Traits of hymenopterans, dipterans and plants that indicate vulnerability to landscape homogenization

Pollination services are currently threatened by land-use changes that lead to landscape homogenization. However, the response of particular species to anthropogenic pressures is variable and, therefore, some species may perform better (winners) and others worse (losers) in the face of landscape homogenization. Our main objective was to understand which plant and pollinator species were the most vulnerable to this landscape disturbance. To evaluate this, we used data on pollinator and plant abundance in 20 study sites located along a gradient of landscape heterogeneity (i.e. diversity of land-cover layers at 500 m and 1 km radius surrounding the study sites) across Mallorca Island (western Mediterranean Basin). For 46 pollinator species (hymenopterans and dipterans) and 162 plant species, we collected functional traits (either by direct measurements or from literature) that reflect the ability of species to adapt to changing environments, and related their abundance to their traits along a gradient of landscape heterogeneity. Landscape heterogeneity influenced the study groups at different scales, affecting Diptera at a smaller scale than Hymenoptera and plants. Although the number of species was not influenced by landscape heterogeneity, the abundance of species was. An increase in landscape heterogeneity favored the abundance of social Hymenoptera compared to solitary ones. The abundance of Hymenoptera that nest in the ground or in cavities increased with landscape heterogeneity, while the abundance of builders decreased. Besides, increasing landscape heterogeneity enhanced the abundance of small and medium sized Hymenoptera, whereas the abundance of large Hymenoptera remained stable along the heterogeneity gradient. Landscape heterogeneity also favored the abundance of parasitoid and anthophilous Diptera. Regarding plants, we found that more heterogeneous landscapes also held a higher abundance of zygomorphic flowers. Understanding the ‘winners’ and ‘losers’ in the face of landscape changes may help prevent and anticipate the effects of global change on the pollination service.