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 efficiency 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 efficiency and abundance of invasive species. 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, were
noted. Location: Kraków area, Poland. 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 inefficient
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 efficiency.