Advantages of Seed Dispersal for a Myrmecochorous Temperate Forest Herb

Abstract

The advantages of ant-mediated seed dispersal for myrmecochorous plants have often been framed in the context of directed dispersal and predator avoidance. Underlying and intertwining themes in these frameworks are the services of (a) moving seeds away from parent plants, (b) placing seeds in safe and ideal locations and occasionally, (c) removing elaiosomes to thwart detection by seed predators. These services are rarely simultaneously investigated from an experimental standpoint to determine which may be most important. Here, we conducted a factorial-designed field experiment to test how survival of seeds of a myrmecochrous forest herb, Asarum canadense (wild ginger), in two forest sites in southwestern Ohio, USA, was affected by the following treatments: distance from parent plant, seed burial, elaiosome removal, and their interactions. We found that when placed in artificial depots consisting of 10 seeds, only seed burial significantly aided seed survival. We supplemented this by conducting a laboratory experiment in which mice were given choices of trays containing either buried seeds with elaiosomes or without elaiosomes at densities higher than those of our field experiment and within the realm of those contained in ant nests. Mice consumed more mass of seeds with elaiosomes, suggesting that elaiosome removal may be advantageous in this context. When taken together, our results highlight the importance of seed burial and elaiosome removal for seed survival of a myrmecochorous forest herb. Though not specifically addressed in our study, the combination of these two services may positively contribute to later life history stages (e.g., seedlings) and population persistence of myrmecochorous plants and may ultimately reveal the importance of other services (e.g., short-distance seed dispersal) and their interactions.