Functional traits of indigenous and exotic ground-dwelling arthropods show contrasting responses to land- use change in an oceanic island, Terceira, Azores

Aim: Land- use change typically goes hand in hand with the introduction of exotic species, which mingle with indigenous species to form novel assemblages. Here, we compare the functional structure of indigenous and exotic elements of ground- dwelling arthropod assemblages across four land- uses of varying management intensity. Location: Terceira Island (Azores, North Atlantic). Methods: We used pitfall traps to sample arthropods in 36 sites across the four land- uses and collated traits related to dispersal ability, body size and resource use. For both indigenous and exotic species, we examined the impact of land- uses on trait di-versity and tested for the existence of non- random assembly processes using null models. We analysed differences in trait composition among land- uses for both indig-enous and exotic species with multivariate analyses. We used point–biserial correla-tions to identity traits significantly correlated with specific land- uses for each element. Results: We recorded 86 indigenous and 116 exotic arthropod species. Under high- intensity land- use, both indigenous and exotic elements showed significant trait clus-tering. Trait composition strongly shifted across land- uses, with indigenous and exotic species being functionally dissimilar in all land- uses. Large- bodied herbivores domi-nated exotic elements in low- intensity land- uses, while small- bodied spiders domi-nated exotic elements in high- intensity land- uses. In contrast, with increasing land- use intensity, indigenous species changed from functionally diverse to being dominated by piercing and cutting herbivores. Main conclusions: Our study revealed two main findings: first, in high- intensity land- uses, trait clustering characterized both indigenous and exotic elements; second, exotic species differed in their functional profile from indigenous species in all land- use types. Overall, our results provide new insights into the functional role of exotic spe-cies in a land- use context, suggesting that, in agricultural landscape, exotic species may contribute positively to the maintenance of some ecosystem functions.