A trait-based approach to assess niche overlap and functional distinctiveness between non-indigenous and native species

Our understanding of the community assembly processes acting on non-indigenous species (NIS), as well as the relationship with native species is limited, especially in marine ecosystems. To overcome this knowledge gap we here develop a trait-based approach based on the functional distinctiveness metric to assess niche overlap between NIS and native species, using high-resolution data on benthic invertebrate communities in the Baltic Sea. Our results show that NIS retain a certain degree of similarity with native species, but display one or a few singular unique traits (e.g., bioturbation ability). Furthermore, we demonstrate that community assembly processes, including both environmental filtering and limiting similarity affect NIS establishment, but that their effects may be highly context dependent, as illustrated by pronounced spatial patterns in distinctiveness. Finally, our trait-based approach provides a generic framework applicable to other areas and organisms, to better understand and address biological invasions. In this work, we present a generic trait-based framework based on functional distinctiveness to address several aspects of biological invasions from a functional and community perspective. The proposed framework is tested using high-resolution data on benthic invertebrates in the Baltic Sea, showing that NIS retain certain similarity with natives while they might display one or few singular traits. In addition, their establishment can be affected by both environmental filtering and limiting similarity, with such effects being highly context-dependent.image