Dispersal distance as a benefit of myrmecochory

Nutrient-enrichment and predator avoidance are generally considered the major benefits of myrmecochory, but this is apparently not so in Australia where some of the greatest known concentrations of myrmecochorus plants occur. Here I demonstrate that distance dispersal is a potential benefit of myrmecochory in the Australian environment. Although mean dispersal distance at a site in southeastern Australia was only 2.1 m, the dispersal curve was characterised by a narrow peak and long tail. A dispersal curve of this shape has been shown by Green (1983) to be optimal when safe sites for seedling establishment are rare, as is typically the case for Australian myrmecochores in the absence of fire. Both mean disperal distance and shape of the dispersal curve are influenced strongly by nest density and dispersion, population size, and territoriality of seed-dispersing ants. I argue that distance dispersal is likely to be a benefit of myrmecochory throughout Australia, independent of any targeting of seeds to ant nests.