Context: Mutualistic interactions between animals and plants shape the structure of plant–animal systems and, subsequently, affect plant-community structure and regeneration. Aims: To assess the effects of plant and rodent functional traits on the formation of mutualistic and predatory interactions regarding seed dispersal and predation in a warm-temperate forest. Methods: Seed scatter-hoarding and predation by six sympatric rodent species on seeds belonging to five sympatric tree species were tested under enclosure conditions. Key results: Functional traits (i.e. rodent body size and seed traits) are important to mutualism/predation in this seed–rodent system. The rodent–seed network is highly nested: large-sized rodents have mutualistic or predatory interactions with both large- and small-sized seed species, but small-sized rodents interacted with small-sized seed species only. Large seeds or seeds with hard coats enhanced mutualism and reduced predation. Conclusion: Body size of rodents and seed traits such as handling time and nutritional value are key factors in the formation of mutualistic and predatory interactions within seed–rodent systems. Implications: To promote seedling establishment in degenerated forests, introducing or protecting large-sized scatter hoarders and reducing the density of pure seed eaters are needed.

Many seed-hoarding species are faced with ephemeral pulses of seeds that result in competition at seed sources and the need to minimize hoarding time