Frugivore richness poorly predicts seed dispersal effectiveness under climate change

Animal-mediated seed dispersal underpins forest maintenance, yet climate change threatens this mutualism by reshaping plant-frugivore overlap. Most projections assume that frugivore richness and binary interactions adequately capture seed dispersal success, overlooking the unequal quantitative and qualitative contributions of individual species. Here, we combine estimates of seed dispersal effectiveness (SDE) with species distribution models to assess climate change impacts on seed dispersal of two keystone trees-the jussara palm (Euterpe edulis) and silver cecropia (Cecropia hololeuca)-in the semideciduous Atlantic Forest. We show that frugivore richness is a poor predictor of future dispersal outcomes: across approximately 60% of projected plant ranges, richness either under- or over-estimated seed dispersal and germination potential. This mismatch was species-specific. For the jussara palm, richness explained < 13% of the variance in climate-driven changes in both dispersal quantity and germination success, whereas for silver cecropia, richness aligned only with germination outcomes. Consequently, projected changes in frugivore assemblages and seed dispersal function can diverge under climate change. Our findings demonstrate that richness-based metrics can misrepresent climate risks to plant-frugivore mutualisms and that incorporating functional measures of SDE yields more accurate forecasts of plant recruitment potential and ecosystem-level disruption-essential for predicting ecosystem resilience in a warming world.