A global review of mistletoe frugivory and seed dispersal: The plant perspective

Mistletoe-frugivore interactions stand out as one of the classic examples of specialized and reciprocal relationships in ecology and evolutionary biology. Additionally, many theoretical advances have been made by using the interactions between mistletoes and their seed dispersers as study models. Although generally well-studied, there is no single global review on mistletoe frugivory and seed dispersal, creating an opportunity to synthesize existing knowledge, identify major gaps, and advance unresolved and new research questions. We conducted a systematic review of studies on mistletoe frugivory and seed dispersal, focusing on taxonomic, geographic, and methodological patterns, showcasing the plant perspective, which has been comparatively underappreciated relative to seed dispersers' perspective. The number of studies (n = 58) and species studied (n = 36) was proportional to the number of species per genus, although several diverse genera remain understudied. We found very few studies in the tropical rainforests and in the north temperate forests. No endangered mistletoe species (n = 58) have been studied, and only one species has been studied in urban areas. Methodologically, searching for seeds or seedlings in potential recruitment sites predominated, while tracking movements of seed dispersers with radio or GPS devices remains poorly used. Mistletoe-frugivore interactions offer excellent study models for exploring a different suite of ecological questions, yet substantial gaps persist across taxa, regions, and biomes. Future studies should prioritize rarer species, especially those threatened and endemic. Studies should also prioritize understudied biomes, such as the tropical rainforests and north temperate forests. We further believe that many unanswered research questions could be clarified using appropriate and modern methods to assess and record interactions between mistletoes and frugivores, thereby advancing the use of these systems as model frameworks for studying the ecological and evolutionary consequences of seed dispersal.