Larger Seeds are Dispersed Farther: the Long-Distance Seed Disperser ant Aphaenogaster famelica Prefers Larger Seeds

Seed dispersal by ants (myrmecochory) is an important life phase in flowering herbs of temperate deciduous forests, and long dispersal is basically preferable in terms of plant fitness. Although it is known that larger ants transport seeds farther, previous studies conflicted whether larger seeds are preferred by large ants. We examine how seed size and ant body size influence removal rate of seeds and their dispersal distance by ants. The obligate myrmecochorous, large-seed bearing Viola hondoensis and ant-ballistic diplochorous, small-seed bearing Viola spp. and Corydalis pallida were comparatively investigated. 1) Ant preference: attraction rate and transportation rate of large V. hondoensis seeds by ants were consistently high regardless of the disperser ant size whilst those rates of small diplochorous seeds were conspicuously lower for large Aphaenogaster ants than for small Pheidole ants, suggesting small seeds are not adapted to be carried by large ants. 2) Dispersal distance: large V. hondoensis seeds were transported for a long distance because they were carried by both large and small ants while the small diplochorous seeds were transported for a short distance because they were carried only by small ants. These results suggest that large seeds are advantageous to attract large ants and to be farther dispersed as far as ant-mediated dispersal is concerned. On the other hand, the diplochorous small seeds do not attract large ants, and so are transported short by ants although they disperse their seeds by ballistic dispersal