Biotic and abiotic factors affect dispersal and spread of an invasive thistle
Models of dispersal and spread are becoming increasingly important as climate change affects species distributions worldwide. Since the effects of climate are likely to affect dispersal traits via phenotypic plasticity, experiments are needed to better understand how species are likely to respond to changing local conditions. However, it is not often clear which traits and which environmental perturbations will significantly affect population spread. To identify important drivers of dispersal responses and their expected effects on population spread, here we analyze the results of a suite of field experiments in which dispersal responses were explicitly quantified in field manipulations of the invasive thistle, Carduus nutans. We examine the relative importance of local factors including climate warming, drought, the presence of generalist and specialist herbivores, and disturbances such as mowing.
We find that in this invasive species, traits that affect dispersal, including seed falling velocity, plant height, and seed release, are all affected by the conditions under which maternal plants are reared. In turn, these responses affect models of population spread and, if ignored, can change projections of dispersal and spread by up to 38%. This species exhibits a great deal of phenotypic plasticity, and some responses to local conditions initially seem counterintuitive. Our work suggests that understanding the relative impact of different biotic and abiotic environmental changes will help us to better predict species distributions in future climates.