Biotic interchange in the Anthropocene: strong asymmetry in East Asian and eastern North American plant invasions

Abstract

AbstractAimModern species invasions result in the global reshuffling of regional floras, but biogeographical biases in floristic exchanges (origin effects) are underexplored. We compared habitat‐level invasion patterns in two environmentally similar regions, and ask whether plant exchanges are also similar or if one region largely invades the other.LocationEastern North America (ENA) and East Asia (EAS).MethodsWe compiled a new dataset of the 1293 naturalized (i.e. non‐native, self‐sustaining) and invasive (i.e. spreading) plant taxa in EAS, including the habitats they invade and their native distributions. We tested for biases by biogeographical origin, growth form and habitat in EAS invasions, and compared them with those for ENA.ResultsEAS contains 51% fewer naturalizations than ENA, but with a similar biogeographical representation. However, invasions in each region show large differences in biogeographical affinity, taxonomic representation and habitat. Invasions in ENA are biased from East Asia (29% invasive), while invaders in EAS come from a fairly uniform set of major temperate regions. Taxonomically, 54% of Asteraceae naturalizations in EAS are invasive compared with only 16% in ENA. Open habitats are highly invaded in both regions (75% of invasions), but forests are significantly more invaded in ENA than EAS (29% vs. 9%). Reciprocal invasions are asymmetric: EAS contributes more woody invaders to ENA than expected (56% woody, P < 0.001), while in EAS nearly all (91%) invaders from ENA are herbaceous.Main conclusionsAlthough they represent regions of similar temperate environments, the origin, taxonomy and habitat affinities of plant invaders in EAS and ENA floristic regions are strongly contrasting. These differences are robust to differences in introduction effort when the invasiveness of species once naturalized is considered. We suggest these patterns support a historical perspective of invasions that invokes differences in regional selection pressures that pre‐adapt certain floras for invasion into particular environmental conditions.