.
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Invasive plant species, unlike agriculture weeds, can successfully occupy and spread to new habitats without further assistance from humans. These plants can apparently invade into new areas already fully occupied by native vegetation, displacing many species. An increasing trade-based global economy, world-wide transport of biological commodities, and opportunities for trans-world travel during the last century have increased the introduction and subsequent colonization of exotic species in many parts of the world (Table 1). Thus, plant invasions from the intentional or unintentional transport of plants to new areas now seriously threaten the biodiversity, structure and function of many of the world’s ecosystems (Crosby, 1986; Ewel et al., 1999; Enserink, 1999).
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Williamson and Fitter adopted a statistical approach to study the proportion of imported species achieving different levels of invasion success--introduced, established, and pest. They found a regularity in these proportions and a predictability about deviations.
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Why do different plant species thrive where they do? This is a difficult question to answer because plants have invaded new niches and subsequently evolved to become better adapted within those niches. Distinguishing the traits that allow successful invasion and those that are evolved adaptations to current environments is not usually possible. We attempt to identify life history components that allow successful invasion by analysing the life history variables and ecological requirements of plant species that have successfully invaded the U.K. in recent years. The British flora is uniquely suited for this analysis because we have precise information on the dates of arrival, rates of spread and final spatial distribution of all our alien vascular plant species. Data on alien plants controls for evolution after invasion because there has been relatively little time for evolution to occur. We use modern phylogenetically-based comparative methods in an attempt to tease apart those components of life histories that have allowed successful invasion (large seeds, tall stature, protracted seed dormancy) from those that are irrelevant (dispersal syndrome, mating system, leaf shape).
Article
The Eurasian and North African distributions of several species of Carduus, Centaurea and Onopordum were examined. Species that occur in Australia were significantly more widespread in their native continents than were species not recorded in Australia. Moreover, most species occurring in Australia characteristically co-exist in a limited subset of European countries. Thus, by implication, widespread species not yet known in Australia are more likely to colonize and establish in Australia than are narrowly distributed species, and widespread species that occur in the specified subset of countries have even higher probabilities of successful colonization of Australia. These findings may aid plant quarantine officials in making decisions with respect to the potential of various taxa to become weeds in Australia.-from Authors
Article
Forty nine British annual species were examined for characters or groups of characters that might relate to their ability to behave as weeds. The weediness score of a species was obtained from the opinions of 65 scientists working in a variety of botanical fields. It is often stated that weeds have groups of characters in common, but five different methods demonstrated that there were no characters which reliably distinguished weeds from non-weeds. A more successful approach may be comparison of the characters that differ between pairs of closely related species of which one is a weed, the other not. This approach identified an extended flowering season as being of potential importance. -from Authors
Article
Weed status in Australia was associated with being geographically widespread in southern Africa, being found in a wide range of climates in southern Africa, being described as a weed or targeted by herbicides in southern Africa, with early introduction and establishment in Australia, and with weediness in regions other than southern Africa. Multiple logistic regressions were used. The best fitting regressions were for weeds present for a long time in Australia (>140 yr). They utilized three variables, namely weed status, climatic range in southern Africa and the existence of congeneric weeds in southern Africa. The highest level of variation explained (43%) was obtained for agricultural weeds using a single variable, weed status in southern Africa. Being recorded as a weed in Australia was related to climatic range and the existence of congeneric weeds in southern Africa (40% of variation explained). Recently-arrived species which were predicted to become weeds are Acacia karroo (Mimosaceae), Arctotis venustra (Asteraceae), Sisymbrium thellungii (Brassicaceae) and Solanum retroflexum (Solanaceae). Analysis of the residuals of the regressions indicated two long-established species which might prove to be good targets for biological control: Mesembryanthemum crystallinum (Aizoaceae) and Watsonia meriana (Iridaceae). -from Authors
Article
Plant species continue to be introduced in North America for various purposes. If the trend continues, it is probable that some will escape cultivation and become invasive in native ecosystems. We present a retrospective analysis of several structural, life history, and biogeographical attributes of woody plants introduced in North America to determine which traits characterize species that have and have not invaded. Predictive models derived from discriminant analysis correctly classified 86.2% of the species in cross-validation, whereas those derived from classification and regression trees classified 76% correctly. From these models we created a hierarchical predictive tree that allows the user to divide species into three categories: admit (low risk of invasiveness), deny admission (high risk of invasiveness), or delay admission for further analyses and/or monitor intensively (risk cannot adequately be assessed based on only the included attributes). We recommend that species that are highly invasive elsewhere not be allowed into the U.S. and that a more conservative introduction policy using a hierarchical predictive method be employed.
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This book summarizes knowledge about invasive species and the problems that they cause in 7 chapters, with the following titles: a framework for the study of invasions; the origins and success and failure of invasions; which communities are invaded by which type of species; the process of spread; ecological consequences of invasions; genetic and evolutionary effects; and implications and communities. Author and subject indexes are provided.
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SUMMARYI apply Decision Theory to the question of how accurate earthquake predictions must be to serve as a reliable basis for action. Even with optimistic estimates of the parameters involved, the lower bound on the required accuracy is extraordinarily demanding, being over 10 times higher than that of current meteorological forecasts. Given the abruptly self-organizing nature of earthquakes, it is extremely unlikely that precursors can attain such levels of accuracy. I therefore conclude that prediction of major earthquakes is, in any practical sense, impossible.
Studies on weed risk assessment. M App Sci Thesis
  • John Wiley
  • Chichester
  • Uk
  • Smith
John Wiley, Chichester, UK Smith CS (1999) Studies on weed risk assessment. M App Sci Thesis, University of Adelaide, South Australia, 100 pp Williamson M (1996) Biological Invasions. Chapman and Hall, London, 244 pp Williamson M (1999) Invasions. Ecography 22: 5–12
Screening plants for weediness: a procedure for assessing species proposed for importation to Australia. A report commissioned by the Australian Weeds Committee Panetta FD (1993) A system of assessing proposed plant introduc-tions for weed potential
  • D P Pheloung
  • Jacobs Wm S Lonsdale
  • Wright
D, Pheloung P, Lonsdale WM, Jacobs S, Mulvaney M and Wright W (1994) Screening plants for weediness: a procedure for assessing species proposed for importation to Australia. A report commissioned by the Australian Weeds Committee Panetta FD (1993) A system of assessing proposed plant introduc-tions for weed potential. Plant Protection Quarterly 8: 10–14
A conceptual framework for ecological risk assessment Comparative ecol-ogy of the native and alien floras of the British Isles
  • Brown
Brown SS and Reinert KH (1992) A conceptual framework for ecological risk assessment. Environmental Toxicology and Chemistry 11: 143–144 Crawley MJ Harvey PH and Purvis A (1996) Comparative ecol-ogy of the native and alien floras of the British Isles. Philo-sophical Transactions of the Royal Society (London) B 351: 1251–1259
Thinking Strategically
  • C Loehle
Studies on weed risk assessment
  • Cs Smith
Screening plants for weediness: a procedure for assessing species proposed for importation to Australia. A report commissioned by the Australian Weeds Committee
  • D Panetta
  • P Pheloung
  • Wm Lonsdale
  • S Jacobs
  • M Mulvaney
  • W Wright
Determining the weed potential of new plant introductions to Australia
  • P Pheloung
Which insect introductions succeed and which fail?
  • D Simberloff
  • Ja Drake
  • Ha Mooney
  • Di Castri
  • F Groves
  • Rh Kruger