Climate warming, land use change and other large-scale alterations in the environment have major impacts on plant population and community dynamics. Whereas a number of species are supposed not to be able keeping up with their moving climate envelopes, other species are highly successful in range expansion. In a recent paper (Engelkes, Morriën et al. Nature 2008), we showed that successful range expanders exposed to non-coevolved and cosmopolitan polyphagous insect herbivores were reduced less than related plant species from the invaded range (north-western Europe). The range expanders also were less negatively influenced by feedback from the soil communities from the invaded range than the native species. Following from this published study, I will provide an overview of work in progress on aboveground and belowground enemy and higher trophic level exposure of exotic plants that are currently expanding their range from lower to higher latitudes as a response to climate warming. I will also show experimental results on consequences for community organization of enemy release in the field. In a range expansion model, we have analyzed the importance of short versus long distance dispersal in relation to climate warming for belowground plant enemy release and the incidence of population outbreaks.
Results/Conclusions
Our model analysis reveals that long distance dispersal during range expansion is crucial for enemy release benefits. Field and greenhouse experiments confirm that, and also show that successful range expanders are almost equally well defended against aboveground and belowground enemies as cross-continental exotic invaders. These differences depend on the species combination considered. We analyzed the aboveground predator load and effectiveness of belowground predators on root herbivores, as well as the (primary and secondary) chemical constitution of the range expanders to detect differences in defensive strategies. Thus, we aim at explaining the patterns in aboveground and belowground enemy exposure observed in our indoor and outdoor experiments and field surveys. In taking an explicit aboveground-belowground multitrophic interactions approach, we conclude that range expansion along latitudinal gradients is also changing aboveground and belowground multitrophic interactions dramatically. We predict that the results can lead to a variety of plant responses, ranging from invasions to extinctions. Our results will be discussed in relation to the massive work that is currently done on climate envelopes and our conclusion is that we can only understand and predict consequences of climate warming when considering plant population and community dynamics from a combined aboveground-belowground multitrophic interactions perspective.