Background/Question/Methods
Previous studies have found both positive and negative relationships between phylogenetic novelty of introduced species, relative to the native community, and invasiveness. We suggest that there are both benefits and costs to being novel. Benefits might include greater competitive ability or greater escape from herbivores or other predators for more novel species. Costs might include loss of mutualisms from the native range, if native mutualists are less likely to switch to more novel hosts. We conducted an experiment at Tyson Research Center, St. Louis, Missouri, USA, on fifteen introduced species have vary in their invasiveness, according to Missouri exotic pest plant council classification, and novelty relative to the native community, where novel species were in genera not found in the native community. We conducted competition removal, using manual removal of competitors, and herbivore removal treatments, using insecticide, and compared the resulting performance relative to controls using plant biomass. We analyzed the resulting effect sizes in the context of the phylogeny using Maddison's paired comparison method. We predicted that more novel species would be better competitors and experience greater escape from herbivory than less novel species. To test a possible cost of novelty, we also conducted pollen supplementation trials on nine invasive species to quantify pollen limitation. We measured phylogenetic novelty for each of these species as the branch length to the nearest native neighbor on a phylogeny of the flora of Tyson Research Center. We then regressed pollen limitation on phylogenetic novelty using phylogenetic independent contrasts. We predicted that more novel species would have greater pollen limitation, if they experience greater "escape" from pollinators.
Results/Conclusions
We find evidence for both greater competitive ability and greater herbivore escape in novel introduced species, relative to less novel introduced species. Both of these mechanisms could explain the greater performance of some novel species. Our preliminary tests for costs in invasive species find no costs of novelty in pollen limitation. This suggests that, for invasive species, loss of mutualist pollinators does not limit reproductive success. Future studies will incorporate a meta-analysis of pollen limitation to more broadly test for costs of pollinator escape in novel introduced species.