Natural habitat loss and exotic plants reduce the functional diversity of flower visitors in a heterogeneous subtropical landscape

1. Functional diversity (FD) of pollinators can increase plant reproductive output and the stability of plant-pollinator communities. Yet, in times of worldwide pollinator declines, effects of global change on pollinator FD remain poorly understood. Loss of natural habitat and exotic plant invasions are two major drivers of global change that particularly threaten pollinator diversity. 2. In a subtropical South African landscape, we investigated changes in the FD of flower visitor assemblages on native and exotic plants along gradients of natural habitat loss and relative abundance of exotic plants. We used a dataset of 1434 flower visitor individuals sampled on 131 focal plants and calculated the FD in three flower visitor traits that are strongly related to plant-flower visitor interactions and pollination processes: proboscis length, proboscis diameter and body length. 3. Multivariate FD of flower visitors decreased with both increasing natural habitat loss and relative exotic abunda...