UC Berkeley

Mutually beneficial interactions between pollinators and flowering plants represent a critical but threatened component of ecosystem function that can underlie the success of ecological restoration. The management and removal of invasive species may give rise to unanticipated changes in plant-pollinator mutualisms because they can alter the composition and functioning of plant-pollinator interactions in a variety of ways. In an attempt to incorporate a functional framework into invasive species management, we conducted a large-scale manipulative experiment to examine the restoration of the plant-pollinator mutualisms and the pollination of a functionally important endemic tree species, Metrosideros polymorpha, following the removal of a competitively dominant invasive floral visitor and arthropod predator, Vespula pensylvanica. The invasive western yellowjacket wasp, Vespula pensylvanica, is an adept and aggressive nectar thief of the partially self-incompatible and pollen limited M. polymorpha. A management strategy utilizing 0.1% fipronil chicken bait with the addition of heptyl butyrate reduced the abundance of V. pensylvanica by 95 ± 1.2% during the 3 months following treatment and maintained a population reduction of 60.9 ± 3.1% a year after treatment in the managed sites when compared with unmanaged sites. The large-scale management of V. pensylvanica demonstrated that V. pensylvanica through both superior exploitative and interference competition inhibits resource partitioning and displaces native and non-native M. polymorpha pollinators. Correspondingly, the removal of V. pensylvanica resulted in the competitive release and restructuring of the pollinator community and the re-establishment of the plant-pollinator mutualisms and pollination of M. polymorpha. This research elucidates the competitive mechanisms and contrasting implications of introduced species on ecological function and provides a framework from which future invasive species management can preserve ecological function and maintain ecosystem resilience.