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Table 6.2Hypotheses evaluated in this chapter, based on factors that are commonly listed as contributing to invasiveness in research papers by Baker (1974),Roy (1990), Rejmánek (2000), Rejmánek et al. (2005), Pyšek and Richardson (2007), Whitney and Gabler (2008), and Firn et al. (2011)FactorHypothesisBasis/rationaleIndependent variablesComments based on analyses1TaxaInvasiveness is correlated with taxonomic section, with species in sectionsGeneaandBromusmore likelyto be invasiveThis is often stated in literatureSection (Genea, Bromus,Ceratochloa, Bromopsis)Species in sectionGeneaandBromuswere the most widelyintroduced and weedy, and species in sectionBromopsiswere the least2Life spanShorter life spans are correlated with invasivenessAnnual grasses have replaced perennial grasses in parts of the western United StatesLife span (short, medium, long)Shorter life span was correlated with both wide introduction and weediness3Year species named and describedSpecies named and described early are more likely to be invasive than those described laterSpecies common in their native ranges are likely to be described early and to be widely introduced and weedyYearSpecies named and described earlier were more likely to be widely introduced and weedy4Effective seed distributionLong lemma awns are correlated with invasivenessLong lemma awns aid in dispersal by vertebrate animals, help to protect the seed from predation, and aid in seed burialMaximum awn lengthLonger maximum awn length was correlated with wide introduction and weediness5Effective seed distributionLow mean seed mass is correlated with invasivenessLow mass seeds may be created in large numbers and more widely dispersedMean seed massLower mean seed mass was marginally correlated with crop weediness. There were no significantcorrelations with wide introduction or other weed categoriesS.Y. Atkinson and C.S. Brown