Tropical hummingbird pollination networks are resistant to short-term experimental removal of a common flowering plant

Abstract

Theory predicts that the structure of plant-pollination networks should withstand disturbance, but experiments testing this prediction remain uncommon. In this study, we simulated the local extinction of a hummingbird-pollinated understory plant, Heliconia tortuosa, from tropical forest fragments using a replicated Before-After-Control-Impact design while quantifying hummingbird abundance and space use (383 hummingbird captures and 72 radio-tagged individuals), floral visitation rates (>19,000 observation hours), and pollination success (529 flowers). We expected that H. tortuosa removal would either result in (i) network collapse, in which hummingbirds vacate fragments and compromise the reproductive success of other flowering plants, or (ii) increased hummingbird reliance on alternative resources (rewiring), leading to sustained fragment use. In our experiment, hummingbird behavior and pollination were remarkably resistant to loss of H. tortuosa, a locally common plant species representing 30-40% of the available nectar resources on average. The exact mechanisms enabling short-term hummingbird persistence after resource removal remain unclear, as we did not discover evidence of rewiring. We hypothesize that physiological adaptations (e.g., torpor and insectivory) may have allowed hummingbird persistence, perhaps alongside high movement ability. With the important caution that short-term experiments may not emulate natural extinction processes, our study provides support for predictions that pollination networks may be robust to plant species loss.