Ant preference for seeds without awns increases removal of exotic relative to native grass seeds

Abstract

1. The removal of seeds by granivorous ants can affect plant recruitment through either seed loss from predation or the dispersal and recruitment of seeds that are removed but not consumed. Consequently, variation in ant selection preferences can influence patterns of seed removal and affect plant community composition, including the spread of exotic plant species.2. We conducted a seed removal experiment to determine whether: 1) rates of removal by ants differed between three native and three exotic grass species in an Australian temperate grassland; and 2) differences in removal rates were associated with the presence or absence of awns.3. We found that seeds of the three exotic species, none of which had awns, were removed by ants at a higher rate than those of the three native species, all of which had awns. Removal rates of native species increased when awns were manually removed, suggesting the awns of native species acted as a removal barrier.4. While we do not know the fate of seeds removed from our experiment, differences among species in removal rates mirrored differences in their spatial spread in a separate seed addition experiment. Exotic species removed by ants at a higher rate in the removal experiment had more widely dispersed seedlings than native species in the seed addition experiment, potentially indicating a role for granivorous ants in dispersing exotic seeds. Identifying ant selection preferences and directly linking removal to seed fate could help explain how exotic grass species move around the landscape.