Estimating competition outcomes between native and invading species using trait and count data

A major challenge in invasion ecology is determining which introduced species pose a threat to resident species through competitive displacement. Since it is impossible to allocate management resources to preventing interactions among all resident and introduced species, methods for identifying instances of potential competitive displacement would greatly help focus precious management resources. Additionally, methods that use readily available data, such as species counts or functional traits, are especially advantageous under urgent invasion timelines compared to those requiring more time-intensive experimental data. Here, we provide a framework for estimating competition outcomes-including displacement-between resident and invading species using species count and functional trait data, two readily available data sources. Our framework provides methods for estimating displacement that is possibly in progress from species count data and estimating possible displacement from functional traits. We apply this framework to the native and introduced gecko species on the Caribbean island of Curaçao. Our work indicates a potential for the displacement of all three native species by introduced species and suggests that the displacement of one native species may already be underway. Given the urgency of the biodiversity crisis, our framework provides a usable tool for the early identification of potentially detrimental interactions from introduced species and provides insights to focus future studies and guide management efforts.