Invasive plant species and competition for pollinators

Sammanfattning: Invasive alien species cause harm to native flora and fauna, and can ultimately via biotic interactions and alterations of the abiotic conditions change entire ecosystems. They have therefore during the last decades gotten more attention and are now recognised as one of the major threats to biodiversity worldwide. When invasive plants establish in an area, one concern is that their presence can affect foraging patterns of pollinators. This can potentially have implications for pollination and reproduction of native plant species, and thus also for the local biodiversity. Here, I investigate this issue by studying how the invasive Japanese rose (Rosa rugosa) affects pollination, pollen loads on stigmas and seed set of the native common bugloss (Anchusa officinalis) in the coastal habitat of Lomma, Scania. During summer 2013 common bugloss plants in patches suffering from different degree of rose invasion were observed and compared. The results show that the two plant species share pollinators, and that the degree of rose invasion in a patch could alter the species composition and foraging behaviours of pollinators visiting the native plant. Different pollinators seem to respond differently to the rose. To understand such patterns the traits and ecology of the species should be considered. The number of visits to a certain plant was positively correlated with its number of flowers, and negatively correlated with the number of adjacent common bugloss flowers. Further, I found indications that the Japanese rose affected pollinator visitation to common bugloss flowers, proportion of correct pollen grains on bugloss stigmas and seed weight. Although no effects were seen on number of seeds, Japanese rose may, by impacting pollinator communities and competing for space and nutrients, impact a variety of native plant species and organisms interacting with those. I suggest that future research and conservation efforts regarding invasive plants use an ecosystem-based approach and include the aspect of complex plant-pollinator interactions.