Similar trait‐based successional assembly in native and introduced plants despite species pool differences

Abstract

Abstract What drives the composition of invaded communities and the local abundance of introduced species are key questions in ecology. Community‐assembly theory provides a useful framework for addressing these questions. Specifically, the environmental filtering model of community assembly predicts that a species' presence and abundance in a community depend on the interaction between its functional traits and the local environmental filters. However, for introduced species, larger‐scale dispersal and introduction‐related filters may restrict their regional trait pool. Here, we tested this framework using long‐term data from 50+ years of old‐field vegetation succession. We asked whether native and introduced plant assemblages followed the same trait‐based assembly rules. We also asked whether local functional dissimilarities between the two can be explained by regional species pool differences, a possibility that has rarely been addressed. We found strong similarities in the assembly processes of native and introduced plants. Average height and seed mass of both groups increased over time, consistent with previous studies of old‐field succession. Moreover, the two showed similar trait–abundance relationships. While there were also some differences, particularly in their trait–incidence relationships, these differences appeared to be minor. Furthermore, we identified species pool constraints on introduced species and found that the exotic species pool was biased towards early successional traits. Lastly, we found that highly invasive exotic species were also likely to deviate from the expected trait–abundance relationship, suggesting a link between the two. These results imply that introduced species generally follow the same assembly rules as native species. They also indicate that species pool differences can result in local functional composition differences, even when the two groups follow the same assembly rules. Moreover, there may be a link between species invasiveness and deviation from assembly rules, which, if further confirmed, provides a potential method of identifying strong invaders. Synthesis: Using data from a long‐term succession study, we showed several similarities, and some differences, in the assembly of native and introduced species assemblages. Our results provide a better understanding of the factors constraining and allowing invasion, and help in the identification of ‘rule breaking’ invaders.