Ecological and taxonomic differences between native and introduced plants of southwestern Ontario

We compared taxonomic and ecological attributes of native and introduced planes (N = 1330 and 484 species. respectively) of southwestern Ontario, using two regional floras (Essex County and Hamilton-Wentworth Regional Municipality) for distributions, and published sources for ecological attributes. Most exotics (86.4%) originate from Europe and Asia. Exotic species tended to occur in families having just one-to-few species locally. Seven families (Amaranthaceae, Asteraceae, Boraginaceae, Brassicaceae, Caryophyllaceae, Fabaceae, and Malvaceae) were significantly over-represented by exotics compared to the distribution of native species in these families, while exotics were significantly under-represented in six families (Cyperaceae, Fagaceae, Juncaceae, Orchidaceae, Potamogotonaceae, and Ranunculaceae). In habitat comparisons, exotic species were significantly over-represented (compared to native species) in disturbed and degraded habitats and moist substrates, while being under-represented in woodland, thicket, and wetland. Introduced species of southwestern Ontario have life history traits that facilitate success in degraded, disturbed and highly fragmented environments. For example, exotics were significantly over-represented by the following life-history traits: short life span, flowering season of four or more months, hermaphrodite sex habit, and very small fruits (< 5 mm). They were significantly under-represented by the monoecious and dioecious sex habits, a flowering period of two months and less, animal-based seed dispersal. and relatively small fruits (5.1 - 10 mm). A separate analysis of exotic species found only in undisturbed communities, showed these species to be more likely to occur in open and moist habitats, to have a tree habit, and an extended flowering period, and to produce many seeds per fruit (> 7).