Ant dispersal and predation affects the availability of seeds for old-field recolonisation in Western Australia

Seed arrival onto abandoned farmlands (old-fields) in south-western Australia can be limited bytheir proximity to native remnant vegetation. As the major seed-harvesting guild, ants could affectseed availability on old-fields by either: (1) affecting the dispersal of elaiosome-bearing seeds fromadjacent remnants; (2) thieving the elaiosome from seeds without affecting their dispersal onto oldfields;or (3) predating seeds, which reduces the availability of seeds for dispersal. The relativeimportance of these ant-seed interactions will depend on the rates of ant-mediated seed dispersalfrom the remnants onto the old-field, as well as the rates of seed predation across these habitats.We sampled the ant communities within two old-fields, within the adjacent eucalypt woodlandremnants and at the boundaries of these two habitats, using pitfall traps to determine the relativeproportions of seed dispersers, elaiosome thieves and seed harvesters within each zone–ants wereassigned to these groups on the basis of our observations of ant-seed interactions. During theseobservations, we followed the fate of elaiosome-bearing Acacia seeds that were offered to antswithin each zone, primarily to estimate rates of seed dispersal and elaiosome thieving. We alsooffered eucalypt seeds to ants in feeding stations to estimate seed predation within each zone. Wefound that the relative proportions of seed dispersers, elaiosome thieves and seed harvesters weresimilar across zones, despite differences in the species composition between sites and a reductionin species richness in the old-fields. None of the Acacia seeds that we offered were dispersed fromeither remnant into the adjacent old-field. The majority of dispersal events were less than 3.6 mfrom the seed source (61%; n = 74) and dispersal beyond 20 m was rare (4%; maximum 28.1 m).Rates of elaiosome thieving and seed predation were not elevated in the old-fields compared withtheir rates in the other zones. Overall, the data indicate that ant-mediated seed dispersal onto oldfieldswas rare and seed predation by ants was similar across habitats.