Avian translocations restore dual interaction networks in an island ecosystem

Abstract

Many island bird species have been driven to extinction by introduced predators. Although poorly understood, these extinctions could have a 2-fold impact on bird-plant mutualisms, because island bird species can serve as both pollinators and seed dispersers. We investigated how avian translocations into a mammal-free reserve in New Zealand affected the structure of bird-flower and bird-fruit interactions. We observed bird-fruit and bird-flower interactions over a 9-year period to establish (1) the extent to which native birds are both nectivorous and frugivorous (i.e. "dual mutualists") and ( 2) how avian translocations and conservation reestablished nectivory and frugivory networks. Results showed that all but one native bird species were dual mutualists. Pairwise species interaction frequencies were positively correlated between networks. However, overall levels of nectivory by each bird species were unrelated to levels of frugivory. Interaction specialization and species strength also did not differ between networks. The reintroduction of threatened and endangered bird species appeared to have restored both interaction networks, and the sequence of species recovery accelerated restorative changes. Overall results indicate that not only does the extinction of dual mutualists have a 2-fold, negative effect on mutualistic interactions with plants, they can also accelerate the recovery of ecosystem services following restoration efforts.

Conspicuous, green flowers are an honest signal of nectar rewards in a bird-pollinated tree (Fuchsia excorticata, Onagraceae)

“…All data were collected over two owering seasons (2019-2020) in a forest reserve on the North Island of New Zealand known as 'Zealandia', which lies close to the coast (41°18.3' S, 174°44.8' E) and experiences a mild, temperate climate (see Burns 2013). The dominant vegetation in the reserve is broadleaf-conifer forest composed of evergreen trees, tree ferns, shrubs and lianas (see Lim and Burns 2022;2023).…”

Network-based restoration strategies maximize ecosystem recovery

“…Although returning a severely degraded ecosystem to its original state can be difficult, it remains a key goal for many conservation and restoration projects 12 , 16 . Traditional attempts to design optimal restoration strategies have focused on single-species 17 , suitable habitat identification 18 , prioritization of sites that maximize spatial rescue effects in communities interconnected by dispersal 19 , or have used low-dimensional models with a few interacting components 20 . More recently, researchers have highlighted the need to shift from single species to entire interaction networks in order to design effective restoration strategies 21 , 22 , with the expectation that the most effective recovery strategy may involve reversing the sequence of species loss that led to the maximum amount of habitat loss or number of secondary extinctions 23 , 24 .…”