Global compositional variation among native and non-native regional insect assemblages emphasizes the importance of pathways

Abstract

Insects are among the world's most eco- logically and economically important invasive spe- cies. Here we assemble inventories of native and non- native species from 20 world regions and contrast relative numbers among these species assemblages. Multivariate ordination indicates that the distribution of species among insect orders is completely different between native and non-native assemblages. Some orders, such as the Psocoptera, Dictyoptera, Sipho- naptera, Thysanoptera, and Hemiptera, are always over-represented in the non-native compared to native assemblages. Other orders, such as the Plecoptera, Trichoptera, Ephemeroptera, Odonata, Mecoptera and Microcoryphila, are consistently under-represented in non-native assemblages. These patterns most likely arise both as a result of variation among taxa in their association with invasion pathways responsible for transporting species among world regions, as well as variation in life-history traits that affect establishment potential. However, our results indicate that species compositions associated with invasiveness are funda- mentally different from compositions related to insu- larity, indicating that colonization of islands selects for a different group of insect taxa than does selection for successful invaders. Native and non-native assem- blage compositions were also related, to a lesser extent, to latitude of the region sampled. Together, these results illustrate the dominant role of invasion