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6 Evaluating Predictive Systems
Pages 111-140

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From page 111...
... A determination that a given nonindigenous plant or plant pest has the potential to become invasive in the United States presumes that information about it and its introduction are known, such as its characteristics; the specific event that brings it into the United States; where, when, and how it is brought in; that it can become established, proliferate, and spread in its new environment; and the harm it would do. The same criteria apply to nonindigenous organisms introduced as biological control agents (Strong and Pemberton 2000~.
From page 112...
... Plant species known to be invasive have routinely sparked awareness of their invasive potential in unexploited new ranges. The World's Worst Weeds, the compendium by Holm et al.
From page 113...
... More important, weather is the stochastic expression of climate, and the persistence of organisms, whether native or introduced, is much influenced by this variation about the mean characteristics of any climate (Mack 1995~. CLIMEX is one example of the models developed to predict the potential ranges of introduced species (Sutherst et al.
From page 114...
... Meteorological data include average monthly maximal and minimal temperatures, relative humidity, and precipitation. The model interpolates monthly average climatic data into weekly values.
From page 115...
... Even if a species' native range appears to have a climate similar to a climate in the United States, the similarity by no means ensures that if it arrives, it will persist, much less that it will become invasive. Evaluation based particularly on the biotic component of a potential target range is also needed.
From page 116...
... However, evolutionary divergence is often so great that most life-history traits differ to some extent among even related taxa, and this divergence makes inferences difficult about the key features responsible for invasiveness. The less closely related the taxa, the more acute the problem becomes; however, even species comparisons involving congeners often reveal large differences in ecology and life history.
From page 117...
... Thus, simply identifying the traits of a species and ignoring the environmental context in which the species occurs limits the information about whether the species can persist, let alone become invasive. Many species fail to display traits usually associated with invasive potential high reproductive performance, wide geographic range, and so on in their native ranges but behave differently in novel ecological settings.
From page 118...
... Indeed, it is probably the general observation that some groups appear more frequently than others on the lists of naturalized species that has motivated the search for traits associated with invasiveness. The search continues despite the recognition that diverse ecological strategies are associated with species' becoming invasive.
From page 119...
... A SCIENTIFIC BASIS FOR PREDICTION? Although neither a species' past performance in new environments nor its assemblage of traits is an adequate guide to forming comprehensive predictions on a species' invasive potential, these tools have value.
From page 120...
... . Having identified characteristics thought to be useful for predicting the likelihood of each of the three stages of the invasion process, the committee asked how we might know, measure, or assign parameters to these characteristics.
From page 121...
... Is the volume of the imported material great? Does the pathogen have a wide geographic range?
From page 122...
... · Is climate similar between the current geographic range and potential destinations? · Is there a history of establishment in a similar environment elsewhere outside its native range?
From page 123...
... For example, to assign parameters to an insect' s movement from a source to a potential destination, the committee thought it important to know whether the insect has a strong association with an imported material, whether it has a broad geographic host range, whether it has high densities periodically in its native range, and the volume of
From page 124...
... Infestation rate will depend in part on the insect' s density in its native range, and density is often associated with geographic range. Furthermore, the likelihood that the species will be transported appears to be related to the size of its geographic range (Ehrlich 1989)
From page 125...
... In addition to averting the release of a potentially invasive species, results of field trials would substantially enhance the ability to detect common patterns of plant performance in new environments. Similar efforts to acquire life history and population level data in situations that approximate field settings would be beneficial for predicting the fate of nonindigenous arthropods and pathogens that are of concern, including species proposed for deliberate introduction.
From page 126...
... Extending these ideas to arthropods and pathogens, including those under consideration for deliberate introduction, would be valuable, although practical considerations associated with experiments in field settings may be more difficult to overcome. Welldesigned studies that obtain information on life history traits, interactions with native species and population level parameters in a realistic environmental context could provide valuable information about the potential for population growth and spread of an arthropod or pathogen in a new habitat, and increase our overall understanding and ability to predict invasiveness.
From page 127...
