Print PageClimate change is causing many plants to migrate poleward in response to changing temperatures. Some of these migratory plants will germinate far beyond their current range, where they will be exposed to new biotic communities. One consequence is that pioneer plants will at least temporarily leave behind their specialist natural enemies. This could increase fitness and potentially accelerate migration rates for some plant species.
To investigate these factors we conducted a seedling transplant experiment and quantified the interactions between migrant plants and existing communities. In this study we address the following questions: 1) Do migrant seedlings experience less herbivory and disease in their new ranges than native seedlings? 2) Are migrant species exposed to less herbivory and disease than in their native range? 3) How important is this to plant growth and survival?
To investigate these questions, ten species of woody plants were planted within and beyond their current distributional ranges and monitored foliar herbivory, pathogen activity, growth, and survival. Seedlings were also planted across light and moisture gradients at each site to separate the effects of environmental covariates that could also affect establishment of the seedlings. Data were analyzed with hierarchical Bayesian models.
Results/Conclusions
Herbivory rates at northern sites were higher for most species, but were especially high for some migrant species including Carya glabra and Robinia psuedoacacia. Herbivory had significant effects on seedling survival, and although the results are highly species specific, we show that some existing communities may have biotic resistance to invasion by southern species. In contrast, pathogen activity was significantly lower for plants occurring beyond their current range: migrant seedlings had an average of 4.9% of their leaf area affected by foliar pathogen activity over the growing season, compared to 9.4% for indigenous plants. In contrast, exotic invasive plants had foliar pathogen levels of 1.4%.
Our results demonstrate that while natural enemy release could be an important factor influencing plant migration rates, negative interactions with existing communities may also be important. Finally, we stress the importance of including biotic interactions in predictions of plant range shifts.
