Exotic species and temporal variation in Hawaiian floral visitation networks

Background/Question/Methods

A major force behind the success of invasive species is escape from antagonistic interactions. However, the potential role of mutualistic interactions involving non-native species has only recently begun to be explored. When plants are introduced into a new environment, their reproductive success can be limited by the lack of a suitable pollinator. If there is no suitable native pollinator, the success of exotic plants may depend on the presence of exotic pollinators, a situation mirrored for exotic plant visitors. This study examines the role of non-native plants and insects in floral visitation networks in Hawaii, in simple ecological communities with a depauperate native pollinator fauna. On the island of Hawaii, in sites that differed with respect to the presence of non-native plants, insect floral visitors were observed and quantified across multiple years and seasons.

Results/Conclusions

Where non-native plants were present, non-native insects were observed to visit both native and non-native plant species, while native insects rarely utilized non-native plant resources. In these sites, the majority of floral visitors comprised non-native bees and syrphid flies. In contrast, in sites dominated by native plants, native bees were major visitors. Thus, the impact of exotic plants and insect visitors on visitation networks was non-symmetrical. Non-native plants relied upon non-native insect taxa, while non-native insect taxa were able to utilize both native and non-native plants. Additionally, the network impacts of certain taxa were not consistent over the observed time periods, indicating that temporal variation may have a strong effect on observed network structure. This study emphasizes that determining the role of mutualistic interactions on the success and impact of invasive species requires looking across a broad time frame and beyond isolated pairwise interactions.