Dispersal of invasive Berberis glaucocarpa in secondary forest occurs mainly by exotic frugivores

Understanding plant invasions is important in conservation ecology and land management, as invasive plant species worldwide have caused irreparable damage and often incur substantial control costs. To record the dispersal vectors for the invasive barberry (Berberis glaucocarpa) in a New Zealand regenerating forest, video cameras were used to film 24 barberry plants in fruit in Kowhai Bush, Kaikoura. During 242 hours of video, a total of 101 foraging events were recorded by four bird species: silvereye (Zosterops lateralis), blackbird (Turdus merula), song thrush (T. philomelos), and starling (Sturnus vulgaris). The four bird species varied in visitation frequency, time spent on plants, and fruit removal rates. The estimated daily contribution to recorded barberry fruit removal was 42.8% by song thrush, 32.6% by silvereye, 24.3% by blackbird, and 0.2% by starling. No endemic bird species were observed feeding on barberry, despite bellbirds (Anthornis melanura) being common in Kowhai Bush. Removal rates for ripe barberry fruit were relatively modest (1.14% per day), but given the ~3 month fruiting season, represented a sizable seed rain in the surrounding forest. Although barberry is now sympatric with several introduced frugivores in New Zealand, none of its dispersers from its native range in Nepal and northern India are present. Instead, dispersal in New Zealand is facilitated primarily by introduced European bird species and native silvereyes.