Effects of seed mass on seed foraging behaviors of two sympatric rodent species

Rodent–seed foraging behavior plays a key role in seed fate and plant regeneration. Seed mass is a central trait influencing seed predation, removal and caching by hoarding rodents. In ecosystems with multiple sympatric rodent species, differential seed use can exert varying selective pressures on seeds. In a semi-natural experiment, we observed how Quercus cerris acorn mass affected seed predation, removal, and dispersal by 2 sympatric rodents of different body sizes, Apodemus flavicollis and A. sylvaticus. For both species, seed mass had a consistent effect in predicting seed fate. We detected a species-specific response in seed predation: A. flavicollis more likely predated heavier acorns, while seed mass was not found to affect acorn use in A. sylvaticus. Seed removal probability was affected by seed mass but it did not differ between the 2 species, which both showed similar removal patterns with respect to seed mass. Although the mass of removed acorns did not differ between the 2 species, the acorn mass to rodent body mass ratio of removed seeds was higher in A. sylvaticus compared with A. flavicollis. The likelihood of predation versus that of dispersal after removal was found to be species-specific: seed dispersal did not vary with seed mass for A. flavicollis, while A. sylvaticus dispersed heavier acorns. These results suggest that the 2 species might play distinct roles in determining seed fate. Our findings highlight the importance of considering species-specific foraging strategies when assessing the role of sympatric hoarding rodents in seed dispersal and forest regeneration.