Background/Question/Methods
It is widely recognized that predicting plant invasions at large biogeographical scales requires jointly accounting for alien species traits and local community filters such as abiotic conditions, biotic interactions and propagule pressure. Despite this recognition, interactions between traits and community filters are generally neglected. Here, we aim to address this limitation by developing a hierarchical framework that builds on trait-based theory to model alien species distributions as a function of spatially explicit variables filtering invasions while jointly accounting for their interactions with species traits. Based on a large dataset of more than 50000 community plots in herbaceous communities throughout France, we built a multi-species hierarchical model of the distribution of the ten most widespread alien plants in French grasslands. In this model we explicitly account for how plant height, specific leaf area (SLA) and seed mass affect alien species occurrence along gradients of human pressure, environmental conditions and native community composition. We finally contrast the results to native species responses along the same gradients.
Results/Conclusions
We show that two out of three traits significantly modulate species’ responses along these broad gradients. Alien plants with exploitative traits (i.e. tall and with high SLA) were less dependent on human pressure, more efficient in resource-rich environments and better at avoiding competition from the natives. Further, even though overall trait values of alien and native species had similar ranges, several trait-gradient interactions were unique to alien plants (e.g. human pressure was only important for supporting alien species with low SLA). Building on these trait-gradient interactions our approach also allows spatially explicit estimations of future invasion risks by novel species with particular sets of traits. By taking the best from multi-species distribution modelling and trait-based theory, our framework paves the way for a generalized mechanistic understanding of how traits influence the success of alien plants and their spatial distributions.