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Data from: Bird extinctions shift bill-flower trait matching in Hawaiian lobelioids

Case, Samuel1; Hagemann, Molly2; Drake, Donald3; Postelli, Katherine3; Pender, Richard3; Millikin, Pryce4; Rico-Guevara, Alejandro1

Published Jul 13, 2026 on Dryad. https://doi.org/10.5061/dryad.sj3tx96kr

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Abstract

Species extinctions can reorganize ecological interactions by altering the distribution of functional traits within communities. These traits structure how species interact, influencing whether encounters result in mutualistic or antagonistic outcomes. However, the mechanisms linking species loss to changes in interaction outcomes remain poorly resolved, particularly in systems where direct observations of past interactions are unavailable.
We examined how recent avian extinctions in the Hawaiian Islands have shifted pairwise trait matching across all possible combinations of nectar-feeding birds and lobelioid plants with available flower length data. We then tested whether this trait-matching axis (bill length minus flower length) predicts pollination-relevant interaction outcomes.
We quantified pairwise trait matching across historical and contemporary bird assemblages on multiple islands and used permutation tests to assess shifts in trait-matching distributions within islands. We then tested whether trait matching predicts pollen contact and nectar robbing using generalized linear mixed-effects models based on observed bird–flower interactions.
Contemporary bird assemblages were shifted toward more negative trait-matching values across most islands, indicating shorter bills relative to floral length following the loss of long-billed nectarivores and a contraction of the trait space previously occupied by the avifauna.
Trait matching strongly predicted interaction outcomes. As bill-length approached flower length, the probability of pollen contact (i.e., contact with floral reproductive structures) increased, whereas the probability of nectar robbing decreased.
These results show that a simple morphological axis can predict consistent differences in bird–flower interaction outcomes across species pairs.
We show how extinction and subsequent shifts in bill–flower matching compress the distribution of trait-defined interactions and alter the balance of interaction outcomes, shifting ecological systems toward persistent but lower-quality interaction regimes.