Dispersal and predation of a Neotropical pioneer tree species, Zanthoxylum ekmanii, by a common ground dwelling ant, Ectatomma ruidum

Ant-mediated seed dispersal has evolved repeatedly in many regions around the world. Most research on ant-mediated seed dispersal focuses on plants that have food bodies called elaiosomes attached to their seeds. However, seeds without elaiosomes can also be attractive to ants. Our previous work demonstrated that ants remove seeds of the pioneer tree species, Zanthoxylum ekmanii that does not provide a food reward. The recruitment of pioneer tree species is limited by the arrival of their seeds into light gaps that are unpredictable in time and space. Ants may bury and incorporate seeds into the seed bank, caching them until conditions suitable for germination occur. To determine whether Ectatomma ruidum acts as a seed disperser of Z. ekmanii, we placed seed depots on the forest floor on Barro Colorado Island and determined the distance and destination seeds were moved. We also created wax castings of E. ruidum colonies to determine the depth that seeds were cached. Out of 75 seeds, 41 were moved by ants and 23 by E. ruidum. Ectatomma ruidum moved seeds from 1.5cm - 405.7cm (mean 115.8cm ± 105.3 s.d.). Fifteen seeds were brought directly into an E. ruidum colony. We used the chamber depths and brood location from the wax castes with a calculated maximum emergence depth based on seed masses to determine if seeds could survive burial in ant nests. Collectively, our data suggest that E. ruidum may be an important species for incorporating seeds of pioneer species into the seed bank.