Moths and butterflies on alien shores – global biogeography of non-native Lepidoptera

Lepidoptera is a highly diverse, predominantly herbivorous insect order,
with species transported to outside their native range largely facilitated
by the global trade of plants and plant-based goods. Analogous to island
disharmony, we examine invasion disharmony, where species filtering during
invasions increases systematic compositional differences between native
and non-native species assemblages, and test whether some families are
more successful at establishing in non-native regions than others. We
compared numbers of non-native, unintentionally introduced Lepidoptera
species with the land area of 11 regions worldwide (Hawaii, North America,
Galapagos, Europe, South Africa, South Korea, Japan, Nansei Islands,
Ogasawara Islands, Australia, New Zealand). Differences among native and
non-native assemblages in the distribution of species among families were
investigated using ordination analysis. We tested whether invasion
disharmony is explained by propagule pressure (proxied by species richness
in border interceptions) and if families were associated with specific
trade commodities. In total, 741 non-native Lepidoptera species,
accounting for 0.47% of the global diversity of lepidopterans, are
established in at least one of the 11 regions. Crambidae, Pyralidae,
Tineidae and Gracillariidae were particularly successful invaders, whereas
the two most species-rich families, Erebidae and Geometridae, were
under-represented among non-native Lepidoptera. Much of the variation in
species numbers in the native, and less so in the non-native assemblages
could be attributed to land area. Although native assemblages were similar
among nearby regions, non-native assemblages were not, suggesting
geography had little effect on invasion disharmony. Comparison of
established with intercepted species revealed that macromoth families were
generally under-represented in establishments, whereas several micromoth
families were under-represented in interceptions. This discrepancy may
relate to greater detectability of larger species or high propagule
pressure via associations with specific invasion pathways. Invasion
disharmony in Lepidoptera appears to be driven by processes unrelated to
the success of native assemblages. While native assemblages developed
through long-term evolutionary radiation, the composition of non-native
assemblages is driven by differential invasion pathways and traits
affecting the establishment of founder populations that vary among
families.