Dispersal of Trillium Seeds by Deer: Implications for Long-Distance Migration of Forest Herbs

Theoretical models of plant range expansion require the assumption of occasional long-distance seed-dispersal events to explain post-glacial migration rates. For the many forest herbs whose seeds are dispersed primarily by ants, there are few documented mechanisms of occasional long-distance dispersal, so models of forest-herb migration have been largely phenomenological. Here we show that viable seeds of Trillium grandiflorum, an ant-dispersed forest herb in eastern North America, are dispersed via ingestion and defecation by white-tailed deer. We also use data from the literature on movement patterns and gut retention times to model a deer-generated seed shadow, showing that most seeds dispersed by deer should travel at least several hundred meters from parent plants, and occasionally >3 km. Our results provide a mechanism of long-distance dispersal that has likely contributed to rates of post-glacial migration and post-agricultural forest colonization. Corresponding Editor: M. L. Cain