Loss of functional diversity rather than species diversity of pollinators decreases community-wide trait matching and pollination function

1. Loss of animal species and functional diversity can degrade ecosystem functions and services in plant-animal mutualistic networks, but their relative effects have rarely been previously examined in natural communities. Contrary to previously published theoretical results, under natural conditions, changes in pollinator functional niches caused by species and functional diversity losses are dynamic and often unpredictable. The lack of studies on natural networks limits our ability to predict future effects of decreasing pollinator diversity on wild and cultivated plants. 2. We quantitatively evaluated the relative effects of pollinator species and functional diversity loss on plant-pollinator trait matching and pollination success across 40 spatiotemporally variable coastal networks. 3. We found that low pollinator functional diversity (low abundance of long-tongued pollinators) reduced community-level plant functional specialization and trait matching between flowers and pollinators by reducing functional floral-niche partitioning among pollinators. In contrast, pollinator species diversity did not influence community-level trait matching. Furthermore, decreasing community-level trait matching had a negative effect on community-level plant pollination success, regardless of flower morphology. 4. The present study demonstrated that pollinator functional diversity loss, rather than species diversity loss, was the main factor contributing to pollination functional loss in the plant-pollinator networks studied. We also demonstrated the importance of assessing functional aspects of plant-pollinator networks to evaluate community-level pollination functional loss under global pollinator decline.