Invader-pollinator paradox: invasive goldenrods benefit from large size pollinators.
Aim: Mutualistic interactions between alien plants and native pollinators are needed to enable plant invasions. Although the increasing abundance of invasive plants in a habitat causes a dramatic decline of native pollinators, pollination services received by invaders are often sustained. This invader-pollinator paradox might be attributed to differences in pollination effectiveness and varying vulnerability to invasion among pollinators with different life history traits. In an experimental study, we explored the relationships between pollinator body size, pollination effectiveness and abundance of invasive species. Location: Kraków area, Poland. Methods: We placed a pair of potted invasive goldenrods (Solidago gigantea) at 25 sites differing in goldenrod abundance (cover: 0%-100%). Floral visitation rate of the potted goldenrods, as well as seed set and viability, was noted. Results: Species richness of pollinators visiting inflorescences decreased with the increase of the goldenrod cover, whereas the floral visitation rate remained unchanged. However, the seed set was positively related to the goldenrod cover. Body size of floral visitors was structured along with the goldenrod cover so that pollinators' size increased with the cover. Also, the seed set of the potted plants, as well as goldenrod seed viability, depended positively on the body size of visiting pollinators. Main conclusions: Invasive goldenrods did not suffer from pollinator shortage and ineffective pollination, especially in habitats densely covered by the invader, due to the presence of large-bodied pollinators. Our study highlights that pollination and reproduction of invasive plants might be sustained through ecological filtering, affecting the composition of pollinators with traits increasing pollination effectiveness.