Invasive Asteraceae plants can enhance community stability by changing pollination network structure, yet intense pollen disturbance to native plants in an oceanic island community

Abstract

Abstract Invasive plant species severely threaten natural plant communities around the world, especially for islands. As introduction rates rise, novel species interactions appear within ecosystems. Studies that focus on invasive plant impacts on native plants, especially on native communities, remain largely unexplored and their conclusions are mixed. We constructed ten quantitative plant-pollinator interaction networks and calculated five network-level structure metrics (interaction evenness, linkage density, specialization, weighted connectance, and weighted nestedness) along an Asteraceae invasion gradient in the Yongxing Island community. We calculated the species-level nested contribution of each plant species in each network, and compared the nested contribution differences between invasive Asteraceae and non-Asteraceae species. Stigmas of three native and four invasive Asteraceae species were collected, and their pollen grains were identified. We analyzed invasive Asteraceae species impacts on native pollination network structure and native plant fitness. Both weighted nestedness and weighted connectance increased significantly as invasive Asteraceae became increasingly dominant. Invasive Asteraceae plants had higher nested contribution compared to native plants in most sites, and their nested contribution difference increased as the Asteraceae proportion increased. Furthermore, in native plant species, the proportion of conspecific pollen grains on stigmas decreased significantly, while the proportion of Asteraceae pollen grains on stigmas increased significantly with Asteraceae invasion level increased. For four invasive Asteraceae species, the proportion of conspecific pollen grains was significantly higher than heterospecific and other Asteraceae pollen grains on the stigmas. These results significantly add to our understanding of how the structure of plant-pollinator interaction networks changes concomitantly with plant invasion intensity. Invasive Asteraceae increase community stability and persistence, and negatively affect native plant fitness by influencing heterospecific pollen deposition on stigmas as invasion level increases. Invasive plants may greatly shape network structure and maintain community stability in oceanic island systems. Heterospecific pollen avoidance may be crucial mechanism facilitating Asteraceae invasion success within native communities, together with their ‘integration’, into plant-pollinator interactions on the Yongxing Island.