In poor taste: leaf palatability traits are not correlated with aboveground enemy release

Many species experience less pressure from herbivores, predators, or pathogens in their introduced range than in their native range. This phenomenon, known as enemy release, is one explanation for the success of introduced plant species worldwide. However, species experience enemy release to different extents, or not at all. Surprisingly, we have little understanding of what types of species or circumstances are associated with strong enemy release. We aimed to test whether ten defensive leaf traits that contribute to plants’ palatability to aboveground herbivores can predict the level of enemy release they experience. Our study expands upon previous work, which found enemy release occurring across 16 plant species studied at 12 sites within their native (5 sites; European) and introduced (7 sites; Australian) ranges. Contrary to all predictions, we found no evidence that enemy release was related to ash content, C:N ratio, hair density, leaf dry matter content, leaf mass per area, cyanogen presence, lipid content, phenolic compounds, oxidative activity, or combined chemical, physical, and total defences. This result demonstrates the need to further assess other traits, or environmental variables that may contribute to enemy release, so that we may more accurately predict when and where it is most likely to occur. Finding that these defensive traits do not predict enemy release in our study system brings us a step closer to understanding the mechanisms underlying successful invasion, which is increasingly important in our rapidly changing world.