Differences in biotic interactions across range edges have only minor effects on plant performance

Abstract

Summary It is widely expected that plant species will expand their ranges poleward in response to climate change. In the process, individuals establishing beyond existing range margins will be exposed to new biotic communities, including different assemblages of natural enemies. The resulting differences in biotic interactions could lead to scenarios of enemy release or biotic resistance, and if the interactions are strong, they could influence plant performance and therefore colonization success. In order to test whether natural enemies will affect range expansion dynamics, we transplanted seven species along a 450‐km latitudinal gradient that spanned the range edges of five of these species. The experiment was conducted over 5 years with ˜ 13 000 seedlings and included pesticide treatments to reduce invertebrate herbivory. We measured foliar damage caused by disease and invertebrate herbivores, seedling survival, light availability, soil moisture, soil nutrient concentrations and several other variables in nine forests located in four regions along the latitudinal gradient. We found that several species (Carya glabra, Liriodendron tulipifera, Quercus velutina and Robinia pseudoacacia) tended to have less foliar disease beyond their range, but there were few substantial differences in herbivory across range edges (with the exception of Liriodendron tulipifera). After accounting for other variables, including environmental conditions and vertebrate herbivory, we found that foliar disease decreased survival for four species (Acer rubrum, Quercus alba, Quercus rubra and Quercus velutina) and foliar herbivory reduced survival for three species (Acer rubrum, Liriodendron tulipifera and Quercus rubra). However, the effects of these biotic interactions on survival were very small (0–5% reductions in survival at observed levels of damage after four years), which is verified by the minor effects of the pesticide treatment on seedling survival. Synthesis. Our results suggest that foliar herbivores and pathogens are unlikely to play a major role in the range expansion dynamics of these temperate tree species.