Impact of landscape alteration and invasions on pollinators: a meta-analysis

1. Alterations in land use and biological invasions are two major components of global change that threaten biodiversity. There is high concern about their impact on pollinators and the pollination services they provide. However, the growing literature shows different, even contradictory results. 2. We present a global meta-analysis of 58 publications reporting 143 studies (37 on landscape alteration and 21 on biological invasions) to assess the extent to which these components affect pollinators, and whether taxonomic and ecosystem-type differences in pollinator responses occur. We also quantified which component of landscape alteration had the largest effect on pollinators and assessed whether animal invasions differ from plant invasions in their effect on native pollinators. 3. Habitat alteration and invasions affected pollinators to the same magnitude by decreasing visitation rates. Vertebrates in altered landscapes and insects (excluding bees) in invaded areas were the most affected pollinator taxa. 4. Pollinator abundance was more reduced in altered forest ecosystems than in altered grasslands; while the reverse pattern was found for pollinator richness. However, the response of pollinators to invasions was independent of ecosystem type. 5. Disturbance of the surrounding matrix was more important in decreasing pollinator visitation rates than fragment size. 6. Invasive animals seemed to have a more consistent negative effect on visitation rates than invasive plants. 7. Synthesis. Our study highlights that different components of global change have similar negative outcomes on pollination patterns, but that responses of pollinators vary among taxa and ecosystem types, as well as the attributes of landscape alteration considered and whether the invader is an animal or a plant.