Data from: Functional outcomes of mutualistic network interactions: a community-scale study of frugivore gut passage on germination

1. Current understanding of mutualistic networks is grounded largely in
data on interaction frequency, yet mutualistic network dynamics are also
shaped by interaction quality—the functional outcomes of individual
interactions on reproduction and survival. The difficulty of obtaining
data on functional outcomes has resulted in limited understanding of
functional variation among a network’s pairwise species interactions, of
the study designs that are necessary to capture major sources of
functional variation, and of predictors of functional variation that may
allow generalization across networks. 2. In this community-scale study, we
targeted a key functional outcome in plant-frugivore networks: the impact
of frugivore gut passage on seed germination. We used captive frugivore
feeding trials and germination experiments in an island ecosystem,
attaining species-level coverage across all extant native frugivores and
the plants they consume to 1) assess sources of functional variation, 2)
separate effects of pulp removal from those of scarification via gut
passage, and 3) test trait-based correlates of gut passage effect sizes.
3. We found antagonistic seed predation effects of a frugivore previously
assumed to be a seed disperser, highlighting the need to consider
functional outcomes rather than interaction frequency alone. The other
frugivores each exhibited similar impacts for individual plant species,
with benefits primarily caused by pulp removal rather than scarification,
supporting the use of animal functional groups in this context. In
contrast, plant species varied widely in impacts of gut passage on
germination. Species with smaller seeds and more frugivore partners had
larger benefits of gut passage, showing promise for network metrics and
functional traits to predict functional variation among plants. 4.
Synthesis. Combining network and demographic approaches, we assessed the
degree and sources of variation in a key functional outcome of
plant-frugivore interactions across an entire network. Using a detailed
study design, our work shows how simpler study designs can capture primary
sources of functional variation and that functional traits and network
metrics may allow generalization across networks. Efficiently measuring
and generalizing sources of functional variation within mutualistic
networks will strengthen our ability to model network dynamics and predict
mutualist responses to global change.