Résumé
Biodiversity can buffer ecosystem functioning against disturbances by allowing species to compensate for the functions lost through the extirpation of other species, a key process known as ecological insurance. Functional ecology has extended this idea by emphasising trait redundancy amongst species that help buffer core ecosystem functions. However, some functions might be supported only by species with distinct combinations of trait values, which are less likely to be redundant within local communities. Here, we present a new and widely applicable framework to quantify the spatial insurance of locally functionally distinct species amongst communities. Our framework characterises how communities can disproportionately insure (functional sources) or depend on (functional sinks) neighbour communities, a dual relationship that is not captured by traditional metrics of functional beta diversity. We illustrate the application of our framework at broad spatial scales for plants and birds, highlighting biogeographic patterns of functional sources and sinks. This trait-based spatial perspective reveals functional vulnerability, as illustrated by bird communities where functional sources were disproportionately impacted by human activities. It also provides a new approach to identify regions that differ in potential resilience to environmental change and to inform conservation strategies grounded in spatial trait distributions, supporting the preservation of functional distinctiveness beyond a focus on local biodiversity metrics.