The ecological and economic advantages of preventing introduction of species likely to become invasive have increased interest in implementing effective screening tools. We compared the accuracy of the Australian Weed Risk Assessment (WRA) system with that across the six geographies in which it has been tested (New Zealand, Hawaii, Hawaii and Pacific Islands, Czech Republic, Bonin Islands and Florida). Inclusion in four of the tests of a secondary screening tool, developed to reduce the number of species requiring further evaluation, decreased the number of species with that outcome by over 60% on average. Averaging across all tests demonstrated that the WRA system accurately identified major invaders 90%, and non‐invaders 70%, of the time. Examined differently, a species of unknown invasive potential is on average likely to be correctly accepted or rejected over 80% of the time for all of these geographies when minor invaders are categorized as invasive. Whereas increasing consistency in definitions and implementation would facilitate understanding of the general application of the WRA system, we believe that this tool functions similarly across islands and continents in tropical and temperate climates and has been sufficiently tested to be adopted as an initial screen for plant species proposed for introduction to a new geography.

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Screening tools that effectively predict which nonnative species are likely to become invasive are necessary because of the disproportionate ecological and economic costs associated with invaders. We tested the effectiveness of the Australian Weed Risk Assessment system (WRA) in distinguishing plant species that are major invaders, minor invaders, and noninvaders in Florida. The test included 158 annuals and perennials in six growth forms from 52 families in 27 orders. The WRA with a secondary screen met all hypothesized accuracy levels: it correctly rejected 92% of test species that have been documented to be invasive in Florida and correctly accepted 73% of the noninvaders. The incorrect rejection of noninvaders was 8% with the remaining 19% of noninvaders falling into the ''evaluate further'' outcome. Only 10% of the 158 species required further evaluation. Invaders of natural areas and agricultural systems were identified with equal accuracy. Receiver operating characteristic analysis demonstrated high separation of invaders from noninvaders. The degree to which the WRA is precautionary may be adjusted by altering the cutoff scores that define the ''accept, evaluate further,'' and ''reject'' outcomes. This approach could be adopted in Florida as a screening mechanism to reduce importation of new invaders.

Ardisia crenata (Myrsinaceae), an evergreen shrub with attractive red fruits introduced from Japan to the USA for ornamental purpose, invades the understory of mesic hardwood forests, forming dense patches (up to 300 stems per m 2 ), and competitively displaces native understory plants by creating dense local shade. Comparison of the wild genotype that grows in mature evergreen broadleaf forests in central Kyushu, Japan, with the ecotype invading north central Florida revealed how selection for desirable cultivars might have inadvertently selected for traits that enhance the invasive potential of the species. In Japanese wild populations in deeply shaded evergreen forests, natural selection apparently maintained efficient architecture with a low degree of self-shading and large seed mass to enhance seedling shade tolerance. Cultivar selection for showy appearance can explain the greater fecundity but smaller seed size observed in the Florida populations compared to the Japanese population. Artificial selection for densely foliated appearance can also explain the greater degree of self-shading and less-efficient light use in the Florida genotype compared to the Japanese wild type grown under a common environment. Furthermore, the Florida ecotype allocated more biomass to root carbohydrate storage. These trait modifications resulted in slower growth rates, but greater competitive ability to cast shade upon neighbors and higher resprouting potential in the Florida populations. How traits are modified through the processes of artificial selection and cultivation must be taken into consideration in the evolutionary ecology of many other invasive plants introduced as ornamental plants.

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