Removal Rates of Seeds Adapted for Dispersal by Ants

Abstract

To learn what scope there may be for a mother plant to modify whether her seeds are removed by ants, and how quickly, we investigated (1) how initial seed removal by ants may vary in times (years, season, time of day) and space (within and between sites, and (2) how large these sources of variation are. We focused on seed of two common ant—dispersed species in a field experiment on 20 x 20 m plots at each o three sites in Kuringai Chase National Park in southeast Australia. The most important influence on removal rate over the first 12 h of exposure was the precise location of seeds on the ground (54% of total variation). This variation did not persist over longer periods of time and, except during winter, all seeds had a high probability of being removed within 2—3 d. Time of year also had a strong influence had a strong influence on removal rate (21% of total variation) with the highest rates occurring in summer and the lowest in winter. These changes were mainly attributable to changes in ambient temperature. Differences in removal rates between the two seed species used was the third most important source of variation (4%). There was significant variation in removal rate between the same months in different years, in two of the three between—year comparisons. The effect of year, and of interactions between year and other factors, accounted for between 7 and 18% of total variation. Complementary experiments showed that ants were the only important removers of seed at the study sites and that seed age up to 1 yr did not influence removal rate. Experiments comparing removal rates of clumped seeds to those of single seeds showed no consistence difference. The high probability of removal of elaiosome—bearing seeds within 2—3 d of seedfall means it is unlikely that ant—dispersed plants in this vegetation ever face the problem of their seeds not being encountered and transported by an ant. Instead, the problem may be how to be removed by those ant species whose behavior will give the seed the best chance of survival and establishment.