... The likelihood of pest introduction is based on the estimated quantity of imported material and "pest opportunity", which is a synthesis of the arrival and establishment stages of the invasion process. It is somewhat incongruous that pest opportunity is measured as a sum of scores that have a probabilistic basis.
From page 128...
... FIGURE 6-2 Qualitative pest risk-assessment procedure used by USDA/APHIS (19971. Risk potential (A)
From page 129...
... of impacts >2 1 none Score High- 3 Medium- 2 Low- 1 2) Host range risk assumed to be correlated with host range Host Range Score · multiple species in multiple High - 3 families · multiple species in one family Medium - 2 · one or more species in one genus Low - 1 4)
From page 130...
... If two or more elements that determine likelihood of introduction are low, pest risk potential is low. FIGURE 6-3 Qualitative pest risk-assessment procedure proposed for use with imported solid-wood packing materials (USDA 2000~.
From page 131...
... active host search or vectored · high propagule pressure Likelihood of introduction = MINIMAL FIGURE 6-3 Continued K 131 Entry potential · repeated historical interceptions _ ~ 2 5 = High · one or more stages likely 2-4 = Moderate to survive transport · not likely to be separated < 1 = Low from host · difficult to detect Spread potential . capable of dispersing > several km/year demonstrated redistribution via human assisted transport high reproductive potential Establishment potential · demonstrated ability to use new hosts · hosts contiguously distributed historical record of establishment ~ High · new populations difficult to detect or · low likelihood of eradication of new populations · broad host range · potential to be more efficient 2 3 = High vector 1-2 = Moderate O=Low Likelihood of association · High · Moderate · Low Entry potential · High · Moderate · Low Establishment potential · High · Moderate · Low High or 2 2 = High 1 = Moderate O=Low 2 5 = High 2-4 = Moderate < 1 = Low Spread potential · High · Moderate · Low \
From page 132...
... Because risk-assessment systems use the same structure as that depicted in Figure 6-1 to assess the likelihood of introduction, they share the limitations identified for a scientifically based prediction of invasion. Foremost among the limitations is that risk-assessment systems require subjective determination of characteristics of nonindigenous species and the environments into which they might be introduced, and they identify the risk of introduction by subjectively placing species and environmental characteristics into likelihood categories.
From page 133...
... Pest risk-assessment systems have value, provided that the reasoning used is underlain by careful documentation. The process of conducting a qualitative risk assessment is at least as valuable as the specific risk values that are produced, because the process, when carefully documented, provides a mechanism for assembling and synthesizing relevant information and knowledge.
From page 134...
... Quantitative scenario analysis (Kaplan 1993, Firko 1995a) has been used to produce quantitative assessments for the likelihood of establishment.
From page 135...
... Quantitative scenario analysis should be expanded to include all aspects of the invasion process, especially when consequences are high. The array of information suggested by the committee in Table 6-1 could be incorporated in scenario analysis to reflect a more comprehensive and realistic perspective on the risk posed by the introduction of pests and of organisms intended as biological control agents.
From page 136...
... The assessment concluded that the nonindigenous plant posed the greatest risk to the wetland system. This assessment intentionally included all parts of the source
From page 137...
... EVALUATING PREDICTIVE SYSTEMS 137 exposure pathway-response relationships and did not focus on only one part or one pathway. The advantage of a scenario system is that it captures the ecological context, as recommended in present ecological risk assessment (Suter 1993, USEPA 1998~.
From page 138...
... The same is true for arthropods and pathogens if host plants on which they have colonized elsewhere exist in the United States. · Climate-matching simulations can narrow the estimated potential range of an introduced species or estimate potential ranges from which invasive species might emerge.
From page 139...
... Evaluation based particularly on the biotic components of a potential target range is also needed, but it is difficult to incorporate this component into a simulation. · Trait-based approaches for predicting invasiveness hold much appeal as a means of providing a general guideline regarding any species' invasive potential.
From page 140...
... Finally, risk assessments that are carefully documented and transparent in the logic used to assemble their ratings would allow public scrutiny and independent evaluation.


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