Impacts of species introductions on the trait diversity of interacting avian frugivores and fleshy-fruited plants depend on native trait diversity

O_LIIntroductions of non-native species to native ecological communities by humans are major drivers of global biodiversity change. At the same time, biotic interactions, such as those between avian frugivores and fleshy-fruited plants, build the backbone of ecosystems. Hence, studying how species introductions influence interacting species of both trophic levels is essential to understand possible functional consequences of global change. C_LIO_LIHere, we take a trait-based approach, focusing on species traits that influence their biotic interactions and related ecosystem functioning, and explore how species introductions affect the diversity of such functional traits within and across assemblages of interacting fleshy-fruited plants and frugivorous birds at several locations across the globe. C_LIO_LISpecifically, we calculate differences in trait diversity and mean trait values, and compare beta trait diversity with and without introduced species, for 25 frugivorous bird and 62 fleshy-fruited plant assemblages. C_LIO_LIIntroduced species tended to increase bird and plant trait diversity in assemblages with low native trait diversity but decreased it in assemblages with higher native trait diversity. In bird assemblages, species introductions shifted mean values towards larger birds with wider bills and more pointed wings. In plant assemblages, mean trait values showed variable changes: fruit length increased and plant height decreased. C_LIO_LIComparisons between assemblages revealed that introduced species reduced the beta trait diversity of both frugivorous birds and fleshy-fruited plants, suggesting biotic homogenisation in terms of their functional traits. C_LIO_LIChanges in trait diversity underscore that species introductions can have functional consequences for biotic interactions and related ecosystem functions, potentially affecting the availability of interaction partners with matching traits and the provisioning of seed dispersal. C_LI