Neglected seed dispersers and research compartmentalisation: how much do we know about what we don't know?

Seed dispersal is critical for long-term ecosystem resilience. However, excessive compartmentalisation of research into particular disperser guilds (e.g. birds) hampers our understanding of their relative contributions to overall seed dispersal, risking erroneous conclusions and overlooking key information gaps. Here, we evaluate how information about over 11 000 interactions between 1902 plant and 455 animal species in Europe accumulated over 400 years, and estimate information completeness across disperser guilds, plant types, and dispersal mechanisms (endozoochory, epizoochory, synzoochory, and myrmecochory). Information regarding the plants dispersed by each group of animals ranges from 27% to 79% sample coverage, with birds of prey (27%), ants (28%), and rodents (31%) particularly understudied. Most research focussed on fleshy-fruited plants rather than dry-fruited plants, and most on internal dispersal as the mechanism (endozoochory). Interestingly, scientists' perceptions of what are the most neglected disperser guilds do not correlate with our sample coverage estimates, showing an inability of the scientific community to identify information gaps. We urge researchers to bridge research silos and to study overlooked guilds, mechanisms, and plant types. Implementing community-level synthesis studies that integrate data across guilds is essential for accurately predicting ecosystem responses to global change and developing effective conservation strategies.