Print PageIndividual biotic interactions in the introduced range of invasive plants have been shown to contribute to their success. But, we have not yet conducted experiments that allow us to investigate the rich interplay of genetic variation in plant traits and geographical variation in the biotic environment to determine their contributions to the success of invasive plants. Critical questions include: (1) Do plant species experience weaker overall biotic regulation in their introduced range than in their native range? (2) Is this regulation weaker in absolute terms and/or compared to other species in each range? (3) Do native genotypes differ from introduced genotypes in their interactions? (4) Do the same species or genotypes experience weak biotic regulation in both their native and introduced ranges? (5) Are the effects of different biotic interactions independent, antagonistic, or synergistic? We tested these questions in eight replicated common gardens in the US and China using the invasive Chinese Tallow Tree (Triadica sebifera, 12 populations from each range) and 4 congeneric pairs of trees (Ulmus, Celtis, Liquidambar, Platanus) with Chinese and US species and factorial insect, foliar fungus, and soil fungus treatments.
Results/Conclusions
We have not found that species are more vigorous in the introduced range as predicted by the Enemies Release Hypothesis. Rather, each genus is more successful (higher survival and growth) in a single range (Celtis - in China, Liquidambar - in US, Platanus - in US, Ulmus - in China) but there was no pattern for US vs China species being more successful in general or in particular ranges. This difference in success is correlated with herbivorous soil nematode loads with genera with higher loads in the US being relatively less successful. But, to date, experimental treatments are not linked to differences in success. Triadica from populations in the US have higher survival and growth in both ranges in all treatments, lower insect herbivore resistance but higher herbivorous nematode resistance, higher aboveground herbivore tolerance but lower belowground tolerance, higher insect herbivore loads in China but higher herbivorous nematode loads in the US. Together these suggest that low insect herbivore loads have contributed to the success of Triadica though ecological and evolutionary mechanisms despite higher nematode loads but the greater performance of US populations in all conditions suggests an important role for selection for rapid aboveground growth in the introduced range.
