COS 96-2
You can run but you can’t hide: Using neighborhood analysis to quantify the effects of herbivory on plant range expansion
Climate change is expected to initiate a process of poleward range expansion for many plant species and range expansion rates will be determined by the success of individuals establishing beyond their range margins. However, these migrant individuals will encounter new communities, and are likely to leave behind specialist natural enemies. If herbivores and pathogens have a strong impact on plant recruitment, then enemy release has the potential to help species successfully colonize new areas.
In order to test the potential for enemy release to impact range expansion, we conducted a transplant experiment and used neighborhood analysis to quantify the importance of conspecific trees to recruitment. In this study we address the following questions: 1) Does the abundance of con-specific neighbors predict herbivore communities and herbivory? 2) How important is this to seedling growth and survival? 3) To what extent does this contribute to the success of seedlings which are planted outside their original range?
Ten species of woody plants were planted within and beyond their current distributional ranges and foliar herbivory, pathogen activity, growth, and survival were monitored for four years. We also assessed invertebrate herbivore communities and treated a subset of seedlings with a pesticide to reduce herbivory. Seedlings were planted across light and moisture gradients at each site to separate the effects of environmental covariates that could also affect establishment. Trees within 15 m of each seedling were mapped and we conducted a neighborhood analysis using a Bayesian framework.
Results/Conclusions
We found significant correlations between con-specific adults and seedling herbivory. However, the sign and strength of these relationships were species specific; the seedlings of some species (e.g., Quercus rubra) had more herbivory in the presence of more con-specific adults, whereas the opposite trend was observed for other species (e.g., Quercus alba). The effects of neighborhood on herbivore communities also varied by species. In contrast, the impacts of herbivory on seedling growth and survival were overwhelmingly negative.
Our results confirm that the effects of herbivory on seedling recruitment vary by species and across range edges. Thus, our findings show that release from specialist herbivores could give some migrant species an advantage over native competitors whereas native herbivores could help prevent some potential migrants from establishing beyond their original ranges. Overall, we demonstrate that biotic interactions will influence plant range expansion and highlight the importance